django model-message in save()方法打印了两次,但对象保存了一次

我使用的是django 2.0.8和Python 3.5。我编写了一个基类,它将行为封装在基类中。

保存对象时,应该打印一次消息。然而,当我运行应该保存对象的代码时,我得到消息“fireofmessage”打印了两次-为什么?

class Likeable(models.Model):
    likes = GenericRelation(Like)


    def action_is_permissible(self, actionable_object, actor):
        ct = ContentType.objects.get_for_model(actionable_object)
        object_id = actionable_object.id
        found_objects = Like.objects.filter(content_type=ct, object_id=object_id, liker=actor)

        return ((len(found_objects) == 0), ct, object_id, found_objects)


    def add_like(self, actionable_object, actor):

        can_add, ct, object_id, found_objects = self.action_is_permissible(actionable_object, actor)

        print(can_add, ct, object_id, found_objects)

        if can_add:
            print('Save Called!')
            # Create like object and save it
            like = self.likes.create(content_type=ct, object_id=object_id, liker=actor)
            like.save()
        else:
            # do nothing
            print('Nothing doing')
            return


    class Meta:
        abstract = True


class Foo(Likeable):
    name = models.CharField(max_length=255,default='')
    objects = models.Manager()

使用示例(略)

foo = Foo.objects.get(id=1)
p = User.objects.get(id=1)

foo.add_like(foo, p) # <- nasty API calling convention, but I digress

True foo 1 <QuerySet []>
Save Called!
Fire of like saved signal
Fire of like saved signal

当对象在数据库中只保存一次时,为什么要打印两次消息?