title: Writing a custom update method for a model in django
body: <p>I would like to write a custom update method for my model.
  Basically I would like to make sure that the fields that being passed to this method are fields that are present in this model.
  I came up with something like this</p>
  
  <pre><code>def update(self,dict):
      #Check if the fields in this data are present in this model
      for key in data:
          if not hasattr(self, key):
              #This property is not present
              data.pop(key)
      self.update(data)
  </code></pre>
  
  <p>However when I do something like this</p>
  
  <pre><code>modelMyobject.objects.filter(xxxxx).update(**dict)
  </code></pre>
  
  <p>This method never gets called. Any suggestions on what I could do to fix this ?</p>