code: def count_unread_messages_for(self, user):
          
          unread_total = self.filter(user=user,
                                     read_at__isnull=True,
                                     deleted_at__isnull=True).count()
  
          return unread_total
docs: Returns the amount of unread messages for this user
  
          :param user:
              A Django :class:`User`
  
          :return:
              An integer with the amount of unread messages.