使用 Django 计数和 Q/F 查询

Question

我想将 Q/F 个对象与计数一起使用，但出现以下错误：

int() argument must be a string or a number, not 'Count'

我想获得所有交易：

start_date 是过去或今天的日期
end_date 是未来或今天的日期或参与（DealsParticipation 模型）低于最大值交易参与者数量（字段 nb_participants）。

我的模特：

class Deals(models.Model):
    u"""List of deals available to the participant 
    """

    brand = models.ForeignKey(Brand_Advertiser, blank=False, null=False, related_name='brands_of_deal')
    start_date = models.DateField(_("Date de debut"), blank=False, null=False, default=datetime.date.today)
    end_date = models.DateField(_("Date de fin"), blank=True, null=True)
    nb_participants=models.PositiveIntegerField(_("Nombre de participants maximum"), default=100, blank=True, null=True)


class DealsParticipation(TimeStampedModel):

    u"""Participation to deals by participants
    """

    deal = models.ForeignKey('Deals', blank=False, null=False, related_name='deal_participation')
    participant = models.ForeignKey(Participant, blank=False, null=False)

我尝试过的：

class CurrentDealsView(ListView):
    model = models.Deals

    def get_queryset(self):
        #get all the deals having started in the past or today and closing in the future or today
        now = datetime.now()
        start_date_condition=Q(start_date__lte=now)
        end_date_condition = Q(end_date__gte=now) | Q(end_date__isnull=True)
        #get all the deals with a number of participations lower than the maximal number of participants
        nb_participants_condition=Q(nb_participants__gt=Count('deal_participation'))
        return models.Deals.objects.filter(start_date_condition & (end_date_condition | nb_participants_condition))

已解决！

正如 emulbreh 所解释的，我不得不在注释中使用计数：

def get_queryset(self):
    #get all the deals having started in the past or today and closing in the future or today
    now = datetime.now()
    start_date_condition=Q(start_date__lte=now)
    end_date_condition = Q(end_date__gte=now) | Q(end_date__isnull=True)
    date_conditions=models.Deals.objects.filter(start_date_condition & end_date_condition)

    #get all the deals with a number of participations lower than the maximal number of participants
    return date_conditions.annotate(participation_count=Count('deal_participation')).filter(nb_participants__gt=F('participation_count'))

Answer 1

聚合函数（如Count）需要与annotate()或aggregate()一起使用。您可以从 filter() 或 Q():

引用带注释的字段

Deals.objects.annotate(
    participation_count=Count('deal_participation')
).filter(
    nb_participants__gt=F('participation_count')
)

有个example in the Django docs

使用 Django 计数和 Q/F 查询

Count and Q/F query with django

django

count

django-queryset

已解决！