Every major component of Rails (Action Mailer, Action Controller, Action View, Active Record and Active Resource) is a Railtie. Each of them is responsible for their own initialization. This makes Rails itself absent of any component hooks, allowing other components to be used in place of any of the Rails defaults.
For example, an extension doing any of the following would require Railtie:
configuring a Rails framework for the application, like setting a generator
adding config.* keys to the environment
setting up a subscriber with ActiveSupport::Notifications
adding rake tasks
Creating your Railtie
The following example demonstrates an extension which can be used with or without Rails.
# lib/my_gem/railtie.rb module MyGem class Railtie < Rails::Railtie end end # lib/my_gem.rb require 'my_gem/railtie' if defined?(Rails)
To add an initialization step from your Railtie to Rails boot process, you just need to create an initializer block:
class MyRailtie < Rails::Railtie initializer "my_railtie.configure_rails_initialization" do # some initialization behavior end end
If specified, the block can also receive the application object, in case you need to access some application specific configuration, like middleware:
class MyRailtie < Rails::Railtie initializer "my_railtie.configure_rails_initialization" do |app| app.middleware.use MyRailtie::Middleware end end
Finally, you can also pass :before and :after as option to initializer, in case you want to couple it with a specific step in the initialization process.
Inside the Railtie class, you can access a config object which contains configuration shared by all railties and the application:
class MyRailtie < Rails::Railtie # Customize the ORM config.app_generators.orm :my_railtie_orm # Add a to_prepare block which is executed once in production # and before each request in development config.to_prepare do MyRailtie.setup! end end
Loading rake tasks and generators
If your railtie has rake tasks, you can tell Rails to load them through the method rake_tasks:
class MyRailtie < Rails::Railtie rake_tasks do load "path/to/my_railtie.tasks" end end
By default, Rails load generators from your load path. However, if you want to place your generators at a different location, you can specify in your Railtie a block which will load them during normal generators lookup:
class MyRailtie < Rails::Railtie generators do require "path/to/my_railtie_generator" end end
Application, Plugin and Engine
A Rails::Engine is nothing more than a Railtie with some initializers already set. And since Rails::Application and Rails::Plugin are engines, the same configuration described here can be used in all three.
Be sure to look at the documentation of those specific classes for more information.
ABSTRACT_RAILTIES = %w(Rails::Railtie Rails::Plugin Rails::Engine Rails::Application)
railties/lib/rails/railtie/configurable.rb railties/lib/rails/railtie/configuration.rb railties/lib/rails/railtie.rb