Extending Rails 4 engine models with concerns

Question

I am trying to extend a model from engine 1 with a concern from engine 2 through an app initializer, but I'm getting some weird behavior, here's what I've got:

Concern

module Engine2
  module Concerns
    module MyConcern

      extend ActiveSupport::Concern

      included do
        puts "Concern included!"
      end

      def jump
        puts 'Jumping!!!!'
      end
    end
  end
end

Initializer

require 'engine2/my_concern'

module Engine1
  class Member
    include Engine2::Concerns::MyConcern
  end
end

When I boot up the application, I see as expect the Concern included! message in the console, and the Member class can call the method jump , but as soon as I change any code in the host app I get the following error:

NoMethodError (undefined method 'jump' for #<Engine1::Member:0x007fe7533b4f10>)

and I have to reload the server, then it works fine again until I make another change in the host app, then it throws the error again, why is this happening and how can I avoid it?

Is there a better place where I should perform the class opening to include the concern instead of the initializer?

Answer 1

So I finally figured it out, basically what happens is that in development mode every model is reloaded on every code change but the initializers are only ran once at startup of the server, so once the code changes in the controller, the model is reloaded but doesn't include the concern anymore and therefore breaks.

I solved it by moving the code of the initializer to a to_prepare block in the application.rb .

For those who don't know, to_prepare adds a preparation callback that will run before every request in development mode, or before the first request in production.