深刻解析当下大热的先后端分离组件django-rest_framework系列二

视图三部曲

一部曲 · 使用混合（mixins）

上一节的视图部分：

from rest_framework.views import APIView from rest_framework.response import Response from .models import * from django.shortcuts import HttpResponse from django.core import serializers from rest_framework import serializers class BookSerializers(serializers.ModelSerializer): class Meta: model=Book fields="__all__" #depth=1 class PublshSerializers(serializers.ModelSerializer): class Meta: model=Publish fields="__all__" depth=1 class BookViewSet(APIView): def get(self,request,*args,**kwargs): book_list=Book.objects.all() bs=BookSerializers(book_list,many=True,context={'request': request}) return Response(bs.data) def post(self,request,*args,**kwargs): print(request.data) bs=BookSerializers(data=request.data,many=False) if bs.is_valid(): print(bs.validated_data) bs.save() return Response(bs.data) else: return HttpResponse(bs.errors) class BookDetailViewSet(APIView): def get(self,request,pk): book_obj=Book.objects.filter(pk=pk).first() bs=BookSerializers(book_obj,context={'request': request}) return Response(bs.data) def put(self,request,pk): book_obj=Book.objects.filter(pk=pk).first() bs=BookSerializers(book_obj,data=request.data,context={'request': request}) if bs.is_valid(): bs.save() return Response(bs.data) else: return HttpResponse(bs.errors) class PublishViewSet(APIView): def get(self,request,*args,**kwargs): publish_list=Publish.objects.all() bs=PublshSerializers(publish_list,many=True,context={'request': request}) return Response(bs.data) def post(self,request,*args,**kwargs): bs=PublshSerializers(data=request.data,many=False) if bs.is_valid(): # print(bs.validated_data)  bs.save() return Response(bs.data) else: return HttpResponse(bs.errors) class PublishDetailViewSet(APIView): def get(self,request,pk): publish_obj=Publish.objects.filter(pk=pk).first() bs=PublshSerializers(publish_obj,context={'request': request}) return Response(bs.data) def put(self,request,pk): publish_obj=Publish.objects.filter(pk=pk).first() bs=PublshSerializers(publish_obj,data=request.data,context={'request': request}) if bs.is_valid(): bs.save() return Response(bs.data) else: return HttpResponse(bs.errors)

咱们使用这一套逻辑，意味着有一张模型表，就要将上面的代码写一遍，代码的复用性不好，全部，咱们要对复用的部分进行封装，咱们经过三步，一步一步的来实现代码的复用和封装。

第一步：大致思路是使用混合类（多继承的形式），借助封装好的mixins类

from rest_framework import mixins

　　咱们能够发现，这些复用的代码中，有两个变量是必需要知道的，一个是模型表中的数据，一个是该模型表对应的serializers对象，因此咱们能够将这两个变量单独给提出来放到类的静态属性中，这样整个类中均可以调用。

使用方法：

将查看全部数据的方法封装到一个类中：

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)

因此，咱们处理查看全部数据的视图时，直接将这个类继承，同时，在get方法中，将list方法返回便可。

一样的方式，将添加数据，查看某一条数据，编辑某一条数据，删除某一条数据也分别封装到一个个类下，只须要在对应的请求方法中，返回继承类中对应的方法便可。

添加数据封装到类：

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 {}

 

查看某一条数据封装的类：

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)

 

编辑数据的类：

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)

 

删除数据的类：

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()

 

经过上面的方式，咱们会有一个疑问，咱们传入的pk值，是怎么处理的。

咱们在处理类的视图函数时，必需要继承一个APIView的类，一样的，也将这个类进行了封装：放到了rest_framework.generics下面的GenericAPIView中；

from rest_framework import views class GenericAPIView(views.APIView): pass

这个类继承了APIView，并进行了相应的扩展。咱们传的pk值，就是在这里被处理的。

处理单条数据时，咱们确定要先将对应的数据取出来，再作对应的处理，一样的，封装到类中确定也作了相似的处理，咱们观察处理单条数据的类，会发现这样一行代码：instance = self.get_object()  很明显，确定是取数据去了，怎么取？不知道，看看，先找到这个方法。咱们从本类和继承的类中依次去找，最后在GenericAPIView中找到了这个方法：

    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

这个方法最终将obj返回了，那就要好奇了，怎么一会儿将obj取出来的，继续查看  obj=get_object_or_404(queryset,**fi..)

def get_object_or_404(queryset, *filter_args, **filter_kwargs): """ Same as Django's standard shortcut, but make sure to also raise 404 if the filter_kwargs don't match the required types. """ try: return _get_object_or_404(queryset, *filter_args, **filter_kwargs) except (TypeError, ValueError, ValidationError): raise Http404

进行了一个异常处理，仍是没有咱们要的内容，继续找  _get_object_or_404(queryset,*...,**...)

def get_object_or_404(klass, *args, **kwargs): """ Uses get() to return an object, or raises a Http404 exception if the object does not exist. klass may be a Model, Manager, or QuerySet object. All other passed arguments and keyword arguments are used in the get() query. Note: Like with get(), an MultipleObjectsReturned will be raised if more than one object is found. """ queryset = _get_queryset(klass) try: return queryset.get(*args, **kwargs) except AttributeError: klass__name = klass.__name__ if isinstance(klass, type) else klass.__class__.__name__ raise ValueError( "First argument to get_object_or_404() must be a Model, Manager, " "or QuerySet, not '%s'." % klass__name ) except queryset.model.DoesNotExist: raise Http404('No %s matches the given query.' % queryset.model._meta.object_name)

这么一堆中，就  queryset.get(*args,**kwargs)  是咱们要的内容，咱们经过url传入pk=val，被**kwargs捕获，传入这个代码中，等同于models.模型类.objects.all().get(**{"pk":val})，这种形式很眼熟，这就是咱们取值的操做。

mixin类编写视图

from rest_framework import mixins from rest_framework import generics class BookViewSet(mixins.ListModelMixin, mixins.CreateModelMixin, generics.GenericAPIView): queryset = Book.objects.all() serializer_class = BookSerializers 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 BookDetailViewSet(mixins.RetrieveModelMixin, mixins.UpdateModelMixin, mixins.DestroyModelMixin, generics.GenericAPIView): queryset = Book.objects.all() serializer_class = BookSerializers 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)

特别须要注意的是，使用这种方式，设计url时，须要传参的url，必须使用分组命名匹配的形式，并且，命名必须是pk，不然报错

urlpatterns = [

　　# 错误写法
    url(r'^books/$',views.Book.as_view()), url(r'^books/(\d+)/$',views.BookDeail.as_view()), 
　　# 正确写法 url(r'^publish/$',views.Publish.as_view()), url(r'^publish/(?P<pk>\d+)/$',views.PublishDeail.as_view()), #必须是pk ]

采用这种方式匹配url，跟封装的源码有关；

class GenericAPIView(views.APIView): """ Base class for all other generic views. """ # You'll need to either set these attributes, # or override `get_queryset()`/`get_serializer_class()`. # If you are overriding a view method, it is important that you call # `get_queryset()` instead of accessing the `queryset` property directly, # as `queryset` will get evaluated only once, and those results are cached # for all subsequent requests. 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' 

上面的代码虽然必定程度上减小了代码的复用性，可是，咱们对于每个模型表任然要进行大量的复用代码。

备注：在继承类中配置了lookup_field属性，If you want to use object lookups other than pk, set 'lookup_field'

第二步：将这些封装的类进一步封装。

二部曲 · 使用通用的基于类的视图

经过使用mixin类，咱们使用更少的代码重写了这些视图，但咱们还能够再进一步。REST框架提供了一组已经混合好（mixed-in）的通用视图，咱们能够使用它来简化咱们的views.py模块。

将咱们不须要接收传参的视图函数总体封装到一个类（查看全部数据，添加数据）

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)

一样的，须要接收一个pk值的视图封装：

class RetrieveUpdateDestroyAPIView(mixins.RetrieveModelMixin, mixins.UpdateModelMixin, mixins.DestroyModelMixin, GenericAPIView): """ Concrete view for retrieving, updating or deleting a model instance. """ 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 patch(self, request, *args, **kwargs): return self.partial_update(request, *args, **kwargs) def delete(self, request, *args, **kwargs): return self.destroy(request, *args, **kwargs)

借助这个封装，进一步的简化代码量

from rest_framework import mixins from rest_framework import generics class BookViewSet(generics.ListCreateAPIView): queryset = Book.objects.all() serializer_class = BookSerializers class BookDetailViewSet(generics.RetrieveUpdateDestroyAPIView): queryset = Book.objects.all() serializer_class = BookSerializers class PublishViewSet(generics.ListCreateAPIView): queryset = Publish.objects.all() serializer_class = PublshSerializers class PublishDetailViewSet(generics.RetrieveUpdateDestroyAPIView): queryset = Publish.objects.all() serializer_class = PublshSerializers

经过上面的代码，咱们已经减小了大量的代码，可是，好像咱们还在复用一些代码，queryset和serializer_class 这两个参数。因此咱们继续封装。

第三步的思路：将接收pk的url和不接受pk的url合为一个视图，会有一个问题，那就是，get请求，咱们无论查看全部数据仍是查看某一条数据，都会走同一个视图，怎么能够解决这个问题？问题的根源是出在分发上，咱们能够重写。

　　咱们将视图合二为一，就须要将继承的全部的类进一步封装。

class ModelViewSet(mixins.CreateModelMixin, mixins.RetrieveModelMixin, mixins.UpdateModelMixin, mixins.DestroyModelMixin, mixins.ListModelMixin, GenericViewSet): """ A viewset that provides default `create()`, `retrieve()`, `update()`, `partial_update()`, `destroy()` and `list()` actions. """ pass

导入：

from rest_framework.viewsets import ModelViewSet

 

三部曲 · viewsets.ModelViewSet

urls.py:

    url(r'^books/$', views.BookViewSet.as_view({"get":"list","post":"create"}),name="book_list"), url(r'^books/(?P<pk>\d+)$', views.BookViewSet.as_view({ 'get': 'retrieve', 'put': 'update', 'patch': 'partial_update', 'delete': 'destroy' }),name="book_detail"),

views.py:

class BookViewSet(viewsets.ModelViewSet): queryset = Book.objects.all() serializer_class = BookSerializers

使用这种方式，url就必须在as_view()方法里，传一个字典参数。而以前是不须要传的，显然，重写了as_view()方法，那咱们就去找这个重写as_view的类。ModelViewSet中前五个是咱们第一步封装的，惟有最后一个GenericViewSet，是重写的

class GenericViewSet(ViewSetMixin, generics.GenericAPIView): """ The GenericViewSet class does not provide any actions by default, but does include the base set of generic view behavior, such as the `get_object` and `get_queryset` methods. """ pass

这个类中经过混合类的方式进行继承，后面的是咱们以前用过的，惟有前面的ViewSetMixin是扩展的，很显然，是这个类重写了as_view()

class ViewSetMixin(object): """ This is the magic. Overrides `.as_view()` so that it takes an `actions` keyword that performs the binding of HTTP methods to actions on the Resource. For example, to create a concrete view binding the 'GET' and 'POST' methods to the 'list' and 'create' actions... view = MyViewSet.as_view({'get': 'list', 'post': 'create'}) """ @classonlymethod def as_view(cls, actions=None, **initkwargs): """ Because of the way class based views create a closure around the instantiated view, we need to totally reimplement `.as_view`, and slightly modify the view function that is created and returned. """ 　　# 此处省略部分源码... def view(request, *args, **kwargs): self = cls(**initkwargs) # We also store the mapping of request methods to actions, # so that we can later set the action attribute. # eg. `self.action = 'list'` on an incoming GET request. self.action_map = actions # Bind methods to actions # This is the bit that's different to a standard view for method, action in actions.items(): handler = getattr(self, action) setattr(self, method, handler) if hasattr(self, 'get') and not hasattr(self, 'head'): self.head = self.get self.request = request self.args = args self.kwargs = kwargs # And continue as usual return self.dispatch(request, *args, **kwargs) # 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=()) # We need to set these on the view function, so that breadcrumb # generation can pick out these bits of information from a # resolved URL. view.cls = cls view.initkwargs = initkwargs view.suffix = initkwargs.get('suffix', None) view.actions = actions return csrf_exempt(view)

　　同样的，这个as_view()最终返回一个view函数，跟以前是同样的，那么接收的这个参数有什么用呢？确定在view函数中，调用了这个参数，并实现了某些东西。（actions接收了传的字典参数）

    for method, action in actions.items(): handler = getattr(self, action) setattr(self, method, handler)

这三行代码是进行了相应的处理，首先，循环这个参数，经过反射获得value对应的函数名（list、create、retrieve、update、destory），最后经过setattr实现了咱们调用哪一个key(method)就会执行对应的value，从而完美的解决了分发的问题。

　　经过这三次分发，实现了代码的复用。

 

总结

 　　经过三层封装，使得咱们能够很是快速的经过几行代码实现一个模型类的增删改查，大大的提升了开发效率。有利就有弊，封装的越完善，就意味着不够灵活。下个系列中，带来restframework中的很是有用的三个套件。