drf中的GenericAPIView(二级视图)

一、概述
二、GenericAPIView实现列表视图
- (一)、get请求获取所有数据
三、GenericAPIView实现详情视图
- (一)、获取某一条数据
- (二)、更新某一条数据
(三)、删除某一条数据
- (四)、lookup_filed和lookup_url_kwarg属性

一、概述

GenericAPIView继承自APIView
为列表视图和详情视图添加了常用的行为和属性，更加方便
可以和一个或者多个Mixin类配合使用
APIView虽然相对于django中的View类开发起来更加的便捷，但是在数据对象和序列化器对象上重复的代码很多，依然不够简洁，GenericAPIView提供了更加简便的方式
- 在类的开头写上queryset、serializer_class、lookup_field、lookup_url_kwarg、filter_backends和pagination_class属性，这样做的优点是：如果这些属性需要改变，只在开头改变即可，很便捷。如果不提取出公共的属性，需要改变很多的地方。
- 调用：
  - 方式一：直接在方法中使用self.属性名的方式调用
  - 方式二：使用self调用GenericAPIView中已经定义好的方法来调用，例如：self.get_queryset()调用queryset属性，self.get_serializer()调用serializer_class属性等
    二、GenericAPIView实现列表视图
    (一)、get请求获取所有数据
```python from rest_framework import status from .models import UserProfile from .serializers import UserProfileSerializers

class UserListGenericView(GenericAPIView): “”” 二级视图列表详情 “”” queryset = UserProfile.objects.all() serializer_class = UserProfileSerializers

def get(self, request):
    # users = self.queryset
    users = self.get_queryset()
    # serializer = self.serializer_class
    serializer = self.get_serializer(instance=users, many=True)
    return Response(serializer.data, status=status.HTTP_200_OK)

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#### (二)、post向数据库中创建一条数据
```python
from rest_framework import status
from .models import UserProfile
from .serializers import UserProfileSerializers
class UserListGenericView(GenericAPIView):
    """ 二级视图列表详情 """
    queryset = UserProfile.objects.all()
    serializer_class = UserProfileSerializers
    def post(self, request):
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        serializer.save()
        return Response(serializer.data, status=status.HTTP_201_CREATED)

三、GenericAPIView实现详情视图

在方法前边写上queryset，queryset=模型名.objects.all()，注意这里必须是all()
在方法中调用的时候需要使用self.get_object()方法，方法内不需要传入任何参数，就可以通过id/pk创建单条数据对象

(一)、获取某一条数据

from rest_framework.generics import GenericAPIView
from rest_framework.response import Response
from rest_framework import status
from .models import UserProfile
from .serializers import UserProfileSerializers
class UserDetailGenericView(GenericAPIView):
    """ 详情视图 """
    queryset = UserProfile.objects.all()
    serializer_class = UserProfileSerializers
    def get(self, request, pk):
        user = self.get_object()
        serializer = self.get_serializer(instance=user)
        return Response(serializer.data, status=status.HTTP_200_OK)

(二)、更新某一条数据

from rest_framework.generics import GenericAPIView
from rest_framework.response import Response
from rest_framework import status
from .models import UserProfile
from .serializers import UserProfileSerializers
class UserDetailGenericView(GenericAPIView):
    """ 详情视图 """
    queryset = UserProfile.objects.all()
    serializer_class = UserProfileSerializers
    def put(self, request, pk):
        user = self.get_object()
        serializer = self.get_serializer(instance=user, data=request.data)
        serializer.is_valid(raise_exception=True)
        serializer.save()
        return Response(serializer.data, status=status.HTTP_201_CREATED)

(三)、删除某一条数据

from rest_framework.generics import GenericAPIView
from rest_framework.response import Response
from rest_framework import status
from .models import UserProfile
from .serializers import UserProfileSerializers
class UserDetailGenericView(GenericAPIView):
    """ 详情视图 """
    queryset = UserProfile.objects.all()
    serializer_class = UserProfileSerializers
    def delete(self, request, pk):
        self.get_object().delete()
        return Response(status=status.HTTP_204_NO_CONTENT)

(四)、lookup_filed和lookup_url_kwarg属性

在使用GenericAPIView时，如果通过url传递参数，参数名默认时pk，如果写id会报如下的错误：

Expected view UserDetailGenericView to be called with a URL keyword argument named "pk". Fix your URL conf, or set the `.lookup_field` attribute on the view correctly.

原因：在源码中设定的是lookup_field字段为’pk’，会先去查找look_url_kwarg参数，如果该参数为空，则取lookup_field为对应的参数名

####源码分析
class GenericAPIView(views.APIView):
  """
  Base class for all other generic views.
  """
  queryset = None
  serializer_class = None
  # If you want to use object lookups other than pk, set 'lookup_field'.
  # For more complex lookup requirements override `get_object()`.
  lookup_field = 'pk'     ------->默认值为pk
  lookup_url_kwarg = None
  # The filter backend classes to use for queryset filtering
  filter_backends = api_settings.DEFAULT_FILTER_BACKENDS
  # The style to use for queryset pagination.
  pagination_class = api_settings.DEFAULT_PAGINATION_CLASS
  def get_object(self):
      queryset = self.filter_queryset(self.get_queryset())
      # Perform the lookup filtering.
      lookup_url_kwarg = self.lookup_url_kwarg or self.lookup_field  ---->如果lookup_url_kwarg不是None，而是id作为参数名，如果为None，则取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)
      # May raise a permission denied
      self.check_object_permissions(self.request, obj)
      return obj

解决办法：

方法一：设定lookup_url_kwarg=”id”，直接取lookup_url_kwarg

方法二：设定lookup_field=”id”，覆盖源码中的pk

class UserDetailGenericView(GenericAPIView):
""" 详情视图 """
queryset = UserProfile.objects.all()
serializer_class = UserProfileSerializers
# lookup_url_kwarg = 'id'
lookup_field = 'id'
def get(self, request, id):
   user = self.get_object()
   serializer = self.get_serializer(instance=user)
   return Response(serializer.data, status=status.HTTP_200_OK)
def put(self, request, id):
   user = self.get_object()
   serializer = self.get_serializer(instance=user, data=request.data)
   serializer.is_valid(raise_exception=True)
   serializer.save()
   return Response(serializer.data, status=status.HTTP_201_CREATED)
def delete(self, request, id):
   self.get_object().delete()
   return Response(status=status.HTTP_204_NO_CONTENT)