轨道4-无方法错误

我正在使用PaperClip、AWS和s3_direct_upload gems上传简单的图像。我在这里学习本教程: http://blog.littleblimp.com/post/53942611764/direct-uploads-to-s3-with-rails-paperclip-and

文件已成功上传到S3,但在后处理过程中,我收到以下错误:

  Completed 500 Internal Server Error in 973ms

  NoMethodError (undefined method `upload_file_name=' for #<Choice:0x007f9ea60e02d0>):
   app/models/choice.rb:60:in `set_upload_attributes'
   app/controllers/choices_controller.rb:24:in `create'

这是我的模型(“Choice”)的样子,其中 upload_file_name 应定义为: https://gist.github.com/dodinas/7237377

你知道我在这里做错了什么吗?非常感谢!