Question

I have a rails app called X and a rails mountable engine called Y.
App X has Devise and engine Y has CanCan which works with the hosts apps devise installation. In order to seperate the concerns of host app and mountable engine, the engine has a CanCan ability model as well as the host app.
My problem is the following, as per CanCan documentation you can change the default ability model like so https://github.com/ryanb/cancan/wiki/Changing-Defaults.
My problem is that if I setup the of default ability class in the mountable engines application controller like so:

module Y
  class ApplicationController < ActionController::Base
    def current_ability 
      @current_ability = Ability.new(current_user)
    end
  end
end

I get the following error:

uninitialized constant Ability

(On a side note, when I edit the file and reload the page without restarting the server it works fine)

If however I put the same method into the host app’s application controller:

class ApplicationController < ActionController::Base
  def current_ability 
    @current_ability = Y::Ability.new(current_user)
  end
end

Everything works as expected (which also means that Devise and CanCan are setup correctly).

Anyone got any ideas of why this is happening? I might not understand mountable engines correctly however I always thought that they are isolated from the host app, thus when accessing a page defined by the mountable engine the host app’s application controller shouldn’t even be executed.

Answer 1

it is most likely that your engines application controller is not loaded at all. Rails engines behave bad if you have same class name in the main app. here is the issue if you want to look at. I would recommend using the explicit declaration in your engine. Use Y::Ability instead of Ability.