多态模型序列化器

Question

我正在使用 Polymorphic 模型来设置通知：

我的模特：

class Notification(PolymorphicModel):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    created_by = models.ForeignKey(ElsUser, on_delete=models.CASCADE, default=None, related_name="creatednotifications")
    created_on = models.DateTimeField(default=timezone.now)
    created_for = models.ForeignKey(ElsUser, on_delete=models.CASCADE, default=None, related_name="receivednotifications")
    read = models.DateTimeField(default=None, null=True, blank=True)
    message = models.CharField(default=None, blank=True, null=True, max_length=800)

    @property
    def total(self):
        return self.objects.filter(created_for=self.request.user).count()

    @property
    def unread(self):
        return self.objects.filter(created_for=self.request.user,read=None).count()

    @property
    def read(self):
        return self.objects.filter(created_for=self.request.user).exclude(read=None).count()    

class WorkflowNotification(Notification):
    # permission_transition = models.ForeignKey(WorkflowStatePermissionTransition, on_delete=models.CASCADE)
    action = models.ForeignKey(UserAction, on_delete=models.CASCADE)

目前我只有一个继承自多态模型的 WorkFlowNotification 模型，但将来会有很多。

我正在尝试获取 API 中已登录用户的通知计数（总数）.. 总数作为属性字段给出以帮助相同

我的序列化器：

class NotificationSerializer(serializers.ModelSerializer):
    total = serializers.ReadOnlyField()
    read = serializers.ReadOnlyField()
    unread = serializers.ReadOnlyField()

    class Meta:
        model = Notification
        fields = ['id', 'total','read', 'unread']

在视图中：

   class NotificationsMeta(generics.ListAPIView):
    serializer_class = NotificationSerializer
    queryset = Notification.objects.all()

当我尝试运行服务器时，它显示：

  Got AttributeError when attempting to get a value for field `total` on serializer `NotificationSerializer`.
The serializer field might be named incorrectly and not match any attribute or key on the `WorkflowNotification` instance.
Original exception text was: Manager isn't accessible via WorkflowNotification instances.

Answer 1

我不确定调用负责在模型中查询的模型属性如何从序列化程序中提供适当的数据。不幸的是，我对此确实存在知识空白。我正在考虑替代解决方案。我希望以下应该有效。

class NotificationSerializer(serializers.ModelSerializer):
    total = serializers.serializers.SerializerMethodField()

    read = serializers.ReadOnlyField()
    unread = serializers.ReadOnlyField()

    class Meta:
        model = Notification
        fields = ['read', 'unread']


    def get_total(self, obj):
        user =  self.context['request'].user 
        return Notification.objects.filter(created_for=user).count()

如果这项工作有效，那么您也可以对已读和未读执行类似的操作。

为了获得 current_user 的通知，我们需要从视图中覆盖 get_queryset。

   class NotificationsMeta(generics.ListAPIView):
    serializer_class = NotificationSerializer
    def get_queryset(self):
       return Notification.objects.filter(created_for=self.request.user)

Answer 2

既然你只需要'meta data'，那么做一个模型序列化器有什么用呢？或者任何序列化程序，就此而言？序列化程序将为您提供模型对象的序列化实例。所以如果你有多个对象，你会得到多个序列化的对象作为响应。

将您的视图设为正常 APIView。因为没有必要序列化任何东西。

class NotificationsMeta(APIView):
    def get(self, request, format=None):
        qs = Notification.objects.filter(created_for=self.request.user)
        response = {
            'total': qs.count(),
            'read': qs.filter(read=None).count(),
            'unread': qs.exclude(read=None).count()
        }
        return Response(response)

现在从您的模型中删除那些属性函数。

我没有测试您的查询，只是从您的模型中复制了它们。您将需要检查它们是否正常工作。希望这有帮助。

多态模型序列化器

Polymorphic models serializer

django

django-rest-framework

django-polymorphic

为了获得 current_user 的通知，我们需要从视图中覆盖 get_queryset。