Django的rest_framework的视图之Mixin类编写视图源码解析

Mixin类编写视图

我们这里用auther表来做演示，先为auther和autherdetail写2个url

    url(r'^autherdetail/(?P<id>\d+)', views.Book_detail_cbv.as_view(), name="autherdetail"),
    url(r'^auther/', views.Book_cbv.as_view(),name="auther"),　　

然后分别为这2个类写对应的序列化的类

class authermodelserializer(serializers.ModelSerializer):
    class Meta:
        model = models.Auther
        fields = "__all__"

下面我们开写视图函数　　

需要在view文件中导入2个模块

from rest_framework import mixins
from rest_framework import generics

　

先介绍一下mixins类，我们主要用mixins类来对queryset对象或者model对象做操作

mixins.ListModelMixin

这个是用来显示queryset的数据

mixins.CreateModelMixin

这个用来创建一条model对象

mixins.RetrieveModelMixin

这个是用来显示一个model对象

mixins.DestroyModelMixin

这个是用来删除一个model对象

mixins.UpdateModelMixin

这个是用来更新一个model对象

　　

下面我们一个一个来看下面的类

1、看下mixins.ListModelMixin

这个类就只有一个方法，list方法，我们看下面的代码其实很熟悉，就是把一个queryset对象做序列化后，然后把序列化后的结果返回

class ListModelMixin(object):
    """
    List a queryset.
    """
    def list(self, request, *args, **kwargs):
        queryset = self.filter_queryset(self.get_queryset())

        page = self.paginate_queryset(queryset)
        if page is not None:
            serializer = self.get_serializer(page, many=True)
            return self.get_paginated_response(serializer.data)

        serializer = self.get_serializer(queryset, many=True)
        return Response(serializer.data)

　　

我们这里看到get_serializer中的参数有个queryset，那么这个queryset是什么呢？

通过上面的图，我们大致可以猜到，是由self.get_queryset()这个方法返回的结果，那么这个方法又干了什么呢？

首先我们要清楚self是什么？

从上面的图我们知道，self其实就是Auther_view这个类的实例对象，这个实例对象根本就没有get_queryset这个方法，但是由于这个类继承了3个类，我们一个一个找，最终在

generics.GenericAPIView这个类中找到了get_queryset这个方法

    def get_queryset(self):
        """
        Get the list of items for this view.
        This must be an iterable, and may be a queryset.
        Defaults to using `self.queryset`.

        This method should always be used rather than accessing `self.queryset`
        directly, as `self.queryset` gets evaluated only once, and those results
        are cached for all subsequent requests.

        You may want to override this if you need to provide different
        querysets depending on the incoming request.

        (Eg. return a list of items that is specific to the user)
        """
        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):
            # Ensure queryset is re-evaluated on each request.
            queryset = queryset.all()
        return queryset

　　

我们可以很清晰的看到get_queryset这个方法返回的结果就是self.queryset

那么self.queryset这个是什么呢？

我们在Auhter_view这个类中已经定义了这个类变量，所以我们这里定义的2个类变量的名称是固定的，不能随意修改的，属于配置项

下面我们走的流程就和之前差不多了

先定义get请求的处理的函数

因为mixins.ListModelMixin这个类是为了显示queryset对象的类，那么下面我们进入这个类

所以我们在get方法中，直接调用list方法的返回结果就是我们想要的结果

2、在来看mixin.CreateModelMixin类

这个类是为了创建一个model对象

首先进入这个类，看下具体的代码

class CreateModelMixin(object):
    """
    Create a model instance.
    """
    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        self.perform_create(serializer)
        headers = self.get_success_headers(serializer.data)
        return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)

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

    def get_success_headers(self, data):
        try:
            return {'Location': str(data[api_settings.URL_FIELD_NAME])}
        except (TypeError, KeyError):
            return {}

　　

下面我们来分析一下代码

首先这里有个self.get_serializer方法，这个方法也在generics.GenericAPIView类中

下面我们在来看下get_serializer方法

    def get_serializer(self, *args, **kwargs):
        """
        Return the serializer instance that should be used for validating and
        deserializing input, and for serializing output.
        """
        serializer_class = self.get_serializer_class()
        kwargs['context'] = self.get_serializer_context()
        return serializer_class(*args, **kwargs)

　　

我们在来看下get_serializer_class这个方法

我们看到非常清楚，这个函数的返回值就是我们先前定义个serializer_class的类变量，所以这个类变量的名称也不能修改，必须要这么写，属于一个配置类的变量

流程我们已经梳理清楚了，下面我们在看下post请求的视图函数

post请求调用的mixins.CreateModelMixin类中的create方法

class CreateModelMixin(object):
    """
    Create a model instance.
    """
    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        self.perform_create(serializer)
        headers = self.get_success_headers(serializer.data)
        return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)

　　

最后我们在看下perform.create这个方法，是不是很熟悉了，调用save方法保存

3、然后来看下mixins.RetriveModelMixin类

先看下这个类的代码

class RetrieveModelMixin(object):
    """
    Retrieve a model instance.
    """
    def retrieve(self, request, *args, **kwargs):
        instance = self.get_object()
        serializer = self.get_serializer(instance)
        return Response(serializer.data)

　　

然后在来看下get_object这个方法干了什么，这个方法同样在generics.GenericAPIView类中，我们一猜就知道这个方法是获取一个model对象，然后对这个model对象进行序列化处理

    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)

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

        return obj

　　

我们看到这个方法确实返回一个obj对象

最后看下get请求，调用mixins。RetrieveModelMixin类中的retieve方法返回我们要查询的结果

4、然后我们在看下mixins.DestroyModelMixin类

直接拿到model独享，然后调用perform_destory方法删除这个model对象

class DestroyModelMixin(object):
    """
    Destroy a model instance.
    """
    def destroy(self, request, *args, **kwargs):
        instance = self.get_object()
        self.perform_destroy(instance)
        return Response(status=status.HTTP_204_NO_CONTENT)

    def perform_destroy(self, instance):
        instance.delete()

　　

然后我们在看下视图函数中是如何处理delete请求的

class Autherdetail_view(mixins.RetrieveModelMixin,mixins.DestroyModelMixin,mixins.UpdateModelMixin,generics.GenericAPIView):
    queryset = models.Auther.objects.all()
    serializer_class = authermodelserializer

    def get(self,request,*args,**kwargs):
        return self.retrieve(request,*args,**kwargs)

    def delete(self,request,*args,**kwargs):
        return self.destroy(request,*args,**kwargs)

　　

直接返回mixins.DestoryModelMixins的detory函数的返回值就可以了

5、最后看下mixins.UpdateModelMixin类

同样，先获取model对象，然后获取序列化类，然后把model对象和request.data一起传递给序列化类

序列化类在调用调用sava方法保存数据

class UpdateModelMixin(object):
    """
    Update a model instance.
    """
    def update(self, request, *args, **kwargs):
        partial = kwargs.pop('partial', False)
        instance = self.get_object()
        serializer = self.get_serializer(instance, data=request.data, partial=partial)
        serializer.is_valid(raise_exception=True)
        self.perform_update(serializer)

        if getattr(instance, '_prefetched_objects_cache', None):
            # If 'prefetch_related' has been applied to a queryset, we need to
            # forcibly invalidate the prefetch cache on the instance.
            instance._prefetched_objects_cache = {}

        return Response(serializer.data)

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

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

　　

我们在看put请求的视图函数

class Autherdetail_view(mixins.RetrieveModelMixin,mixins.DestroyModelMixin,mixins.UpdateModelMixin,generics.GenericAPIView):
    queryset = models.Auther.objects.all()
    serializer_class = authermodelserializer

    def get(self,request,*args,**kwargs):
        return self.retrieve(request,*args,**kwargs)

    def delete(self,request,*args,**kwargs):
        return self.destroy(request,*args,**kwargs)

    def put(self,request,*args,**kwargs):
        return self.update(request,*args,**kwargs)