Guides.rubyonrails.org

Chapters

1. Upgrading to Rails 4.2
2. Major Features
   • Active Job, Action Mailer #deliver_later
   • Adequate Record
   • Web Console
   • Foreign key support
3. Railties
   • Removals
   • Deprecations
   • Notable changes
4. Action Pack
   • Removals
   • Deprecations
   • Notable changes
5. Action View
   • Deprecations
   • Notable changes
6. Action Mailer
   • Deprecations
   • Notable changes
7. Active Record
   • Removals
   • Deprecations
   • Notable changes
8. Active Model
   • Removals
   • Deprecations
   • Notable changes
9. Active Support
   • Removals
   • Deprecations
   • Notable changes
10. Credits

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 Upgrading Ruby on Rails guide.

2 Major Features

2.1 Active Job, Action Mailer #deliver_later

Active Job is a new framework in Rails 4.2. It is an adapter layer on top of queuing systems like Resque, Delayed Job, Sidekiq, and more. You can write your jobs to Active Job, and it'll run on all these queues with no changes. (It comes pre-configured with an inline runner.)

Building on top of Active Job, Action Mailer now comes with a #deliver_later method, which adds your email to be sent as a job to a queue, so it doesn't bog down the controller or model.

The new GlobalID library makes it easy to pass Active Record objects to jobs by serializing them in a generic form. This means you no longer have to manually pack and unpack your Active Records by passing ids. Just give the job the straight Active Record object, and it'll serialize it using GlobalID, and deserialize it at run time.

2.2 Adequate Record

Rails 4.2 comes with a performance improvement feature called Adequate Record for Active Record. A lot of common queries are now up to twice as fast in Rails 4.2!

2.3 Web Console

New applications generated from Rails 4.2 now comes with the Web Console gem by default.

Web Console is an IRB console available in the browser. In development mode, you can go to /console and do your work right there. It will also be made available on all exception pages and allows you to jump between the different points in the backtrace.

2.4 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 Railties

Please refer to the Changelog for detailed changes.

3.1 Removals

• The rails application command has been removed without replacement. (Pull Request)

3.2 Deprecations

• Deprecated Rails::Rack::LogTailer without replacement. (Commit)

3.3 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 an after_bundle callback for use in Rails templates. (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/production.rb
  MyApp::Application.configure do
    config.middleware.use ExceptionNotifier, config_for(:exception_notification)
  end
  
  

  (Pull Request)

• Introduced a --skip-gems option in the app generator to skip gems such as turbolinks and coffee-rails that do not have their own specific flags. (Commit)

• Introduced a bin/setup script to enable automated setup code when bootstrapping an application. (Pull Request)

• Changed 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 Rails.gem_version as a convenience method to return Gem::Version.new(Rails.version). (Pull Request)

4 Action Pack

Please refer to the Changelog for detailed changes.

4.1 Removals

• respond_with and the class-level respond_to were 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)

• Removed deprecated AbstractController::Helpers::ClassMethods::MissingHelperError in favor of AbstractController::Helpers::MissingHelperError. (Commit)

4.2 Deprecations

• 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)

4.3 Notable changes

• Rails will now automatically include the template's digest in ETags. (Pull Request)

• render nothing: true or rendering a nil body no longer add a single space padding to the response body. (Pull Request)

• Introduced the always_permitted_parameters option to configure which parameters are permitted globally. The default value of this configuration is ['controller', 'action']. (Pull Request)

• The *_filter family methods have been removed from the documentation. Their usage is discouraged in favor of the *_action family 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 is depending on these methods, you should use the replacement *_action methods instead. These methods will be deprecated in the future and eventually removed from Rails.

  (Commit 1, 2)

• Added HTTP method MKCALENDAR from RFC-4791 (Pull Request)

• *_fragment.action_controller notifications now include the controller and action name in the payload. (Pull Request)

• Segments that are passed into URL helpers are now automatically escaped. (Commit)

• Improved the Routing Error page with fuzzy matching for route search. (Pull Request)

• Added an option to disable logging of CSRF failures. (Pull Request)

5 Action View

Please refer to the Changelog for detailed changes.

5.1 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)

5.2 Notable changes

• 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)

• The form helpers no longer generate a <div> element with inline CSS around the hidden fields. (Pull Request)

• Placeholder I18n follows the same convention as label I18n. (Pull Request)

6 Action Mailer

Please refer to the Changelog for detailed changes.

6.1 Deprecations

• Deprecated *_path helpers in mailers. Always use *_url helpers instead. (Pull Request)

• Deprecated deliver / deliver! in favour of deliver_now / deliver_now!. (Pull Request)

6.2 Notable changes

• Introduced deliver_later which enqueues a job on the application's queue to deliver the mailer asynchronously. (Pull Request)

• Added the show_previews configuration option for enabling mailer previews outside of the development environment. (Pull Request)

7 Active Record

Please refer to the Changelog for detailed changes.

7.1 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 ActiveRecord, such as for XML Serialization. (Pull Request)

7.2 Deprecations

• Deprecated swallowing of errors inside after_commit and after_rollback. (Pull Request)

• Deprecated calling DatabaseTasks.load_schema without a connection. Use DatabaseTasks.load_schema_current instead. (Commit)

• Deprecated Reflection#source_macro without replacement as it is no longer needed in Active Record. (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 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 depends on the instance state (i.e. those defined with a scope that takes an argument) without replacement. (Commit)

• 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 the Ruby range does 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)

7.3 Notable changes

• The PostgreSQL adapter now supports the JSONB datatype in PostgreSQL 9.4+. (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)

• Added a :required option to singular associations, which defines a presence validation on the association. (Pull Request)

• Introduced ActiveRecord::Base#validate! that raises RecordInvalid if the record is invalid. (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)

• Introduced the bin/rake db:purge task to empty the database for the current environment. (Commit)

• ActiveRecord::Dirty now detects in-place changes to mutable values. Serialized attributes on ActiveRecord models will no longer save when unchanged. This also works with other types such as string columns and json columns on PostgreSQL. (Pull Requests 1, 2, 3)

• Added support for #pretty_print in ActiveRecord::Base objects. (Pull Request)

• PostgreSQL and SQLite adapters no longer add a default limit of 255 characters on string columns. (Pull Request)

• 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 behaviour was deprecated on Rails 4.1.) (Pull Request)

• Introduced #validate as an alias for #valid?. (Pull Request)

• #touch now accepts multiple attributes to be touched at once. (Pull Request)

• Added support for fractional seconds for MySQL 5.6 and above. (Pull Request 1, 2)

• Added support for the citext column type in PostgreSQL adapter. (Pull Request)

• Added support for user-created range types in PostgreSQL adapter. (Commit)

8 Active Model

Please refer to the Changelog for detailed changes.

8.1 Removals

• Removed deprecated Validator#setup without replacement. (Pull Request)

8.2 Deprecations

• Deprecated reset_#{attribute} in favor of restore_#{attribute}. (Pull Request)

• Deprecated ActiveModel::Dirty#reset_changes in favor of #clear_changes_information. (Pull Request)

8.3 Notable changes

• 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 disallow 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)

• Introduced #validate as an alias for #valid?. (Pull Request)

9 Active Support

Please refer to the Changelog for detailed changes.

9.1 Removals

• Removed deprecated Numeric#ago, Numeric#until, Numeric#since, Numeric#from_now. (Commit)

• Removed deprecated string based terminators for ActiveSupport::Callbacks. (Pull Request)

9.2 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)

9.3 Notable changes

• The travel_to test helper now truncates the usec component to 0. (Commit)

• ActiveSupport::TestCase now randomizes the order that test cases are ran by default. (Commit)

• Introduced Object#itself as an identity function. (Commit 1, 2)

• Object#with_options can now be used without an explicit receiver. (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)

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 today. Kudos to all of them.

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