title: Django admin process file after upload complete
body: <p>How do I process any operation on file after its upload is completed?</p>
  
  <p>I need to copy uploaded file on remote server immedeatly after upload, get response from remote server and put it into database.</p>
  
  <p>I have tried to do it in save_model of ModelAdmin like this:</p>
  
  <pre><code>class MyAdmin(admin.ModelAdmin):
      def save_model(self, request, obj, form, change):
          obj.answer = remote_upload(obj.file.path)
          obj.save()
  </code></pre>
  
  <p>remote_upload is self-written function, it successfully uploads a file, if I run it directly. but it fails in save_model.
  obj.file.path returns an MEDIA_PATH + filename and it looks like file is missing on moment of of save_model executing.</p>
  
  <p>How should I copy file the right way?</p>
  
  <p>ps. It looks like there is FileUploadHandler.upload_complete(), but I'm not sure if (and how) I can use it.</p>