Django（55）GenericAPIView源码分析

源码分析

GenericAPIView继承自APIView，也就是在APIView基础上再做了一层封装，源码如下：

class GenericAPIView(views.APIView):
    queryset = None
    serializer_class = None

    lookup_field = 'pk'
    lookup_url_kwarg = None

    filter_backends = api_settings.DEFAULT_FILTER_BACKENDS

    pagination_class = api_settings.DEFAULT_PAGINATION_CLASS

    def get_queryset(self):
        assert self.queryset is not None, (
            "'%s' should either include a `queryset` attribute, "
            "or override the `get_queryset()` method."
            % self.__class__.__name__
        )

        queryset = self.queryset
        if isinstance(queryset, QuerySet):
            queryset = queryset.all()
        return queryset

    def get_object(self):
        queryset = self.filter_queryset(self.get_queryset())

        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)

        self.check_object_permissions(self.request, obj)

        return obj

    def get_serializer(self, *args, **kwargs):
        serializer_class = self.get_serializer_class()
        kwargs.setdefault('context', self.get_serializer_context())
        return serializer_class(*args, **kwargs)

    def get_serializer_class(self):
        assert self.serializer_class is not None, (
            "'%s' should either include a `serializer_class` attribute, "
            "or override the `get_serializer_class()` method."
            % self.__class__.__name__
        )

        return self.serializer_class

    def get_serializer_context(self):
        return {
            'request': self.request,
            'format': self.format_kwarg,
            'view': self
        }

    def filter_queryset(self, queryset):
        for backend in list(self.filter_backends):
            queryset = backend().filter_queryset(self.request, queryset, self)
        return queryset

    @property
    def paginator(self):
        if not hasattr(self, '_paginator'):
            if self.pagination_class is None:
                self._paginator = None
            else:
                self._paginator = self.pagination_class()
        return self._paginator

    def paginate_queryset(self, queryset):
        if self.paginator is None:
            return None
        return self.paginator.paginate_queryset(queryset, self.request, view=self)

    def get_paginated_response(self, data):
        assert self.paginator is not None
        return self.paginator.get_paginated_response(data)

我们可以看到GenericAPIView中定义了6个类属性和8个方法，接下来一个个分析

类属性

• queryset = None
• serializer_class = None
• lookup_field = 'pk'
• lookup_url_kwarg = None
• filter_backends = api_settings.DEFAULT_FILTER_BACKENDS
• pagination_class = api_settings.DEFAULT_PAGINATION_CLASS

queryset

  queryset是用来控制视图返回给前端的数据。如果没什么逻辑，可以直接写在视图的类属性中，如果逻辑比较复杂，也可以重写get_queryset方法用来返回一个queryset对象。如果重写了get_queryset，那么以后获取queryset的时候就需要通过调用get_queryset方法。因为queryset` 这个属性只会调用一次，以后所有的请求都是使用他的缓存。

serializer_class

  serializer_class用来验证和序列化数据的。也是可以通过直接设置这个属性，也可以通过重写get_serializer_class来实现。

lookup_field

在检索的时候，根据什么参数进行检索。默认是pk，也就是主键。

lookup_url_kwarg

在检索的url中的参数名称。默认没有设置，跟lookup_field保持一致。

filter_backends

用于查询集过滤的过​​滤器类，默认是[]

pagination_class

用于查询集分页的样式。默认为None

方法

• get_queryset
• get_object
• get_serializer
• get_serializer_class
• get_serializer_context
• filter_queryset

get_queryset

def get_queryset(self):
    # 断言queryset是否不为None
    assert self.queryset is not None, (
        "'%s' should either include a `queryset` attribute, "
        "or override the `get_queryset()` method."
        % self.__class__.__name__
    )

    # 定义queryset属性，获取父类的queryset，如果父类没有定义类属性`queryset`，那么默认值就是None，就会报上面断言的错误
    queryset = self.queryset
    # 如果queryset是QuerySet对象，那么返回全部内容
    if isinstance(queryset, QuerySet):
        queryset = queryset.all()
    # 如果不是queryset，那么直接返回
    return queryset

get_queryset默认是返回数据库全部数据，如果想返回其他数据，需要自定义

get_object

def get_object(self):
    queryset = self.filter_queryset(self.get_queryset())

    # 查找过滤的条件，默认是pk
    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)

    # 可能会引发权限被拒绝
    self.check_object_permissions(self.request, obj)

    return obj

该方法是用于在数据检索(通过pk查找)的时候，返回一条数据的。

get_serializer

def get_serializer(self, *args, **kwargs):
    serializer_class = self.get_serializer_class()
    kwargs.setdefault('context', self.get_serializer_context())
    return serializer_class(*args, **kwargs)

返回应该用于验证和反序列化输入以及序列化输出的序列化器实例

get_serializer_class

def get_serializer_class(self):
    assert self.serializer_class is not None, (
        "'%s' should either include a `serializer_class` attribute, "
        "or override the `get_serializer_class()` method."
        % self.__class__.__name__
    )

    return self.serializer_class

返回用于序列化的类。默认使用self.serializer_class。如果您需要根据传入请求提供不同的序列化，您可能需要重写它。

get_serializer_context

def get_serializer_context(self):
    return {
        'request': self.request,
        'format': self.format_kwarg,
        'view': self
    }

提供给序列化的额外上下文。

filter_queryset

def filter_queryset(self, queryset):
    for backend in list(self.filter_backends):
        queryset = backend().filter_queryset(self.request, queryset, self)
    return queryset

给定一个查询集，使用正在使用的过滤器对其进行过滤。您不太可能想要覆盖此方法，但如果您想将配置的过滤后端应用到默认查询集，您可能需要从列表视图或自定义get_object 方法中调用它。

实战案例

class StudentsGenericView(GenericAPIView):
    queryset = Student.objects.all()  # 定义了类属性queryset，告诉视图要针对哪个模型做处理
    serializer_class = StudentModelSerializer  # 定义类属性serlializer_class，告诉视图你的序列化的类是什么
    def get(self, request, *args, **kwargs):
        pk = kwargs.get("pk")
        if pk:
            many = False
            query = self.get_object()  # 通过pk检索数据，返回一条数据
        else:
            many = True
            query = self.get_queryset()  # 返回动态的数据集，默认返回全部
        serializer = self.get_serializer(query, many=many)  # 如果数据对象是queryset对象，many需要为True
        return APIResponse(results=serializer.data)