Django---分页器、中间件


分页

Django的分页器（paginator）

view

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from django.shortcuts import render,HttpResponse

# Create your views here.

from app01.models import *

from django.core.paginator import Paginator, EmptyPage, PageNotAnInteger


def index(request):


</span><span style="color: #800000;">'''</span><span style="color: #800000;">
批量导入数据:

Booklist=[]
for i in range(100):
    Booklist.append(Book(title="book"+str(i),price=30+i*i))
Book.objects.bulk_create(Booklist)
</span><span style="color: #800000;">'''</span>

<span style="color: #800000;">'''</span><span style="color: #800000;">



分页器的使用:


book_list=Book.objects.all()

paginator = Paginator(book_list, 10)

print("count:",paginator.count)           #数据总数
print("num_pages",paginator.num_pages)    #总页数
print("page_range",paginator.page_range)  #页码的列表



page1=paginator.page(1) #第1页的page对象
for i in page1:         #遍历第1页的所有数据对象
    print(i)

print(page1.object_list) #第1页的所有数据


page2=paginator.page(2)

print(page2.has_next())            #是否有下一页
print(page2.next_page_number())    #下一页的页码
print(page2.has_previous())        #是否有上一页
print(page2.previous_page_number()) #上一页的页码



# 抛错
#page=paginator.page(12)   # error:EmptyPage

#page=paginator.page("z")   # error:PageNotAnInteger

</span><span style="color: #800000;">'''</span><span style="color: #000000;">


book_list</span>=<span style="color: #000000;">Book.objects.all()

paginator </span>= Paginator(book_list, 10<span style="color: #000000;">)
page </span>= request.GET.get(<span style="color: #800000;">'</span><span style="color: #800000;">page</span><span style="color: #800000;">'</span>,1<span style="color: #000000;">)
currentPage</span>=<span style="color: #000000;">int(page)


</span><span style="color: #0000ff;">try</span><span style="color: #000000;">:
    </span><span style="color: #0000ff;">print</span><span style="color: #000000;">(page)
    book_list </span>=<span style="color: #000000;"> paginator.page(page)
</span><span style="color: #0000ff;">except</span><span style="color: #000000;"> PageNotAnInteger:
    book_list </span>= paginator.page(1<span style="color: #000000;">)
</span><span style="color: #0000ff;">except</span><span style="color: #000000;"> EmptyPage:
    book_list </span>=<span style="color: #000000;"> paginator.page(paginator.num_pages)


</span><span style="color: #0000ff;">return</span> render(request,<span style="color: #800000;">"</span><span style="color: #800000;">index.html</span><span style="color: #800000;">"</span>,{<span style="color: #800000;">"</span><span style="color: #800000;">book_list</span><span style="color: #800000;">"</span>:book_list,<span style="color: #800000;">"</span><span style="color: #800000;">paginator</span><span style="color: #800000;">"</span>:paginator,<span style="color: #800000;">"</span><span style="color: #800000;">currentPage</span><span style="color: #800000;">"</span>:currentPage})</pre>



 


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index.html:

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" 
    integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
</head>
<body>

<div class="container">


<span style="color: #0000ff;">&lt;</span><span style="color: #800000;">h4</span><span style="color: #0000ff;">&gt;</span>分页器<span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">h4</span><span style="color: #0000ff;">&gt;</span>
<span style="color: #0000ff;">&lt;</span><span style="color: #800000;">ul</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">

    {% for book in book_list %}
         </span><span style="color: #0000ff;">&lt;</span><span style="color: #800000;">li</span><span style="color: #0000ff;">&gt;</span>{{ book.title }} -----{{ book.price }}<span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">li</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">
    {% endfor %}

 </span><span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">ul</span><span style="color: #0000ff;">&gt;</span>


<span style="color: #0000ff;">&lt;</span><span style="color: #800000;">ul </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="pagination"</span><span style="color: #ff0000;"> id</span><span style="color: #0000ff;">="pager"</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">

             {% if book_list.has_previous %}
                </span><span style="color: #0000ff;">&lt;</span><span style="color: #800000;">li </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="previous"</span><span style="color: #0000ff;">&gt;&lt;</span><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="/index/?page={{ book_list.previous_page_number }}"</span><span style="color: #0000ff;">&gt;</span>上一页<span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">a</span><span style="color: #0000ff;">&gt;&lt;/</span><span style="color: #800000;">li</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">
             {% else %}
                </span><span style="color: #0000ff;">&lt;</span><span style="color: #800000;">li </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="previous disabled"</span><span style="color: #0000ff;">&gt;&lt;</span><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="#"</span><span style="color: #0000ff;">&gt;</span>上一页<span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">a</span><span style="color: #0000ff;">&gt;&lt;/</span><span style="color: #800000;">li</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">
             {% endif %}


             {% for num in paginator.page_range %}

                 {% if num == currentPage %}
                   </span><span style="color: #0000ff;">&lt;</span><span style="color: #800000;">li </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="item active"</span><span style="color: #0000ff;">&gt;&lt;</span><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="/index/?page={{ num }}"</span><span style="color: #0000ff;">&gt;</span>{{ num }}<span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">a</span><span style="color: #0000ff;">&gt;&lt;/</span><span style="color: #800000;">li</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">
                 {% else %}
                   </span><span style="color: #0000ff;">&lt;</span><span style="color: #800000;">li </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="item"</span><span style="color: #0000ff;">&gt;&lt;</span><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="/index/?page={{ num }}"</span><span style="color: #0000ff;">&gt;</span>{{ num }}<span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">a</span><span style="color: #0000ff;">&gt;&lt;/</span><span style="color: #800000;">li</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">

                 {% endif %}
             {% endfor %}



             {% if book_list.has_next %}
                </span><span style="color: #0000ff;">&lt;</span><span style="color: #800000;">li </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="next"</span><span style="color: #0000ff;">&gt;&lt;</span><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="/index/?page={{ book_list.next_page_number }}"</span><span style="color: #0000ff;">&gt;</span>下一页<span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">a</span><span style="color: #0000ff;">&gt;&lt;/</span><span style="color: #800000;">li</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">
             {% else %}
                </span><span style="color: #0000ff;">&lt;</span><span style="color: #800000;">li </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="next disabled"</span><span style="color: #0000ff;">&gt;&lt;</span><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="#"</span><span style="color: #0000ff;">&gt;</span>下一页<span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">a</span><span style="color: #0000ff;">&gt;&lt;/</span><span style="color: #800000;">li</span><span style="color: #0000ff;">&gt;</span><span style="color: #000000;">
             {% endif %}

        </span><span style="color: #0000ff;">&lt;/</span><span style="color: #800000;">ul</span><span style="color: #0000ff;">&gt;</span>



</div>


</body>

</html>

 
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扩展

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def index(request):

book_list</span>=<span style="color: #000000;">Book.objects.all()

paginator </span>= Paginator(book_list, 15<span style="color: #000000;">)
page </span>= request.GET.get(<span style="color: #800000;">'</span><span style="color: #800000;">page</span><span style="color: #800000;">'</span>,1<span style="color: #000000;">)
currentPage</span>=<span style="color: #000000;">int(page)

</span><span style="color: #008000;">#</span><span style="color: #008000;">  如果页数十分多时，换另外一种显示方式</span>
<span style="color: #0000ff;">if</span> paginator.num_pages&gt;30<span style="color: #000000;">:

    </span><span style="color: #0000ff;">if</span> currentPage-5&lt;1<span style="color: #000000;">:
        pageRange</span>=range(1,11<span style="color: #000000;">)
    </span><span style="color: #0000ff;">elif</span> currentPage+5&gt;<span style="color: #000000;">paginator.num_pages:
        pageRange</span>=range(currentPage-5,paginator.num_pages+1<span style="color: #000000;">)

    </span><span style="color: #0000ff;">else</span><span style="color: #000000;">:
        pageRange</span>=range(currentPage-5,currentPage+5<span style="color: #000000;">)

</span><span style="color: #0000ff;">else</span><span style="color: #000000;">:
    pageRange</span>=<span style="color: #000000;">paginator.page_range


</span><span style="color: #0000ff;">try</span><span style="color: #000000;">:
    </span><span style="color: #0000ff;">print</span><span style="color: #000000;">(page)
    book_list </span>=<span style="color: #000000;"> paginator.page(page)
</span><span style="color: #0000ff;">except</span><span style="color: #000000;"> PageNotAnInteger:
    book_list </span>= paginator.page(1<span style="color: #000000;">)
</span><span style="color: #0000ff;">except</span><span style="color: #000000;"> EmptyPage:
    book_list </span>=<span style="color: #000000;"> paginator.page(paginator.num_pages)


</span><span style="color: #0000ff;">return</span> render(request,<span style="color: #800000;">"</span><span style="color: #800000;">index.html</span><span style="color: #800000;">"</span>,locals())</pre>



 


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中间件

中间件的概念

中间件顾名思义，是介于request与response处理之间的一道处理过程，相对比较轻量级，并且在全局上改变django的输入与输出。因为改变的是全局，所以需要谨慎实用，用不好会影响到性能。

Django的中间件的定义：

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Middleware is a framework of hooks into Django’s request/response processing. <br>It’s a light, low-level “plugin” system for globally altering Django’s input or output.

如果你想修改请求，例如被传送到view中的HttpRequest对象。 或者你想修改view返回的HttpResponse对象，这些都可以通过中间件来实现。

可能你还想在view执行之前做一些操作，这种情况就可以用 middleware来实现。

大家可能频繁在view使用request.user吧。 Django想在每个view执行之前把user设置为request的属性，于是就用了一个中间件来实现这个目标。所以Django提供了可以修改request 对象的中间件 AuthenticationMiddleware。

Django默认的Middleware：

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MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]
 
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每一个中间件都有具体的功能。

自定义中间件

中间件中一共有四个方法：

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process_request

process_view


process_exception


process_response

 
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process_request，process_response

当用户发起请求的时候会依次经过所有的的中间件，这个时候的请求时process_request,最后到达views的函数中，views函数处理后，在依次穿过中间件，这个时候是process_response,最后返回给请求者。

上述截图中的中间件都是django中的，我们也可以自己定义一个中间件，我们可以自己写一个类，但是必须继承MiddlewareMixin

需要导入

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from django.utils.deprecation import MiddlewareMixin

 

注意：在使用之前需要在settings中配置一下,在MIDDLEWARE中加上我们自定义的中间件，注意顺序，从上往下加载读取，这个顺序会影响执行顺序

in views:

def index(request):

</span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #008080;">view函数...</span><span style="color: #800000;">"</span><span style="color: #000000;">)
</span><span style="color: #0000ff;">return</span> HttpResponse(<span style="color: #800000;">"</span><span style="color: #800000;">OK</span><span style="color: #800000;">"</span>)</pre>

in Mymiddlewares.py：

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from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import HttpResponse

class Md1(MiddlewareMixin):


</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_request(self,request):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md1请求</span><span style="color: #800000;">"</span><span style="color: #000000;">)


 
    def process_response(self,request,response):
        print("Md1返回")
        return response

class Md2(MiddlewareMixin):


</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_request(self,request):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md2请求</span><span style="color: #800000;">"</span><span style="color: #000000;">)<br>        <span style="color: #008000;">#<span style="color: #008000;">return HttpResponse("Md2中断")</span></span>
</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_response(self,request,response):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md2返回</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span> response</pre>



 


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结果：

Md1请求
Md2请求
view函数...
Md2返回
Md1返回

注意：如果当请求到达请求2的时候直接不符合条件返回，即return HttpResponse("Md2中断")，程序将把请求直接发给中间件2返回，然后依次返回到请求者，结果如下：

返回Md2中断的页面，后台打印如下：

Md1请求
Md2请求
Md2返回
Md1返回

流程图如下：

 

即：

当  def process_request

# 无返回值：继续执行后续中间件和视图函数
# 有返回值：执行自己的process_response和上面的response

process_view

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process_view(self, request, callback, callback_args, callback_kwargs)

 Mymiddlewares.py修改如下

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from django.utils.deprecation import MiddlewareMixin
from django.shortcuts import HttpResponse

class Md1(MiddlewareMixin):


</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_request(self,request):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md1请求</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #008000;">#</span><span style="color: #008000;">return HttpResponse("Md1中断")</span>
<span style="color: #0000ff;">def</span><span style="color: #000000;"> process_response(self,request,response):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md1返回</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> response

</span><span style="color: #ff0000;">def process_view(self, request, callback, callback_args, callback_kwargs):
    print("Md1view")



class Md2(MiddlewareMixin):


</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_request(self,request):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md2请求</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span> HttpResponse(<span style="color: #800000;">"</span><span style="color: #800000;">Md2中断</span><span style="color: #800000;">"</span><span style="color: #000000;">)
</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_response(self,request,response):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md2返回</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> response

</span><span style="color: #ff0000;">def process_view(self, request, callback, callback_args, callback_kwargs):
    print("Md2view")</span></pre>



 


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结果如下：

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Md1请求
Md2请求
Md1view
Md2view
view函数...
Md2返回
Md1返回
 
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下图进行分析上面的过程：

当最后一个中间的process_request到达路由关系映射之后，返回到中间件1的process_view，然后依次往下，到达views函数，最后通过process_response依次返回到达用户。

process_view可以用来调用视图函数：

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class Md1(MiddlewareMixin):

</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_request(self,request):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md1请求</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #008000;">#</span><span style="color: #008000;">return HttpResponse("Md1中断")</span>
<span style="color: #0000ff;">def</span><span style="color: #000000;"> process_response(self,request,response):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md1返回</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> response

</span><span style="color: #ff0000;">def process_view(self, request, callback, callback_args, callback_kwargs):

    # return HttpResponse("hello")

    response=callback(request,*callback_args,**callback_kwargs)
    return response</span></pre>



 


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结果如下：

Md1请求
Md2请求
view函数...
Md2返回
Md1返回

注意：process_view如果有返回值，会越过其他的process_view以及视图函数，但是所有的process_response都还会执行。

process_exception

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process_exception(self, request, exception)

示例修改如下：

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class Md1(MiddlewareMixin):

</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_request(self,request):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md1请求</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #008000;">#</span><span style="color: #008000;">return HttpResponse("Md1中断")</span>
<span style="color: #0000ff;">def</span><span style="color: #000000;"> process_response(self,request,response):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md1返回</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> response

</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_view(self, request, callback, callback_args, callback_kwargs):

    </span><span style="color: #008000;">#</span><span style="color: #008000;"> return HttpResponse("hello")</span>

    <span style="color: #008000;">#</span><span style="color: #008000;"> response=callback(request,*callback_args,**callback_kwargs)</span>
    <span style="color: #008000;">#</span><span style="color: #008000;"> return response</span>
    <span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">md1 process_view...</span><span style="color: #800000;">"</span><span style="color: #000000;">)

</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_exception(self):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">md1 process_exception...</span><span style="color: #800000;">"</span><span style="color: #000000;">)



class Md2(MiddlewareMixin):


</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_request(self,request):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md2请求</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #008000;">#</span><span style="color: #008000;"> return HttpResponse("Md2中断")</span>
<span style="color: #0000ff;">def</span><span style="color: #000000;"> process_response(self,request,response):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">Md2返回</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> response
</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_view(self, request, callback, callback_args, callback_kwargs):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">md2 process_view...</span><span style="color: #800000;">"</span><span style="color: #000000;">)

</span><span style="color: #0000ff;">def</span><span style="color: #000000;"> process_exception(self):
    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">md1 process_exception...</span><span style="color: #800000;">"</span>)</pre>



 


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结果如下：

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Md1请求
Md2请求
md1 process_view...
md2 process_view...
view函数...

Md2返回

Md1返回

 
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流程图如下：

当views出现错误时：

 将md2的process_exception修改如下：

  def process_exception(self,request,exception):

    </span><span style="color: #0000ff;">print</span>(<span style="color: #800000;">"</span><span style="color: #800000;">md2 process_exception...</span><span style="color: #800000;">"</span><span style="color: #000000;">)
    </span><span style="color: #0000ff;">return</span> HttpResponse(<span style="color: #800000;">"</span><span style="color: #800000;">error</span><span style="color: #800000;">"</span>)</pre>

结果如下：

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Md1请求
Md2请求
md1 process_view...
md2 process_view...
view函数...
md2 process_exception...
Md2返回
Md1返回
 
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原文地址：https://www.cnblogs.com/wq-mr-almost/p/10347123.html