ORM
- 对象关系映射(Object relational mapping)
- 实现实体(数据模型)和数据库的解耦
- 将sql语句的操作转换成对对象的操作
切换mysql数据库
-
先创建数据库
create database models charset=utf8
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在settings中
DATABASES = { 'default': { 'ENGINE': 'django.db.backends.mysql', 'NAME': "models", 'USER':'root', 'PASSWORD':'admin', 'HOST':'127.0.0.1', 'PORT':3306 } }
查看执行的sql语句
- connection.queries 指的是执行过的所有的语句,最后一条也就是我们刚刚执行的语句
def showsql():
from django.db import connection
queries = connection.queries
print queries[-1]['sql']
根据已有的数据库生成model(数据模型)
python manage.py inspectdb > 模块/models.py
Django的ORM类库很有可能会有惰性加载或者懒加载
CURD
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retrieve(检索)
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Movie.objects.all()获得所有的数据
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` LIMIT 21
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get()方法
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Movie.objects.get(mid = 1000)
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` WHERE `movie`.`mid` = 1000
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Movie.objects.get(mid__exact =1000 )
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没有数据(DoesNotExist)或者大于1个数据都会出错(MultipleObjectsReturned)
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filter()过滤条件
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Movie.objects.filter(mid__gt=1000)
SELECT
movie
.mid
,movie
.mname
,movie
.mdesc
,movie
.mimg
,movie
.mlink
FROMmovie
WHEREmovie
.mid
> 1000 LIMIT 21
-
-
Movie.objects.filter(mid__lt=1000)
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` WHERE `movie`.`mid` < 1000 LIMIT 21
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Movie.objects.filter(mid__lte=1000)
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Movie.objects.filter(mid__gte=1000)
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Movie.objects.filter(mid__range=(1,1000))
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` WHERE `movie`.`mid` BETWEEN 1 AND 1000 LIMIT 21
-
Movie.objects.filter(mname__contains='爱情')
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` WHERE `movie`.`mname` = '%爱情%' LIMIT 21
-
Movie.objects.filter(mname__startswith='爱情')
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` WHERE `movie`.`mname` LIKE BINARY '爱情%' LIMIT 21
-
遇到了脏数据(数据清洗)
- name多行文本,有很多空格,换行符
for m in Movie.objects.all():
m.mname=m.mname.strip()
m.save()
- 查询(爱情开头,了结尾)
- Movie.objects.filter(mname__startswith='爱情',mname__endswith='了')
- Movie.objects.filter(mname__startswith='爱情').filter(mname__endswith='了')
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` WHERE (`movie`.`mname` LIKE BINARY '爱情%' AND `movie`.`mname` LIKE BINARY '%了') LIMIT 21
-
时间相关的
-
User.objects.filter(birthday__in=('2000-11-20','2017-11-11'))
SELECT `movie_user`.`id`, `movie_user`.`name`, `movie_user`.`birthday` FROM `movie_user` WHERE `movie_user`.`birthday` IN ('2017-11-11', '2000-11-20') LIMIT 21
-
-
查询最近活跃的用户(F(函数))
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查询的电影不包含爱情的
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Movie.objects.exclude(mname__contains='爱情')
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` WHERE NOT (`movie`.`mname` LIKE BINARY '%爱情%') LIMIT 21
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获得第一条数据
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Movie.objects.first()
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` ORDER BY `movie`.`mid` ASC LIMIT 1
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获得最后一条语句
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Movie.objects.last()
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` ORDER BY `movie`.`mid` DESC LIMIT 1
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惰性查询
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再查询多条数据的时候,什么时候用什么时候查
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movies = Movie.objects.all()
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这时候,有没有查询数据,没有
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什么时候用什么时候查询
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print movies
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多余超过一个数据,会惰性查询
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一个数据get,first,last都不会
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再查询多条数据的时候,不用全部查询过来,而是查询有限的个数(21) 1.11.6
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切割 [1,2,3][1:2]
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Movie.objects.all()[:5]
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Movie.objects.all()[10:20]
SELECT `movie`.`mid`, `movie`.`mname`, `movie`.`mdesc`, `movie`.`mimg`, `movie`.`mlink` FROM `movie` LIMIT 10 OFFSET 10
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用途 分页
-
Pagnitor
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排序
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Movie.objects.order_by('-mid').all()降序
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Movie.objects.order_by('mid').all()
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Movie.objects.order_by('mname','-mid')多个字段排序
-
-
使用values查询 部分属性
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QuerySet 结果集
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惰性,什么时候使用什么时候查询
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缓存
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聚合函数
-
针对一系列记录的
-
count,max,min,avg,sum
from django.db.models import Count
Movie.objects.aggregate(Count('*'))
SELECT COUNT(*) AS `count` FROM `movie`
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分组
-
group_by (分组),聚合一旦和分组使用
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聚合函数,就会统计同一组下面的记录
-
统计类别下面有多少篇文章
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Post.objects.values('category__name').annotate(count= Count('*'))
SELECT `post_category`.`name`, COUNT(*) AS `count` FROM `post_post` INNER JOIN `post_category` ON (`post_post`.`category_id` = `post_category`.`id`) GROUP BY `post_category`.`name` ORDER BY NULL LIMIT 21
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修改字段
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时间分组聚合
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Post.objects.values('created').annotate(count = Count('*'))
SELECT `post_post`.`created`, COUNT(*) AS `count` FROM `post_post` GROUP BY `post_post`.`created` ORDER BY NULL
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原生的操作
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Post.objects.raw('select * from post_post ') 查询语句
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connection (默认的数据连接对象)
from django.db import connection cursor = connection.cursor() cursor.execute('crud sql') cursor.close()
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timedelta (专门时间+-操作)
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Post.objects.update(created = F('created')+timedelta(days = -1)) 更新当前帖子的时间
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F('created')获得当前帖子的时间
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Post.objects.filter(id = 2).update(created = F('created')+timedelta(days = -100))
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Post.objects.filter(created__gte=date.today()+timedelta(days= -200))
SELECT `post_post`.`id`, `post_post`.`title`, `post_post`.`category_id`, `post_post`.`created` FROM `post_post` WHERE `post_post`.`created` >= '2017-04-08' LIMIT 21
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热帖
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Post.objects.filter(remark__gte=F('read')/2).filter(remark__gte=50)
SELECT `post_post`.`id`, `post_post`.`title`, `post_post`.`category_id`, `post_post`.`created`, `post_