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

代码如下：

pip install sqlalchemy

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

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

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

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

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

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='[email protected]')
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', '[email protected]')
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

代码如下：

sqlite> select * from users;
1|rsj217|[email protected]
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

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

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

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。