In Rails 3.0, a Rails::Application object was introduced which is nothing more than an Engine but with the responsibility of coordinating the whole boot process.
Initialization
Rails::Application is responsible for executing all railties and engines initializers. It also executes some bootstrap initializers (check Rails::Application::Bootstrap) and finishing initializers, after all the others are executed (check Rails::Application::Finisher).
Configuration
Besides providing the same configuration as Rails::Engine and Rails::Railtie, the application object has several specific configurations, for example “cache_classes”, “consider_all_requests_local”, “filter_parameters”, “logger” and so forth.
Check Rails::Application::Configuration to see them all.
Routes
The application object is also responsible for holding the routes and reloading routes whenever the files change in development.
Middlewares
The Application is also responsible for building the middleware stack.
Booting process
The application is also responsible for setting up and executing the booting process. From the moment you require “config/application.rb” in your app, the booting process goes like this:
1 2 3 4 5 6 7 8 9 10 11 12 | 1) require "config/boot.rb" to setup load paths2) require railties and engines3) Define Rails.application as "class MyApp::Application < Rails::Application"4) Run config.before_configuration callbacks5) Load config/environments/ENV.rb6) Run config.before_initialize callbacks7) Run Railtie#initializer defined by railties, engines and application. One by one, each engine sets up its load paths, routes and runs its config/initializers/* files.8) Custom Railtie#initializers added by railties, engines and applications are executed9) Build the middleware stack and run to_prepare callbacks10) Run config.before_eager_load and eager_load! if eager_load is true11) Run config.after_initialize callbacks |
Multiple Applications
If you decide to define multiple applications, then the first application
that is initialized will be set to Rails.application, unless
you override it with a different application.
To create a new application, you can instantiate a new instance of a class that has already been created:
1 2 3 4 5 | class Application < Rails::Applicationendfirst_application = Application.newsecond_application = Application.new(config: first_application.config) |
In the above example, the configuration from the first application was used
to initialize the second application. You can also use the
initialize_copy on one of the applications to create a copy of
the application which shares the configuration.
If you decide to define rake tasks, runners, or initializers in an
application other than Rails.application, then you must run
those these manually.