title: Updating selection of objects, each with a different value in bulk (Django)
body: <p>Imagine I have a python dictionary where keys are existing user ids, and values are scores to be added to those users' existing scores. </p>
  
  <p>For example: <code>{1: 1580, 4: 540, 2: 678}</code> (this could stretch to <code>n</code> k,v pairs)</p>
  
  <p>I need to update the scores of all these user objects (updated_score = original_score + new_score). One way to do it is iteratively, like so:</p>
  
  <pre><code>from django.db.models import F
  scores = {1: 1580, 4: 540, 2: 678}
  for user_id,score_to_add in scores.iteritems():
      UserProfile.objects.filter(user_id=user_id).update(score=F('score')+score_to_add)
  </code></pre>
  
  <p>But that's multiple DB calls. Can I do it in a single call? An illustrative example would be great. As you would have guessed, this is for a Django project. </p>