django - 如何在父序列化程序中获取总子项

Question

我想在父(票务柜台)序列化程序中显示与票务柜台关联的 worker 总数。

下面是两个序列化器:

class TicketCounterSerializer(serializers.ModelSerializer):
 workers = WorkerToCounterSerializer(many=True, read_only=True)    
 class Meta:
     model = TicketCounter
     fields = (
               'ticket_counter_name',
               'ticket_counter_description',
               'ticket_counter_address',
               'workers',
               )


class WorkerToCounterSerializer(serializers.ModelSerializer):
 class Meta:
     model = WorkerToTicketCounter
     fields = (
         'user',
         'ticket_counter',
         'worker',
     )

模型:

class TicketCounter(models.Model):
   user = models.ForeignKey(User, on_delete=models.CASCADE)
   ticket_counter_name = models.CharField(max_length=100, default="")
   ticket_counter_description = models.CharField(max_length=1500, default="")
   ticket_counter_address = models.CharField(max_length=1500, default="")


class WorkerToTicketCounter(models.Model):
   user = models.ForeignKey(User, on_delete=models.CASCADE)
   ticket_counter = models.ForeignKey(TicketCounter,related_name="workers")
   worker = models.ForeignKey(User,related_name='worker_for_ticket_counter')

这是我得到结果的方式:

{
        "ticket_counter_name": "First",
        "ticket_counter_description": "firsty",
        "ticket_counter_address": "222fdssssss",
        "workers": [
            {
                "user": 1,
                "ticket_counter": 3,
                "worker": 4,

            },
            {
                "user": 1,
                "ticket_counter": 3,
                "worker": 5,

            },

        ]
 }

这是我想要的

{
        "ticket_counter_name": "First",
        "ticket_counter_description": "firsty",
        "ticket_counter_address": "222fdssssss",
        "workers": 2 # just the total count
 }

如何只显示总数？

Answer 1

您可以使用注释 来完成此操作，并将其序列化为 IntegerField，例如:

class TicketCounterSerializer(serializers.ModelSerializer):
    num_workers = <b>serializers.IntegerField()</b>
    class Meta:
        model = TicketCounter
        fields = (
            'ticket_counter_name',
            'ticket_counter_description',
            'ticket_counter_address',
            'num_workers',
         )

在 ViewSet 中，我们可以指定:

from django.db.models import Count

class TicketCounterViewSet(viewsets.ListApiView):
    <b>queryset = TicketCounter.objects.annotate(num_workers=Count('workers'))</b>
    serializer_class = TicketCounterSerializer

因此，我们使用属性 num_workers 注释每个 TicketCounter 对象，该属性包含相关 WorkerToTicketCounter 对象的数量。

但我个人认为该模型有一些奇怪的名称:TicketCounter 看起来并不像一个计数器。虽然我不知道您的应用程序的全部范围，但我认为名为 Ticket 和 Worker 的模型可能更有意义。