rest-framework框架——视图三部曲
一、mixins类编写视图
1、配置url
urlpatterns = [ ... re_path(r'^authors/$', views.AuthorView.as_view(), name="author"), re_path(r'^authors/(?P<pk>\d+)/$', views.AuthorDetailView.as_view(), name="detail_author") ]
2、编写Author的序列化类
/app01/serializer.py:
class AuthorModelSerializers(serializers.ModelSerializer): class Meta: model = Author fields = "__all__"
3、编写Author的视图
# Author from rest_framework import mixins, generics class AuthorView(mixins.ListModelMixin, # 扩展了列出查询集功能 mixins.CreateModelMixin, # 扩展了创建和保存新模型实例功能 generics.GenericAPIView): # 继承扩展了REST框架的APIView类,为标准列表和详细视图添加了常见的行为 queryset = Author.objects.all() # 配置queryset:告知这个类这次处理的数据 serializer_class = AuthorModelSerializers # 告知处理用到的序列化组件 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 AuthorDetailView(mixins.RetrieveModelMixin, # 扩展在响应中实现返回现有模型实例功能(获取单条数据) mixins.DestroyModelMixin, # 扩展现有模型实例的删除功能 mixins.UpdateModelMixin, # 扩展更新和保存现有模型实例功能 generics.GenericAPIView): queryset = Author.objects.all() # 配置queryset:告知这个类这次处理的数据 serializer_class = AuthorModelSerializers # 告知处理用到的序列化组件 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)
注意:
(1)queryset和serializer_class变量
这两个变量是必须的。queryset告知这个类这次处理的数据。serializer_class告知这个类数据处理用到的序列化组件。
(2)五类mixins作用和对应的http方法
(3)GenericAPIView
这个类扩展了REST框架的
APIView类,为标准列表和详细视图添加了常见的行为。
提供的每个具体的通用视图都是通过把
GenericAPIView与一个或多个mixin类进行组合来构建的。
(4)测试验证
二、Mixins源码分析
1、CreateModelMixin
class CreateModelMixin(object): """Create a model instance ==>创建一个实例""" def create(self, request, *args, **kwargs): # 获取相关serializer serializer = self.get_serializer(data=request.data) # 进行serializer的验证;raise_exception=True,一旦验证不通过,不再往下执行,直接引发异常 serializer.is_valid(raise_exception=True) # 调用perform_create()方法,保存实例 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): # 保存实例 serializer.save() def get_success_headers(self, data): try: return {'Location': str(data[api_settings.URL_FIELD_NAME])} except (TypeError, KeyError): return {}
注意:
(1)perform_create( )对serializer直接进行save保存,当在一些情境下,需要对perform_create( )进行重写。
(2)这个类的运行流程如下所示:
2、ListModelMixin
class ListModelMixin(object): """List a queryset.==> 列表页获取""" def list(self, request, *args, **kwargs): queryset = self.filter_queryset(self.get_queryset()) # 这是一个分页功能,如果在viewset中设置了pagination_class,那么这里就会起作用 # 获取当前页的queryset,如果不存在分页,返回None page = self.paginate_queryset(queryset) if page is not None: # 分页不为空,那么不能简单的执行Response(serializer.data) # 还需要将相关的page信息序列化在进行响应 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)
ListModelMixin一般用来获取列表页,不需要重写方法。
3、RetriveModelMixin
class RetrieveModelMixin(object): """ Retrieve a model instance.==> 获取某一个对象的具体信息 """ def retrieve(self, request, *args, **kwargs): # 一般访问的url都为/obj/id/这种新式 # get_object()可以获取到这个id的对象 # 注意在viewset中设置lookup_field获取重写get_object()方法可以指定id具体对象是什么~! instance = self.get_object() serializer = self.get_serializer(instance) return Response(serializer.data)
4、DestoryModelMixin
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()
5、总结
这一章简要分析了源码的内容以及各个mixins的逻辑,最重要的还是学会重写它们相关的方法。一般情况下,当我们在操作某一个model的时候,涉及到另外一个model中数据的修改,那么就需要对这个mixins下执行save的逻辑的方法进行重写。
三、使用通用的基于类的视图
通过使用mixin类,使用更少的代码重写了这些视图,但我们还可以再进一步。REST框架提供了一组已经混合好(mixed-in)的通用视图,我们可以使用它来简化我们的
views.py模块。
from rest_framework import mixins, generics class AuthorView(generics.ListCreateAPIView): queryset = Author.objects.all() # 配置queryset:告知这个类这次处理的数据 serializer_class = AuthorModelSerializers # 告知处理用到的序列化组件 class AuthorDetailView(generics.RetrieveUpdateDestroyAPIView): queryset = Author.objects.all() # 配置queryset:告知这个类这次处理的数据 serializer_class = AuthorModelSerializers # 告知处理用到的序列化组件
1、ListCreateAPIView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)
可以看到源码中将Mixins混合类和get\post函数都封装进去了。
2、RetrieveUpdateDestroyAPIView源码
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)
其他RetrieveDestroyAPIView、RetrieveUpdateAPIView、UpdateAPIView、DestroyAPIView等封装方式完全类似。
四、运用viewsets.ModelViewSet的视图
1、改写urls.py
from django.contrib import admin from django.urls import path, re_path from app01 import views urlpatterns = [ path('admin/', admin.site.urls), '''代码省略''' # re_path(r'^authors/$', views.AuthorView.as_view(), name="author"), # re_path(r'^authors/(?P<pk>\d+)/$', views.AuthorDetailView.as_view(), name="detail_author"), # as_view参数指定什么请求走什么方法 re_path(r'^authors/$', views.AuthorViewSet.as_view({"get": "list", "post": "create"}), name="author_list"), re_path(r'^authors/(?P<pk>\d+)/$', views.AuthorViewSet.as_view({ 'get': 'retrieve', 'put': 'update', 'patch': 'partial_update', 'delete': 'destroy' }), name="author_detail"), ]
注意:
(1)as_view参数
利用参数来指定什么请求方式由哪一个内部方法来执行。尤其注意两种不同get请求用不同的方法来处理。
2、引入viewsets改写视图
from rest_framework import viewsets class AuthorViewSet(viewsets.ModelViewSet): queryset = Author.objects.all() # 配置queryset:告知这个类这次处理的数据 serializer_class = AuthorModelSerializers # 告知处理用到的序列化组件
五、ModelViewSet源码分析
1、查看viewsets.ModelViewSet源码
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
ModelViewSet继承了所有五个混合类。还继承了GenericViewSet类。
2、查看GenericViewSet源码
class GenericViewSet(ViewSetMixin, generics.GenericAPIView): pass
可以看到GenericViewSet继承了前面学的generics.GenericAPIView类,这个类扩展了REST框架的
APIView类,但是它并没有改写dispatch方法,因此url中可以添加参数与它无关。
GenericViewSet还继承了ViewSetMixin类。
3、查看分析ViewSetMixin源码
class ViewSetMixin(object): """ Overrides `.as_view()` so that it takes an `actions` keyword that performs the binding of HTTP methods to actions on the Resource. 覆盖as_view方法需要接收一个actions参数来实现将HTTP方法绑定到资源。 For example, to create a concrete view binding the 'GET' and 'POST' methods to the 'list' and 'create' actions... 举例来说,如果要创建一个具体视图绑定'GET'和'POST'方法到'list'和'create'操作。可写为如下格式: 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. """ # actions must not be empty actions来接收{'get': 'list', 'post': 'create'} if not actions: # 为空则报错 raise TypeError("The `actions` argument must be provided when " "calling `.as_view()` on a ViewSet. For example " "`.as_view({'get': 'list'})`") # sanitize keyword arguments for key in initkwargs:..... # 这里的值是空的 def view(request, *args, **kwargs):... return csrf_exempt(view) # 执行as_view 最终返回的还是view函数
注意:
(1)分析函数传参方式:**字典传参等同于关键字传参。
def foo(action=None, **kwargs): print(action) print(kwargs) foo({"a": 1}, b=2, c=3) """ {'a': 1} {'b': 2, 'c': 3} """ foo(a=2, b=3) """ None {'a': 2, 'b': 3} """ foo(**{"a": 1, "b": 3}) """ None {'a': 1, 'b': 3} """ foo({"a": 1, "b": 3}) """ {'a': 1, 'b': 3} {} """
由此可见as_view传递的参数{"get": "list", "post": "create"}是ViewSetMixin内改写的as_view方法,由actions参数来接收的。
由于acitons默认值是None,因此not None其实是True,if not actions: 其实是actions为空则报错的意思。
(2)as_view函数最终返回值是view函数
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 # 传入的字典数据{'get': 'list', 'post': 'create'} # Bind methods to actions # This is the bit that's different to a standard view for method, action in actions.items(): # method:请求方式 action:实例方法 handler = getattr(self, action) # 反射得到self.list self.create方法 setattr(self, method, handler) # 给请求方式设置对应的实例方法 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)
在view函数中用self.action_map = actions 来接收传入的字典数据{'get': 'list', 'post': 'create'}。
循环for method, action in actions.items(): 拿到method:请求方式和action:实例方法。
再通过反射方法:handler = getattr(self, action) 得到self.list self.create方法。
最后通过反射方法setattr(self, method, handler) 给请求方式设置对应的实例方法:以后再找getattr(self, "get")的时候找到是self.list;找getattr(self, "post")的时候找到是self.create;
(3)反射方法详解
1. getattr()函数是Python自省的核心函数,具体使用大体如下: class A: def __init__(self): self.name = 'zhangjing' #self.age='24' def method(self): print"method print" Instance = A() print getattr(Instance , 'name, 'not find') #如果Instance 对象中有属性name则打印self.name的值,否则打印'not find' print getattr(Instance , 'age', 'not find') #如果Instance 对象中有属性age则打印self.age的值,否则打印'not find' print getattr(a, 'method', 'default') #如果有方法method,否则打印其地址,否则打印default print getattr(a, 'method', 'default')() #如果有方法method,运行函数并打印None否则打印default 2. hasattr(object, name) 说明:判断对象object是否包含名为name的特性(hasattr是通过调用getattr(ojbect, name)是否抛出异常来实现的) 3. setattr(object, name, value) 这是相对应的getattr()。参数是一个对象,一个字符串和一个任意值。字符串可能会列出一个现有的属性或一个新的属性。这个函数将值赋给属性的。该对象允许它提供。例如,setattr(x,“foobar”,123)相当于x.foobar = 123。 4. delattr(object, name) 与setattr()相关的一组函数。参数是由一个对象(记住python中一切皆是对象)和一个字符串组成的。string参数必须是对象属性名之一。该函数删除该obj的一个由string指定的属性。delattr(x, 'foobar')=del x.foobar
4、找到view函数执行完后最终返回dispatch方法 并完成分析
从ModelViewSet——》GenericViewSet——》GenericAPIView——》APIView一路回溯到APIView才找到dispatch方法。
def dispatch(self, request, *args, **kwargs): self.args = args self.kwargs = kwargs request = self.initialize_request(request, *args, **kwargs) self.request = request self.headers = self.default_response_headers # deprecate? try: self.initial(request, *args, **kwargs) # Get the appropriate handler method if request.method.lower() in self.http_method_names: handler = getattr(self, request.method.lower(), self.http_method_not_allowed) else: handler = self.http_method_not_allowed response = handler(request, *args, **kwargs) except Exception as exc: response = self.handle_exception(exc) self.response = self.finalize_response(request, response, *args, **kwargs) return self.response
当访问是走的路由是re_path(r'^authors/$', views.AuthorViewSet.as_view({"get": "list", "post": "create"}), name="author_list"),get请求handler对应的是self.list。
而当访问走的路由是re_path(r'^authors/(?P<pk>\d+)/$', views.AuthorViewSet.as_view({'get': 'retrieve',....
此时get请求handler对应的是self.retrieve。
如此就实现了两个类合成一个类。
5、找到并执行list方法
查看ModelViewSet源码:
class ModelViewSet(mixins.CreateModelMixin, mixins.RetrieveModelMixin, mixins.UpdateModelMixin, mixins.DestroyModelMixin, mixins.ListModelMixin, GenericViewSet):
在ListModelMixin找到list方法:
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)
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