如何在gem中扩展ApplicationController？

Question

我想我会想出一种巧妙的方法在Rails 3.xgem中扩展ApplicationController。

在我的gem的lib/my_namespace/my_controller.rb中，我有：

class MyNamespace::MyController < ApplicationController

  before_filter :some_method
  after_filter :another_method

  def initialize
    # getting classname of the subclass to use for lookup of the associated model, etc.
    # and storing the model_class in an instance variable
    # ...
  end

  # define :some_method, :another_method, etc.
  # ...

private
  attr_accessor :subclass_defined_during_initialize # etc.

  # etc.
end

但是当Gem被加载时，app/controllers/application_controller.rb还没有被加载，所以它失败了：

/path/to/rvm/gemset/gems/activesupport-3.2.6/lib/active_support/dependencies.rb:251:
in `require': cannot load such file -- my_gem_name/application_controller (LoadError)

作为解决办法，我在gem的ApplicationController的lib/gem_namespace/application_controller.rb中定义了以下内容：

class ApplicationController < ActionController::Base
end

我假设即使我在那里定义了它，它也会在我的Rails 3应用程序的app/controllers/application_controller.rb中重新定义，这样扩展ApplicationController的应用程序中的控制器和扩展MyNamespace::MyController的控制器都将直接或间接地扩展在app/controllers/application_controller.rb中定义的ApplicationController。

但是，我们注意到在加载gem之后，扩展ApplicationController的控制器无法访问app/controllers/application_controller.rb中定义的方法。另外，ApplicationHelper (app/helpers/application_helper.rb)模块不再由其他助手模块加载。

如何在gem中的控制器中扩展ApplicationController以定义before_filter和after_filter，并使用initialize访问类名以确定关联模型的类，然后它可以在其方法中存储和使用该类？

更新2012/10/22

我想出的是：

在lib/your_gem_name/railtie.rb中

module YourGemsModuleName
  class Railtie < Rails::Railtie
    initializer "your_gem_name.action_controller" do
    ActiveSupport.on_load(:action_controller) do
      puts "Extending #{self} with YourGemsModuleName::Controller"
      # ActionController::Base gets a method that allows controllers to include the new behavior
      include YourGemsModuleName::Controller # ActiveSupport::Concern
    end
  end
end

在lib/your_gem_name/controller.rb中

module YourGemsModuleName
  module Controller
    extend ActiveSupport::Concern

    # note: don't specify included or ClassMethods if unused

    included do
      # anything you would want to do in every controller, for example: add a class attribute
      class_attribute :class_attribute_available_on_every_controller, instance_writer: false
    end

    module ClassMethods
      # notice: no self.method_name here, because this is being extended because ActiveSupport::Concern was extended
      def make_this_controller_fantastic
        before_filter :some_instance_method_available_on_every_controller # to be available on every controller
        after_filter :another_instance_method_available_on_every_controller # to be available on every controller
        include FantasticStuff
      end
    end

    # instance methods to go on every controller go here
    def some_instance_method_available_on_every_controller
      puts "a method available on every controller!"
    end

    def another_instance_method_available_on_every_controller
      puts "another method available on every controller!"
    end

    module FantasticStuff
      extend ActiveSupport::Concern

      # note: don't specify included or ClassMethods if unused

      included do
        class_attribute :class_attribute_only_available_on_fantastic_controllers, instance_writer: false
      end

      module ClassMethods
        # class methods available only if make_this_controller_fantastic is specified in the controller
        def some_fanastic_class_method
          put "a fantastic class method!"
        end
      end

      # instance methods available only if make_this_controller_fantastic is specified in the controller
      def some_fantastic_instance_method
        puts "a fantastic instance method!"
      end

      def another_fantastic_instance_method
        puts "another fantastic instance method!"
      end
    end
  end
end

Answer 1

这是一个吉斯特，它演示如何访问子类的类并将其存储在实例变量中，并在“前”和“后”筛选器中访问它。它使用包含方法。

Answer 2

对于这种特定的功能，我建议在gem中创建一个模块，并将该模块包含在应用程序控制器中

class ApplicationController < ActionController::Base
  include MyCoolModule
end

添加前面的过滤器等(将此添加到模块中)

def self.included(base)
  base.send(:before_filter, my_method)
end

更新:您可能只需要做一个更干净的base.before_filter :my_method。

Answer 3

真理要简单得多，也要灵活得多。

将此添加到lib/engine.rb中：class Engine < Rails::Engine; end

然后简单地使用：

ActionController::Base.class_eval do

  include SomethingFromMineGemModule

  # or:
  def hello_from_gem
    'Hey people!'
  end

end