title: Why won't my GenericForeignKey cascade when deleting?
body: <p>I'm creating a custom commenting system which can attache comments to any model using the contenttypes GenericForeignKey.</p>
  
  <pre><code>class Comment(models.Model):
      body = models.TextField(verbose_name='Comment')
      user = models.ForeignKey(User)
      parent = models.ForeignKey('self', null=True, blank=True)
      created = models.DateTimeField(auto_now_add=True)
      content_type = models.ForeignKey(ContentType)
      object_id = models.PositiveIntegerField()
      content_object = generic.GenericForeignKey('content_type', 'object_id')
  </code></pre>
  
  <p>It is my understanding that when the model the comment is attached to is deleted, the delete should cascade and remove the comment as well.</p>
  
  <p>Unfortunately, this isn't happening and I'm stumped.  Are there any common reasons why the default delete behaviour would change?</p>