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如何获取父序列化程序中的子级总数

django-serializer django-rest-framework django

Naroju · 技术社区 · 6 年前

我想在父(票证计数器)序列化程序中显示与票证计数器关联的工人总数。

下面是两个序列化程序:

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',
     )

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')

下面是我如何得到结果的:

{
        "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,

            },

        ]
 }

这就是我想要的

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

如何只显示总计数?

1 回复 | 直到 6 年前

willeM_ Van Onsem 6 年前

你可以用一个注释 ,并将其序列化为 IntegerField ,例如:

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

在 ViewSet ,我们可以指定:

from django.db.models import Count

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

因此,我们对每一个 TicketCounter 具有属性的对象 num_workers 相关 WorkerToTicketCounter 对象。

票务计数器 Ticket ,和 Worker