Question

I have found a few articles addressing the issue of helpers within an engine not being accessible to the consuming (parent) application. To make sure we are all on the same page, let’s say we have this:

module MyEngine
  module ImportantHelper
    def some_important_helper
      ...do something important...
    end
  end
end

If you look at the rails engine documentation in the “Isolated engine’s helpers” (L293), it says:

  # Sometimes you may want to isolate engine, but use helpers that are defined for it.
  # If you want to share just a few specific helpers you can add them to application's
  # helpers in ApplicationController:
  #
  # class ApplicationController < ActionController::Base
  #   helper MyEngine::SharedEngineHelper
  # end
  #
  # If you want to include all of the engine's helpers, you can use #helpers method on an engine's
  # instance:
  #
  # class ApplicationController < ActionController::Base
  #   helper MyEngine::Engine.helpers
  # end

So if I ask anybody consuming my engine to add this to their application_controller.rb, then they will get access to all my important helper methods:

class ApplicationController < ActionController::Base
  helper MyEngine::ImportantHelper
end

This is what I want and it works, but that’s kind of a pain, especially if, as is my use case, everything the engine exposes can/should be used anywhere in the consuming app. So I dug around a bit more and found a solution that suggested I do the following:

module MyEngine
  class Engine < Rails::Engine
    isolate_namespace MyEngine

    config.to_prepare do
      ApplicationController.helper(ImportantHelper)
    end
  end
end

Now this is exactly what I want: to add all my ImportantHelper method to the parent app’s application helper. However, it doesn’t work. Can anybody help me figure out why this more-better solution does not work?

I am running ruby 1.8.7 with rails 3.1.3. Let me know if I missed any important info germane to the issue, and thanks in advance.

Answer 1

You can create an initializer to accomplish this like so:

module MyEngine
  class Engine < Rails::Engine
    initializer 'my_engine.action_controller' do |app|
      ActiveSupport.on_load :action_controller do
        helper MyEngine::ImportantHelper
      end
    end
  end
end