simple_uploaded.rb

class SimpleUploaded < ActiveRecord::Base
  mount_uploader :uploaded_file, SomeUploader
end

some_uploader.rb

# encoding: utf-8

class SomeUploader < CarrierWave::Uploader::Base
  storage :file

  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end
end

test_script.rb

original = SimpleUploaded.new
original.uploaded_file = File.open("Gemfile")
original.save!

duplicate = original.dup

raise "The uploader points to the wrong model" if duplicate.uploaded_file.model.id == original.id