def CustomComment(models.Model):
   comment = models.TextInput()
   content_type    = models.ForeignKey(ContentType, related_name="colllaboration_set", null=True, blank=True)
   object_id       = models.PositiveIntegerField(null=True, blank=True)
   content_object  = generic.GenericForeignKey(ct_field='content_type', fk_field='object_id')
   #more fields