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init guide: Cover the action_dispatch/railtie require from rails.rb

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Ryan Bigg 2010-12-28 15:06:26 +10:00
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railties/guides/source/initialization.textile
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@ -914,3 +914,115 @@ Then this Railtie sets up three more initializers:
* +active_support.initialize_time_zone+ * +active_support.initialize_time_zone+
We will cover what each of these initializers do when they run. We will cover what each of these initializers do when they run.
Once the +active_support/railtie+ file has finished loading the next file required from +railties/lib/rails.rb+ is the +action_dispatch/railtie+.
h4. +activesupport/lib/action_dispatch/railtie.rb+
This file defines the +ActionDispatch::Railtie+ class, but not before requiring +action_dispatch+.
h4. +activesupport/lib/action_dispatch.rb+
This file attempts to locate the +active_support+ and +active_model+ libraries by looking a couple of directories back from the current file and then adds the +active_support+ and +active_model+ +lib+ directories to the load path, but only if they aren't already, which they are.
<ruby>
activesupport_path = File.expand_path('../../../activesupport/lib', __FILE__)
$:.unshift(activesupport_path) if File.directory?(activesupport_path) && !$:.include?(activesupport_path)
activemodel_path = File.expand_path('../../../activemodel/lib', __FILE__)
$:.unshift(activemodel_path) if File.directory?(activemodel_path) && !$:.include?(activemodel_path)
</ruby>
In effect, these lines only define the +activesupport_path+ and +activemodel_path+ variables and nothing more.
The next two requires in this file are already done, so they are not run:
<ruby>
require 'active_support'
require 'active_support/dependencies/autoload'
</ruby>
The following require is to +action_pack+ (+activesupport/lib/action_pack.rb+) which has a 22-line copyright notice at the top of it and ends in a simple require to +action_pack/version+. This file, like other +version.rb+ files before it, defines the +ActionPack::VERSION+ constant:
<ruby>
module ActionPack
module VERSION #:nodoc:
MAJOR = 3
MINOR = 1
TINY = 0
PRE = "beta"
STRING = [MAJOR, MINOR, TINY, PRE].compact.join('.')
end
end
</ruby>
Once +action_pack+ is finished, then +active_model+ is required.
h4. +activemodel/lib/active_model.rb+
This file makes a require to +active_model/version+ which defines the version for Active Model:
<ruby>
module ActiveModel
module VERSION #:nodoc:
MAJOR = 3
MINOR = 1
TINY = 0
PRE = "beta"
STRING = [MAJOR, MINOR, TINY, PRE].compact.join('.')
end
end
</ruby>
Once the +version.rb+ file is loaded, the +ActiveModel+ module has its autoloaded constants defined as well as a sub-module called +ActiveModel::Serializers+ which has autoloads of its own. When the +ActiveModel+ module is closed the +active_support/i18n+ file is required.
h4. +activesupport/lib/active_support/i18n.rb+
This is where the +i18n+ gem is required and first configured:
<ruby>
begin
require 'i18n'
require 'active_support/lazy_load_hooks'
rescue LoadError => e
$stderr.puts "You don't have i18n installed in your application. Please add it to your Gemfile and run bundle install"
raise e
end
I18n.load_path << "#{File.dirname(__FILE__)}/locale/en.yml"
</ruby>
In effect, the +I18n+ module first defined by +i18n_railtie+ is extended by the +i18n+ gem, rather than the other way around. This has no ill effect. They both work on the same way.
This is another spot where +active_support/lazy_load_hooks+ is required, but it has already been required so it's not loaded again.
If +i18n+ cannot be loaded, the user is presented with an error which says that it cannot be loaded and recommends that it's added to the +Gemfile+. However, in a normal Rails application this gem would be loaded.
Once it has finished loading, the +I18n.load_path+ method is used to add the +activesupport/lib/active_support/locale/en.yml+ file to I18n's load path. When the translations are loaded in the initialization process, this is one of the files where they will be sourced from.
The loading of this file finishes the loading of +active_model+ and so we go back to +action_dispatch+.
h4. Back to +activesupport/lib/action_dispatch.rb+
The remainder of this file requires the +rack+ file from the Rack gem which defines the +Rack+ module. After +rack+, there's autoloads defined for the +Rack+, +ActionDispatch+, +ActionDispatch::Http+, +ActionDispatch::Session+. A new method called +autoload_under+ is used here, and this simply prefixes the files where the modules are autoloaded from with the path specified. For example here:
<ruby>
autoload_under 'testing' do
autoload :Assertions
...
</ruby>
The +Assertions+ module is in the +action_dispatch/testing+ folder rather than simply +action_dispatch+.
Finally, this file defines a top-level autoload, the +Mime+ constant.
h4. Back to +activesupport/lib/action_dispatch/railtie.rb+
After +action_dispatch+ is required in this file, the +ActionDispatch::Railtie+ class is defined and is yet another class that inherits from +Rails::Railtie+. This class defines some initial configuration option defaults for +config.action_dispatch+ before setting up a single initializer called +action_dispatch.configure+.
With +action_dispatch/railtie+ now complete, we go back to +railties/lib/rails.rb+.