Ruby on Rails 3.1: What's New, Release History & Support Lifecycle

What Is New in Ruby on Rails 3.1

How does the new Asset Pipeline change asset management in Rails 3.1?

The Asset Pipeline introduces a unified, pre-processing pipeline for CSS, JavaScript, and images, powered by Sprockets.

All assets live under app/assets, lib/assets or vendor/assets. You declare dependencies with directives such as //= require jquery in application.js or *= require_tree . in application.css. During deployment, rake assets:precompile concatenates, minifies and fingerprints files, producing digested URLs like /assets/application-3f2c1e9c.css.

Configuration lives in config/application.rb and the environment files:

# config/application.rb
config.assets.enabled = true
config.assets.version = '1.0'

# config/environments/production.rb
config.assets.compress = true
config.assets.digest   = true
config.assets.compile  = false

In practice, this means you no longer need to manually manage cache-busting query strings or hand-roll concatenated files; the pipeline does it for you.

Why is jQuery the default JavaScript library in Rails 3.1?

Rails 3.1 ships with the jquery-rails gem and the application generator automatically includes jquery and jquery_ujs in the asset manifest.

To switch back to Prototype you can run rails new myapp -j prototype or replace the gems in the Gemfile. The new default reflects the broader community adoption of jQuery and provides unobtrusive JavaScript helpers out of the box.

Typical app/assets/javascripts/application.js now looks like:

//= require jquery
//= require jquery_ujs
//= require_tree .

This matters if your existing codebase relies on Prototype helpers; you'll need to update selectors and remote forms accordingly.

What is HTTP Streaming and when should I enable it?

HTTP Streaming lets the server begin sending the response body while still generating the rest of the page, reducing perceived latency for large pages.

It is opt-in, requires Ruby 1.9.2 or newer, and needs a web server that supports streaming (e.g., NGINX with Unicorn). Enable it per-controller with stream or by using ActionController::Live in Rails 3.1.

class PostsController < ActionController::Base
  stream
  def index
    response.stream.write "Chunk 1"
    # heavy processing ...
    response.stream.write "Chunk 2"
    response.stream.close
  end
end

Use streaming for dashboards, long-polling APIs, or any endpoint where early data delivery improves user experience.

What breaking changes should I watch for when upgrading to Rails 3.1?

Several APIs were removed or altered, so you need to adjust your code before the upgrade.

• Ruby version must be ≥ 1.8.7; Ruby 1.9.1 segfaults, so upgrade to 1.9.2.
• RJS configuration (config.action_view.debug_rjs) is gone; remove it from development.rb.
• Asset helper options :cache and :concat are ignored; delete them from view helpers.
• CSV fixtures are deprecated and will disappear in 3.2; migrate to YAML or factories.
• Auto-link helper was extracted; add the rails_autolink gem if you still need it.
• rhtml and rxml template handlers were removed; use ERB, Haml, or Slim instead.
• Association destroy now only removes join-table rows for has_and_belongs_to_many and has_many :through; update any code that relied on the old behavior.
• Default config.action_dispatch.x_sendfile_header is nil; configure it per server if you use X-Sendfile.

Most teams will need to run their test suite after these changes; the asset pipeline will also surface missing assets early.