d之后存在Django相关字段

Question

我有一个订单模型和其他与之相关的模型。用户可以删除这些项目中的任何一个，我必须检查删除后订单是否为空，如果为真，则设置为active False。一些基本的代码来说明它

class Order(models.Model):
    paid = models.BooleanField(default=False)
    active = models.BooleanField(default=True)
    user = models.ForeignKey(settings.AUTH_USER_MODEL)

    def empty_order():
         """
         I must implement it
         """

class HomeOrder(models.Model):
    ...
    order = models.OneToOneField(Order, related_name='primary_home')

class TourOrder(models.Model):
    ...
    order = models.ForeignKey(Order, related_name='tours')

我有一个post\u delete signals，它连接到与订单相关的每个模型：

post_delete.connect(delete_order_if_empty, sender=HomeOrder)
post_delete.connect(delete_order_if_empty, sender=TourOrder)

def delete_order_if_empty(sender, instance, **kwargs):
    if instance.order.empty_order():
        instance.order.active = False
        instance.order.save()

一个订单可以有一个家，所以如果家存在，我可以做order.primary\u主页如果家不存在，它将引发AttributeError，因为它是一个OneToOne关系。你知道吗

一个订单可以有很多行程，所以在空订单方法中，我想做如下检查。你知道吗

def empty_order():
    home = hasattr(self, 'primary_home')  # Avoid AttributeError exception
    tours = self.tours.exists()
    this_order_has_something = primary_home or tours
    return not this_order_has_something

现在，当我删除一个同胚序时，信号被触发，但是空的方法从未意识到这个同胚序不再存在。示例：

>>>o=Order.objects.create(...)
>>>o.primary_home # raise AttributeError
>>>h=HomeOrder.objetcs.create(order=o, ...)
>>>o.primary_home  # <HomeOrder: home-xx>
>>>h.delete()
>>>o.primary_home # still <HomeOrder: home-xx> Why?
>>>o.refresh_from_db()   
>>>o.primary_home # again <HomeOrder: home-xx>