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SQLAlchemy 教程

SQLAlchemy 教程

作者: e0ccb34883c9 | 来源:发表于2015-04-12 00:02 被阅读23076次

    SQLAlchemy 是python 操作数据库的一个库。能够进行 orm 映射官方文档 sqlchemy
    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

    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

    >>> 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='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

    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

    >>> 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.

    注:本文转载自
    http://rsj217.diandian.com/post/2014-01-09/40060713434

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