DRF 将数据传递到相关字段答案

【问题标题】：DRF pass data into RelatedFieldDRF 将数据传递到相关字段
【发布时间】：2018-08-03 15:59:07
【问题描述】：

我有一个序列化器和一个用于通用外键关系的相关字段这应该用于序列化 content_object 这是一个 ContentType 实例。我需要检查我在相关字段中序列化的Notification 对象的type，以正确知道哪些附加字段要序列化到其中的data 参数中。实现这一目标的最佳方法是什么？

class NotificationRelatedField(serializers.RelatedField):

    def to_representation(self, value):
        data = {}
        # Need to check notification 'type' here
        return data


class NotificationRetrieveSerializer(serializers.ModelSerializer):
    content_object = NotificationRelatedField(read_only=True)

    class Meta:
        model = Notification
        fields = [
            'id',
            'created_at',
            'is_read',
            'type',
            'content_object',
        ]

【问题讨论】：

标签： python django django-rest-framework

【解决方案1】：

您可以使用SerializerMethodField 作为序列化通用 FK 关系，

class Content_Model_1_serializer(serializers.ModelSerializer):
    # you code
class Content_Model_2_serializer(serializers.ModelSerializer):
    # your code

class NotificationRetrieveSerializer(serializers.ModelSerializer):
    content_object = serializers.SerializerMethodField(read_only=True)

    def get_content_object(self, notification):
        if isinstance(notification.content_object, Content_Model_1):
            return Content_Model_1_serializer(notification.content_object).data
        if isinstance(notification.content_object, Content_Model_2):
            return Content_Model_2_serializer(notification.content_object).data
        ## and so on
        return None  # default case

    class Meta:
        model = Notification
        fields = [
            'id',
            'created_at',
            'is_read',
            'type',
            'content_object',
        ]

Content_Model_1 和 Content_Model_2 是通过通用 FK 关系关联的模型，Content_Model_1_serializer 和 Content_Model_2_serializer 是三个序列化器。

【讨论】：

【解决方案2】：

您需要重写序列化程序的to_representation 方法，以使用Notification 实例而不是字段的值来调用字段的to_representation 方法。

示例：

class NotificationRetrieveSerializer(serializers.ModelSerializer):
    content_object = NotificationRelatedField(read_only=True)

    class Meta:
        model = Notification
        fields = [
            'id',
            'created_at',
            'is_read',
            'type',
            'content_object',
        ]

    # override to_representation method
    def to_representation(self, instance):
        # python3 for `super` call
        result = super().to_representation(instance)

        # python2 for `super` call
        # result = super(
        #     NotificationRetrieveSerializer, self
        # ).to_representatio(instance)

        # here you call your field's `to_representation` with current instance
        # as the argument rather than as the `value` of the field.
        result['content_object'] = content_object_field.to_representation(instance)

        return result

class NotificationRelatedField(serializers.RelatedField):

    # here `value` is now the `Notification` instance
    def to_representation(self, value):
        data = {}

        # get the type and this field's value
        type = value.type
        content_object = value.content_object

        return data

【讨论】：