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刚开始写views.py模块的代码，一般都是用def定义的函数视图，不过DRF更推荐使用class定义的类视图，这能让我们的代码更符合DRY（Don't Repeat Yourself）设计原则：
rest_framework.views.APIView是DRF封装的API视图，继承了django.views.generic.base.View：
我们用它把函数视图改写成类视图，编辑snippets/views.py：
from snippets.models import Snippetfrom snippets.serializers import SnippetSerializerfrom django.http import Http404from rest_framework.views import APIViewfrom rest_framework.response import Responsefrom rest_framework import statusclass SnippetList(APIView): """ List all snippets, or create a new snippet. """ def get(self, request, format=None): snippets = Snippet.objects.all() serializer = SnippetSerializer(snippets, many=True) return Response(serializer.data) def post(self, request, format=None): serializer = SnippetSerializer(data=request.data) if serializer.is_valid(): serializer.save() return Response(serializer.data, status=status.HTTP_201_CREATED) return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST) class SnippetDetail(APIView): """ Retrieve, update or delete a snippet instance. """ def get_object(self, pk): try: return Snippet.objects.get(pk=pk) except Snippet.DoesNotExist: raise Http404 def get(self, request, pk, format=None): snippet = self.get_object(pk) serializer = SnippetSerializer(snippet) return Response(serializer.data) def put(self, request, pk, format=None): snippet = self.get_object(pk) serializer = SnippetSerializer(snippet, data=request.data) if serializer.is_valid(): serializer.save() return Response(serializer.data) return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST) def delete(self, request, pk, format=None): snippet = self.get_object(pk) snippet.delete() return Response(status=status.HTTP_204_NO_CONTENT)
类视图的代码跟函数视图是非常类似的，区别在于GET、POST等方法是用的函数而不是if语句，可以更好的解耦代码。
改了views.py代码后，需要同时修改snippets/urls.py：
from django.urls import pathfrom rest_framework.urlpatterns import format_suffix_patternsfrom snippets import viewsurlpatterns = [ path('snippets/', views.SnippetList.as_view()), path('snippets/ /', views.SnippetDetail.as_view()),]urlpatterns = format_suffix_patterns(urlpatterns) 为什么要加个as_view()方法？
因为path()的参数必须是可调用的，在源码中能看到elif callable(view)：
def _path(route, view, kwargs=None, name=None, Pattern=None): if isinstance(view, (list, tuple)): # For include(...) processing. pattern = Pattern(route, is_endpoint=False) urlconf_module, app_name, namespace = view return URLResolver( pattern, urlconf_module, kwargs, app_name=app_name, namespace=namespace, ) # callable判断 elif callable(view): pattern = Pattern(route, name=name, is_endpoint=True) return URLPattern(pattern, view, kwargs, name) else: raise TypeError('view must be a callable or a list/tuple in the case of include().') as_view()方法返回了一个内部定义的可调用函数：
@classonlymethoddef as_view(cls, **initkwargs): """Main entry point for a request-response process.""" for key in initkwargs: if key in cls.http_method_names: raise TypeError( 'The method name %s is not accepted as a keyword argument ' 'to %s().' % (key, cls.__name__) ) if not hasattr(cls, key): raise TypeError("%s() received an invalid keyword %r. as_view " "only accepts arguments that are already " "attributes of the class." % (cls.__name__, key)) # 内部定义了可调用函数 def view(request, *args, **kwargs): self = cls(**initkwargs) self.setup(request, *args, **kwargs) if not hasattr(self, 'request'): raise AttributeError( "%s instance has no 'request' attribute. Did you override " "setup() and forget to call super()?" % cls.__name__ ) return self.dispatch(request, *args, **kwargs) view.view_class = cls view.view_initkwargs = initkwargs # take name and docstring from class update_wrapper(view, cls, updated=()) # and possible attributes set by decorators # like csrf_exempt from dispatch update_wrapper(view, cls.dispatch, assigned=()) return view DRF提供了rest_framework.mixins模块，封装了类视图常用的增删改查方法：
比如新增CreateModelMixin：
class CreateModelMixin: """ 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 {} 类视图继承了Mixin后，可以直接使用它的.create()方法，类似的还有.list()、.retrieve()、.update()和.destroy()。我们按照这个思路来简化snippets/views.py代码：
from snippets.models import Snippetfrom snippets.serializers import SnippetSerializerfrom rest_framework import mixinsfrom rest_framework import genericsclass SnippetList(mixins.ListModelMixin, mixins.CreateModelMixin, generics.GenericAPIView): queryset = Snippet.objects.all() serializer_class = SnippetSerializer def get(self, request, *args, **kwargs): return self.list(request, *args, **kwargs) def post(self, request, *args, **kwargs): return self.create(request, *args, **kwargs)class SnippetDetail(mixins.RetrieveModelMixin, mixins.UpdateModelMixin, mixins.DestroyModelMixin, generics.GenericAPIView): queryset = Snippet.objects.all() serializer_class = SnippetSerializer def get(self, request, *args, **kwargs): return self.retrieve(request, *args, **kwargs) def put(self, request, *args, **kwargs): return self.update(request, *args, **kwargs) def delete(self, request, *args, **kwargs): return self.destroy(request, *args, **kwargs)
瞬间少了好多代码，真够DRY的。
什么是mixin？
维基百科的解释：
In object-oriented programming languages, a mixin (or mix-in) is a class that contains methods for use by other classes without having to be the parent class of those other classes.
不太好理解。
换句话说，mixin类提供了一些方法，我们不会直接用这些方法，而是把它添加到其他类来使用。
还是有点抽象。
再简单点说，mixin只不过是实现多重继承的一个技巧而已。
这下应该清楚了。
如果仔细看snippets/views.py的代码，就会发现我们用到了from rest_framework import generics：
和generics.GenericAPIView：
这是DRF提供的通用API类视图，mixins只提供了处理方法，views.py中的类要成为视图，还需要继承GenericAPIView，GenericAPIView继承了本文第一小节提到的rest_framework.views.APIView。除了GenericAPIView，我们还可以用其他的类视图进一步简化代码：
from snippets.models import Snippetfrom snippets.serializers import SnippetSerializerfrom rest_framework import genericsclass SnippetList(generics.ListCreateAPIView): queryset = Snippet.objects.all() serializer_class = SnippetSerializerclass SnippetDetail(generics.RetrieveUpdateDestroyAPIView): queryset = Snippet.objects.all() serializer_class = SnippetSerializer
看看ListCreateAPIView的源码：
class ListCreateAPIView(mixins.ListModelMixin, mixins.CreateModelMixin, GenericAPIView): """ Concrete view for listing a queryset or creating a model instance. """ def get(self, request, *args, **kwargs): return self.list(request, *args, **kwargs) def post(self, request, *args, **kwargs): return self.create(request, *args, **kwargs)
真DRY！
学到这里，已经开始感受到了Django REST framework的强大之处了，我觉得学一个框架，不仅要看如何使用，还需要了解它的设计思路和底层实现，这样才能更好的总结为自己的编程思想，写出更漂亮的代码。
参考资料：
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