Django REST framework 教程3 Class Based Views

API views也可以使用class based views来编写，而不是function based views。你会发现这是一种很有效的模式，能够让我们复用代码，保持代码DRY。

使用class based views重写 API

我们先来把root视图转换为class based view。在 views.py中进行一些重构：

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)

目前为止进展顺利，尽管和之前的写法仍有相似，但是在不同的HTTP方法之前做到了分离，下面将 views.py 中另外一个视图进行重构：

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)

现在的写法仍然和function based view有些类似，接下来修改 urls.py 来使用class based views。

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)

这样API就重构完成了，服务器运行之后API和之前完全相同。

使用 mixins

使用 class based views 的一个好处就是能构建可复用的机制。

在我们目前基于模型的视图中，诸如create/retrieve/update/delete的API经常出现。REST framework’s mixin 提供了这类通用的行为。

下面来学习使用mixin构建视图，编辑 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)

我们来花点时间解释一下它的机制。首先用 GenericAPIView创建了视图，然后添加了 ListModelMixin 和CreateModelMixin。

base class提供了核心的功能， mixin classes提供了 .list() 和.create()功能。然后绑定到 get 和post方法中。

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)

我们再一次用了 GenericAPIViewclass来提供核心功能，用mixins来提供 .retrieve(), .update() 和.destroy() 功能。

使用generic class based views

使用mixin classes 已然减少了代码量，但是还能进一步优化。REST framework 提供了一系列mixed-in generic views，利用它可以将 views.py 进一步瘦身：

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

使用了之后，代码进一步的简洁了。在part 4中，我们将会了解到的API添加用户和权限管理的方式。

使用class based views重写 API

使用 mixins

使用generic class based views

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