Railtie is the core of the Rails framework and provides several hooks to extend Rails and/or modify the initialization process.
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.
Developing a Rails extension does not require any implementation of Railtie, but if you need to interact with the Rails framework during or after boot, then Railtie is needed.
For example, an extension doing any of the following would require Railtie:
creating initializers
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
To extend Rails using Railtie, create a Railtie class which inherits from Rails::Railtie within your extension's namespace. This class must be loaded during the Rails boot process.
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
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
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.
# File lib/rails/railtie.rb, line 160 def abstract_railtie? ABSTRACT_RAILTIES.include?(name) end
# File lib/rails/railtie.rb, line 142 def console(&blk) @load_console ||= [] @load_console << blk if blk @load_console end
# File lib/rails/railtie.rb, line 154 def generators(&blk) @generators ||= [] @generators << blk if blk @generators end
# File lib/rails/railtie.rb, line 129 def inherited(base) unless base.abstract_railtie? base.send(:include, Railtie::Configurable) subclasses << base end end
# File lib/rails/railtie.rb, line 164 def railtie_name(name = nil) @railtie_name = name.to_s if name @railtie_name ||= generate_railtie_name(self.name) end
# File lib/rails/railtie.rb, line 136 def rake_tasks(&blk) @rake_tasks ||= [] @rake_tasks << blk if blk @rake_tasks end
# File lib/rails/railtie.rb, line 148 def runner(&blk) @load_runner ||= [] @load_runner << blk if blk @load_runner end
# File lib/rails/railtie.rb, line 125 def subclasses @subclasses ||= [] end
# File lib/rails/railtie.rb, line 170 def generate_railtie_name(class_or_module) ActiveSupport::Inflector.underscore(class_or_module).gsub("/", "_") end
# File lib/rails/railtie.rb, line 177 def config @config ||= Railtie::Configuration.new end
# File lib/rails/railtie.rb, line 181 def eager_load! end
# File lib/rails/railtie.rb, line 184 def load_console(app=self) self.class.console.each { |block| block.call(app) } end
# File lib/rails/railtie.rb, line 204 def load_generators(app=self) self.class.generators.each { |block| block.call(app) } end
# File lib/rails/railtie.rb, line 188 def load_runner(app=self) self.class.runner.each { |block| block.call(app) } end
# File lib/rails/railtie.rb, line 192 def load_tasks(app=self) extend Rake::DSL if defined? Rake::DSL self.class.rake_tasks.each { |block| self.instance_exec(app, &block) } # load also tasks from all superclasses klass = self.class.superclass while klass.respond_to?(:rake_tasks) klass.rake_tasks.each { |t| self.instance_exec(app, &t) } klass = klass.superclass end end
# File lib/rails/railtie.rb, line 208 def railtie_namespace @railtie_namespace ||= self.class.parents.detect { |n| n.respond_to?(:railtie_namespace) } end