Django---分页器、中间件

时间:2022-09-12 03:53:23

分页

Django的分页器(paginator)

view

 
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):

    '''
    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)
    '''

    '''
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

    '''


    book_list=Book.objects.all()

    paginator = Paginator(book_list, 10)
    page = request.GET.get('page',1)
    currentPage=int(page)


    try:
        print(page)
        book_list = paginator.page(page)
    except PageNotAnInteger:
        book_list = paginator.page(1)
    except EmptyPage:
        book_list = paginator.page(paginator.num_pages)


    return render(request,"index.html",{"book_list":book_list,"paginator":paginator,"currentPage":currentPage})
 

index.html:

 
<!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"> <h4>分页器</h4> <ul> {% for book in book_list %} <li>{{ book.title }} -----{{ book.price }}</li> {% endfor %} </ul> <ul class="pagination" id="pager"> {% if book_list.has_previous %} <li class="previous"><a href="/index/?page={{ book_list.previous_page_number }}">上一页</a></li> {% else %} <li class="previous disabled"><a href="#">上一页</a></li> {% endif %} {% for num in paginator.page_range %} {% if num == currentPage %} <li class="item active"><a href="/index/?page={{ num }}">{{ num }}</a></li> {% else %} <li class="item"><a href="/index/?page={{ num }}">{{ num }}</a></li> {% endif %} {% endfor %} {% if book_list.has_next %} <li class="next"><a href="/index/?page={{ book_list.next_page_number }}">下一页</a></li> {% else %} <li class="next disabled"><a href="#">下一页</a></li> {% endif %} </ul> </div> </body> </html>
 

扩展

 
def index(request):


    book_list=Book.objects.all()

    paginator = Paginator(book_list, 15)
    page = request.GET.get('page',1)
    currentPage=int(page)

    #  如果页数十分多时,换另外一种显示方式
    if paginator.num_pages>30:

        if currentPage-5<1:
            pageRange=range(1,11)
        elif currentPage+5>paginator.num_pages:
            pageRange=range(currentPage-5,paginator.num_pages+1)

        else:
            pageRange=range(currentPage-5,currentPage+5)

    else:
        pageRange=paginator.page_range


    try:
        print(page)
        book_list = paginator.page(page)
    except PageNotAnInteger:
        book_list = paginator.page(1)
    except EmptyPage:
        book_list = paginator.page(paginator.num_pages)


    return render(request,"index.html",locals())
 
 

中间件

Django---分页器、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

 
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',
]
 

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:

 
process_request

process_view

process_exception

process_response
 

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。

Django---分页器、中间件

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

 Django---分页器、中间件

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):

    print("view函数...")
    return HttpResponse("OK")

in Mymiddlewares.py:

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

class Md1(MiddlewareMixin):

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

class Md2(MiddlewareMixin):

    def process_request(self,request):
        print("Md2请求")
#return HttpResponse("Md2中断")
def process_response(self,request,response): print("Md2返回") return response
 

 

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:

Django---分页器、中间件 

 

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

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

class Md1(MiddlewareMixin):

    def process_request(self,request):
        print("Md1请求")
        #return HttpResponse("Md1中断")
    def process_response(self,request,response):
        print("Md1返回")
        return response

    def process_view(self, request, callback, callback_args, callback_kwargs):
        print("Md1view")

class Md2(MiddlewareMixin):

    def process_request(self,request):
        print("Md2请求")
        return HttpResponse("Md2中断")
    def process_response(self,request,response):
        print("Md2返回")
        return response

    def process_view(self, request, callback, callback_args, callback_kwargs):
        print("Md2view")
 

结果如下:

 
Md1请求
Md2请求
Md1view
Md2view
view函数...
Md2返回
Md1返回
 

下图进行分析上面的过程:

Django---分页器、中间件

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:

 
class Md1(MiddlewareMixin):

    def process_request(self,request):
        print("Md1请求")
        #return HttpResponse("Md1中断")
    def process_response(self,request,response):
        print("Md1返回")
        return response

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

        # return HttpResponse("hello")

        response=callback(request,*callback_args,**callback_kwargs)
        return response
 

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:

 
class Md1(MiddlewareMixin):

    def process_request(self,request):
        print("Md1请求")
        #return HttpResponse("Md1中断")
    def process_response(self,request,response):
        print("Md1返回")
        return response

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

        # return HttpResponse("hello")

        # response=callback(request,*callback_args,**callback_kwargs)
        # return response
        print("md1 process_view...")

    def process_exception(self):
        print("md1 process_exception...")



class Md2(MiddlewareMixin):

    def process_request(self,request):
        print("Md2请求")
        # return HttpResponse("Md2中断")
    def process_response(self,request,response):
        print("Md2返回")
        return response
    def process_view(self, request, callback, callback_args, callback_kwargs):
        print("md2 process_view...")

    def process_exception(self):
        print("md1 process_exception...")
 

结果如下:

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

Md2返回
Md1返回
 

流程图如下:

当views出现错误时:

Django---分页器、中间件

 将md2process_exception修改如下:

  def process_exception(self,request,exception):

        print("md2 process_exception...")
        return HttpResponse("error")

结果如下:

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