教程3：类视图

我们也可以使用类视图来编写API的view,而不是函数视图。正如我们了解的，类视图是一种非常给力的模式让我们重用代码，保持DRY原则。

使用类视图重写API

我们来使用类视图来重写views.py:

from snippets.models import Snippet
from snippets.serializers import SnippetSerializer
from django.http import Http404
from rest_framework.views import APIView
from rest_framework.response import Response
from rest_framework import status


class 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)

目前看起来还不错，和之前的写法一样，但更清晰的分离了HTTP的请求方法。我们也需要修改单一的实例视图：

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)

好极了，这也和函数视图非常相似。

因为使用了类视图，我们也需要改写urls.py:

from django.conf.urls import url
from rest_framework.urlpatterns import format_suffix_patterns
from snippets import views

urlpatterns = [
    url(r'^snippets/$', views.SnippetList.as_view()),
    url(r'^snippets/(?P<pk>[0-9]+)/$', views.SnippetDetail.as_view()),
]

urlpatterns = format_suffix_patterns(urlpatterns)

使用Mixins

使用类视图的一大优点就是可以方便的重用代码，目前我们使用了很多相似的代码来进行增删改查操作，这些常见的操作已经被封装在了REST framework的mixins类中。让我们使用mixins再次修改views.py:

from snippets.models import Snippet
from snippets.serializers import SnippetSerializer
from rest_framework import mixins
from rest_framework import generics

class 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)

我们花点时间来看看这里发生了什么：我们使用GenericAPIView、ListModelMixin、CreateModelMixin改写了代码，基类提供了核心功能，而mixin类则提供了.list()和.ctreae()的行为，这里我们显式绑定GET方法和POST方法对应的功能，一切都很简单：

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)

类似的，我们使用GenericAPIView提供核心功能而mixin提供.retrieve()、.update()和.destroy()行为。

使用通用类视图

使用mixin类重写views让我们的代码比之前简洁了很多，但我们可以更进一步。REST framework提供了通用类视图来让代码更加精简：

from snippets.models import Snippet
from snippets.serializers import SnippetSerializer
from rest_framework import generics


class SnippetList(generics.ListCreateAPIView):
    queryset = Snippet.objects.all()
    serializer_class = SnippetSerializer


class SnippetDetail(generics.RetrieveUpdateDestroyAPIView):
    queryset = Snippet.objects.all()
    serializer_class = SnippetSerializer

WOW,真的酷毙了！我们节省的大量的时间，代码也更加强壮、简洁、符合Django风格。