title: Django update on queryset to change ID of ForeignKey
body: <p>I am trying to update the ids of a bunch of objects and a related table that refers to the objects.</p>
  
  <pre><code>class Test(models.Model):
      id=models.IntegerField(primary_key=True)
  
  class Question(models.Model):
      id=models.AutoField(primary_key=True)
      test=models.ForeignKey('Test',db_column='testId')
  
  
  d={1:2,5:10}
  
  for fr,to in d.items():
      Test.objects.filter(id=fr).update(id=to)
      Question.objects.filter(test_id=fr).update(test_id=to)
  </code></pre>
  
  <p>I have tried <code>test_id</code>, <code>test__id</code> and <code>testId</code> but get this error message:</p>
  
  <pre><code>django.db.models.fields.FieldDoesNotExist: Question has no field named 'test_id'
  </code></pre>
  
  <p>Is this currently possible?</p>
  
  <p>Edit: I would prefer not to have to load the <code>Test</code> object for each id change.</p>