More at More Ruby on Rails

Ruby on Rails 4.0 Release Notes

Highlights in Rails 4.0:

These release notes cover only the major changes. To know about various bug fixes and changes, please refer to the change logs or check out the list of commits in the main Rails repository on GitHub.

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 to 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

Give a list and then talk about each of them briefly. We can point to relevant code commits or documentation from these sections.

Rails 4.0

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.

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/ dir. 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 where(...).first_or_initialize.
    • find_or_create_by_... can be rewritten using find_or_create_by(...) or where(...).first_or_create.
    • find_or_create_by_...! can be rewritten using find_or_create_by!(...) or where(...).first_or_create!.

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.


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 master. Make sure to check Edge Guides first to verify if the issues are already fixed or not on the master 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 in the rubyonrails-docs mailing list.