Follow a particular model class, updating associated Activity objects automatically.

def follow_model(self, model):
        """
        Follow a particular model class, updating associated Activity objects automatically.
        """
        if model:
          self.models_by_name[model.__name__.lower()] = model
          signals.post_save.connect(create_or_update, sender=model)
          signals.post_delete.connect(self.remove_orphans, sender=model)