to_representation 采用两种不同的值类型

Question

看不懂to_reprsentation(self, value)好吧，我有这样的案例

• 当我使用postman 时，当我发布并创建订单并且to_reprsentation 中的value 是int 类型时，状态返回“ORDERED, ...”

• 当我打开localhost:8000/orders/时，我得到Order对象不能转换成int，value这次是Order类型。

我搜索了我找到的每一篇文章，我不理解to_representation和to_internal_value这两种方法

models.py

class Product(models.Model):
    title = models.CharField(max_length=120)
    price = models.FloatField(max_length=20)

    def __str__(self):
        return f"{self.title} - {self.price}"

    class Meta:
        ordering = ['price']

    @property
    def images(self):
        for image in Image.objects.filter(product=self):
            yield image.src.url

和

class STATUS:
    UNORDERED = 0
    ORDERED = 1
    BEING_PROCESSED = 2
    BEING_DELIVERED = 3
    DELIVERED = 4
    RECEIVED = 5
    REFUND_REQUESTED = 6

和

class Order(models.Model):
    ORDER_STATUS = (
        (STATUS.UNORDERED, 'Unordered'),
        (STATUS.ORDERED, 'Ordered'),
        (STATUS.BEING_PROCESSED, 'Being processed'),
        (STATUS.BEING_PROCESSED, 'Being Delivered'),
        (STATUS.DELIVERED, 'Delivered'),
        (STATUS.RECEIVED, 'Received'),
        (STATUS.REFUND_REQUESTED, 'Refund requested')
    )

    products = models.ManyToManyField(Product)  #
    status = models.IntegerField(choices=ORDER_STATUS, default=STATUS.UNORDERED)

    class Meta:
        ordering = ['pk']

serializers.py

class ProductSerializer(serializers.ModelSerializer):
    images = serializers.SerializerMethodField()

    class Meta:
        model = Product
        fields = ['id', 'title', 'price', 'images']

    def get_images(self, obj):
        request = self.context.get('request', None)
        for url in obj.images:
            yield request.build_absolute_uri(url)


class StatusField(serializers.RelatedField):
    def to_internal_value(self, value):
        try:
            if int(value) > STATUS.ORDERED:
                raise APIException("Can't update an ordered order.")
        except ValueError:
            raise APIException('Unknown order status code')
        except TypeError:
            raise APIException('Order status must be an integer.')
        return value

    def to_representation(self, value):
        if isinstance(value, Order):
            return value.status if value.status <= STATUS.ORDERED else APIException('Hi')
        # if int(value) == 0:
        #     return "Unordered"
        # elif int(value) == 1:
        #     return "Ordered"
        # elif int(value) == 2:
        #     return "Being processed"
        # elif int(value) == 3:
        #     return "Being Delivered"
        # elif int(value) == 4:
        #     return "Delivered"
        # elif int(value) == 5:
        #     return "Received"
        # elif int(value) == 6:
        #     return "Refund requested"
        # raise serializers.ValidationError('Invalid order status code')


class OrderSerializer(serializers.ModelSerializer):
    products = ProductSerializer(many=True)
    status = StatusField(queryset=Order.objects.all())

    class Meta:
        model = Order
        fields = ['id', 'status', 'products']
        depth = 2

    def create(self, validated_data):  # needs auth
        products_list = validated_data.pop('products')
        order = Order.objects.create(**validated_data)
        for product_data in products_list:
            product = Product.objects.create(**product_data)
            order.products.add(product)
        order.save()
        return order

    def update(self, instance, validated_data):
        products_data = validated_data.pop('products')

        if instance.status >= STATUS.ORDERED:
            raise APIException("Can't update an ordered order")

        instance.status = validated_data.get('status', instance.status)

如果我使用 if isInstance，它会起作用，但我确实想知道为什么有时它返回 Order 而其他时候它返回 int

文档说 The value argument will typically be a model instance. 而这在我的案例中没有发生。

我错过了什么？

提前致谢。

Answer 1

序列化程序文档中描述的字段用于自定义关系字段。这就是文档通常说正在输入模型实例的原因。 status 字段适用于 serializers.IntegerField，而不适用于 serializers.RelationField。

不需要继承单独的 StatusField 来进行状态验证。相反，您可以使用validate_<fieldname> 函数。验证在保存时完成。

class OrderSerializer(serializers.ModelSerializer):
    def validate_status(self, value):
        try:
            if int(value) > STATUS.ORDERED:
                raise APIException("Can't update an ordered order.")
        except ValueError:
            raise APIException('Unknown order status code')
        except TypeError:
            raise APIException('Order status must be an integer.')
        return value

文档：https://www.django-rest-framework.org/api-guide/serializers/#field-level-validation

另外，从 django 3.0 开始，您可以使用models.IntegerChoices。如果您使用的是 django 3.0，则可以考虑使用它。文档：https://docs.djangoproject.com/en/3.0/ref/models/fields/#enumeration-types