深刻解析當下大熱的先後端分離組件django-rest_framework系列二

視圖三部曲

一部曲 · 使用混合（mixins）

上一節的視圖部分：

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)

咱們使用這一套邏輯，意味着有一張模型表，就要將上面的代碼寫一遍，代碼的複用性不好，全部，咱們要對複用的部分進行封裝，咱們經過三步，一步一步的來實現代碼的複用和封裝。

第一步：大致思路是使用混合類（多繼承的形式），藉助封裝好的mixins類

from rest_framework import mixins

　　咱們能夠發現，這些複用的代碼中，有兩個變量是必需要知道的，一個是模型表中的數據，一個是該模型表對應的serializers對象，因此咱們能夠將這兩個變量單獨給提出來放到類的靜態屬性中，這樣整個類中均可以調用。

使用方法：

將查看全部數據的方法封裝到一個類中：

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，咱們處理查看全部數據的視圖時，直接將這個類繼承，同時，在get方法中，將list方法返回便可。

一樣的方式，將添加數據，查看某一條數據，編輯某一條數據，刪除某一條數據也分別封裝到一個個類下，只須要在對應的請求方法中，返回繼承類中對應的方法便可。

添加數據封裝到類：

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 {}

 

查看某一條數據封裝的類：

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)

 

編輯數據的類：

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)

 

刪除數據的類：

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()

 

經過上面的方式，咱們會有一個疑問，咱們傳入的pk值，是怎麼處理的。

咱們在處理類的視圖函數時，必需要繼承一個APIView的類，一樣的，也將這個類進行了封裝：放到了rest_framework.generics下面的GenericAPIView中；

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

這個類繼承了APIView，並進行了相應的擴展。咱們傳的pk值，就是在這裏被處理的。

處理單條數據時，咱們確定要先將對應的數據取出來，再作對應的處理，一樣的，封裝到類中確定也作了相似的處理，咱們觀察處理單條數據的類，會發現這樣一行代碼：instance = self.get_object()  很明顯，確定是取數據去了，怎麼取？不知道，看看，先找到這個方法。咱們從本類和繼承的類中依次去找，最後在GenericAPIView中找到了這個方法：

    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

這個方法最終將obj返回了，那就要好奇了，怎麼一會兒將obj取出來的，繼續查看  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

進行了一個異常處理，仍是沒有咱們要的內容，繼續找  _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)

這麼一堆中，就  queryset.get(*args,**kwargs)  是咱們要的內容，咱們經過url傳入pk=val，被**kwargs捕獲，傳入這個代碼中，等同於models.模型類.objects.all().get(**{"pk":val})，這種形式很眼熟，這就是咱們取值的操做。

mixin類編寫視圖

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)

特別須要注意的是，使用這種方式，設計url時，須要傳參的url，必須使用分組命名匹配的形式，並且，命名必須是pk，不然報錯

urlpatterns = [

　　# 錯誤寫法
    url(r'^books/$',views.Book.as_view()), url(r'^books/(\d+)/$',views.BookDeail.as_view()), 
　　# 正確寫法 url(r'^publish/$',views.Publish.as_view()), url(r'^publish/(?P<pk>\d+)/$',views.PublishDeail.as_view()), #必須是pk ]

採用這種方式匹配url，跟封裝的源碼有關；

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' 

上面的代碼雖然必定程度上減小了代碼的複用性，可是，咱們對於每個模型表任然要進行大量的複用代碼。

備註：在繼承類中配置了lookup_field屬性，If you want to use object lookups other than pk, set 'lookup_field'

第二步：將這些封裝的類進一步封裝。

二部曲 · 使用通用的基於類的視圖

經過使用mixin類，咱們使用更少的代碼重寫了這些視圖，但咱們還能夠再進一步。REST框架提供了一組已經混合好（mixed-in）的通用視圖，咱們能夠使用它來簡化咱們的views.py模塊。

將咱們不須要接收傳參的視圖函數總體封裝到一個類（查看全部數據，添加數據）

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)

一樣的，須要接收一個pk值的視圖封裝：

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)

藉助這個封裝，進一步的簡化代碼量

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

經過上面的代碼，咱們已經減小了大量的代碼，可是，好像咱們還在複用一些代碼，queryset和serializer_class 這兩個參數。因此咱們繼續封裝。

第三步的思路：將接收pk的url和不接受pk的url合爲一個視圖，會有一個問題，那就是，get請求，咱們無論查看全部數據仍是查看某一條數據，都會走同一個視圖，怎麼能夠解決這個問題？問題的根源是出在分發上，咱們能夠重寫。

　　咱們將視圖合二爲一，就須要將繼承的全部的類進一步封裝。

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

導入：

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

使用這種方式，url就必須在as_view()方法裏，傳一個字典參數。而以前是不須要傳的，顯然，重寫了as_view()方法，那咱們就去找這個重寫as_view的類。ModelViewSet中前五個是咱們第一步封裝的，惟有最後一個GenericViewSet，是重寫的

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

這個類中經過混合類的方式進行繼承，後面的是咱們以前用過的，惟有前面的ViewSetMixin是擴展的，很顯然，是這個類重寫了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. """ 　　# 此處省略部分源碼... 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)

　　同樣的，這個as_view()最終返回一個view函數，跟以前是同樣的，那麼接收的這個參數有什麼用呢？確定在view函數中，調用了這個參數，並實現了某些東西。（actions接收了傳的字典參數）

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

這三行代碼是進行了相應的處理，首先，循環這個參數，經過反射獲得value對應的函數名（list、create、retrieve、update、destory），最後經過setattr實現了咱們調用哪一個key(method)就會執行對應的value，從而完美的解決了分發的問題。

　　經過這三次分發，實現了代碼的複用。

 

總結

 　　經過三層封裝，使得咱們能夠很是快速的經過幾行代碼實現一個模型類的增刪改查，大大的提升了開發效率。有利就有弊，封裝的越完善，就意味着不夠靈活。下個系列中，帶來restframework中的很是有用的三個套件。