Rails Engine - Gems dependencies, how to load them into the application?

Question

I\'m doing an engine here, it works alright in stand alone.

When I transform it into a gem, and load it inside another application, I get a lot of undefined errors,

Answer 1

from paperclip's README :

For Non-Rails usage:

class ModuleName < ActiveRecord::Base
  include Paperclip::Glue
  ...
end

I had the same issue and that fixed it for me.