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

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='[e-mail]')
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', '[e-mail]')
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|[e-mail]
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。