Django-进阶 分页，中间件
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())
自定义分页器
"""
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)
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。
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 |
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：
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：
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：
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：
Md1请求 Md2请求 md1 process_view... md2 process_view... view函数... md2 process_exception... Md2返回 Md1返回
