Django，从模型更新

Question

假设我有这个小模型:

class Deal(models.Model):
    purchases = models.IntegerField(default=0)#amount of purchases so far

    increase_purchases(self,to_add):
        self.update( purchases =self.purchases + to_add)

当我尝试从 shell 使用这个 increase_purchases 模型时:

>>> x = Deal.objects.get(id=1)
>>> x.increase_purchases(4)
AttributeError: 'Deal' object has no attribute 'update'

如何为模型编写适当的函数，以便我可以根据需要更新选定的查询购买？

Answer 1

根据您的示例和描述，您可能想要这样的东西:

class Deal(models.Model):        
    purchase_count = models.IntegerField(default=0)

    def purchase(self, quantity=1):
       self.purchase_count = self.purchase_count + quantity

我同意 Ignacio；修改对象然后保存。所以在 shell 中:

> great_deal = Deal.objects.get(id=1)
> great_deal.purchase(4)
> great_deal.save()
> # or w/o an explicite argument it will record a single purchase
> # great_deal.purchase()

是的，我在 Deal 模型中稍微重命名了一些东西。这样看起来更具描述性。