在 Django Rest Framework (2.3.5) 中序列化 ManyToMany 抛出 ValueError答案

【问题标题】：Serializing ManyToMany in Django Rest Framework (2.3.5) throws ValueError在 Django Rest Framework (2.3.5) 中序列化 ManyToMany 抛出 ValueError
【发布时间】：2013-07-29 22:16:02
【问题描述】：

我有一个我认为是非常简单的序列化程序设置，但是当我尝试将数据放入我的 API 时，我收到以下错误：

ValueError: 实例应该是一个查询集或其他可迭代的许多=真

这是视图：

class QuizAPI(generics.RetrieveUpdateDestroyAPIView):
    model = Quiz
    serializer_class = QuizSerializer
    lookup_field = 'activity_id'

和序列化器：

class MediaResourceSerializer(serializers.ModelSerializer):
    owner = serializers.PrimaryKeyRelatedField(many=False, read_only=True)

    class Meta:
        model = MediaResource
        fields = ('owner', 'name', 'type', 'url')

class AnswerSerializer(serializers.ModelSerializer):
    class Meta:
        model = Answer
        fields = ('text','is_correct','order')

class QuestionSerializer(serializers.ModelSerializer):
    answers = AnswerSerializer(many=True, required=False)
    resources = MediaResourceSerializer(many=True, required=False)

    class Meta:
        model = Question
        fields = ( 
            'question_id', 
            'type', 
            'order', 
            'question_text', 
            'explanation', 
            'resources', 
            'grading_weight', 
            'answers' 
        )

class QuizSerializer(serializers.ModelSerializer):
    questions = QuestionSerializer(many=True, required=False)
    created_by = serializers.PrimaryKeyRelatedField(many=False, read_only=True)

    class Meta:
        model = Quiz
        fields = (
            'activity_id', 
            'name',  
            'is_hidden', 
            'created_by', 
            'created_date', 
            'last_updated', 
            'sharable', 
            'questions'
        )

如果我从 QuizSerializer 中注释掉“问题”字段，它运行得很好（当然没有问题数据）。

** 编辑：这是 PUT 调用负载：

activity_id: 4
created_by: 1
created_date: "2013-07-29T20:39:47.981Z"
is_hidden: false
last_updated: null
name: "This is only a test"
questions: []
sharable: true

【问题讨论】：

我从未解决过这个问题，但最终我的工作是只为我的应用序列化平面结构。

标签： python django rest serialization django-rest-framework

【解决方案1】：

问题看起来是嵌套表示do not support read–write，并且为写入操作序列化平面结构是要走的路。

【讨论】：

【解决方案2】：

对于模型之间的嵌套关系，在我看来，最好和最简单的方法是使用不同的序列化器

我的情况

class UserViewSet(viewsets.ModelViewSet):
    queryset = User.objects.all()

    def get_serializer_class(self):
        if self.request.method == 'GET':
            return GetUserModelSerializer
        else:
            return UserModelSerializer

你的情况：

class QuizAPI(generics.RetrieveUpdateDestroyAPIView):
    model = Quiz
    #serializer_class = QuizSerializer
    lookup_field = 'activity_id'

    def get_serializer_class(self):
        if self.request.method == 'GET':
            return QuizNestedSerializer
        else: # Means POST, PUT etc.
            return QuizSimpleSerializer

class QuizSimpleSerializer(serializers.ModelSerializer):
    # remove these lines
    # questions = QuestionSerializer(many=True, required=False)
    # created_by = serializers.PrimaryKeyRelatedField(many=False, read_only=True)

    class Meta:
        model = Quiz
        fields = (
            'activity_id', 
            'name',  
            'is_hidden', 
            'created_by', 
            'created_date', 
            'last_updated', 
            'sharable', 
            'questions'
        )

class QuizNestedSerializer(serializers.ModelSerializer):
    questions = QuestionSerializer(many=True, required=False)
    created_by = serializers.PrimaryKeyRelatedField(many=False, read_only=True)

    class Meta:
        model = Quiz
        fields = (
            'activity_id', 
            'name',  
            'is_hidden', 
            'created_by', 
            'created_date', 
            'last_updated', 
            'sharable', 
            'questions'
        )

【讨论】：