django http404 详解

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【引子】

今天在看django的官方文档的时候看到get_object_or_404这个函数感觉比较奇怪。这个主要来自于它的功能，如果要查询的对象

存在那么就返回对象；如果对象不存在那么就要报404 Not Found ；但是404 Not Found并不是它的返回值，而django直接返回

了404页面、这个感觉就比较奇怪了。

1、对get_object_or_404的一次失败地模拟

from django.shortcuts import render
from django.http import Http404,HttpResponsedef fun_get_object_or_404(pk=None):
if pk == 1:
return 1
else:
return HttpResponse('object is not found ...')def index(request):
obj = fun_get_object_or_404()
return HttpResponse("object is {0}".format(obj))

先看一下view的执行结果吧

从返回的内容我们可以看出来、view对HttpResponse的处理并不像middleware中的那样；middleware只要是遇到return HttpResponse 这样的

内容就会马上返回response对象到浏览器；那get_object_or_404 是怎么实现的呢？

2、get_object_or_404 的官方实现

def get_object_or_404(klass, *args, **kwargs):
"""
Use get() to return an object, or raise a Http404 exception if the object
does not exist. klass may be a Model, Manager, or QuerySet object. All other passed
arguments and keyword arguments are used in the get() query. Like with QuerySet.get(), MultipleObjectsReturned is raised if more than
one object is found.
"""
queryset = _get_queryset(klass)
try:
return queryset.get(*args, **kwargs)
except AttributeError:
klass__name = klass.__name__ if isinstance(klass, type) else klass.__class__.__name__
raise ValueError(
"First argument to get_object_or_404() must be a Model, Manager, "
"or QuerySet, not '%s'." % klass__name
)
except queryset.model.DoesNotExist:
raise Http404('No %s matches the given query.' % queryset.model._meta.object_name)