Python的ORM框架SQLAlchemy入门教程

SQLAlchemy 是python 操作数据库的一个库。能够进行 orm 映射，SQLAlchemy“采用简单的Python语言，为高效和高性能的数据库访问设计，实现了完整的企业级持久模型”

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.eng
4000
ine.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

复制代码代码如下:

>>> 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

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

<Mapper at 0x31bcfd0; User> 

>>> 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

<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

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)

<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。