title: undefined method `attachment_will_change!'
body: <p>I have never seen this error before, <code>undefined method 'attachment_will_change!' for #&lt;Movie:0x00000106b16000&gt;</code></p>
  
  <p>Possibly something to do with carrierwave.</p>
  
  <p>Params in movie model.</p>
  
  <pre><code>def movie_params
     params.require(:movie).permit(:title, :rating, :total_gross, :attachment)
  end
  </code></pre>
  
  <p>carrierwave.rb in initializers.</p>
  
  <pre><code>CarrierWave.configure do |config|
  
    config.fog_credentials = {
  
      :provider               =&gt; 'abc',        # required
      :aws_access_key_id      =&gt; 'abcabc',     # required
      :aws_secret_access_key  =&gt; 'abcabcabc',  # required
  
    }
  
    config.fog_directory  = 'abcabc'  # required
    config.fog_public     = false     # optional, defaults to true
    config.fog_attributes = {'Cache-Control'=&gt;'max-age=315576000'}  # optional, defaults to {}
  
  end
  </code></pre>
  
  <p>imageuploader</p>
  
  <pre><code>   include CarrierWave::MiniMagick
  
  storage :fog
  
      def store_dir
          "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
        end
  
       version :thumb do
          process :resize_to_fit =&gt; [50, 50]
        end
  
       def extension_white_list
          %w(jpg jpeg gif png)
        end
  
      end
  </code></pre>