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=<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。