As I promised at RailsConf, we’re finally good to go on the Rails 3.1: Release Candidate. This is a fantastically exciting release. We have three new star features and an even greater number of just awesome improvements. First the stars:

The Asset Pipeline
The star feature of 3.1 is the asset pipeline powered by Sprockets 2.0. It makes CSS and JavaScript first-class code citizens and enables proper organization, including use in plugins and engines. See my RailsConf keynote for a full tour. This comes with SCSS as the default for stylesheets and CoffeeScript as the default for JavaScript. Much documentation is on the way for this.

HTTP Streaming
This lets the browser download your stylesheet and javascripts while the server is still generating the response. The result is noticeable faster pages. It’s opt-in and does require support from the web server as well, but the popular combo of nginx and unicorn is ready to take advantage of it. There’s a great Railscast on HTTP streaming and the API documentation is strong too.

jQuery is now the default
We’ve made jQuery the default JavaScript framework that ships with Rails, but it’s silly easy to switch back to Prototype if you fancy. It’s all bundled up in the jquery-rails and prototype-rails gems. Just depend on the one you’d like in the Gemfile and it’ll Just Work.

Other good stuff:

• Reversible migrations: DRY migrations that know how to revert themselves. Cleaner, nicer migrations.
• Mountable engines: Engines can now have their own routing and helper scope. They can also take advantage of the asset pipeline (more documentation on this soon). Read the story behind mountable engines (even if the asset stuff is now out of date).
• Identity Map: It’s not enabled by default because of some important caveats that are still to be ironed out, but if you can deal with those, it’s a great way to cut down on the number of queries your app will trigger. Faster is better!
• Prepared statements: Active Record now uses cached prepared statements, which is a big boost for PostgreSQL in all cases and a boost for MySQL on complex statements.
• Rack::Cache on by default: This makes it possible to use HTTP caching with conditional get as a replacement for page caching (which we’ll soon factor into a plugin and remove from core).
• Turn test-output on Ruby 1.9: Much nicer test output courtesy of the Turn gem. It’s on with new applications by default on Ruby 1.9.
• Force SSL: It’s now easier than ever to keep your app safe with force_ssl. Either per-app or per-controller.
• Role-based mass-assignment protection: attr_protected now accepts roles, so it’s easier do deal with admin/non-admin splits and more.
• has_secure_password: Dead-simple BCrypt-based passwords. Now there’s no excuse not to roll your own authentication scheme.
• Custom serializers: Serialize objects with JSON or whatever else you’d like.

You can also check out the an even longer changelog and get a video overview from Railscast.

If you’re starting a new application, it’s strongly recommended that you do so using Ruby 1.9.2. Rails will continue to support 1.8.x until Rails 4.0, but it’s considered the legacy option. Ruby 1.9.x is where the action is. Get on board and enjoy the massive speed boost.

You can install the Rails 3.1: Release Candidate with gem install rails --pre. Enjoy and report any release candidate issues on Github. We expect to release the final version in a couple of weeks if all goes well.