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  • Django-进阶 分页,中间件

    分页

    Django的分页器(paginator)

    view

    复制代码
    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})
    复制代码

    index.html:

    复制代码
    <!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>
    复制代码

    扩展

    复制代码
    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())
    复制代码

    自定义分页器

    复制代码
    """
    分页组件使用示例:
    
        obj = Pagination(request.GET.get('page',1),len(USER_LIST),request.path_info)
        page_user_list = USER_LIST[obj.start:obj.end]
        page_html = obj.page_html()
    
        return render(request,'index.html',{'users':page_user_list,'page_html':page_html})
    
    
    """
    
    
    class Pagination(object):
    
        def __init__(self,current_page,all_count,base_url,per_page_num=2,pager_count=11):
            """
            封装分页相关数据
            :param current_page: 当前页
            :param all_count:    数据库中的数据总条数
            :param per_page_num: 每页显示的数据条数
            :param base_url: 分页中显示的URL前缀
            :param pager_count:  最多显示的页码个数
            """
    
            try:
                current_page = int(current_page)
            except Exception as e:
                current_page = 1
    
            if current_page <1:
                current_page = 1
    
            self.current_page = current_page
    
            self.all_count = all_count
            self.per_page_num = per_page_num
    
            self.base_url = base_url
    
            # 总页码
            all_pager, tmp = divmod(all_count, per_page_num)
            if tmp:
                all_pager += 1
            self.all_pager = all_pager
    
    
            self.pager_count = pager_count
            self.pager_count_half = int((pager_count - 1) / 2)
    
        @property
        def start(self):
            return (self.current_page - 1) * self.per_page_num
    
        @property
        def end(self):
            return self.current_page * self.per_page_num
    
        def page_html(self):
            # 如果总页码 < 11个:
            if self.all_pager <= self.pager_count:
                pager_start = 1
                pager_end = self.all_pager + 1
            # 总页码  > 11
            else:
                # 当前页如果<=页面上最多显示11/2个页码
                if self.current_page <= self.pager_count_half:
                    pager_start = 1
                    pager_end = self.pager_count + 1
    
                # 当前页大于5
                else:
                    # 页码翻到最后
                    if (self.current_page + self.pager_count_half) > self.all_pager:
                        pager_end = self.all_pager + 1
                        pager_start = self.all_pager - self.pager_count + 1
                    else:
                        pager_start = self.current_page - self.pager_count_half
                        pager_end = self.current_page + self.pager_count_half + 1
    
            page_html_list = []
    
            first_page = '<li><a href="%s?page=%s">首页</a></li>' % (self.base_url,1,)
            page_html_list.append(first_page)
    
            if self.current_page <= 1:
                prev_page = '<li class="disabled"><a href="#">上一页</a></li>'
            else:
                prev_page = '<li><a href="%s?page=%s">上一页</a></li>' % (self.base_url,self.current_page - 1,)
    
            page_html_list.append(prev_page)
    
            for i in range(pager_start, pager_end):
                if i == self.current_page:
                    temp = '<li class="active"><a href="%s?page=%s">%s</a></li>' % (self.base_url,i, i,)
                else:
                    temp = '<li><a href="%s?page=%s">%s</a></li>' % (self.base_url,i, i,)
                page_html_list.append(temp)
    
            if self.current_page >= self.all_pager:
                next_page = '<li class="disabled"><a href="#">下一页</a></li>'
            else:
                next_page = '<li><a href="%s?page=%s">下一页</a></li>' % (self.base_url,self.current_page + 1,)
            page_html_list.append(next_page)
    
            last_page = '<li><a href="%s?page=%s">尾页</a></li>' % (self.base_url,self.all_pager,)
            page_html_list.append(last_page)
    
            return ''.join(page_html_list)
    复制代码

    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:

    1
    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

    复制代码
    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',
    ]
    复制代码

    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:

    复制代码
    process_request
    
    process_view
    
    process_exception
    
    process_response
    复制代码

    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

    1
    from django.utils.deprecation import MiddlewareMixin

     

    in views:

    def index(request):
    
        print("view函数...")
        return HttpResponse("OK")

    in Mymiddlewares.py:

    复制代码
    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
    复制代码

    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:

     

    process_view

    1
    process_view(self, request, callback, callback_args, callback_kwargs)

     Mymiddlewares.py修改如下

    复制代码
    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")
    复制代码

    结果如下:

    复制代码
    Md1请求
    Md2请求
    Md1view
    Md2view
    view函数...
    Md2返回
    Md1返回
    复制代码

    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:

    复制代码
    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
    复制代码

    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

    1
    process_exception(self, request, exception)

    示例修改如下:

    复制代码
    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...")
    复制代码

    结果如下:

    复制代码
    Md1请求
    Md2请求
    md1 process_view...
    md2 process_view...
    view函数...
    
    Md2返回
    Md1返回
    复制代码

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

    结果如下:

    复制代码
    Md1请求
    Md2请求
    md1 process_view...
    md2 process_view...
    view函数...
    md2 process_exception...
    Md2返回
    Md1返回
    复制代码
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  • 原文地址:https://www.cnblogs.com/wangmo/p/8594209.html
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