python - Django: AttributeError: 'Q' 对象没有属性 'count'

Question

我尝试统计所有与会者的数量。我创建了以下for循环和查询集。但是，我总是收到错误 AttributeError: 'Q' object has no attribute 'count'。您知道如何解决这个问题吗？

# Get count of attendees per ticket and then combine these
tickets = Ticket.objects.filter(event=3)
count = 0
for ticket in tickets:
    new_count = ticket.attendees.filter=Q(
        canceled=False,
        order__status__in=(
            OrderStatus.PAID,
            OrderStatus.PENDING,
            OrderStatus.PARTIALLY_REFUNDED,
            OrderStatus.FREE,
        ),
    ).count()
    count += new_count
print(count)

Answer 1

您分配给 .filter:请注意，您编写的是 .filter=Q(，而不是 .filter(Q(...)).

您可以通过以下方式解决此问题:

tickets = Ticket.objects.filter(event=3)
count = 0
for ticket in tickets:
    new_count = ticket.attendees<b>.filter</b>(
        canceled=False,
        order__status__in=(
            OrderStatus.PAID,
            OrderStatus.PENDING,
            OrderStatus.PARTIALLY_REFUNDED,
            OrderStatus.FREE,
        )
    ).count()
    count += new_count
print(count)

话虽如此，我认为您可以通过如下所示的单个调用更有效地处理此问题:

Attendee.objects.filter(
    <b>ticket__event=3</b>,
    canceled=False,
    order__status__in=(
        OrderStatus.PAID,
        OrderStatus.PENDING,
        OrderStatus.PARTIALLY_REFUNDED,
        OrderStatus.FREE,
    )
).count()

因此，我们在此计算持有 event=3 的门票的参加者数量。这可能比进行 n 次查询更有效。