django rest框架在执行partial_update时删除validated_data中的多个到多个字段

我的序列化程序包括两个嵌套的序列化程序，因此根据文档，我将重写此序列化程序的更新方法 . 但是，发送到此更新方法的validated_data字段已“清除”，并且不存在多对多字段 .

serializer.initial_data是

QueryDict: {u'exchange': [u'1', u'9']}

此ModelSerializer的update（）内的validated_data是

{'adgroup_name'：你'adgroup_name'，你'creative'：[]，更新中的validated_data（）'campaign_id'：， u'exchange': [] }

基本上删除或清理了“交换”字段！我该如何避免这种情况？模型：

class AdGroup(models.Model):
adgroup_name = models.CharField(max_length=200, verbose_name="Name")
exchange = models.ManyToManyField(Exchange, verbose_name="Exchange")
creative = models.ManyToManyField(Creative, verbose_name="Creative")

更新视图中的代码：

class AdGroupViewSet(mixins.CreateModelMixin, mixins.RetrieveModelMixin, mixins.UpdateModelMixin, mixins.ListModelMixin, viewsets.GenericViewSet):
        queryset = AdGroup.objects.all().order_by('-id')
        serializer_class = AdGroupSerializer
        filter_fields = ('campaign_id',)
        def update(self,

 request, *args, **kwargs):
            try:
                partial = kwargs.pop('partial', False)
                instance = self.get_object()        
                serializer = self.get_serializer(instance, data=request.data, partial=partial)

                print 'view serializer data is'
                print serializer.initial_data
                serializer.is_valid(raise_exception=True)
                self.perform_update(serializer)
                return Response(serializer.data)
            except Exception as e:          
                print "update in viewset error "+str(e)
                traceback.print_exc()

        def perform_update(self, serializer):
                serializer.save()


        def partial_update(self, request, *args, **kwargs):
                kwargs['partial'] = True
                print 'partial update called with'
                print request.data
            return self.update(request, *args, **kwargs)

序列化程序代码是：

class AdGroupSerializer(serializers.ModelSerializer):
    exchange = ExchangeSerializer(many=True)
    creative = CreativeSerializer_reduced(many=True)
    class Meta:
        model = AdGroup
        fields = ('id','name','exchange','creative')

    def update(self, instance, validated_data):
        try:
            print 'serialzier update called and the validated_data is'
            print validated_data
            if validated_data['state']:
                print 'state is sent'
                instance.state = validated_data['state']

            if validated_data['exchange']:
                print 'exchange is  sent'
                print validated_data['exchange']
                instance.exchange = validated_data['exchange']

            if validated_data['creative']:
                print 'creaitve is sent'
                print validated_data['creative']
                instance.creative = validated_data['creative']

            instance.save()
            return instance
        except Exception as e:
            logger.info("Update Serializer error is "+str(e))

Exchange序列化程序是：

class ExchangeSerializer(serializers.ModelSerializer):
    class Meta:
        model = Exchange
        fields = ('id','name', )

Creaitve序列化器是：

class CreativeSerializer_reduced(serializers.ModelSerializer):

    class Meta:
        model = Creative
        fields = ('id','creative_name')