h2. Ruby on Rails 3.0 Release Notes
Rails 3.0 is a landmark release as it delivers on the Merb/Rails merge promise made in December 2008. Rails 3.0 provides major upgrades to all of the components of Rails, including a complete overhaul of the router and query APIs.
One of the main achievements of this release, is that while there are loads of new features, old APIs have been deprecated with warnings wherever possible, so that you can implement the new features and conventions at your own pace. There is a backwards compatibility layer that will be supported during 3.0.x and removed in 3.1.
Rails 3.0 adds Active Model ORM abstraction, Abstract Controller generic controller abstraction as well as a consistent Plugin API giving developers full access to all the Rails internals that make Action Mailer, Action Controller, Action View, Active Record and Active Resource work.
These release notes cover the major upgrades, but don't include every little bug fix and change. If you want to see everything, check out the "list of commits":http://github.com/rails/rails/commits/master in the main Rails repository on GitHub.
endprologue.
h3. Upgrading from Rails 2.3.5 to Rails 3.0
As always, having a high coverage, passing test suite is your friend when upgrading. You should also first upgrade to Rails 2.3.5 and make sure your application still runs as expected before attempting to update to Rails 3.0. In general, the upgrade from Rails 2.x to 3.0 centers around three big changes:
h4. New Ruby Version Requirement
WARNING: Rails only runs on version 1.8.7 of Ruby or later. Support for previous versions of Ruby has been dropped and Rails 3.0 will no longer boot on any of these versions.
h4. The new boot process
As part of the shift to treating Rails apps as Rack endpoints, you are now required to have a +config/application.rb+ file, which takes over much of the work +config/environment.rb+ used to handle. Along with that comes a lot of internal change to the boot process, but those changes are mostly internal.
h4. Gems and gems and gems
The +config.gem+ method is gone and has been replaced by using +bundler+ and a +Gemfile+, see "Vendoring Gems":#vendoring-gems below.
h4. New APIs
Both the router and query interface have seen significant, breaking changes. There is a backwards compatibility layer that is in place and will be supported until the 3.1 release.
h4. Upgrade Process
To help with the upgrade process, a plugin named "Rails Upgrade":http://github.com/rails/rails_upgrade has been created to automate part of it.
Simply install the plugin, then run +rake rails:upgrade:check+ to check your app for pieces that need to be updated (with links to information on how to update them). It also offers a task to generate a +Gemfile+ based on your current +config.gem+ calls and a task to generate a new routes file from your current one. To get the plugin, simply run the following:
script/plugin install git://github.com/rails/rails_upgrade.git
You can see an example of how that works at "Rails Upgrade is now an Official Plugin":http://omgbloglol.com/post/364624593/rails-upgrade-is-now-an-official-plugin
Aside from Rails Upgrade tool, if you need more help, there are people on IRC and "rubyonrails-talk":http://groups.google.com/group/rubyonrails-talk that are probably doing the same thing, possibly hitting the same issues. Be sure to blog your own experiences when upgrading so others can benefit from your knowledge!
More information - "The Path to Rails 3: Approaching the upgrade":http://omgbloglol.com/post/353978923/the-path-to-rails-3-approaching-the-upgrade
h3. Application Creation
As stated above, you must be on Ruby 1.8.7 or later to boot up a Rails application. Rails will no longer boot on Ruby 1.8.6 or earlier.
Rails 3.0 is designed to run on 1.8.7 and also support Ruby 1.9.
There have been a few changes to the +rails+ script that's used to generate Rails applications:
* The application name, rails my_app, can now optionally be a path instead rails ~/code/my_app, your rails application will be name spaced under the application name you pass the +rails+ command.
* Additionally, any flags you need to generate the application now need to come after the application path, for example:
$ rails myapp --database=mysql
h4. 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 then read and acted on by the new "Bundler":http://github.com/wycats/bundler gem, which then vendors all your gems into the vendor directory, making your Rails application isolated from system gems.
More information: - "Using bundler":http://yehudakatz.com/2009/11/03/using-the-new-gem-bundler-today/
h4. Living on the Edge
Due to the use of +Gemfile+, the concept of freezing Rails was dropped, because it's always bundled/frozen inside your application. By default, it uses your system gems when bundling; however, if you want to bundle straight from the Git repository, you can pass the edge flag:
$ rails myapp --edge
More information:
* "Spinning up a new Rails app":http://yehudakatz.com/2009/12/31/spinning-up-a-new-rails-app/
* "Rails 3 and Passenger":http://cakebaker.42dh.com/2010/01/17/rails-3-and-passenger/
h3. Rails Architectural Changes
There are six major changes in the architecture of Rails.
h4. Railties Restrung
Railties was updated to provide a consistent plugin API for the entire Rails framework as well as a total rewrite of generators and the Rails bindings, the result is that developers can now hook into any significant stage of the generators and application framework in a consistent, defined manner.
h4. All Rails core components are decoupled
With the merge of Merb and Rails, one of the big jobs was to remove the tight coupling between Rails core components. This has now been achieved, and all Rails core components are now using the same API that you can use for developing plugins. This means any plugin you make, or any core component replacement (like DataMapper or Sequel) can access all the functionality that the Rails core components have access to and extend and enhance at will.
More information: - "The Great Decoupling":http://yehudakatz.com/2009/07/19/rails-3-the-great-decoupling/
h4. Active Model Abstraction
Part of decoupling the core components was extracting all ties to Active Record from Action Pack. This has now been completed. All new ORM plugins now just need to implement Active Model interfaces to work seamlessly with Action Pack.
More information: - "Make Any Ruby Object Feel Like ActiveRecord":http://yehudakatz.com/2010/01/10/activemodel-make-any-ruby-object-feel-like-activerecord/
h4. Controller Abstraction
Another big part of decoupling the core components was creating a base superclass that is separated from the notions of HTTP in order to handle rendering of views etc. This creation of +AbstractController+ allowed +ActionController+ and +ActionMailer+ to be greatly simplified with common code removed from all these libraries and put into Abstract Controller.
More Information: - "Rails Edge Architecture":http://yehudakatz.com/2009/06/11/rails-edge-architecture/
h4. Arel Integration
"Arel":http://github.com/brynary/arel (or Active Relation) has been taken on as the underpinnings of Active Record and is now required for Rails (it is installed for you when you do a gem bundle). Arel provides an SQL abstraction that simplifies out Active Record and provides the underpinnings for the relation functionality in Active Record.
More information: - "Why I wrote Arel":http://magicscalingsprinkles.wordpress.com/2010/01/28/why-i-wrote-arel/.
h4. Mail Extraction
Action Mailer ever since its beginnings has had monkey patches, pre parsers and even delivery and receiver agents, all in addition to having TMail vendored in the source tree. Version 3 changes that with all email message related functionality abstracted out to the "Mail":http://github.com/mikel/mail gem. This again reduces code duplication and helps create definable boundaries between Action Mailer and the email parser.
More information: - "New Action Mailer API in Rails 3":http://lindsaar.net/2010/1/26/new-actionmailer-api-in-rails-3
h3. Documentation
The documentation in the Rails tree is being updated with all the API changes, additionally, the "Rails Edge guides":http://guides.rails.info/ are being updated one by one to reflect the changes in Rails 3.0. The guides at "guides.rubyonrails.org":http://guides.rubyonrails.org/ however will continue to contain only the stable version of Rails (at this point, version 2.3.5, until 3.0 is released).
More Information: - "Rails Documentation Projects":http://weblog.rubyonrails.org/2009/1/15/rails-documentation-projects.
h3. Railties
With the decoupling of the main Rails frameworks, Railties got a huge overhaul so as to make linking up frameworks, engines or plugins as painless and extensible as possible:
* Each application now has it's own name space, application is started with YourAppName.boot for example, makes interacting with other applications a lot easier.
* You now have access to Rails.config which provides huge amount of configuration settings for your application.
* Anything under Rails.root/app is now added to the load path, so you can make app/observers/user_observer.rb and Rails will load it without any modifications.
* Rails 3.0 now provides a Rails.config object, which provides a central repository of all sorts of Rails wide configuration options.
Application generation has received extra flags allowing you to skip the installation of test-unit, Active Record, Prototype and Git. Also a new --dev flag has been added which sets the application up with the +Gemfile+ pointing to your Rails checkout (which is determined by the path to the +rails+ binary). See rails --help for more info.
Railties generators got a huge amount of attention in Rails 3.0, basically:
* Generators were completely rewritten and are backwards incompatible.
* Rails templates API and generators API were merged (they are the same as the former).
* Generators are no longer loaded from special paths anymore, they are just found in the Ruby load path, so calling script/generate foo will look for generators/foo_generator.
* New generators provide hooks, so any template engine, ORM, test framework can easily hook in.
* New generators allow you to override the templates by placing a copy at RAILS_ROOT/lib/templates.
* Rails::Generators::TestCase is also supplied so you can create your own generators and test them.
Also, the views generated by Railties generators had some overhaul:
* Views now use +div+ tags instead of +p+ tags.
* Scaffolds generated now make use of _form partials, instead of duplicated code in the edit and new views.
* Scaffold forms now use f.submit which returns "Create ModelName" or "Update ModelName" depending on the state of the object passed in.
Finally a couple of enhancements were added to the rake tasks:
* rake db:forward was added, allowing you to roll forward your migrations individually or in groups.
* rake routes CONTROLLER=x was added allowing you to just view the routes for one controller.
Railties now deprecates:
* RAILS_ROOT in favour of Rails.root,
* RAILS_ENV in favour of Rails.env, and
* RAILS_DEFAULT_LOGGER in favour of Rails.logger.
PLUGIN/rails/tasks, and PLUGIN/tasks are no longer loaded all tasks now must be in PLUGIN/lib/tasks.
More information:
* "Discovering Rails 3 generators":http://blog.plataformatec.com.br/2010/01/discovering-rails-3-generators
* "Making Generators for Rails 3 with Thor":http://caffeinedd.com/guides/331-making-generators-for-rails-3-with-thor
h3. Action Pack
There have been significant internal and external changes in Action Pack.
h4. Abstract Controller
Abstract Controller pulls out the generic parts of Action Controller into a reusable module that any library can use to render templates, render partials, helpers, translations, logging, any part of the request response cycle. This abstraction allowed ActionMailer::Base to now just inherit from +AbstractController+ and just wrap the Rails DSL onto the Mail gem.
It also provided an opportunity to clean up Action Controller, abstracting out what could to simplify the code.
Note however that Abstract Controller is not a user facing API, you will not run into it in your day to day use of Rails.
More Information: - "Rails Edge Architecture":http://yehudakatz.com/2009/06/11/rails-edge-architecture/
h4. Action Controller
* application_controller.rb now has protect_from_forgery on by default.
* The cookie_verifier_secret has been moved to initializers/cookie_verification_secret.rb.
* The session_store configuration has moved to initializers/session_store.rb.
* cookies.secure allowing you to set encrypted values in cookies with cookie.secure[:key] => value.
* cookies.permanent allowing you to set permanent values in the cookie hash cookie.permanent[:key] => value that raise exceptions on signed values if verification failures.
* You can now pass :notice => 'This is a flash message' or :alert => 'Something went wrong' to the format call inside a +respond_to+ block. The flash[] hash still works as previously.
* respond_with method has now been added to your controllers simplifying the venerable +format+ blocks.
* ActionController::Responder added allowing you flexibility in how your responses get generated.
Deprecations:
* filter_parameter_logging is deprecated in favour of config.filter_parameters << :password.
More Information:
* "Render Options in Rails 3":http://www.engineyard.com/blog/2010/render-options-in-rails-3/
* "Three reasons to love ActionController::Responder":http://weblog.rubyonrails.org/2009/8/31/three-reasons-love-responder
h4. Action Dispatch
Action Dispatch is new in Rails 3.0 and provides a new, cleaner implementation for routing.
* Big clean up and re-write of the router, the Rails router is now +rack_mount+ with a Rails DSL on top, it is a stand alone piece of software.
* Routes defined by each application are now name spaced within your Application module, that is:
# Instead of:
ActionController::Routing::Routes.draw do
map.resources :posts
end
# You do:
AppName::Application.routes do
resources :posts
end
* Added +match+ method to the router, you can also pass any Rack application to the matched route.
* Added +constraints+ method to the router, allowing you to guard routers with defined constraints.
* Added +scope+ method to the router, allowing you to namespace routes for different languages or different actions, for example:
scope 'es' { resources :projects,
:path_names => { :edit => 'cambiar' },
:as => 'projeto' }
# Gives you the edit action with /es/projeto/1/cambiar
* Added +root+ method to the router as a short cut for match '/', :to => path.
* You can pass optional segments into the match, for example match "/:controller(/:action(/:id))(.:format)", each parenthesized segment is optional.
* Routes can be expressed via blocks, for example you can call controller :home { match '/:action' }.
NOTE. The old style map commands still work as before with a backwards compatibility layer, however this will be removed in the 3.1 release.
Deprecations
* The catch all route for non-REST applications (/:controller/:action/:id) is now commented out.
* Routes :path_prefix no longer exists and :name_prefix now automatically adds "_" at the end of the given value.
More Information:
* "The Rails 3 Router: Rack it Up":http://yehudakatz.com/2009/12/26/the-rails-3-router-rack-it-up/
* "Revamped Routes in Rails 3":http://rizwanreza.com/2009/12/20/revamped-routes-in-rails-3
* "Generic Actions in Rails 3":http://yehudakatz.com/2009/12/20/generic-actions-in-rails-3/
h4. Action View
Major re-write was done in the Action View helpers, implementing Unobtrusive JavaScript (UJS) hooks and removing the old inline AJAX commands. This enables Rails to use any compliant UJS driver to implement the UJS hooks in the helpers.
What this means is that all previous remote_ helpers have been removed from Rails core and put into the "Prototype Legacy Helper":http://github.com/rails/prototype_legacy_helper. To get UJS hooks into your HTML, you now pass :remote => true instead. For example:
form_for @post, :remote => true
Produces: