Rails::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, Active Record, etc.) implements 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 extension does not require implementing a railtie, but if you need to interact with the
Rails framework during or after boot, then a railtie is needed.
For example, an extension doing any of the following would need a railtie:
Railsframework for the application, like setting a generator
config.*keys to the environment
setting up a subscriber with
adding Rake tasks
Rails using a railtie, create a subclass of
Rails::Railtie. This class must be loaded during the
Rails boot process, and is conventionally called
The following example demonstrates an extension which can be used with or without
# lib/my_gem/railtie.rb module MyGem class Railtie < Rails::Railtie end end # lib/my_gem.rb require "my_gem/railtie" if defined?(Rails::Railtie)
To add an initialization step to the
Rails boot process from your railtie, just define the initialization code with the
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
:after as options to
initializer, in case you want to couple it with a specific step in the initialization process.
Railties 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
If your railtie has Rake tasks, you can tell
Rails to load them through the method
class MyRailtie < Rails::Railtie rake_tasks do load "path/to/my_railtie.tasks" end end
Rails loads 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
Since filenames on the load path are shared across gems, be sure that files you load through a railtie have unique names.
Run another program when the
Rails server starts
In development, it's very usual to have to run another process next to the
Server. In example you might want to start the Webpack or React server. Or maybe you need to run your job scheduler process like Sidekiq. This is usually done by opening a new shell and running the program from here.
Rails allow you to specify a
server block which will get called when a
Rails server starts. This way, your users don't need to remember to have to open a new shell and run another program, making this less confusing for everyone. It can be used like this:
class MyRailtie < Rails::Railtie server do WebpackServer.start end end
An engine is nothing more than a railtie with some initializers already set. And since
Rails::Application is an engine, the same configuration described here can be used in both.
Be sure to look at the documentation of those specific classes for more information.
|ABSTRACT_RAILTIES||=||%w(Rails::Railtie Rails::Engine Rails::Application)|
Class Public methods
Allows you to configure the railtie. This is the same method seen in
Railtie::Configurable, but this module is no longer required for all subclasses of
Railtie so we provide the class method here.
Rails::Railtie cannot be instantiated, any methods that call
instance are intended to be called only on subclasses of a
railtie_name(name = nil) Link
Instance Public methods
This is used to create the
config object on Railties, an instance of
Railtie::Configuration, that is used by Railties and
Application to store related configuration.