Question

我有以下型号：

class Vehicle(models.Model):
    name = models.CharField(max_length=180, verbose_name='Nazwa')
    variant = models.IntegerField(default=0)
    route = models.ForeignKey(Route)
    active = models.BooleanField(default=True)
    class Meta:
        unique_together = ("name", "variant")
    def save(self, *args, **kwargs):
        vehicles = Vehicle.objects.filter(name=self.name).order_by('-variant')
        try:
            self.variant = vehicles[0].variant+1
        except:
            pass            
        super(Vehicle, self).save(*args, **kwargs)

问题是，当我创建新对象时，该名称不会出现在数据库中，它会创建variant = 1而不是default 0的对象。当我创建另一个具有相同名称的对象variant is incremented by 2 instead of 1时因此，当我创建具有相同名称的多个对象时，variants仅以奇数进行，e.g.: 1,3,5,7,9,11... 我的模特出了什么问题？

Answer 1

代码出错：您之前未检查此模型是否已保存。测试用例：

vehicle = models.Vehicle(name='Foo')
vehicle.save() #variant==0 by default
Vehicle.active = False
vehicle.save() #there is already a record with this name. Increment variant anyway

这种方法对我来说更好看：

def save(self, *args, **kwargs):
    if self.id is None: #works only when saved first time
        self.variant = Vehicle.objects.filter(name=self.name).count()
    super(Vehicle, self).save(*args, **kwargs)

独特的价值问题

1 个答案: