多对多创建第三张表的三种方式
# 1.全自动创建
# 优势:自动创建第三张表，并且提供了add，remove，set，clear四种操作与正反向查询
# 劣势:第三张表无法创建更多的字段，扩展性很差
class Book(models.Model):
title = models.CharField(max_length=32)
authors = models.ManyToManyField(to='Author')
class Author(models.Model):
name = models.CharField(max_length=32)
# 2.纯手动创建
# 优势:第三张表的扩展性强
# 劣势: 编写麻烦,手动录入的字段多，不再支持add，remove，set，clear以及正反向查询
class Book(models.Model):
title = models.CharField(max_length=32)
class Author(models.Model):
name = models.CharField(max_length=32)
class Book_Author(models.Model):
book = models.ForeignKey(to='Book',on_delete=models.CASCADE)
author = models.ForeignKey(to='Author',on_delete=models.CASCADE)
others = models.CharField(max_length=32)
join_time = models.DateField(auto_now_add=True)
# 3.半自动创建
# 优势: 第三张表由自己创建，扩展性强，正反向查询依旧可用
# 劣势: 编写麻烦，不支持add，remove，set，clear
class Book(models.Model):
title = models.CharField(max_length=32)
authors = models.ManyToManyField(to='Author', through='Book_Author', through_field=('book','author'))
class Author(models.Model):
name = models.CharField(max_length=32)
class Book_Author(models.Model):
book = models.ForeignKey(to='Book',on_delete=models.CASCADE)
author = models.ForeignKey(to='Author',on_delete=models.CASCADE)
others = models.CharField(max_length=32)
join_time = models.DateField(auto_now_add=True)
django内置的序列化组件(drf前身)
"""前后端分离的项目，视图函数只需要返回json格式的数据即可"""
from app01 import models
from django.http import JsonResponse
def ab_ser_func():
# 1.查询所有的书记对象
book_queryset = models.Book.objects.all() # # queryset [对象、对象]
# 2.封装成大字典返回 {{'pk':'','title':'',{}，{}'}}
data_dict = {} # 设置一个空字典存取数据
for book_obj in book_queryset:
temp_dict = {}
temp_dict['pk'] = book_obj.pk
temp_dict['title'] = book_obj.title
temp_dict['price'] = book_obj.price
temp_dict['info'] = book_obj.info
data_dict[book_obj.pk] = temp_dict # {1:{},2:{},3:{},4:{}}
return JsonResponse(data_dict)
"""前端查后端的接口的网站 ： bejson.com"""
# django的序列化组件
# 1.导入内置的序列化模块
from django.core import serializers
# 2.调用该模块下的方法，第一个参数是你想以什么样方式来序列化数据
res = serializers.serialize('json', book_queryset)
return HttpResponse(res)
orm批量操作数据
模型层：
class Books(models.Model):
title = models.CharField(max_length=32)
# 1.普通循环插入数据
- 前端：
<body>
{% for book_obj in book_questset %}
<p>{{ book_obj.title }}</p>
{% endfor %}
</body>
- 后端：
def ab_bk_func(request):
# 1.往books表中插入了10万条数据
"""直接循环插入的话需要10s才能插入500条左右的数据"""
for i in range(1,100000):
models.Books.objects.create(title='第%s本书' % i)
# 2.查询所有的表中并展示到前端页面
book_queryset = models.Books.objects.all()
return render(request,'BkPage.html',locals())
# 2.使用orm语句操作批量插入
- 前端
<body>
{% for book_obj in book_questset %}
<p>{{ book_obj.title }}</p>
{% endfor %}
</body>
- 后端
"""使用orm进行批量插入的的话5s左右就可以将10万条数据插入完毕"""
book_obj_list = [] # 可以用列表生成式[... for i in ... if ...] 生成器表达式(... for i in ... if ...)
for i in range(1,100000):
# 类名加括号产生对象
book_obj = models.Books(title='第%s本书' % i)
book_obj_list.append(book_obj)
# 批量插入数据
models.Books.objects.bulk_create(book_obj_list)
book_queryset = models.Books.objects.all()
return render(request,'BkPage.html',locals())
分页器
# 为何要存在分页器？
"""推导过程"""
- 1.queryset支持切片操作(正数)
- 2.研究各个参数之间的数学关系
每页固定展示多少条数据、起始位置、终止位置
- 3.自定义页码参数
current_page = request.GET.get('page')
- 4.前端展示分页器样式
- 5.总页码数问题
divmod方法
- 6.前端页面页码个数渲染问题
后端产生,前端渲染
# 推导流程
def index(request):
book_data = models.Book.objects.all()
# 计算一共的数据条数
all_count = book_data.count()
# 2.自定义每一页展示的数据条数
per_page_num = 10
# 获取总页数
all_page_num,more =divmod(all_count,per_page_num)
if more:
all_page_num += 1
# 1.获取前端想要展示的页码，获取用户指定的配置，如果没有配置就默认展示第一页
current_page = request.GET.get('page', 1)
try: # 由于后端接受到的前端数据是字符串类型所以我们这里做类型转换处理加异常捕获
current_page = int(current_page)
except Exception as e:
current_page = 1
html_page =''
for i in range(current_page - 5, current_page + 6):
html_page += '<li><a href="?page=%s">%s</a></li>' % (i, i)
# # 3.定义切片的起始位置
# start_num = 0
# # 4.定义切片的中止位置
# end_num = 10
start_num = (current_page - 1) * per_page_num
end_num = current_page * per_page_num
book_query = models.Book.objects.all()
return render(request,'book_list.html', locals())
"""
current_page、per_page_num、start_page、end_page四个参数之间的数据关系。
当per_page_num = 10
current_page start_page end_page
1 0 10
2 10 20
3 20 30
4 30 40
per_page_num = 5
current_page start_page end_page
1 0 5
2 5 10
3 10 15
4 15 20
可以很明显的看出规律
start_page = (current_page - 1) * per_page_num
end_page = current_page* per_page_num
"""
- 1.QuerySet切片操作
- 2.分页样式添加
- 3.页码展示(divmod)
- 4.渲染所有的页码标签
"""前端模板语法虽然不支持range，但是我们可以通过后端创建好html标签传递给html页面使用"""
自定义分页器的使用
# 1.django会自带分页器模块但是使用起来麻烦，所以我们自己封装了一个只需要掌握使用的方法
- 将代码单独放入一个文件夹，当作一个模块导入使用
class Pagination(object):
def __init__(self, current_page, all_count, 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 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
# 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 = []
# 添加前面的nav和ul标签
page_html_list.append('''
<nav aria-label='Page navigation>'
<ul class='pagination'>
''')
first_page = '<li><a href="?page=%s">首页</a></li>' % (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="?page=%s">上一页</a></li>' % (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="?page=%s">%s</a></li>' % (i, i,)
else:
temp = '<li><a href="?page=%s">%s</a></li>' % (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="?page=%s">下一页</a></li>' % (self.current_page + 1,)
page_html_list.append(next_page)
last_page = '<li><a href="?page=%s">尾页</a></li>' % (self.all_pager,)
page_html_list.append(last_page)
# 尾部添加标签
page_html_list.append('''
</nav>
</ul>''')
return ''.join(page_html_list)
- 后端代码:
# 导入自定义模块
from app01.plugins import mypage
def index(request):
book_list = models.Book.objects.all()
current_page = request.GET.get("page",1)
all_count = book_list.count()
page_obj = Pagination(current_page=current_page,all_count=all_count,per_page_num=10)
page_queryset = book_list[page_obj.start:page_obj.end]
return render(request,'booklist.html',locals())
- 前端代码:
<div class="container">
<div class="row">
<div class="col-md-8 col-md-offset-2">
{% for book in page_queryset %}
<p>{{ book.title }}</p>
{% endfor %}
{{ page_obj.page_html|safe }}
</div>
</div>
</div>
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