Django Class Based View

本节内容

一   Class Based View 基于类的视图

　　1.  类的视图 View

　　2.  类的视图 TemplateView

　　3.  类的视图 login_required解决方法

二  通用视图

　　1.  通用视图 - ListView

　　2.  通用视图 - DetailView

　　3.  通用视图 - FormView

一  Class Based View 基于类的视图

function view 存在问题，无法继承复用，尤其时框架封装好的类用不了，function组装复用更擅长

class based view 代码更简洁

简单样例

version 1

# urls.py
from django.conf.urls import url
from mysite import views as my_view

urlpatterns = [
    url(r'^about/', my_view.about),
]

# mysite/views.py
from django.shortcuts import render

def about(request):
    return render(request, 'about.html')

基本的function based view

version 2

# urls.py
from django.views.generic import TemplateView
urlpatterns = [
    url(r'^about/', TemplateView.as_view(template_name='about.html')),
]

# mysite/views.py
from django.shortcuts import render

def about(request):
    return render(request, 'about.html')

TemplateView.as_view(template_name='about.html'))  方法 as_view()，参数template_name=‘网页模板’

version 3

# mysite/views.py
from django.views.generic import TemplateView
class AboutView(TemplateView):
    template_name = 'about.html'

#mysite/urls.py
from mysite import views as my_view

urlpatterns = [
    url(r'^about/', my_view.AboutView.as_view()),
]

说明：

• as_view()返回的是一个function object

• 模板名字作为as_view参数传进去，也可以作为类变量设置template_name = '网页模板'

1.  类的视图 View

# mysite/views.py
def my_view(request):
    if request.method == 'GET':
        return render(request, 'about.html')
    elif request.method == 'POST':
        return HttpResponse('post it')
    elif request.method == 'HEAD':
        return HttpResponse('head it')

# mysite/urls.py
from mysite import views
urlpatterns = [
    url(r'^about/', views.my_view),
]

等价于 类图公共基类View

# mysite/views.py
from django.shortcuts import render,HttpResponse
from django.views.generic import View

class MyView(View):
    def get(self, request):
        return render(request, 'about.html')

    def post(self, request):
        return HttpResponse('post it')

    def head(self, request):
        return HttpResponse('head it')

# mysite/urls.py
from mysite import views as my_view
urlpatterns = [
    url(r'^about/', my_view.MyView.as_view()),
]

类视图好处就是可以直接继承和覆盖

# mysite/views.py
from django.views.generic import View
class GreetingView(View):
    greeting = 'Good Day'
    def get(self, request):
        return HttpResponse(self.greeting)

class MorningGreeting(GreetingView):
    greeting = 'Morning to ya'

# mysite/urls.py
urlpatterns = [
my_view.GreetingView.as_view(greeting="G'day")),
]

源码分析

class View(object):
    # 所有views的公共类，仅仅实现 dispatch方法和简单安全性验证

    http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']

    def __init__(self, **kwargs):
        for key, value in six.iteritems(kwargs):
            setattr(self, key, value)

    @classonlymethod
    def as_view(cls, **initkwargs):
        # request-response的主入口点

        for key in initkwargs:
            # 不能有get,post等方法名的参数，后续有setattr()操作，会覆盖原始请求方法
            if key in cls.http_method_names:
                raise TypeError("You tried to pass in the %s method name as a "
                                "keyword argument to %s(). Don't do that."
                                % (key, cls.__name__))

            # 如果传入了一个没有定义的类属性，就报错；如有greeting属性，就不报错
            if not hasattr(cls, key):
                raise TypeError("%s() received an invalid keyword %r. as_view "
                                "only accepts arguments that are already "
                                "attributes of the class." % (cls.__name__, key))

        # 定义了类似闭包的视图函数
        def view(request, *args, **kwargs):
            self = cls(**initkwargs)  # 调用__init__()进行实例化
            if hasattr(self, 'get') and not hasattr(self, 'head'):
                self.head = self.get
            self.request = request
            self.args = args
            self.kwargs = kwargs
            return self.dispatch(request, *args, **kwargs) # 调用 self.dispatch()进行处理

        # 对view object设置了一些属性
        view.view_class = cls
        view.view_initkwargs = initkwargs

        # 更新文档说明
        update_wrapper(view, cls, updated=())

        # and possible attributes set by decorators
        # like csrf_exempt from dispatch
        update_wrapper(view, cls.dispatch, assigned=())
        return view

    def dispatch(self, request, *args, **kwargs):
        # 将request.method反射到类相应的方法上，并执行
        if request.method.lower() in self.http_method_names:
            # 如果有如get，就handler=get；如果没有handler = self.http_method_not_allowed
            handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
        else:
            handler = self.http_method_not_allowed
        return handler(request, *args, **kwargs)

    def http_method_not_allowed(self, request, *args, **kwargs):
        logger.warning(
            'Method Not Allowed (%s): %s', request.method, request.path,
            extra={'status_code': 405, 'request': request}
        )
        return http.HttpResponseNotAllowed(self._allowed_methods())

    def options(self, request, *args, **kwargs):
        """
        Handles responding to requests for the OPTIONS HTTP verb.
        """
        response = http.HttpResponse()
        response['Allow'] = ', '.join(self._allowed_methods())
        response['Content-Length'] = ''
        return response

    def _allowed_methods(self):
        return [m.upper() for m in self.http_method_names if hasattr(self, m)]

类View

#!/usr/bin/env python3
# -*-coding:utf-8 -*-
# __author__:Jonathan
# email:nining1314@gmail.com

from django.shortcuts import HttpResponse
from django import http
from django.utils import six
from django.utils.decorators import classonlymethod
from django.conf.urls import url

class View(object):
    http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']

    def __init__(self, **kwargs):
        for key, value in six.iteritems(kwargs):
            setattr(self, key, value)

    @classonlymethod
    def as_view(cls, **initkwargs):
        for key in initkwargs:
            if key in cls.http_method_names:
                raise TypeError("禁止 %s 作为 %s()关键字参数" % (key, cls.__name__))
            if not hasattr(cls, key):
                raise TypeError("类 %s() 接收到非法参数 %s，只接受类存在类属性" % (cls.__name__, key))

        def view(request, *args, **kwargs):
            # 把 as_view()传入的关键字参数，赋值为相应的类变量
            self = cls(**initkwargs)  # 类的实例化，虽然只是一行代码，要理解原理：是有很多行代码执行完的结果
            if hasattr(self, 'get') and not hasattr(self, 'head'):
                self.head = self.get
            self.request = request
            self.args = args
            self.kwargs = kwargs
            return self.dispatch(request, *args, **kwargs)  # 一行代码，代表的是self.dispatch()的执行结果

        # 函数也是一种对象，可以有自己的属性****
        view.view_class = cls
        view.view_initkwargs = initkwargs

        # 返回闭合的函数对象
        return view

    def dispatch(self, request, *args, **kwargs):
        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
        return handler(request, *args, **kwargs)   # 一行代码，代表的是handler()的执行结果
    """最终dispatch结果：根据request.method.lower()得到相应的http请求方法，反射到同名类方法，执行"""

    def http_method_not_allowed(self, request, *args, **kwargs):
        return http.HttpResponseNotAllowed(self._allowed_methods())

    def _allowed_methods(self):
        return [m.upper() for m in self.http_method_names if hasattr(self, m)]

class MyView(View):
    def get(self, request):
        return HttpResponse('get it')

    def post(self, request):
        return HttpResponse('post it')

    def head(self, request):
        return HttpResponse('head it')

urlpatterns = [
    url(r'^my_view/', MyView.as_view()),
]

吃透类View

说明：

• as_view返回一个 view function

• as_view接收参数是可以覆盖类定义的变量

• __init__检查as_view传入的参数是否在类中定义

• View.as_view()返回函数视图的view 对象，说明类视图只是对原有的函数视图进行了封装，而没有否定函数view的作用

• view function运行时会调用dispatch，根据用户的request.method路由到get, post等方法

最终得出结论：

View类 在没有更改原Django逻辑的情况下，可以用类来编写view，每个http请求会使用对应类的同名方法进行处理

2.  类的视图 TemplateView

class ContextMixin(object):
    # 渲染模板时，处理需要的上下文参数

    def get_context_data(self, **kwargs):
        if 'view' not in kwargs:
            kwargs['view'] = self
        return kwargs

class TemplateResponseMixin(object):
    # 渲染模板，Mixin一般是小功能类封装，被其他类继承

    template_name = None
    template_engine = None
    response_class = TemplateResponse
    content_type = None

    def render_to_response(self, context, **response_kwargs):
        # 进行模板渲染，render()是个函数，response_class()是个类，实现本质目标没多大区别

        response_kwargs.setdefault('content_type', self.content_type)
        return self.response_class(
            request=self.request,
            template=self.get_template_names(),
            context=context,
            using=self.template_engine,
            **response_kwargs
        )

    def get_template_names(self):
        if self.template_name is None:
            raise ImproperlyConfigured(
                "TemplateResponseMixin requires either a definition of "
                "'template_name' or an implementation of 'get_template_names()'")
        else:
            return [self.template_name]

class TemplateView(TemplateResponseMixin, ContextMixin, View):
    # 实现get()方法，有渲染上文参数，有渲染操作

    def get(self, request, *args, **kwargs):
        context = self.get_context_data(**kwargs)
        return self.render_to_response(context)

类TemplateView

说明：

• 每个Mixin只提供部分功能，最终需要类整合

• TemplateResponseMixin提供render_to_response() 方法，渲染模板

• ContentMixin提供get_context_data()方法，提供渲染数据

• View提供get，post用户访问接口

• 面向对象编程：如何拆分功能模块，如何组装功能模块

3.  类的视图 login_required解决方法

3.1  封装Mixin(推荐)

from django.contrib.auth.decorators import login_required

class LoginRequiredMixin(object):
    @classmethod
    def as_view(cls, **initkwargs):
        view = super(LoginRequiredMixin, cls).as_view(**initkwargs)
        return login_required(view)

class MyView(LoginRequiredMixin, ...):
    pass

3.2 装饰类

from django.contrib.auth.decorators import login_required
from django.utils.decorators import method_decorator
from django.views.generic import TemplateView

class ProtectedView(TemplateView):
    template_name = 'secret.html'

    @method_decorator(login_required)
    def dispatch(self, request, *args, **kwargs):
        return super(ProtectedView, self).dispatch(*args, **kwargs)

推荐学习网站：http://devdocs.io/

二  通用视图

通用视图(generic class base view) 和 class base view 概念上不是一回事

Class Base View 是指用类的方式去写视图

通用视图 是用Class Base View的方式将我们常用的增、删、改、查封装成可扩展的类，使用时直接继承、快速实现

1.  通用视图 - ListView

配置编程，获取数据列表

from django.db import models

class Publisher(models.Model):
    name = models.CharField(max_length=30)
    address = models.CharField(max_length=50)
    city = models.CharField(max_length=60)
    state_province = models.CharField(max_length=30)
    country = models.CharField(max_length=50)
    website = models.URLField()

    def __str__(self):
        return self.name

class Author(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=40)
    email = models.EmailField()

    def __str__(self):
        return '%s %s' % (self.first_name, self.last_name)

class Book(models.Model):
    title = models.CharField(max_length=100)
    authors = models.ManyToManyField('Author')
    publisher = models.ForeignKey('Publisher')
    publication_date = models.DateField(auto_now_add=True)

    def __str__(self):
        return self.title

models.py

from django.views.generic import ListView
from .models import Publisher

class PublisherList(ListView):
    model = Publisher  # 类属性：指定解析的model
    # queryset = Publisher.objects.all()[0:1]      # 和model二选一，获取指定数据
    context_object_name = 'publishers'             # 默认object_list，前端渲染时的上下文参数
    # template_name = 'books/publisher_list.html'  # 指定渲染的模板文件，默认值model名小写_list.html

    # 联系类的queryset，而该方法为实例的定制
    def get_queryset(self):
        print(self.request)  # 根据 self.request进行判断，返回符合条件的queryset
        return Publisher.objects.all()[0:1]

urlpatterns = [
    url(r'^publishers/$', views.PublisherList.as_view(), name='publishers'),
]

说明：

• multi object list view

• model、queryset和get_queryset三者之间关系

• content_object_name

• template_name

源码UML图分析：

2.  通用视图 - DetailView

显示一个object的详情页面

from django.views.generic import DetailView
from .models import Publisher
from .models import Book

class PublisherDetail(DetailView):
    model = Publisher
    context_object_name = 'publisher'  # 模板渲染对象，默认值object

    def get_context_data(self, **kwargs):
        context = super(PublisherDetail, self).get_context_data(**kwargs)
        context['book_list'] = Book.objects.all()  # 附加额外选软数据
        return context

'''
    # 默认的object，是从url里的pk获取的
    def get_object(self, queryset=None):
        object = super(PublisherDetail, self).get_object()
        # 进行更新操作
        # object.last_accessed = timezone.now()
        # object.save()
        return object
'''

urlpatterns = [
    url(r'^publisher/(?P<pk>[0-9]+)/$', views.PublisherDetail.as_view(), name='publisher-detail'),
]

说明：

• Single object detail view

• get_context_data

• content_object_name

• get_object

源码UML图分析：

3.  通用视图 - FormView

• FormView

• CreateView，UpdateView，DeleteView