Python的ORM框架SQLAlchemy入门教程
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
复制代码 代码如下:pip install sqlalchemy
导入如果没有报错则安装成功
复制代码 代码如下:>>> 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
复制代码 代码如下:
(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
复制代码 代码如下:
>>> 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
复制代码 代码如下:
(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
复制代码 代码如下:
>>> 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=
>>>
实例化一个插入句柄
复制代码 代码如下:
>>> i = users_table.insert()
>>> i
>>> 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
>>> 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
>>>
数据库内容为
复制代码 代码如下:
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
复制代码 代码如下:
>>> 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
>>> ul = User()
>>> ul.name
>>> print ul
User(None, None)
>>> print ul.name
None
>>>
建立会话
查询
复制代码 代码如下:
>>> session = create_session()
>>> session
>>> query = session.query(User)
>>> query
>>> 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
复制代码 代码如下:
>>> 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)
>>> 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。