Ruby on Rails 4.0 Release Notes¶ ↑
Highlights in Rails 4.0:
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Ruby 2.0 preferred; 1.9.3+ required
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Strong Parameters
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Turbolinks
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Russian Doll Caching
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 in the main Rails repository on GitHub.
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.
Creating a Rails 4.0 application¶ ↑
You should have the 'rails' RubyGem installed $ rails new myapp $ cd myapp
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
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
Major Features¶ ↑

Upgrade¶ ↑
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Ruby 1.9.3 (commit) - Ruby 2.0 preferred; 1.9.3+ required
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New deprecation policy - Deprecated features are warnings in Rails 4.0 and will be removed in Rails 4.1.
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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.
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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.
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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.
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ActiveModel mass assignment protection (commit) - Rails 3 mass assignment protection is deprecated. Instead, use strong parameters.
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ActiveResource (commit) - ActiveResource is extracted to a separate gem. ActiveResource was not widely used.
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vendor/plugins removed (commit) - Use a Gemfile to manage installed gems.
ActionPack¶ ↑
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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 (
commentsfrom/posts/1/commentsand/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
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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.
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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.
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Decouple ActionView from ActionController (commit) - ActionView was decoupled from ActionPack and will be moved to a separated gem in Rails 4.1.
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Do not depend on ActiveModel (commit) - ActionPack no longer depends on ActiveModel.
General¶ ↑
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ActiveModel::Model (commit) -
ActiveModel::Model, a mixin to make normal Ruby objects to work with ActionPack out of box (ex. forform_for) -
New scope API (commit) - Scopes must always use callables.
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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.
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Support for specifying transaction isolation level (commit) - Choose whether repeatable reads or improved performance (less locking) is more important.
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Dalli (commit) - Use Dalli memcache client for the memcache store.
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Notifications start & finish (commit) - Active Support instrumentation reports start and finish notifications to subscribers.
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Thread safe by default (commit) - Rails can run in threaded app servers without additional configuration. Note: Check that the gems you are using are threadsafe.
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PATCH verb (commit) - In Rails, PATCH replaces PUT. PATCH is used for partial updates of resources.
Security¶ ↑
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match do not catch all (commit) - In the routing DSL, match requires the HTTP verb or verbs to be specified.
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html entities escaped by default (commit) - Strings rendered in erb are escaped unless wrapped with
raworhtml_safeis 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) andX-Content-Type-Options(prevents the browser from opening a jpeg as an exe).
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.
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Hash-based & Dynamic finder methods (GitHub)
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Mass assignment protection in Active Record models (GitHub, Pull Request)
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ActiveRecord::SessionStore (GitHub, Pull Request)
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Active Resource (GitHub, Pull Request, Blog)
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Action Caching (GitHub, Pull Request)
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Page Caching (GitHub, Pull Request)
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Sprockets (GitHub)
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Performance tests (GitHub, Pull Request)
Documentation¶ ↑
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Guides are rewritten in GitHub Flavored Markdown.
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Guides have a responsive design.
Railties¶ ↑
Please refer to the Changelog for detailed changes.
Notable changes¶ ↑
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New test locations
test/models,test/helpers,test/controllers, andtest/mailers. Corresponding rake tasks added as well. (Pull Request) -
Your app's executables now live in the
bin/directory. Runrake rails:update:binto getbin/bundle,bin/rails, andbin/rake. -
Threadsafe on by default
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Ability to use a custom builder by passing
--builder(or-b) torails newhas been removed. Consider using application templates instead. (Pull Request)
Deprecations¶ ↑
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config.threadsafe!is deprecated in favor ofconfig.eager_loadwhich provides a more fine grained control on what is eager loaded. -
Rails::Pluginhas gone. Instead of adding plugins tovendor/pluginsuse gems or bundler with path or git dependencies.
Action Mailer¶ ↑
Please refer to the Changelog for detailed changes.
Notable changes¶ ↑
Deprecations¶ ↑
Active Model¶ ↑
Please refer to the Changelog for detailed changes.
Notable changes¶ ↑
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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.
Deprecations¶ ↑
Active Support¶ ↑
Please refer to the Changelog for detailed changes.
Notable changes¶ ↑
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Replace deprecated
memcache-clientgem withdalliinActiveSupport::Cache::MemCacheStore. -
Optimize
ActiveSupport::Cache::Entryto reduce memory and processing overhead. -
Inflections can now be defined per locale.
singularizeandpluralizeaccept locale as an extra argument. -
Object#trywill 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 newObject#try!. -
String#to_datenow raisesArgumentError: invalid dateinstead ofNoMethodError: undefined method 'div' for nil:NilClasswhen given an invalid date. It is now the same asDate.parse, and it accepts more invalid dates than 3.x, such as:
“ # ActiveSupport 3.x "asdf".to_date # =>
NoMethodError: undefined methoddiv' 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 “`
Deprecations¶ ↑
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Deprecate
ActiveSupport::TestCase#pendingmethod, useskipfrom MiniTest instead. -
ActiveSupport::Benchmarkable#silencehas been deprecated due to its lack of thread safety. It will be removed without replacement in Rails 4.1. -
ActiveSupport::JSON::Variableis deprecated. Define your own#as_jsonand#encode_jsonmethods for custom JSON string literals. -
Deprecates the compatibility method
Module#local_constant_names, useModule#local_constantsinstead (which returns symbols). -
BufferedLoggeris deprecated. UseActiveSupport::Logger, or the logger from Ruby standard library. -
Deprecate
assert_presentandassert_blankin favor ofassert object.blank?andassert object.present?
Action Pack¶ ↑
Please refer to the Changelog for detailed changes.
Notable changes¶ ↑
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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.
Deprecations¶ ↑
Active Record¶ ↑
Please refer to the Changelog for detailed changes.
Notable changes¶ ↑
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Improve ways to write
changemigrations, making the oldup&downmethods no longer necessary.-
The methods
drop_tableandremove_columnare now reversible, as long as the necessary information is given. The methodremove_columnused to accept multiple column names; instead useremove_columns(which is not revertible). The methodchange_tableis also reversible, as long as its block doesn't callremove,changeorchange_default -
New method
reversiblemakes it possible to specify code to be run when migrating up or down. See the Guide on Migration -
New method
revertwill revert a whole migration or the given block. If migrating down, the given migration / block is run normally. See the Guide on Migration
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Adds PostgreSQL array type support. Any datatype can be used to create an array column, with full migration and schema dumper support.
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Add
Relation#loadto explicitly load the record and returnself. -
Model.allnow returns anActiveRecord::Relation, rather than an array of records. UseRelation#to_aif 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
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mysqlandmysql2connections will setSQL_MODE=STRICT_ALL_TABLESby default to avoid silent data loss. This can be disabled by specifyingstrict: falsein yourdatabase.yml. -
Remove IdentityMap.
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Remove automatic execution of EXPLAIN queries. The option
active_record.auto_explain_threshold_in_secondsis no longer used and should be removed. -
Adds
ActiveRecord::NullRelationandActiveRecord::Relation#noneimplementing the null object pattern for the Relation class. -
Added
create_join_tablemigration helper to create HABTM join tables. -
Allows PostgreSQL hstore records to be created.
Deprecations¶ ↑
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Deprecated the old-style hash based finder API. This means that methods which previously accepted “finder options” no longer do.
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All dynamic methods except for
find_by_...andfind_by_...!are deprecated. Here's how you can rewrite the code:-
find_all_by_...can be rewritten usingwhere(...). -
find_last_by_...can be rewritten usingwhere(...).last. -
scoped_by_...can be rewritten usingwhere(...). -
find_or_initialize_by_...can be rewritten usingfind_or_initialize_by(...). -
find_or_create_by_...can be rewritten usingfind_or_create_by(...). -
find_or_create_by_...!can be rewritten usingfind_or_create_by!(...).
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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.