django - Django REST Framework 序列化程序中的嵌套注释字段

Question

我正在尝试查看 Django REST Framework 序列化程序中的嵌套注释(聚合/计算)字段。这将允许更干净地使用带注释的字段。这个帖子类似于Aggregate (and other annotated) fields in Django Rest Framework serializers但是我想要一个类似的技术来嵌套工作。下面的方法是可见的，它是如何在没有嵌套的情况下工作的，以及它似乎如何不与嵌套一起工作。

我知道这可以手动(使用 Django View )或使用重载我不感兴趣的数据库的方法来实现。但也许这个问题有一个高性能和优雅的解决方案。

以下作品(非嵌套)

楷模

class IceCreamCompany(models.Model):
    name = models.CharField(max_length=255)


class IceCreamTruck(models.Model):
    company = models.ForeignKey('IceCreamCompany', related_name='trucks')
    capacity = models.IntegerField()


class IceCreamTruckDriver(models.Model):
    name = models.CharField(max_length=255)
    first_name = models.CharField(max_length=255)
    truck = models.ForeignKey('IceCreamTruck', related_name='drivers')

序列化器

class IceCreamTruckDriverSerializer(serializers.ModelSerializer):

    class Meta:
        model = IceCreamTruckDriver
        fields = ('name', 'first_name')


class IceCreamTruckSerializer(serializers.ModelSerializer):
    drivers = IceCreamTruckDriverSerializer(many=True, read_only=True)

    class Meta:
        model = IceCreamTruck
        fields = ('capacity', 'drivers')


class IceCreamCompanySerializer(serializers.ModelSerializer):
    trucks = IceCreamTruckSerializer(many=True, read_only=True)
    amount_of_trucks = serializers.IntegerField()

    class Meta:
        model = IceCreamCompany
        fields = ('name', 'trucks', 'amount_of_trucks')

View 集

class IceCreamCompanyViewSet(viewsets.ModelViewSet):
    queryset = IceCreamCompany.objects.prefetch_related('trucks', 'trucks__drivers')\
                           .annotate(amount_of_trucks=Count('trucks'))\
                           .all()

    serializer_class = IceCreamCompanySerializer

结果

"results": [
        {
            "name": "Pete Ice Cream",
            "trucks": [
                {
                    "capacity": 35,
                    "drivers": [
                        {
                            "name": "Damian",
                            "first_name": "Ashley"
                        },
                        {
                            "name": "Wilfrid",
                            "first_name": "Lesley"
                        }
                    ]
                },
                {
                    "capacity": 30,
                    "drivers": [
                        {
                            "name": "Stevens",
                            "first_name": "Joseph"
                        }
                    ]
                },
                {
                    "capacity": 30,
                    "drivers": []
                }
            ],
            "amount_of_trucks": 3
        }
    ]

以下不起作用(嵌套)

相同型号

序列化器

class IceCreamTruckDriverSerializer(serializers.ModelSerializer):

    class Meta:
        model = IceCreamTruckDriver
        fields = ('name', 'first_name')


class IceCreamTruckSerializer(serializers.ModelSerializer):
    drivers = IceCreamTruckDriverSerializer(many=True, read_only=True)
    amount_of_drivers = serializers.IntegerField()

    class Meta:
        model = IceCreamTruck
        fields = ('capacity', 'drivers', 'amount_of_drivers')


class IceCreamCompanySerializer(serializers.ModelSerializer):
    trucks = IceCreamTruckSerializer(many=True, read_only=True)

    class Meta:
        model = IceCreamCompany
        fields = ('name', 'trucks')

View 集

class IceCreamCompanyViewSet(viewsets.ModelViewSet):
    queryset = IceCreamCompany.objects.prefetch_related('trucks', 'trucks__drivers')\
                           .annotate(trucks__amount_of_drivers=Count('trucks__drivers'))\
                           .all()

    serializer_class = IceCreamCompanySerializer

结果

AttributeError at /ice/
Got AttributeError when attempting to get a value for field `amount_of_drivers` on serializer `IceCreamTruckSerializer`.
The serializer field might be named incorrectly and not match any attribute or key on the `IceCreamTruck` instance.
Original exception text was: 'IceCreamTruck' object has no attribute 'amount_of_drivers'.

Answer 1

作为引用，还可以在模型 IceCreamTruck 上注释每辆卡车的司机数量，例如使用自定义管理器:

class AnnotatedManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().annotate(amount_of_drivers=Count('drivers'))

class IceCreamTruck(models.Model):
    company = models.ForeignKey('IceCreamCompany', related_name='trucks')
    capacity = models.IntegerField()

    objects = AnnotatedManager()

那么你不需要注释 View 集，因为 amount_of_drivers已在 trucks 上注释:

class IceCreamCompanyViewSet(viewsets.ModelViewSet):
    queryset = IceCreamCompany.objects.prefetch_related('trucks', 'trucks__drivers').all()
    serializer_class = IceCreamCompanySerializer 

它应该比在序列化器内计数更有效。