如何在Django Model Serializer中实现透传字段？

我是Django Rest Framework（DRF）新手，现在通过AJAX调用后端DRF API，希望传递请求成功后UI中要调用的JavaScript函数名称，用同一个AJAX函数处理多个UI交互，返回时动态执行对应的成功回调方法。

当前AJAX函数逻辑如下：

var saveEditedData = function (event) {
    let parentElement = event.parentElement;
    let enctype = (event.enctype) ? event.enctype : "application/x-www-form-urlencoded";
    let method = (event.method) ? event.method : "POST";

    $.ajax({
        cache: false,
        contentType: false,
        data: event.data,
        enctype: enctype,
        processData: false,
        type: method,
        url: event.url,
        success: function (response){
            console.log(response);
            if (response['onSuccessFn']){
                successFns[response['onSuccessFn']](response);
            } 
        },
        error: function (response) {
            let errors = response["responseJSON"]["errors"];
            displayErrors(parentElement, errors);
        }
    });
}

我使用的DRF序列化器及示例入站数据如下：

class DocumentCategorySerializer(serializers.ModelSerializer):
    id = serializers.ReadOnlyField()
    on_success_fn = serializers.SerializerMethodField()

    class Meta:
        model = DocumentCategory
        fields = ['id', 'name', 'description', 'on_success_fn']

    def get_on_success_fn(self, obj):
        return self.data['on_success_fn']

示例入站数据

• name: TestCategory
• description: Testing this
• on_success_fn: addCategorySuccessFn

现在遇到的问题是：模型序列化器的所有字段都来自数据库，添加的SerializerMethodField无法透传输入值，需要实现一个“透传”字段——输入什么值就输出什么值。

方法一：通过临时属性+自定义序列化输出 #

这种方法直接在序列化器中处理，接收前端传入的字段值，临时存储到实例属性中，最后在序列化输出时加入响应：

class DocumentCategorySerializer(serializers.ModelSerializer):
    id = serializers.ReadOnlyField()
    # 定义为可读写字段，允许接收前端输入
    on_success_fn = serializers.CharField(required=False, write_only=False)

    class Meta:
        model = DocumentCategory
        fields = ['id', 'name', 'description', 'on_success_fn']

    def create(self, validated_data):
        # 从验证数据中取出on_success_fn，不存入数据库
        on_success_fn = validated_data.pop('on_success_fn', None)
        # 创建模型实例
        instance = super().create(validated_data)
        # 将值存入实例临时属性
        if on_success_fn is not None:
            instance.on_success_fn = on_success_fn
        return instance

    def update(self, instance, validated_data):
        on_success_fn = validated_data.pop('on_success_fn', None)
        instance = super().update(instance, validated_data)
        if on_success_fn is not None:
            instance.on_success_fn = on_success_fn
        return instance

    def to_representation(self, instance):
        # 基础序列化输出
        representation = super().to_representation(instance)
        # 如果实例有临时属性，添加到响应中
        if hasattr(instance, 'on_success_fn') and instance.on_success_fn:
            representation['on_success_fn'] = instance.on_success_fn
        return representation

方法二：通过上下文(Context)传递字段值 #

这种方法在视图层获取前端传入的字段值，存入序列化器上下文，再在序列化输出时取出加入响应：

视图层代码

from rest_framework import viewsets
from .models import DocumentCategory
from .serializers import DocumentCategorySerializer

class DocumentCategoryViewSet(viewsets.ModelViewSet):
    queryset = DocumentCategory.objects.all()
    serializer_class = DocumentCategorySerializer

    def perform_create(self, serializer):
        # 从请求数据中获取on_success_fn，存入序列化器上下文
        serializer.context['on_success_fn'] = self.request.data.get('on_success_fn')
        serializer.save()

    def perform_update(self, serializer):
        serializer.context['on_success_fn'] = self.request.data.get('on_success_fn')
        serializer.save()

序列化器代码

class DocumentCategorySerializer(serializers.ModelSerializer):
    id = serializers.ReadOnlyField()

    class Meta:
        model = DocumentCategory
        fields = ['id', 'name', 'description']

    def to_representation(self, instance):
        representation = super().to_representation(instance)
        # 从上下文取出字段值，添加到响应
        on_success_fn = self.context.get('on_success_fn')
        if on_success_fn:
            representation['on_success_fn'] = on_success_fn
        return representation

为什么之前的SerializerMethodField不行？ #

1. SerializerMethodField默认是只读字段，无法接收前端传入的输入值；
2. 你在get_on_success_fn中调用self.data['on_success_fn']会触发递归调用，导致程序报错。

内容的提问来源于stack exchange，提问作者SeaSky