title: Django update an instance using another instance
body: <p>For instance, I have instance a1 and a2.</p>
  
  <p>I'd like to update a1 to be same as a2. (except id field)</p>
  
  <p>Following is what I came up with, not sure if it will work though and if there's a better way.</p>
  
  <pre><code>a2_data = model_to_dict(a2, exclude=['id'])
  
  A.objcects.filter(id=a1.id).update(**a2_data)
  </code></pre>