Django as_view

write by 2019-07-26 23:43

1.介绍

  在开始之前讲之前，我们先看django的类视图拥有自动查找指定方法的功能, 通过调用是通过as_view()方法实现

urls.py

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

urlpatterns = [
    path('list', BookView.as_view()),
    path('retrieve/<int:id>', BookEditView.as_view()),
]

views.py

from django.shortcuts import render
from django.views import View
from django.http import HttpResponse, JsonResponse
from django.core import serializers
from .models import Book, Publisher
import json

from rest_framework.views import APIView
from rest_framework.response import Response
from .serializers import BookSerializer

class BookView(APIView):
    def get(self, request):
        # book_obj = Book.objects.first()
        # ret = BookSerializer(book_obj)
        # return Response(ret.data)
        book_list = Book.objects.all()
        ret = BookSerializer(book_list, many=True)
        return Response(ret.data)

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

2. 自动匹配方法

  为什么as_view能自动匹配指定的方法。

先看源码

 @classonlymethod
    def as_view(cls, **initkwargs):  # 实际上是一个闭包  返回 view函数
        """
        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):  # 作用：增加属性， 调用dispatch方法 
            self = cls(**initkwargs)  # 创建一个 cls 的实例对象， cls 是调用这个方法的 类（Demo）
            if hasattr(self, 'get') and not hasattr(self, 'head'):
                self.head = self.get
            self.request = request  # 为对象增加 request， args， kwargs 三个属性
            self.args = args
            self.kwargs = kwargs
            return self.dispatch(request, *args, **kwargs)  # 找到指定的请求方法， 并调用它
        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,
        if request.method.lower() in self.http_method_names:  # 判断请求的方法类视图是否拥有， http_method_names=['get', 'post']
            handler = getattr(self, request.method.lower(), self.http_method_not_allowed)  # 如果存在 取出该方法
        else:
            handler = self.http_method_not_allowed
        return handler(request, *args, **kwargs)  # 执行该方法

简化

 @classonlymethod
    def as_view(cls, **initkwargs):  # 实际上是一个闭包  返回 view函数
        """
        Main entry point for a request-response process.
        """
        def view(request, *args, **kwargs):  # 作用：增加属性， 调用dispatch方法 
            self = cls(**initkwargs)  # 创建一个 cls 的实例对象， cls 是调用这个方法的 类（Demo）
            if hasattr(self, 'get') and not hasattr(self, 'head'):
                self.head = self.get
            self.request = request  # 为对象增加 request， args， kwargs 三个属性
            self.args = args
            self.kwargs = kwargs
            return self.dispatch(request, *args, **kwargs)  # 找到指定的请求方法， 并调用它

        return view

    def dispatch(self, request, *args, **kwargs):
        # Try to dispatch to the right method; if a method doesn't exist,
        if request.method.lower() in self.http_method_names:  # 判断请求的方法类视图是否拥有， http_method_names=['get', 'post']
            handler = getattr(self, request.method.lower(), self.http_method_not_allowed)  # 如果存在 取出该方法
        else:
            handler = self.http_method_not_allowed
        return handler(request, *args, **kwargs)  # 返回该请求方法执行的结果

再简化

def as_view(): # 校验 + 返回view方法
    # 一些校验
    ...
    def view(): # 执行视图
        # 增加 为对象request, args, kwargs 属性
        ...
        return dispatch() # 调用指定的请求方法
    return view

def dispatch(): # 真正的查找指定的方法, 并调用该方法
    ...
    return handler()

调用顺序: as_view --> view --> dispatch

• 可以看出as_view实际上是一个闭包, 它的作用做一些校验工作, 再返回view方法.
• 而view方法的作用是给请求对象补充三个参数, 并调用 dispatch方法处理
• dispatch方法查找到指定的请求方法, 并执行

可以得出结论: 实际上真正实现查找的方法是 dispatch方法