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 defaults.
Developing a 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:
-
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
Creating a Railtie
To extend Rails using a railtie, create a subclass of Rails::Railtie
. This class must be loaded during the Rails boot process, and is conventionally called MyNamespace::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::Railtie)
Initializers
To add an initialization step to the Rails boot process from your railtie, just define the initialization code with the initializer
macro:
class MyGem::Railtie < Rails::Railtie
initializer "my_gem.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 MyGem::Railtie < Rails::Railtie
initializer "my_gem.configure_rails_initialization" do |app|
app.middleware.use MyGem::Middleware
end
end
Finally, you can also pass :before
and :after
as options to initializer
, in case you want to couple it with a specific step in the initialization process.
Configuration
Railties can access a config object which contains configuration shared by all railties and the application:
class MyGem::Railtie < Rails::Railtie
# Customize the ORM
config.app_generators.orm :my_gem_orm
# Add a to_prepare block which is executed once in production
# and before each request in development.
config.to_prepare do
MyGem.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 MyGem::Railtie < Rails::Railtie
rake_tasks do
load "path/to/my_gem.tasks"
end
end
By default, 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 MyGem::Railtie < Rails::Railtie
generators do
require "path/to/my_gem_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 Rails 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 MyGem::Railtie < Rails::Railtie
server do
WebpackServer.start
end
end
Application
and Engine
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.
- A
- C
- G
- I
- R
- S
Constants
ABSTRACT_RAILTIES | = | %w(Rails::Railtie Rails::Engine Rails::Application) |
Attributes
[R] | load_index |
Class Public methods
abstract_railtie?() Link
configure(&block) Link
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.
console(&blk) Link
generators(&blk) Link
inherited(subclass) Link
instance() Link
Since Rails::Railtie
cannot be instantiated, any methods that call instance
are intended to be called only on subclasses of a Railtie
.
railtie_name(name = nil) Link
rake_tasks(&blk) Link
runner(&blk) Link
server(&blk) Link
subclasses() Link
Class Protected methods
increment_load_index() Link
Instance Public methods
config() Link
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.