engine.rb

module Crowdster
  class Engine < ::Rails::Engine
    isolate_namespace Crowdster

    config.to_prepare do
      if Crowdster.config
        Crowdster.config.user_class.constantize.class_eval do
          has_many :campaigns, class_name: 'Crowdster::Campaign'
        end
      end
    end
  end
end