path: root/guides/source/4_2_release_notes.md

Ruby on Rails 4.2 Release Notes
===============================

Highlights in Rails 4.2:

* Active Job, Action Mailer #deliver_later
* Adequate Record
* Web Console
* Foreign key support

These release notes cover only the major changes. To learn about various bug
fixes and changes, please refer to the change logs or check out the [list of
commits](https://github.com/rails/rails/commits/master) in the main Rails
repository on GitHub.

--------------------------------------------------------------------------------

NOTE: This document is a work in progress, please help to improve this by sending
a [pull request](https://github.com/rails/rails/edit/master/guides/source/4_2_release_notes.md).

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](upgrading_ruby_on_rails.html#upgrading-from-rails-4-1-to-rails-4-2)


Major Features
--------------

### 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](https://github.com/resque/resque), [Delayed
Job](https://github.com/collectiveidea/delayed_job),
[Sidekiq](https://github.com/mperham/sidekiq), and more.

You can write your jobs with the Active Job API, 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.

### Adequate Record

Adequate Record is a set of refactorings that make Active Record `find` and
`find_by` methods and some association queries upto 2x faster.

It works by caching SQL query patterns while executing the Active Record calls.
The cache helps skip parts of the computation involved in the transformation of
the calls into SQL queries. More details in [Aaron Patterson's
post](http://tenderlovemaking.com/2014/02/19/adequaterecord-pro-like-activerecord.html).

Nothing special has to be done to activate this feature. Most `find` and
`find_by` calls and association queries will use it automatically. Examples:

```ruby
Post.find 1  # caches query pattern
Post.find 2  # uses the cached pattern

Post.find_by_title 'first post'  # caches query pattern
Post.find_by_title 'second post' # uses the cached pattern

post.comments        # caches query pattern
post.comments(true)  # uses cached pattern
```

The caching is not used in the following scenarios:

- The model has a default scope
- The model uses single table inheritance to inherit from another model
- `find` with a list of ids. eg:

  ```ruby
  Post.find(1,2,3)
  OR
  Post.find [1,2]
  ```

- `find_by` with sql fragments:

  ```ruby
  Post.find_by "published_at < ?", 2.weeks.ago
  ```

### Web Console

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

Web Console is a set of debugging tools for your Rails application. It will add
an interactive console on every error page, a `console` view helper and a VT100
compatible terminal.

The interactive console on the error pages lets you execute code where the
exception originated. It's quite handy to introspect the state that led to the
error.

The `console` view helper launches an interactive console within the context of
the view where it is invoked.

Finally, you can launch a VT100 terminal that runs `rails console`. If you need
to create or modify existing test data, you can do that straight from the
browser.

### 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.

```ruby
# 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](http://api.rubyonrails.org/v4.2.0/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-add_foreign_key)
and
[remove_foreign_key](http://api.rubyonrails.org/v4.2.0/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-remove_foreign_key)
for a full description.


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.

### `render` with a String argument

Previously, calling `render "foo/bar"` in a controller action is 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.

### `respond_with` / class-level `respond_to`

`respond_with` and the corresponding class-level `respond_to` have been moved to
the `responders` gem. To use the following, add `gem 'responders', '~> 2.0'` to
your Gemfile:

```ruby
# 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:

```ruby
# 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
```

### Default host for `rails server`

Due to a [change in Rack](https://github.com/rack/rack/commit/28b014484a8ac0bbb388e7eaeeef159598ec64fc),
`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 would continue to work as before on your own machine.

However, with this change you would no longer be able to access the Rails server
from a different machine (e.g. your development environment is in a virtual
machine and you would like to access it from the host machine), you would need
to 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.

### Production logging

The default log level in the `production` environment is now `:debug`. This
makes it consistent with the other environments, and ensures plenty of
information is available to diagnose problems.

It can be returned to the previous level, `:info`, in the environment
configuration:

```ruby
# config/environments/production.rb

# Decrease the log volume.
config.log_level = :info
```

### 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.

With a new sanitization algorithm, the sanitized output will change for certain
pathological inputs.

If you have particular need for the exact output of the old sanitizer, you can
add `rails-deprecated_sanitizer` to your Gemfile, and it will automatically
replace the new implementation. Because it is opt-in, the legacy gem will not
give deprecation warnings.

`rails-deprecated_sanitizer` will be supported for Rails 4.2 only; it will not
be maintained for Rails 5.0.

See [the blog post](http://blog.plataformatec.com.br/2014/07/the-new-html-sanitizer-in-rails-4-2/)
for more detail on the changes in the new sanitizer.

### `assert_select`

`assert_select` is now based on Nokogiri, making it (TODO: betterer).

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.

    ```
    a[href=/]      =>     a[href="/"]
    a[href$=/]     =>     a[href$="/"]
    ```

*   DOMs built from HTML source containing invalid HTML with improperly
    nested elements may differ.

    For example:

    ``` ruby
    # 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`).

    ``` ruby
    # 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
    ```


Railties
--------

Please refer to the [Changelog][railties] for detailed changes.

### Removals

*   The `rails application` command has been removed without replacement.
    ([Pull Request](https://github.com/rails/rails/pull/11616))

### Deprecations

*   Deprecated `Rails::Rack::LogTailer` without replacement.
    ([Commit](https://github.com/rails/rails/commit/84a13e019e93efaa8994b3f8303d635a7702dbce))

### Notable changes

*   Introduced `web-console` in the default application Gemfile.
    ([Pull Request](https://github.com/rails/rails/pull/11667))

*   Added a `required` option to the model generator for associations.
    ([Pull Request](https://github.com/rails/rails/pull/16062))

*   Introduced an `after_bundle` callback for use in Rails templates.
    ([Pull Request](https://github.com/rails/rails/pull/16359))

*   Introduced the `x` namespace for defining custom configuration options:

    ```ruby
    # 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:

    ```ruby
    Rails.configuration.x.payment_processing.schedule # => :daily
    Rails.configuration.x.payment_processing.retries  # => 3
    Rails.configuration.x.super_debugger              # => true
    ```

    ([Commit](https://github.com/rails/rails/commit/611849772dd66c2e4d005dcfe153f7ce79a8a7db))

*   Introduced `Rails::Application.config_for` to load a configuration for the
    current environment.

    ```ruby
    # 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
    Rails.application.configure do
      config.middleware.use ExceptionNotifier, config_for(:exception_notification)
    end
    ```

    ([Pull Request](https://github.com/rails/rails/pull/16129))

*   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](https://github.com/rails/rails/commit/10565895805887d4faf004a6f71219da177f78b7))

*   Introduced a `bin/setup` script to enable automated setup code when
    bootstrapping an application.
    ([Pull Request](https://github.com/rails/rails/pull/15189))

*   Changed default value for `config.assets.digest` to `true` in development.
    ([Pull Request](https://github.com/rails/rails/pull/15155))

*   Introduced an API to register new extensions for `rake notes`.
    ([Pull Request](https://github.com/rails/rails/pull/14379))

*   Introduced `Rails.gem_version` as a convenience method to return
    `Gem::Version.new(Rails.version)`.
    ([Pull Request](https://github.com/rails/rails/pull/14101))


Action Pack
-----------

Please refer to the [Changelog][action-pack] for detailed changes.

### 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](https://github.com/rails/rails/pull/16526))

*   Removed deprecated `AbstractController::Helpers::ClassMethods::MissingHelperError`
    in favor of `AbstractController::Helpers::MissingHelperError`.
    ([Commit](https://github.com/rails/rails/commit/a1ddde15ae0d612ff2973de9cf768ed701b594e8))

### Deprecations

*   Deprecated the `only_path` option on `*_path` helpers.
    ([Commit](https://github.com/rails/rails/commit/aa1fadd48fb40dd9396a383696134a259aa59db9))

*   Deprecated `assert_tag`, `assert_no_tag`, `find_tag` and `find_all_tag` in
    favor of `assert_select`.
    ([Commit](https://github.com/rails/rails-dom-testing/commit/b12850bc5ff23ba4b599bf2770874dd4f11bf750))

*   Deprecated support for setting the `:to` option of a router to a symbol or a
    string that does not contain a `#` character:

    ```ruby
    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](https://github.com/rails/rails/commit/cc26b6b7bccf0eea2e2c1a9ebdcc9d30ca7390d9))

### Notable changes

*   Rails will now automatically include the template's digest in ETags.
    ([Pull Request](https://github.com/rails/rails/pull/16527))

*   `render nothing: true` or rendering a `nil` body no longer add a single
    space padding to the response body.
    ([Pull Request](https://github.com/rails/rails/pull/14883))

*   Introduced the `always_permitted_parameters` option to configure which
    parameters are permitted globally. The default value of this configuration
    is `['controller', 'action']`.
    ([Pull Request](https://github.com/rails/rails/pull/15933))

*   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 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](https://github.com/rails/rails/commit/6c5f43bab8206747a8591435b2aa0ff7051ad3de),
    [2](https://github.com/rails/rails/commit/489a8f2a44dc9cea09154ee1ee2557d1f037c7d4))

*   Added HTTP method `MKCALENDAR` from RFC-4791
    ([Pull Request](https://github.com/rails/rails/pull/15121))

*   `*_fragment.action_controller` notifications now include the controller
    and action name in the payload.
    ([Pull Request](https://github.com/rails/rails/pull/14137))

*   Segments that are passed into URL helpers are now automatically escaped.
    ([Commit](https://github.com/rails/rails/commit/5460591f0226a9d248b7b4f89186bd5553e7768f))

*   Improved the Routing Error page with fuzzy matching for route search.
    ([Pull Request](https://github.com/rails/rails/pull/14619))

*   Added an option to disable logging of CSRF failures.
    ([Pull Request](https://github.com/rails/rails/pull/14280))

*   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](http://guides.rubyonrails.org/asset_pipeline.html#cdns) if you are
    serving assets from your Rails server in production.
    ([Pull Request](https://github.com/rails/rails/pull/16466))

*   The way `assert_select` works has changed; specifically a different library
    is used to interpret css selectors, build the transient DOM that the
    selectors are applied against, and to extract the data from that DOM. These
    changes should only affect edge cases. Examples:
    *  Values in attribute selectors may need to be quoted if they contain
       non-alphanumeric characters.
    *  DOMs built from HTML source containing invalid HTML with improperly
       nested elements may differ.
    *  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`).


Action View
-------------

Please refer to the [Changelog][action-view] for detailed changes.

### Deprecations

*   Deprecated `AbstractController::Base.parent_prefixes`.
    Override `AbstractController::Base.local_prefixes` when you want to change
    where to find views.
    ([Pull Request](https://github.com/rails/rails/pull/15026))

*   Deprecated `ActionView::Digestor#digest(name, format, finder, options = {})`.
    Arguments should be passed as a hash instead.
    ([Pull Request](https://github.com/rails/rails/pull/14243))

### Notable changes

*   `render "foo/bar"` now expands to `render template: "foo/bar"` instead of
    `render file: "foo/bar"`.
    ([Pull Request](https://github.com/rails/rails/pull/16888))

*   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](https://github.com/rails/rails/pull/7698))

*   The form helpers no longer generate a `<div>` element with inline CSS around
    the hidden fields.
    ([Pull Request](https://github.com/rails/rails/pull/14738))

*   Placeholder I18n follows the same convention as `label` I18n.
    ([Pull Request](https://github.com/rails/rails/pull/16438))


Action Mailer
-------------

Please refer to the [Changelog][action-mailer] for detailed changes.

### Deprecations

*   Deprecated `*_path` helpers in mailers. Always use `*_url` helpers instead.
    ([Pull Request](https://github.com/rails/rails/pull/15840))

*   Deprecated `deliver` / `deliver!` in favour of `deliver_now` / `deliver_now!`.
    ([Pull Request](https://github.com/rails/rails/pull/16582))

### Notable changes

*   Introduced `deliver_later` which enqueues a job on the application's queue
    to deliver emails asynchronously.
    ([Pull Request](https://github.com/rails/rails/pull/16485))

*   Added the `show_previews` configuration option for enabling mailer previews
    outside of the development environment.
    ([Pull Request](https://github.com/rails/rails/pull/15970))


Active Record
-------------

Please refer to the [Changelog][active-record] for detailed changes.

### Removals

*   Removed `cache_attributes` and friends. All attributes are cached.
    ([Pull Request](https://github.com/rails/rails/pull/15429))

*   Removed deprecated method `ActiveRecord::Base.quoted_locking_column`.
    ([Pull Request](https://github.com/rails/rails/pull/15612))

*   Removed deprecated `ActiveRecord::Migrator.proper_table_name`. Use the
    `proper_table_name` instance method on `ActiveRecord::Migration` instead.
    ([Pull Request](https://github.com/rails/rails/pull/15512))

*   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](https://github.com/rails/rails/pull/15184))

### Deprecations

*   Deprecated swallowing of errors inside `after_commit` and `after_rollback`.
    ([Pull Request](https://github.com/rails/rails/pull/16537))

*   Deprecated calling `DatabaseTasks.load_schema` without a connection. Use
    `DatabaseTasks.load_schema_current` instead.
    ([Commit](https://github.com/rails/rails/commit/f15cef67f75e4b52fd45655d7c6ab6b35623c608))

*   Deprecated `Reflection#source_macro` without replacement as it is no longer
    needed in Active Record.
    ([Pull Request](https://github.com/rails/rails/pull/16373))

*   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](https://github.com/rails/rails/pull/15754))

*   Deprecated `serialized_attributes` without replacement.
    ([Pull Request](https://github.com/rails/rails/pull/15704))

*   Deprecated returning `nil` from `column_for_attribute` when no column
    exists. It will return a null object in Rails 5.0
    ([Pull Request](https://github.com/rails/rails/pull/15878))

*   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](https://github.com/rails/rails/commit/ed56e596a0467390011bc9d56d462539776adac1))

*   Deprecated passing Active Record objects to `.find` or `.exists?`. Call
    `#id` on the objects first.
    (Commit [1](https://github.com/rails/rails/commit/d92ae6ccca3bcfd73546d612efaea011270bd270),
    [2](https://github.com/rails/rails/commit/d35f0033c7dec2b8d8b52058fb8db495d49596f7))

*   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](https://github.com/rails/rails/commit/91949e48cf41af9f3e4ffba3e5eecf9b0a08bfc3))

### Notable changes

*   The PostgreSQL adapter now supports the `JSONB` datatype in PostgreSQL 9.4+.
    ([Pull Request](https://github.com/rails/rails/pull/16220))

*   The `#references` method in migrations now supports a `type` option for
    specifying the type of the foreign key (e.g. `:uuid`).
    ([Pull Request](https://github.com/rails/rails/pull/16231))

*   Added a `:required` option to singular associations, which defines a
    presence validation on the association.
    ([Pull Request](https://github.com/rails/rails/pull/16056))

*   Introduced `ActiveRecord::Base#validate!` that raises `RecordInvalid` if the
    record is invalid.
    ([Pull Request](https://github.com/rails/rails/pull/8639))

*   `ActiveRecord::Base#reload` now behaves the same as `m = Model.find(m.id)`,
    meaning that it no longer retains the extra attributes from custom
    `select`s.
    ([Pull Request](https://github.com/rails/rails/pull/15866))

*   Introduced the `bin/rake db:purge` task to empty the database for the
    current environment.
    ([Commit](https://github.com/rails/rails/commit/e2f232aba15937a4b9d14bd91e0392c6d55be58d))

*   `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](https://github.com/rails/rails/pull/15674),
    [2](https://github.com/rails/rails/pull/15786),
    [3](https://github.com/rails/rails/pull/15788))

*   Added support for `#pretty_print` in `ActiveRecord::Base` objects.
    ([Pull Request](https://github.com/rails/rails/pull/15172))

*   PostgreSQL and SQLite adapters no longer add a default limit of 255
    characters on string columns.
    ([Pull Request](https://github.com/rails/rails/pull/14579))

*   `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](https://github.com/rails/rails/pull/14569))

*   Introduced `#validate` as an alias for `#valid?`.
    ([Pull Request](https://github.com/rails/rails/pull/14456))

*   `#touch` now accepts multiple attributes to be touched at once.
    ([Pull Request](https://github.com/rails/rails/pull/14423))

*   Added support for fractional seconds for MySQL 5.6 and above.
    (Pull Request [1](https://github.com/rails/rails/pull/8240),
    [2](https://github.com/rails/rails/pull/14359))

*   Added support for the `citext` column type in PostgreSQL adapter.
    ([Pull Request](https://github.com/rails/rails/pull/12523))

*   Added support for user-created range types in PostgreSQL adapter.
    ([Commit](https://github.com/rails/rails/commit/4cb47167e747e8f9dc12b0ddaf82bdb68c03e032))


Active Model
------------

Please refer to the [Changelog][active-model] for detailed changes.

### Removals

*   Removed deprecated `Validator#setup` without replacement.
    ([Pull Request](https://github.com/rails/rails/pull/10716))

### Deprecations

*   Deprecated `reset_#{attribute}` in favor of `restore_#{attribute}`.
    ([Pull Request](https://github.com/rails/rails/pull/16180))

*   Deprecated `ActiveModel::Dirty#reset_changes` in favor of
    `#clear_changes_information`.
    ([Pull Request](https://github.com/rails/rails/pull/16180))

### Notable changes

*   Introduced the `restore_attributes` method in `ActiveModel::Dirty` to restore
    the changed (dirty) attributes to their previous values.
    (Pull Request [1](https://github.com/rails/rails/pull/14861),
    [2](https://github.com/rails/rails/pull/16180))

*   `has_secure_password` no longer disallows blank passwords (i.e. passwords
    that contains only spaces) by default.
    ([Pull Request](https://github.com/rails/rails/pull/16412))

*   `has_secure_password` now verifies that the given password is less than 72
    characters if validations are enabled.
    ([Pull Request](https://github.com/rails/rails/pull/15708))

*   Introduced `#validate` as an alias for `#valid?`.
    ([Pull Request](https://github.com/rails/rails/pull/14456))


Active Support
--------------

Please refer to the [Changelog][active-support] for detailed changes.

### Removals

*   Removed deprecated `Numeric#ago`, `Numeric#until`, `Numeric#since`,
    `Numeric#from_now`.
    ([Commit](https://github.com/rails/rails/commit/f1eddea1e3f6faf93581c43651348f48b2b7d8bb))

*   Removed deprecated string based terminators for `ActiveSupport::Callbacks`.
    ([Pull Request](https://github.com/rails/rails/pull/15100))

### Deprecations

*   Deprecated `Kernel#silence_stderr`, `Kernel#capture` and `Kernel#quietly`
    without replacement.
    ([Pull Request](https://github.com/rails/rails/pull/13392))

*   Deprecated `Class#superclass_delegating_accessor`, use
    `Class#class_attribute` instead.
    ([Pull Request](https://github.com/rails/rails/pull/14271))

*   Deprecated `ActiveSupport::SafeBuffer#prepend!` as
    `ActiveSupport::SafeBuffer#prepend` now performs the same function.
    ([Pull Request](https://github.com/rails/rails/pull/14529))

### Notable changes

*   `Object#try` and `Object#try!` can now be used without an explicit receiver.
    ([Commit](https://github.com/rails/rails/commit/5e51bdda59c9ba8e5faf86294e3e431bd45f1830),
    [Pull Request](https://github.com/rails/rails/pull/17361))

*   Introduced 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](https://github.com/rails/rails/commit/53e877f7d9291b2bf0b8c425f9e32ef35829f35b))

*   The `travel_to` test helper now truncates the `usec` component to 0.
    ([Commit](https://github.com/rails/rails/commit/9f6e82ee4783e491c20f5244a613fdeb4024beb5))

*   Introduced `Object#itself` as an identity function.
    (Commit [1](https://github.com/rails/rails/commit/702ad710b57bef45b081ebf42e6fa70820fdd810),
    [2](https://github.com/rails/rails/commit/64d91122222c11ad3918cc8e2e3ebc4b0a03448a))

*   `Object#with_options` can now be used without an explicit receiver.
    ([Pull Request](https://github.com/rails/rails/pull/16339))

*   Introduced `String#truncate_words` to truncate a string by a number of words.
    ([Pull Request](https://github.com/rails/rails/pull/16190))

*   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](https://github.com/rails/rails/pull/15819))

*   The `humanize` inflector helper now strips any leading underscores.
    ([Commit](https://github.com/rails/rails/commit/daaa21bc7d20f2e4ff451637423a25ff2d5e75c7))

*   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](https://github.com/rails/rails/commit/b16c36e688970df2f96f793a759365b248b582ad))


Credits
-------

See the
[full list of contributors to Rails](http://contributors.rubyonrails.org/) for
the many people who spent many hours making Rails the stable and robust
framework it is today. Kudos to all of them.

[railties]:       https://github.com/rails/rails/blob/4-2-stable/railties/CHANGELOG.md
[action-pack]:    https://github.com/rails/rails/blob/4-2-stable/actionpack/CHANGELOG.md
[action-view]:    https://github.com/rails/rails/blob/4-2-stable/actionview/CHANGELOG.md
[action-mailer]:  https://github.com/rails/rails/blob/4-2-stable/actionmailer/CHANGELOG.md
[active-record]:  https://github.com/rails/rails/blob/4-2-stable/activerecord/CHANGELOG.md
[active-model]:   https://github.com/rails/rails/blob/4-2-stable/activemodel/CHANGELOG.md
[active-support]: https://github.com/rails/rails/blob/4-2-stable/activesupport/CHANGELOG.md