Ruby-on-rails – Rails 3.1: Better way to expose an engine’s helper within the client app

helpersrails-enginesruby-on-railsruby-on-rails-3.1view-helpers

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.

Best Answer

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

Related Solutions

Ruby-on-rails – How to call controller/view helper methods from the console in Ruby on Rails

To call helpers, use the helper object:

$ ./script/console
>> helper.number_to_currency('123.45')
=> "R$ 123,45"

If you want to use a helper that's not included by default (say, because you removed helper :all from ApplicationController), just include the helper.

>> include BogusHelper
>> helper.bogus
=> "bogus output"

As for dealing with controllers, I quote Nick's answer:

> app.get '/posts/1'
> response = app.response
# you now have a rails response object much like the integration tests

> response.body            # get you the HTML
> response.cookies         # hash of the cookies

# etc, etc

Rails 3.1: Engine vs. Mountable App

I have noticed the following:

Full Engine

With a full engine, the parent application inherits the routes from the engine. It is not necessary to specify anything in parent_app/config/routes.rb. Specifying the gem in Gemfile is enough for the parent app to inherit the models, routes etc. The engine routes are specified as:

# my_engine/config/routes.rb 
Rails.application.routes.draw do 
  # whatever 
end

No namespacing of models, controllers, etc. These are immediately accessible to the parent application.

Mountable Engine

The engine's namespace is isolated by default:

# my_engine/lib/my_engine/engine.rb
module MyEngine 
  class Engine < Rails::Engine 
    isolate_namespace MyEngine 
  end 
end

With a mountable engine, the routes are namespaced and the parent app can bundle this functionality under a single route:

# my_engine/config/routes.rb 
MyEngine::Engine.routes.draw do 
  #whatever 
end 

# parent_app/config/routes.rb 
ParentApp::Application.routes.draw do 
    mount MyEngine::Engine => "/engine", :as => "namespaced" 
end

Models, controllers, etc are isolated from the parent application - although helpers can be shared easily.

These are the main differences I have spotted. Perhaps there are others? I have asked over here, but have yet to receive a response.

My impression is that since a full engine does not isolate itself from the parent application, it is best used as a standalone application adjacent to the parent app. I believe name clashes could occur.

A mountable engine could be used in situations where you want to avoid name conflicts and bundle the engine under one specific route in the parent application. For example, I am working on building my first engine designed for customer service. The parent application could bundle it's functionality under a single route such as:

mount Cornerstone::Engine => "/cornerstone", :as => "help"

If I'm way off in my assumptions, someone please let me know and I'll fix this response. I have made a small article about the subject here Cheers!

Best Answer

Related Solutions

Ruby-on-rails – How to call controller/view helper methods from the console in Ruby on Rails

Rails 3.1: Engine vs. Mountable App

Related Topic