ChaptersThis tutorial assumes you have basic Rails knowledge from reading the Getting Started with Rails Guide.
1 Creating a Rails App
First, let's create a simple Rails application using the rails new command.
We will use this application to play and discover all the commands described in this guide.
You can install the rails gem by typing gem install rails, if you don't have it already.
1.1 rails new
The first argument we'll pass to the rails new command is the application name.
$ rails new my_app
create
create README.md
create Rakefile
create config.ru
create .gitignore
create Gemfile
create app
...
create tmp/cache
...
run bundle install
Rails will set up what seems like a huge amount of stuff for such a tiny command! We've got the entire Rails directory structure now with all the code we need to run our simple application right out of the box.
If you wish to skip some files from being generated or skip some libraries, you can append any of the following arguments to your rails new command:
| Argument | Description |
|---|---|
--skip-git |
Skip git init, .gitignore, and .gitattributes |
--skip-docker |
Skip Dockerfile, .dockerignore and bin/docker-entrypoint |
--skip-keeps |
Skip source control .keep files |
--skip-action-mailer |
Skip Action Mailer files |
--skip-action-mailbox |
Skip Action Mailbox gem |
--skip-action-text |
Skip Action Text gem |
--skip-active-record |
Skip Active Record files |
--skip-active-job |
Skip Active Job |
--skip-active-storage |
Skip Active Storage files |
--skip-action-cable |
Skip Action Cable files |
--skip-asset-pipeline |
Skip Asset Pipeline |
--skip-javascript |
Skip JavaScript files |
--skip-hotwire |
Skip Hotwire integration |
--skip-jbuilder |
Skip jbuilder gem |
--skip-test |
Skip test files |
--skip-system-test |
Skip system test files |
--skip-bootsnap |
Skip bootsnap gem |
--skip-dev-gems |
Skip adding development gems |
These are just some of the options that rails new accepts. For a full list of options, type rails new --help.
1.2 Preconfigure a Different Database
When creating a new Rails application, you have the option to specify what kind of database your application is going to use. This will save you a few minutes, and certainly many keystrokes.
Let's see what a --database=postgresql option will do for us:
$ rails new petstore --database=postgresql
create
create app/controllers
create app/helpers
...
Let's see what it put in our config/database.yml:
# PostgreSQL. Versions 9.3 and up are supported.
#
# Install the pg driver:
# gem install pg
# On macOS with Homebrew:
# gem install pg -- --with-pg-config=/usr/local/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"
#
default: &default
adapter: postgresql
encoding: unicode
# For details on connection pooling, see Rails configuration guide
# https://guides.rubyonrails.org/configuring.html#database-pooling
pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
development:
<<: *default
database: petstore_development
...
It generated a database configuration corresponding to our choice of PostgreSQL.
2 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:
bin/rails consolebin/rails serverbin/rails testbin/rails generatebin/rails db:migratebin/rails db:createbin/rails routesbin/rails dbconsolerails new app_name
You can get a list of rails commands available to you, which will often depend on your current directory, by typing rails --help. Each command has a description, and should help you find the thing you need.
$ rails --help
Usage:
bin/rails COMMAND [options]
You must specify a command. The most common 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 Load fixtures into the ...
db:migrate Migrate the database ...
db:migrate:status Display status of migrations
db:rollback Roll the schema back to ...
db:schema:cache:clear Clears a db/schema_cache.yml file
db:schema:cache:dump Create a db/schema_cache.yml file
db:schema:dump Create a database schema file (either db/schema.rb or db/structure.sql ...
db:schema:load Load a database schema file (either db/schema.rb or db/structure.sql ...
db:seed Load the seed data ...
db:version Retrieve the current schema ...
...
restart Restart app by touching ...
tmp:create Create tmp directories ...
2.1 bin/rails server
The bin/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, bin/rails server will run our new shiny Rails app:
$ cd my_app
$ bin/rails server
=> Booting Puma
=> Rails 7.0.0 application starting in development
=> Run `bin/rails server --help` for more startup options
Puma starting in single mode...
* Version 3.12.1 (ruby 2.5.7-p206), codename: Llamas in Pajamas
* 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: bin/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.
2.2 bin/rails generate
The bin/rails generate command uses templates to create a whole lot of things. Running bin/rails generate by itself gives a list of available generators:
You can also use the alias "g" to invoke the generator command: bin/rails g.
$ bin/rails generate
Usage:
bin/rails generate GENERATOR [args] [options]
...
...
Please choose a generator below.
Rails:
assets
channel
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 bin/rails server --help.
$ bin/rails generate controller
Usage:
bin/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:
`bin/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 test_unit
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 bin/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:
bin/rails generate model NAME [field[:type][:index] field[:type][:index]] [options]
...
ActiveRecord options:
[--migration], [--no-migration] # Indicates when to generate migration
# Default: true
...
Description:
Generates a new model. Pass the model name, either CamelCased or
under_scored, and an optional list of attribute pairs as arguments.
...
For a list of available field types for the type parameter, refer to the API documentation for the add_column method for the SchemaStatements module. The index parameter generates a corresponding index for the column.
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/20190416145729_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
create test/system/high_scores_test.rb
invoke helper
create app/helpers/high_scores_helper.rb
invoke test_unit
invoke jbuilder
create app/views/high_scores/index.json.jbuilder
create app/views/high_scores/show.json.jbuilder
create app/views/high_scores/_high_score.json.jbuilder
The generator creates the model, views, controller, resource route, and database migration (which creates the high_scores table) for HighScore. And it adds tests for those.
The migration requires that we migrate, that is, run some Ruby code (the 20190416145729_create_high_scores.rb file from the above output) 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 that command below.
$ 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!)
2.3 bin/rails console
The console command lets you interact with your Rails application from the command line. On the underside, bin/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: bin/rails c.
You can specify the environment in which the console command should operate.
$ bin/rails console -e staging
If you wish to test out some code without changing any data, you can do that by invoking bin/rails console --sandbox.
$ bin/rails console --sandbox
Loading development environment in sandbox (Rails 7.1.0)
Any modifications you make will be rolled back on exit
irb(main):001:0>
2.3.1 The app and helper Objects
Inside the bin/rails console you have access to the app and helper instances.
With the app method you can access named route helpers, as well as do requests.
irb> app.root_path
=> "/"
irb> 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.
irb> helper.time_ago_in_words 30.days.ago
=> "about 1 month"
irb> helper.my_custom_helper
=> "my custom helper"
2.4 bin/rails dbconsole
bin/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: bin/rails db.
If you are using multiple databases, bin/rails dbconsole will connect to the primary database by default. You can specify which database to connect to using --database or --db:
$ bin/rails dbconsole --database=animals
2.5 bin/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: bin/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
2.6 bin/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: bin/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
2.7 bin/rails 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 7.0.0
Ruby version 2.7.0 (x86_64-linux)
RubyGems version 2.7.3
Rack version 2.0.4
JavaScript Runtime Node.js (V8)
Middleware: Rack::Sendfile, ActionDispatch::Static, ActionDispatch::Executor, ActiveSupport::Cache::Strategy::LocalCache::Middleware, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, ActionDispatch::RemoteIp, Sprockets::Rails::QuietAssets, Rails::Rack::Logger, ActionDispatch::ShowExceptions, WebConsole::Middleware, ActionDispatch::DebugExceptions, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::Migration::CheckPending, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, Rack::Head, Rack::ConditionalGet, Rack::ETag
Application root /home/foobar/my_app
Environment development
Database adapter sqlite3
Database schema version 20180205173523
2.8 bin/rails 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 command 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.
2.9 bin/rails db:
The most common commands of the db: rails namespace are migrate and create, and it will pay off to try out all of the migration rails commands (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.
2.10 bin/rails notes
bin/rails notes searches through your code for comments beginning with a specific keyword. You can refer to bin/rails notes --help for information about usage.
By default, it will search in app, config, db, lib, and test directories for FIXME, OPTIMIZE, and TODO annotations in files with extension .builder, .rb, .rake, .yml, .yaml, .ruby, .css, .js, and .erb.
$ bin/rails notes
app/controllers/admin/users_controller.rb:
* [ 20] [TODO] any other way to do this?
* [132] [FIXME] high priority for next deploy
lib/school.rb:
* [ 13] [OPTIMIZE] refactor this code to make it faster
* [ 17] [FIXME]
2.10.1 Annotations
You can pass specific annotations by using the --annotations argument. By default, it will search for FIXME, OPTIMIZE, and TODO.
Note that annotations are case sensitive.
$ bin/rails notes --annotations FIXME RELEASE
app/controllers/admin/users_controller.rb:
* [101] [RELEASE] We need to look at this before next release
* [132] [FIXME] high priority for next deploy
lib/school.rb:
* [ 17] [FIXME]
2.10.2 Tags
You can add more default tags to search for by using config.annotations.register_tags. It receives a list of tags.
config.annotations.register_tags("DEPRECATEME", "TESTME")
$ bin/rails notes
app/controllers/admin/users_controller.rb:
* [ 20] [TODO] do A/B testing on this
* [ 42] [TESTME] this needs more functional tests
* [132] [DEPRECATEME] ensure this method is deprecated in next release
2.10.3 Directories
You can add more default directories to search from by using config.annotations.register_directories. It receives a list of directory names.
config.annotations.register_directories("spec", "vendor")
$ bin/rails notes
app/controllers/admin/users_controller.rb:
* [ 20] [TODO] any other way to do this?
* [132] [FIXME] high priority for next deploy
lib/school.rb:
* [ 13] [OPTIMIZE] Refactor this code to make it faster
* [ 17] [FIXME]
spec/models/user_spec.rb:
* [122] [TODO] Verify the user that has a subscription works
vendor/tools.rb:
* [ 56] [TODO] Get rid of this dependency
2.10.4 Extensions
You can add more default file extensions to search from by using config.annotations.register_extensions. It receives a list of extensions with its corresponding regex to match it up.
config.annotations.register_extensions("scss", "sass") { |annotation| /\/\/\s*(#{annotation}):?\s*(.*)$/ }
$ bin/rails notes
app/controllers/admin/users_controller.rb:
* [ 20] [TODO] any other way to do this?
* [132] [FIXME] high priority for next deploy
app/assets/stylesheets/application.css.sass:
* [ 34] [TODO] Use pseudo element for this class
app/assets/stylesheets/application.css.scss:
* [ 1] [TODO] Split into multiple components
lib/school.rb:
* [ 13] [OPTIMIZE] Refactor this code to make it faster
* [ 17] [FIXME]
spec/models/user_spec.rb:
* [122] [TODO] Verify the user that has a subscription works
vendor/tools.rb:
* [ 56] [TODO] Get rid of this dependency
2.11 bin/rails routes
bin/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.
2.12 bin/rails test
A good description of unit testing in Rails is given in A Guide to Testing Rails Applications
Rails comes with a test framework called minitest. Rails owes its stability to the use of tests. The commands available in the test: namespace helps in running the different tests you will hopefully write.
2.13 bin/rails 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 commands will help you clear and create the Rails.root/tmp directory:
bin/rails tmp:cache:clearclearstmp/cache.bin/rails tmp:sockets:clearclearstmp/sockets.bin/rails tmp:screenshots:clearclearstmp/screenshots.bin/rails tmp:clearclears all cache, sockets, and screenshot files.bin/rails tmp:createcreates tmp directories for cache, sockets, and pids.
2.14 Miscellaneous
bin/rails initializersprints out all defined initializers in the order they are invoked by Rails.bin/rails middlewarelists Rack middleware stack enabled for your app.bin/rails statsis great for looking at statistics on your code, displaying things like KLOCs (thousands of lines of code) and your code to test ratio.bin/rails secretwill give you a pseudo-random key to use for your session secret.bin/rails time:zones:alllists all the timezones Rails knows about.
2.15 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 "task_name[value 1,value2,value3]" # separate multiple args with a comma
$ bin/rails db:nothing
If you 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.
task task_that_requires_app_code: [:environment] do
User.create!
end
Feedback
You're encouraged to help improve the quality of this guide.
Please contribute if you see any typos or factual errors. To get started, you can read our documentation contributions section.
You may also find incomplete content or stuff that is not up to date. Please do add any missing documentation for main. Make sure to check Edge Guides first to verify if the issues are already fixed or not on the main branch. Check the Ruby on Rails Guides Guidelines for style and conventions.
If for whatever reason you spot something to fix but cannot patch it yourself, please open an issue.
And last but not least, any kind of discussion regarding Ruby on Rails documentation is very welcome on the official Ruby on Rails Forum.