批量插入数据与分页的原理及推导
批量插入数据
【1】准备数据
class Book(models.Model):
title = models.CharField(max_length=32)【2】一条一条插入
- 后端
def ab_many(request):
# (1)先给Book表插入一万条数据
for i in range(1000):
models.Book.objects.create(title=f'第{i}本书')
# (2)将所有数据查询到并展示给前端页面
book_queryset = models.Book.objects.all()
return render(request, 'ab_many.html', locals())- 前端
{% for book_obj in book_queryset %}
{{ book_obj.title }}
{% endfor %}效果就是，有一种网络很高的感觉，页面一直在转圈圈
【3】优化-批量插入
def ab_many(request):
# 批量插入
boo_list = []
for i in range(1000):
book_obj = models.Book.objects.create(title=f'第{i}本书')
boo_list.append(book_obj)
models.Book.objects.bulk_create(boo_list)
return render(request, 'ab_many.html', locals())- 当我们想向数据库批量插入数据的时候，使用ORM提供的bulk_create方法能够大大的减少操作的时间
分页的原理及推导
当查询的数据太多的时候，一页展示不完，分页码展示
"""
总数据 每页展示 总页数
100 10 10
101 10 11
99 10 10
怎么计算出来总页数
总数据 / 每页展示 = 总页数
有余数+1
没有余数=商
"""
divmod分页类
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
@property
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('''
''')
return ''.join(page_html_list)