rest-framework框架——视图三部曲

摘要：

Queryset告诉这个类这次要处理什么数据。serializer_Class告诉这个类用于数据处理的序列化组件。五种类型的混合及其相应的http方法GenericAPIView这个类扩展了REST框架的APIView类，并为标准列表和详细视图添加了常见行为。提供的每个特定常规视图都是通过将GenericAPIView与一个或多个mixin类组合来构建的。因此，还必须自定义创建方法。

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

　　 rest-framework框架——视图三部曲第1张

（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

　　 rest-framework框架——视图三部曲第2张 rest-framework框架——视图三部曲第3张

二、基于mixins封装视图示例

1、基本视图

# 方式三：基于rest_framework框架实现序列化（pip install djangorestframework）
from rest_framework.views import APIView
from rest_framework.response import Response
from .serializers import BookSerializer   # 自定义序列化类


class BookView(APIView):
    query_set = Book.objects.all()        # 将query_set抽离
    serializer_class = BookSerializer     # 拿到序列化器

    def get(self, request):
        # 第一个图书对象
        # book_obj = Book.objects.first()
        # ret = BookSerializer(book_obj)

        # book_list = Book.objects.all()
        book_list = self.query_set
        # ret = BookSerializer(book_list, many=True)    # 使用序列化器序列化
        ret = self.serializer_class(book_list, many=True)
        """
        序列化的数据保存在ret.data中
        """
        return Response(ret.data)
    """
    得出来的结果会使用Django REST framework模板，在serializers.py中定制好序列化类后，显示效果如下所示：
    HTTP 200 OK
    Allow: GET, HEAD, OPTIONS
    Content-Type: application/json
    Vary: Accept

    [
        {
            "id": 1,
            "title": "python开发",
            "category": "Python",
            "pub_time": "2011-08-27",
            "publisher": {
                "id": 1,
                "title": "人民日报社"
            },
            "author": [
                {
                    "id": 1,
                    "name": "xxx"
                },
                {
                    "id": 2,
                    "name": "sssxx"
                }
            ]
        },
       ...
    ]
    """

    def post(self, request):
        print(request.data)
        serializer = BookSerializer(data=request.data)  # 序列化器校验前端传回来的数据
        if serializer.is_valid():
            serializer.save()   # 验证成功后保存数据库
            # 因为ModelSerializer的create方法不支持source的用法。因此必须还自定义一个create方法。
            return Response(serializer.validated_data)   # validated_data存放验证通过的数据
        else:
            return Response(serializer.errors)           # errors存放错误信息

    '''
    发送post请求接口设计
    POST /books/list
    {
        "title": "nodejs的使用教程",
        "w_category": "1",
        "pub_time": "2018-10-27",
        "publisher_id": 1,
        "author_list": [1,2,3]
    }
    '''


class BookEditView(APIView):
    def get(self, request, id):
        """查看单条数据"""
        book_obj = Book.objects.filter(id=id).first()
        ret = BookSerializer(book_obj)
        return Response(ret.data)

    '''
    GET /books/retrieve/3
    {
        "id": 3,
        "title": "Linux开发",
        "category": "Linux",
        "pub_time": "2008-08-27",
        "publisher": {
            "id": 3,
            "title": "长江日报社"
        },
        "author": [
            {
                "id": 1,
                "name": "阿萨德"
            },
            {
                "id": 3,
                "name": "阿斯达"
            }
        ]
    }
    '''

    def put(self, request, id):
        """更新操作"""
        book_obj = Book.objects.filter(id=id).first()
        serializer = BookSerializer(
            book_obj,             # 待更新对象
            data=request.data,    # 要更新的数据
            partial=True          # 重点：进行部分验证和更新
        )
        if serializer.is_valid():
            serializer.save()     # 保存
            return Response(serializer.validated_data)   # 返回验证通过的数据
            # return Response(serializers.data)    # 返回所有数据
        else:
            return Response(serializer.errors)      # 返回验证错误的数据

    def delete(self, request, id):
        """删除操作"""
        book_obj = Book.objects.filter(id=id).first()
        book_obj.delete()
        return Response("")

2、基于mixins封装视图

　　升级：改写使用通用类，继承通用方法。

class GenericAPIView(APIView):
    # 通用APIView模板类
    query_set = None
    serializer_class = None

    def get_queryset(self):
        return self.query_set

    def get_serializer(self, *args, **kwargs):
        return self.serializer_class(*args, **kwargs)   # 实例化,且接收所有的参数


class BookView(GenericAPIView):
    # 以方法的形式调用获取
    query_set = Book.objects.all()
    serializer_class = BookSerializer

    def get(self, request):
        book_list = self.get_queryset()
        ret = self.get_serializer(book_list, many=True)
        return Response(ret.data)

    def post(self, request):
        serializer = BookSerializer(data=request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data)
        else:
            return Response(serializer.errors)

3、第一次封装

class GenericAPIView(APIView):
    # 通用APIView模板类
    query_set = None
    serializer_class = None

    def get_queryset(self):
        return self.query_set

    def get_serializer(self, *args, **kwargs):
        return self.serializer_class(*args, **kwargs)   # 实例化,且接收所有的参数


class ListModelMixin(object):
    def list(self, request):
        queryset = self.get_queryset()
        ret = self.get_serializer(queryset, many=True)
        return Response(ret.data)


class CreateModelMixin(object):
    def create(self, request):
        serializer = self.get_serializer(data=request.data)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data)
        else:
            return Response(serializer.errors)


class RetrieveModelMixin(object):
    def retrieve(self, request, id):   # 查看单条数据
        book_obj = self.get_queryset().filter(id=id).first()
        ret = self.get_serializer(book_obj)
        return Response(ret.data)


class UpdateModelMixin(object):
    def update(self, request, id):
        book_obj = self.get_queryset().filter(id=id).first()
        serializer = self.get_serializer(
            book_obj,  # 待更新对象
            data=request.data,  # 要更新的数据
            partial=True  # 重点：进行部分验证和更新
        )
        if serializer.is_valid():
            serializer.save()  # 保存
            return Response(serializer.validated_data)  # 返回验证通过的数据
            # return Response(serializers.data)    # 返回所有数据
        else:
            return Response(serializer.errors)  # 返回验证错误的数据


class DestroyModelMixin(object):
    def delete(self, request, id):
        book_obj = self.get_queryset().filter(id=id).first()
        book_obj.delete()
        return Response("")

class BookView(GenericAPIView, ListModelMixin, CreateModelMixin):   # 一层封装
    query_set = Book.objects.all()
    serializer_class = BookSerializer

    def get(self, request):
        return self.list(request)

    def post(self, request):
        return self.create(request)


class BookEditView(GenericAPIView, RetrieveModelMixin, UpdateModelMixin, DestroyModelMixin):  # 一层封装
    query_set = Book.objects.all()
    serializer_class = BookSerializer

    def get(self, request, id):
        """查看单条数据"""
        return self.retrieve(request, id)

    def put(self, request, id):
        """更新操作"""
        return self.update(request, id)

    def delete(self, request, id):
        """删除操作"""
        return self.destroy(request, id)

4、第二次封装

　　进一步封装如下所示：

# 二层封装
class ListCreateAPIView(GenericAPIView, ListModelMixin, CreateModelMixin):
    pass


class RetrieveUpdateDestroyAPIView(GenericAPIView, RetrieveModelMixin, UpdateModelMixin, DestroyModelMixin):
    pass


# class BookView(GenericAPIView, ListModelMixin, CreateModelMixin):   # 一层封装
class BookView(ListCreateAPIView):          # 使用二层封装
    query_set = Book.objects.all()
    serializer_class = BookSerializer

    def get(self, request):
        return self.list(request)

    def post(self, request):
        return self.create(request)


# class BookEditView(GenericAPIView, RetrieveModelMixin, UpdateModelMixin, DestroyModelMixin):  # 一层封装
class BookEditView(RetrieveUpdateDestroyAPIView):     # 使用二层封装
    query_set = Book.objects.all()
    serializer_class = BookSerializer

    def get(self, request, id):
        """查看单条数据"""
        return self.retrieve(request, id)

5、第三次封装

　　经过两次封装后，剩下两个视图，但依然不够简洁。由于两个get请求的返回值不同，写了两个视图来解决。

　　现在可以通过路由传参的方式来解决上述问题。

(1)改写urls.py

from django.urls import path, include
from .views import BookView, BookEditView, BookModelViewSet


urlpatterns = [
    # path('list', BookView.as_view()),   # 查看所有的图书
    # 注意url中参数命名方式，2.0之前的写法：'retrieve/(?P<id>d+)'
    # 2.0之后的写法：<>内声明类型，冒号后面跟着关键字参数
    # path('retrieve/<int:id>', BookEditView.as_view())   # 单条数据查看

    path('list', BookModelViewSet.as_view({"get": "list", "post": "create"})),
    path('retrieve/<int:id>', BookModelViewSet.as_view({"get": "retrieve", "put": "update", "delete": "destroy"}))
]

(2)使as_view支持传参

　　as_view方法本身是不支持传参的，因此需要重写该方法。

class ViewSetMixin(object):
    def as_view(self):
        """
        按照参数指定的去匹配
        get-->list
        :return:
        """
        pass

class BookModelViewSet(ViewSetMixin, GenericAPIView, ListModelMixin, CreateModelMixin,
                       RetrieveModelMixin, UpdateModelMixin, DestroyModelMixin):
    pass

　　但是我们不用自己去定义该方法，可以直接使用框架已经提供好的ViewSetMixin：

from rest_framework.viewsets import ViewSetMixin

　　它做的主要事情就是重写as_view方法：

class ViewSetMixin:
    @classonlymethod
    def as_view(cls, actions=None, **initkwargs):
        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
            # 这里actions是前面url中提供的字典参数{"get": "list", "post": "create"}
            for method, action in actions.items():
                # 循环得到的method是get，action是list
                handler = getattr(self, action)   # self是自己的视图类
                setattr(self, method, handler)   # 在自己的视图类中找list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
            # 做分发：get-->self.get；post-->self.post
            return self.dispatch(request, *args, **kwargs)

　　由于self.get已经等于self.list，分发get对应的是list。

(3)视图改写

from rest_framework.viewsets import ViewSetMixin

class BookModelViewSet(ViewSetMixin, GenericAPIView, ListModelMixin, CreateModelMixin,
                       RetrieveModelMixin, UpdateModelMixin, DestroyModelMixin):
    query_set = Book.objects.all()
    serializer_class = BookSerializer

　　由于get去匹配时已经自动对应到了self.list方法。因此不再自定义视图方法。

(4)简化继承

from rest_framework.viewsets import ViewSetMixin

class ModelViewSet(ViewSetMixin, GenericAPIView, ListModelMixin, CreateModelMixin, RetrieveModelMixin, UpdateModelMixin, DestroyModelMixin):
    pass

class BookModelViewSet(ModelViewSet):
    query_set = Book.objects.all()
    serializer_class = BookSerializer

三、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：

　　 rest-framework框架——视图三部曲第4张

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。

四、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getpost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。

五、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)

六、视图组件总结

1、DRF所有视图文件

　　所有的视图类在如下这四个文件内：

from rest_framework import views       # APIView
from rest_framework import generics    # 公共通用视图类：GenericAPIView，及各种组合视图类CreateAPIView、ListAPIView、RetrieveAPIView等
from rest_framework import mixins      # 混合继承类：CreateModelMixin、ListModelMixin、RetrieveModelMixin、UpdateModelMixin、DestroyModelMixin
from rest_framework import viewsets    # 重写as_view: ViewSetMixin;其他类都是帮助去继承ViewSetMixin

2、DRF视图图谱

　　视图类继承顺序，如Django REST Framework视图图谱所示：

　　 rest-framework框架——视图三部曲第5张

　　首先 django是继承 view的，DRF是从APIView开始继承起，APIView封装了request，其中包含了data、query_params等属性、方法。

　　然后 GenericAPIView封装了 get_queryset() 和 get_serializer()；ViewSetMixin重写了 as_view()方法。

　　随后 GenericViewSet帮忙继承GenericAPIView和ViewSetMixin。

　　最后最高层的封装是 ModelViewSet。