Rails 4 Upgrade Notes and TODOs

The following is a list of changes that aren't necessarily documented / useful to have a reference for.

Be sure you've read the official guides and release notes.

Also review the CHANGELOGs in the GitHub repository.

Pre-upgrade

Recommended changes before upgrading. These are not necessary, but can be made while still on Rails 3.2 and will ease the amount of work required to upgrade.

Gems

• Review your dependencies on http://www.ready4rails4.net/
• Switch to using the strong_parameters gem prepare for the removal of attr_accessible and/or attr_protected. attr_accessible and attr_protected have been extracted to a gem if this isn't feasible.
• Update to the latest version of simple_form. This will require removing all HTML markup from simple_form's i18n file. You will still have to update simple_form as part of the Rails update process, but you won't have to deal with HTML markup in i18n for labels.
• Update to the latest version of devise so you'll have strong_parameters support out of the box. Also forces you to deal with some of the upstream changes made to devise separately from updating Rails.
• Ensure you're using the latest database_cleaner gem to include the following fix: DatabaseCleaner/database_cleaner#253

Asset Pipeline

• Switch [asset-type]-url helpers in any sass files to asset-url('file', [asset-type]).
• Add vendor/images to precompile path
• Remove :assets group from Gemfile and remove RAILS_GROUP functionality from Bundler.require in config/application.rb. NOTE: To avoid bloating you application start-up time, consider vendoring assets that are provided as-is by a gem without additional functionality.

ActiveModel

• Use multi-line anchors for regular expressions when using the ActiveModel :format validator.

ActiveRecord

• Use to_a when you want an Array instead of an ActiveRecord::Relation.
• Wrap all relations passed to scope in a lambda.

Configuration

• Specify config.eager_load in all environments.
• Use http://railsdiff.org/ to review upcoming changes to the code generated by rails new to see any additional configuration changes that may affect you.

Post-Update

Changes to make after updating to Rails 4. The above changes are all included if you didn't make them before updating.

Gems

• Remove version requirements for sass-rails, coffee-rails and uglifier
• If using haml, use haml-rails to correclty configure cache_digests
• Remove strong_parameters, cache_digests and sextant from the Gemfile if present.

Asset Pipeline

• Switch all -url sass helpers to be asset-url('file.ext').

Configuration

• Specify compressors for CSS and JavaScript.

# remove
config.assets.compress = true

# add
config.assets.js_compressor = :uglifier
config.assets.css_compressor = :sass

Misc

• Convert db/schema.rb to use 1.9 hash syntax using rake db:schema:dump. This makes commits for the first migration under Rails 4 readable since it won't include coverting the syntax of the schema file.

Syntax (optional / deprecations)

• In controllers, use (before|after)_action instead of (before|after)_filter
• Switch to Model#update over Model#update_attributes
• Use Model.all instead of Model.scoped.