python - 如何在 django rest 框架 generics.RetrieveAPIView 中使用限制

Question

由于 django rest 框架中的 generics.RetrieveAPIView 应该只返回一条记录，我想在 get 查询方法中使用限制，如下所示

class PortUserView(generics.RetrieveAPIView):
    lookup_field = 'user'

    def get_queryset(self):

        return PortUser.objects.all()[:1]

出现类似这样的错误“一旦切片已被获取，就无法过滤查询”。

我的代码有什么问题？

Answer 1

您无需担心在retrieve 时从查询集中返回单个对象。 DRF 将使用其在 GenericAPIView 中定义的 .get_object() 为您自动处理 .

您只需使用以下代码，DRF 就会为您处理retrieve 操作。

class PortUserView(generics.RetrieveAPIView):
    lookup_field = 'user'
    queryset = PortUser.objects.all()

get_object(self)

Returns an object instance that should be used for detail views. Defaults to using the lookup_field parameter to filter the base queryset.

retrieve 操作的源代码:

def retrieve(self, request, *args, **kwargs):
    instance = self.get_object() # here the object is retrieved
    serializer = self.get_serializer(instance)
    return Response(serializer.data)

我们可以看到 DRF 使用 .get_object() 函数从查询集中获取对象。为了执行过滤，它使用 View 中定义的 lookup_field。

这里是实际的 get_object() 代码，使事情更清楚。

def get_object(self):
        """
        Returns the object the view is displaying.

        You may want to override this if you need to provide non-standard
        queryset lookups.  Eg if objects are referenced using multiple
        keyword arguments in the url conf.
        """
        queryset = self.filter_queryset(self.get_queryset())

        # Perform the lookup filtering.
        lookup_url_kwarg = self.lookup_url_kwarg or self.lookup_field

        assert lookup_url_kwarg in self.kwargs, (
            'Expected view %s to be called with a URL keyword argument '
            'named "%s". Fix your URL conf, or set the `.lookup_field` '
            'attribute on the view correctly.' %
            (self.__class__.__name__, lookup_url_kwarg)
        )

        filter_kwargs = {self.lookup_field: self.kwargs[lookup_url_kwarg]}
        obj = get_object_or_404(queryset, **filter_kwargs) # <-- can see that filtering is performed on the base of 'lookup_field'

        # May raise a permission denied
        self.check_object_permissions(self.request, obj)

        return obj # will return the single retrieved object