delayed_paperclip invoke sweeper with paperclip after_post_process method

has_delayed_paperclip.rb

# http://stackoverflow.com/questions/14300427/how-do-i-add-a-model-specific-configuration-option-to-a-rails-concern
module HasDelayedPaperclip
  extend ActiveSupport::Concern

  module ActiveRecord
    def custom_process_in_background(name, options = {})
      process_in_background(name, options)

      include HasDelayedPaperclip

      after_post_process :clear_cache
    end
  end

  module ClassMethods
    # nothing yet
  end

  module InstanceMethods
    def clear_cache
      # http://pjkh.com/articles/manually-invoking-a-rails-sweeper/
      sweeper_class = (self.class.to_s + 'Sweeper').constantize
      sweeper_class.instance.after_save(self)
    end
  end
end