day54 django模块render ,FBV与CBV ,django之settings源码,模板层,自定义标签/过滤器,模板的继承与导入,单表的增删改查...

男娘i 2023-08-17 17:48 72阅读 0赞

# render #

render返回一个HTML页面 而且还能给该页面传数据

## render内部原理 ##

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from django.shortcuts import render,HttpResponse
    
    # Create your views here.
    from django.template import Template,Context
    
    
    def index(request):
        temp = Template('<h1>{
          { user }}</h1>')
        con = Context({
         'user':{
         'name':'baobo','age':'18'}})
        res = temp.render(con)
        print(res)
        return HttpResponse(res)

理论:  
先将所有的内容读取字符串,在用Context将信息传进去,然后将数据返回给前端.

# FBV与CBV #

视图函数并不只是函数,也可以是类.

FBV:面向函数式编程,基于函数的视图.

CBV:面向对象式编程,基于类的视图.

基于cbv的视图

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from app01 import views
    
    urlpatterns = [
        url(r'^admin/', admin.site.urls),
        url(r'^index/', views.index),
        url(r'^login/', views.Login.as_view()),
    ]

urls.py

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from django.shortcuts import render,HttpResponse
    
    from django.views import View
    
    class Login(View):
        def get(self,request):
            print('login的get')
            return render(request,'login.html')
        def post(self,request):
            return HttpResponse('from post')

views.py

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<!DOCTYPE html>
    <html>
    <head>
        <meta charset="utf-8">
        <title>Title</title>
        <script src="https://cdn.bootcss.com/jquery/3.4.1/jquery.min.js"></script>
    </head>
    <body>
    <form action="" method="post">
        <input type="text" name="username">
        <input type="submit">
    </form>
    </body>
    </html>

页面

![1659204-20190918205836537-103114474.png][]

![1659204-20190918205922024-164059309.png][]

由此得到了一个问题:为什么get请求来就会走类里面的get方法,post请求来就会走类里面的post方法

分析:

![1659204-20190918210347793-516479370.png][]

从源头开始分析:

函数名加括号时,执行优先级最高,所以程序会先执行as\_view()方法.

点进View查看源码,去查看as\_view()

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@classonlymethod
        def as_view(cls, **initkwargs):
            """
            Main entry point for a request-response process.
            """
            for key in initkwargs:
                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__))
                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))
    
            def view(request, *args, **kwargs):
                self = cls(**initkwargs)
                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)
            view.view_class = cls
            view.view_initkwargs = initkwargs
    
            # 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=())
            return view
    
        def dispatch(self, request, *args, **kwargs):
            # Try to dispatch to the right method; if a method doesn't exist,
            # defer to the error handler. Also defer to the error handler if the
            # request method isn't on the approved list.
            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)

源码

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@classonlymethod
        def as_view(cls, **initkwargs):   #cls是自己写的类Login
            def view(request, *args, **kwargs):
            self = cls(**initkwargs)   #实例化产生Login的对象 即self=Login(**initkwargs)
                if hasattr(self, 'get') and not hasattr(self, 'head'):  #判断
                    self.head = self.get
                self.request = request
                self.args = args
                self.kwargs = kwargs
                #为对象新增属性    
                return self.dispatch(request, *args, **kwargs)  #返回信息
                #diapatch返回什么,浏览器就收到什么
                #涉及到了一个对象的查找属性或方法的顺序 -- 先在对象本身找,然后从产生对象的类里面找,再到产生对象的类的父类中进行查找,依次往后.
            return view

分析

通过源码发现url匹配条件可以变形为 url('^login/',views.view)

得出结论

FBV 和 CBV 在 路由匹配上是一致的,都是url + 函数的内存地址

当浏览器在输入login会立刻触发view函数的运行:

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def dispatch(self, request, *args, **kwargs):
            # Try to dispatch to the right method; if a method doesn't exist,
            # defer to the error handler. Also defer to the error handler if the
            # request method isn't on the approved list.
    
            #判断请求方式是否在默认的八个方法中
            if request.method.lower() in self.http_method_names:
            # http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']
    
                #getattr 反射获取类产生的属性或方法
                #以GET为例, handler = getattr(self,'get','取不到报错信息')
                #handler = get(request)
                handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
            else:
                handler = self.http_method_not_allowed
            return handler(request, *args, **kwargs)     
            #直接调用我们自己的写的类里面的get方法
            #源码中先通过判断请求方法是否符合默认的八个方法,然后通过反射获取到自定义类中的对应方法执行

点进源码,查看dispath

# django之settings源码 #

前提:

1.django除了暴露给用户一个settings.py配置文件之外  自己内部还有一个全局的配置文件
    2.我们在使用配置文件的时候 可以直接直接导入暴露给用户的settings.py也可以使用django全局的配置文件 并且后者居多
        from django.conf import settings
    3.django的启动入口是manage.py

问题

为什么settings的常量都是大写

import os
        import sys
    
        if __name__ == "__main__":
        # django在启动的时候 就会往全局的大字典中设置一个键值对  值是暴露给用户的配置文件的路径字符串
                        
             os.environ.setdefault("DJANGO_SETTINGS_MODULE", "day54.settings")

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settings = LazySettings()
    重复导入一个文件,单例模式

点进源码,查看

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class LazySettings(LazyObject):
        def _setup(self, name=None):
           # os.environ你可以把它看成是一个全局的大字典
           # 从大字典中取值    键为DJANGO_SETTINGS_MODULE  值为day54.settings
            #settings_mode = 'day54.settings'
            settings_module = os.environ.get(ENVIRONMENT_VARIABLE)
            # Settings('day54.settings')
            self._wrapped = Settings(settings_module)

点击LazySettings,进入源码

转载于:https://www.cnblogs.com/komorebi/p/11544636.html

[ContractedBlock.gif]: https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif
[ExpandedBlockStart.gif]: /images/20230808/a6d7df435435434dae734e853aaa4e3f.png
[1659204-20190918205836537-103114474.png]: /images/20230808/3a1b312454c347b48108c8592e675114.png
[1659204-20190918205922024-164059309.png]: /images/20230808/e4770a1742e9433c886420e5bf88828a.png
[1659204-20190918210347793-516479370.png]: /images/20230808/fb61652cb6054e91b01d6fff3fba480e.png