Ruby on Rails 4.2: What's New, Release History & Support Lifecycle

What Is New in Ruby on Rails 4.2

How does Rails 4.2 simplify background job processing?

Rails 4.2 introduces Active Job, a single API that abstracts over Resque, Sidekiq, Delayed Job and other queuing back-ends.

Jobs are defined by subclassing ActiveJob::Base and can receive Active Record objects directly because Global ID serialises them as URIs.

class TrashableCleanupJob < ActiveJob::Base
  def perform(trashable, depth)
    trashable.cleanup(depth)
  end
end

Action Mailer now ships with deliver_later, which enqueues the email as an Active Job instead of sending it synchronously.

UserMailer.welcome_email(user).deliver_later

In practice this means you can add background processing to an existing app with a single gem change and no code rewrite.

What database performance and schema enhancements arrive in Rails 4.2?

Rails 4.2 adds Adequate Record, which caches common find and find_by queries as prepared statements, cutting the SQL generation overhead by up to 2×.

Post.find(1)   # first call creates the prepared statement
Post.find(2)   # subsequent call reuses it

The migration DSL now supports foreign keys for MySQL, MySQL2 and PostgreSQL, and these keys are dumped into schema.rb so they survive schema loading.

add_foreign_key :articles, :authors
remove_foreign_key :accounts, column: :owner_id

This matters if you rely on referential integrity at the database level or need the extra performance boost from prepared statements.

Which developer productivity tools are baked into new Rails 4.2 apps?

New Rails 4.2 applications include the Web Console gem, giving you an interactive Ruby console on every error page and a console helper for on-demand debugging.

The config.x namespace lets you store arbitrary configuration without polluting the main config namespace.

# config/environments/production.rb
config.x.payment_processing.schedule = :daily
config.x.payment_processing.retries  = 3

Rails 4.2 also adds Rails.application.config_for for loading environment-specific YAML files, and a bin/setup script that standardises project bootstrapping.

What are the key breaking changes you must address when upgrading to Rails 4.2?

Watch out for these upgrade-time gotchas:

• render with a string argument now renders a template; use render file: "foo/bar" if you need to render a raw file.
• respond_with and class-level respond_to have been removed; add gem "responders", "~> 2.0" to continue using them.
• rails server now binds to localhost by default; start with rails server -b 0.0.0.0 to expose it on the network.
• :status symbols have changed - :request_entity_too_large is now :payload_too_large, etc.
• render nothing: true no longer adds a space; prefer head :ok for empty responses.
• filter callbacks are deprecated in favour of *_action equivalents (e.g., before_action instead of before_filter).

Most teams can upgrade by running the test suite, fixing the above items, and adding the responders gem if needed.