如何通过Queryset获取Django中已激活Pin对应Ticket的总金额

我正在开发一款活动应用，需要获取已激活的Pin对应的Ticket的总金额，但编写代码后出现错误：'QuerySet' object has no attribute 'ticket'。以下是我的模型和视图代码，求正确实现方法：

模型代码 #

class Ticket(models.Model):
    event = models.ForeignKey(Event, on_delete=models.CASCADE)
    price = models.PositiveIntegerField()
    category = models.CharField(max_length=100, choices=PASS, default=None, blank=False, null=False)
    added_date = models.DateField(auto_now_add=True)

    def __str__(self):
        return f"{self.event} "

    #Prepare the url path for the Model
    def get_absolute_url(self):
        return reverse("ticket-detail", args=[str(self.id)])

    def generate_pin():
        return ''.join(str(randint(0, 9)) for _ in range(6))

class Pin(models.Model):
    ticket = models.ForeignKey(Ticket, on_delete=models.CASCADE)
    value = models.CharField(max_length=6, default=generate_pin, blank=True)
    added = models.DateTimeField(auto_now_add=True,  blank=False)
    reference = models.UUIDField(primary_key = True, editable = False, default=uuid.uuid4)
    status = models.CharField(max_length=30, default='Not Activated')

    #Save Reference Number
    def save(self, *args, **kwargs):
         self.reference == str(uuid.uuid4())
         super().save(*args, **kwargs) 

    def __unicode__(self):
        return self.ticket

    class Meta:
        unique_together = ["ticket", "value"]

    def __str__(self):
         return f"{self.ticket}"

    def get_absolute_url(self):
        return reverse("pin-detail", args=[str(self.id)])

原视图代码 #

from django.db.models import Count, Sum
def profile(request):    
    amount_sold_pins = Pin.objects.filter(status='Activated')
    total_sold_tickets = amount_sold_pins.ticket.price
    total = total_sold_tickets.aggregate(total = 
    Sum('price')).get('total') or 0

context = {
    'guest':reservations,
    'total':total,
}

return render(request, 'user/profile.html', context)

错误原因 #

amount_sold_pins是Pin对象的查询集合（QuerySet），不是单个Pin实例，所以不能直接通过.ticket.price访问关联的Ticket属性。QuerySet没有ticket这个属性，这就是报错的根源。

正确实现方案 #

直接通过Pin的查询集，关联到Ticket的price字段进行聚合求和，修改后的视图代码如下：

from django.db.models import Sum
def profile(request):    
    # 过滤已激活的Pin，关联到Ticket的price字段求和
    total = Pin.objects.filter(status='Activated').aggregate(
        total=Sum('ticket__price')
    )['total'] or 0

    # 注意：原代码里的reservations变量需确保已正确定义并赋值
    context = {
        'guest': reservations,
        'total': total,
    }

    return render(request, 'user/profile.html', context)

额外优化提示 #

1. 模型里的generate_pin方法：需要加上@staticmethod装饰器，否则作为默认值调用时会报错（缺少实例参数）：

@staticmethod
def generate_pin():
    return ''.join(str(randint(0, 9)) for _ in range(6))

2. Pin模型的save方法：里面的self.reference == str(uuid.uuid4())是比较运算符，不是赋值，应改成=；另外字段定义已设置default=uuid.uuid4，这段赋值逻辑可以直接删除，避免重复生成UUID：

def save(self, *args, **kwargs):
    super().save(*args, **kwargs) 

内容的提问来源于stack exchange，提问作者apollos