Python的ORM框架SQLAlchemy入门教程
时间:2023-01-17 03:41:05
SQLAlchemy的理念是,SQL数据库的量级和性能重要于对象集合;而对象集合的抽象又重要于表和行。
一 安装 SQLAlchemy
pip install sqlalchemy
导入如果没有报错则安装成功
>>> import sqlalchemy
>>> sqlalchemy.__version__
'0.9.1'
>>>
二 使用 sqlalchemy对数据库操作
1. 定义元信息,绑定到引擎
(env)ghost@ghost-H61M-S2V-B3:~/project/flask/fsql$ python
Python 2.7.3 (default, Apr 10 2013, 05:13:16)
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from sqlalchemy import *
>>> from sqlalchemy.orm import *
>>> engine = create_engine('sqlite:///./sqlalchemy.db', echo=True) # 定义引擎
>>> metadata = MetaData(engine) # 绑定元信息
>>>
2.创建表格,初始化数据库
>>> users_table = Table('users', metadata,
... Column('id', Integer, primary_key=True),
... Column('name', String(40)),
... Column('email', String(120)))
>>>
>>> users_table.create()
2014-01-09 10:03:32,436 INFO sqlalchemy.engine.base.Engine
CREATE TABLE users (
id INTEGER NOT NULL,
name VARCHAR(40),
email VARCHAR(120),
PRIMARY KEY (id)
)
2014-01-09 10:03:32,436 INFO sqlalchemy.engine.base.Engine ()
2014-01-09 10:03:32,575 INFO sqlalchemy.engine.base.Engine COMMIT
>>>
执行上述代码,我们就创建 一个 users 表,有id, name, email 三个字段
(env)ghost@ghost-H61M-S2V-B3:~/project/flask/fsql$ sqlite3 sqlalchemy.db
SQLite version 3.7.13 2012-06-11 02:05:22
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> .tables
users
sqlite>
3. 基本操作,插入
如果已经table表已经存在, 第二次运行就不许要 create了, 使用 autoload 设置
>>> from sqlalchemy import *
>>> from sqlalchemy.orm import *
>>> engine = create_engine('sqlite:///./sqlalchemy.db', echo=True)
>>> metadata = MetaData(engine)
>>> users_table = Table('users', metadata, autoload=True)
2014-01-09 10:20:01,580 INFO sqlalchemy.engine.base.Engine PRAGMA table_info("users")
2014-01-09 10:20:01,581 INFO sqlalchemy.engine.base.Engine ()
2014-01-09 10:20:01,582 INFO sqlalchemy.engine.base.Engine PRAGMA foreign_key_list("users")
2014-01-09 10:20:01,583 INFO sqlalchemy.engine.base.Engine ()
2014-01-09 10:20:01,583 INFO sqlalchemy.engine.base.Engine PRAGMA index_list("users")
2014-01-09 10:20:01,583 INFO sqlalchemy.engine.base.Engine ()
>>> users_table
Table('users', MetaData(bind=Engine(sqlite:///./sqlalchemy.db)), Column('id', INTEGER(), table=<users>, primary_key=True, nullable=False), Column('name', VARCHAR(length=40), table=<users>), Column('email', VARCHAR(length=120), table=<users>), schema=None)
>>>
实例化一个插入句柄
>>> i = users_table.insert()
>>> i
<sqlalchemy.sql.dml.Insert object at 0x31bc850>
>>> print i
INSERT INTO users (id, name, email) VALUES (?, ?, ?)
>>> i.execute(name='rsj217', email='rsj21@gmail.com')
2014-01-09 10:24:02,250 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, email) VALUES (?, ?)
2014-01-09 10:24:02,250 INFO sqlalchemy.engine.base.Engine ('rsj217', 'rsj21@gmail.com')
2014-01-09 10:24:02,251 INFO sqlalchemy.engine.base.Engine COMMIT
<sqlalchemy.engine.result.ResultProxy object at 0x31bce10>
>>> i.execute({'name': 'ghost'},{'name': 'test'})
2014-01-09 10:24:57,537 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name) VALUES (?)
2014-01-09 10:24:57,537 INFO sqlalchemy.engine.base.Engine (('ghost',), ('test',))
2014-01-09 10:24:57,537 INFO sqlalchemy.engine.base.Engine COMMIT
<sqlalchemy.engine.result.ResultProxy object at 0x31bcd50>
>>>
数据库内容为
sqlite> select * from users;
1|rsj217|rsj21@gmail.com
2|ghost|
3|test|
sqlite>
查询 删除和插入类似 都需要先实例一个 sqlalchemy.sql.dml 对象
三 使用 ORM
使用 orm 就是 将 python class 与 数据库的 table 映射,免去直接写 sql 语句
创建映射
>>> class User(object):
... def __repr__(self):
... return '%s(%r, %r)' % (self.__class__.__name__, self.name, self.email)
...
>>> mapper(User, users_table) # 创建映射
<Mapper at 0x31bcfd0; User>
>>> ul = User()
>>> ul.name
>>> print ul
User(None, None)
>>> print ul.name
None
>>>
建立会话
查询
>>> session = create_session()
>>> session
<sqlalchemy.orm.session.Session object at 0x31bef10>
>>> query = session.query(User)
>>> query
<sqlalchemy.orm.query.Query object at 0x31bee50>
>>> u = query.filter_by(name='rsj217').first()
2014-01-09 10:44:23,809 INFO sqlalchemy.engine.base.Engine SELECT users.id AS users_id, users.name AS users_name, users.email AS users_email
FROM users
WHERE users.name = ?
LIMIT ? OFFSET ?
2014-01-09 10:44:23,809 INFO sqlalchemy.engine.base.Engine ('rsj217', 1, 0)
>>> u.name
u'rsj217'
>>>
插入
>>> from sqlalchemy import *
>>> from sqlalchemy.orm import *
>>> engine = create_engine('sqlite:///./sqlalchemy.db')
>>> metadata = MetaData(engine)
>>> users_table = Table('users', metadata, autoload=True)
>>> class User(object): pass
...
>>> mapper(User, users_table)
<Mapper at 0x18185d0; User>
>>> Session = sessionmaker(bind=engine)
>>> session = Session()
>>> u = User()
>>> u.name = 'new'
>>> session.add(u)
>>> session.flush()
>>> session.commit()
>>>
注意建立会话的方式, sqlalchemy 的版本不同 sessionmaker 的方式更好
剩下删除 关系 事物等高级操作就参考官方文档了。
标签:Python,ORM,SQLAlchemy
0
投稿
猜你喜欢
python变量赋值机制踩坑记录
2021-08-19 08:59:44
Python实现爬取知乎神回复简单爬虫代码分享
2023-03-23 19:00:10
python单例模式实例分析
2021-11-02 12:17:49
Python单元测试及unittest框架用法实例解析
2022-06-18 05:35:29
Windows下python3.7安装教程
2023-02-16 16:39:11
实例讲解Python3中abs()函数
2023-06-14 02:21:55
python 第三方库的安装及pip的使用详解
2023-12-27 07:06:53
利用Python如何生成便签图片详解
2021-01-02 18:09:52
django 使用内置messages的操作
2023-04-23 13:35:56
第一类工厂与哈希对象
2009-12-28 13:14:00
弹性+固宽布局
2009-05-15 12:19:00
解决用CSS控制DIV居中失效的问题
2010-04-05 21:53:00
python实现串口通信的示例代码
2023-08-04 03:44:24
Pandas读取csv时如何设置列名
2023-11-25 19:54:55
IBatis.net连接MySql 问题与故障的解决方案
2011-06-02 09:38:00
解决python3 网络请求路径包含中文的问题
2023-07-09 00:14:23
Python处理PPT文件的实用知识点总结
2021-04-26 04:11:10
js字符串日期yyyy-MM-dd转化为date示例代码
2023-08-06 16:35:58
如何把ASP源代码编写成DLL组件
2007-10-19 13:49:00
python制作填词游戏步骤详解
2023-03-09 19:46:47