django-rest-framework PUT manytomany通过模型

Question

我有一个与m2m关系的Django模型使用直通模型：

models.py

class ModelA(models.Model):
    name = models.CharField(max_length=64)

class ModelB(models.Model):
    name = models.CharField(max_length=64)
    other_models = models.ManyToManyField("ModelA", through="ModelC")

class ModelC(models.Model):
    model_a = models.ForeignKey("ModelA", related_name="link_to_model_a")
    model_b = models.ForeignKey("ModelB", related_name="link_to_model_b")
    some_other_info = models.TextField()
    class Meta:
        unique_together = ("model_a", "model_b", )

我想使用django-rest-framework序列化它：

serializers.py

class ModelCSerializer(ModelSerializer):
    class Meta:
        model = ModelC
        fields = ('id', 'model_a', 'model_b', 'some_other_info', )

class QModelBSerializer(ModelSerializer):
    class Meta:
        model = ModelB
        fields = ('id', 'other_models', )
    other_models = ModelCSerializer(many=True, required=False, source="link_to_model_b")

现在，对于现有模型，GET正确显示：

{
  "id": 2,
  "name": "i am an instance of model_b",
  "other_models": [
    {"id": 1, "model_a": 1,"model_b": 2, "some_other_info":"here is some other info"}
  ],
}

但是，如果我尝试将某些数据丢失，则会失败并返回unique_together错误。我认为将此作为PUT发送会导致更新（不应该引发unique_together错误）而不是创建？这是PUT的代码：

views.py

class ModelBDetail(APIView):
    def put(self, request, pk, format=None):
        model = ModelB.objects.get(id=pk)
        serializer = ModelBSerializer(model, data=request.data, context={"request": request})
        if serializer.is_valid():  # THIS IS RETURNING FALSE
            serializer.save()
            return Response(serializer.data)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

有什么想法吗？

Answer 1

Django rest框架文档指出开发人员需要实现creates and updates for nested representations。

Answer 2

尽管@Ivan对于编写我自己的创建和放大是正确的。更新fn，我看到的具体问题是嵌套序列化没有与之关联的实例属性。

新代码如下所示：

serializers.py

class ModelBSerializer(ModelSerializer):

    ....

    def update(self, model_instance, validated_data):
        model_c_serializer = self.fields["other_models"]

        model_c_data = validated_data.pop(model_c_serializer.source, [])

        for key, value in validated_data.iteritems():
            setattr(model_instance, key, value)
        model_instance.save()

        model_c_serializer.update(model_instance.link_to_model_b.all(),
model_c_data)

        return model_instance

class ModelCSerializer(ModelSerializer):

    ...

    def to_internal_value(self, data):

        # this is as good a place as any to set the instance
        try:
            model_class = self.Meta.model
            self.instance = model_class.objects.get(pk=data.get("id"))
        except ObjectDoesNotExist:
            pass

        return super(ModelCSerializer, self).to_internal_value(data)

基本上，我明确地为嵌套序列化程序调用{​​{1}}，并且我还强制每个嵌套的序列化程序检查为实例传递给它们的数据。