SQLAlchemy 操做實踐

SQLAlchemy 是python操做數據庫的最好用的一個庫,可以進行ORM映射.它爲高效和高性能的數據庫訪問設計，實現了完整的企業級持久模型。SQLAlchemy的理念是，SQL數據庫的量級和性能重要於對象集合；而對象集合的抽象又重要於表和行。

對數據庫的操做有傳統寫sql和ORM操做兩種方式, 不過我估計第二種應該是採用SQLAlchemy的主要緣由吧.

官方文檔爲: http://docs.sqlalchemy.org/en/rel_0_9/

一 安裝 SQLAlchemy

pip install sqlalchemy

導入若是沒有報錯則安裝成功

>>> import sqlalchemy
>>> sqlalchemy.__version__
'0.9.1'
>>>

二 使用 sqlalchemy對數據庫操做
(1). 定義元信息，綁定到引擎

>>> from sqlalchemy import *
>>> from sqlalchemy.orm import *
>>> engine = create_engine('sqlite:///./sqlalchemy.db', echo=True)  # 定義引擎 
>>> metadata = MetaData(engine) # 綁定元信息
>>>

(2).建立表格，初始化數據庫

>>> 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
>>>

執行上述代碼，咱們就建立 一個 users 表，有id， name， email 三個字段

(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). 基本操做，插入
若是已經table表已經存在， 第二次運行就不準要 create了， 使用 autoload 設置

>>> 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)
>>>

實例化一個插入句柄

>> 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>
>>>

數據庫內容爲

sqlite> select * from users;
1|rsj217|rsj21@gmail.com
2|ghost|
3|test|
sqlite>

查詢 刪除和插入相似 都須要先實例一個 sqlalchemy.sql.dml 對象

 

三 使用 ORM
使用 orm 就是 將 python class 與 數據庫的 table 映射，免去直接寫 sql 語句
建立映射

>>> class User(object):
...     def __repr__(self):
...             return '%s(%r, %r)' % (self.__class__.__name__, self.name, self.email)
... 
>>> mapper(User, users_table)  # 建立映射
<Mapper at 0x31bcfd0; User> 
>>> ul = User()
>>> ul.name
>>> print ul
User(None, None)
>>> print ul.name
None
>>>

創建會話
查詢

>>> 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()
>>>

注意創建會話的方式， sqlalchemy 的版本不一樣 sessionmaker 的方式更好 剩下刪除 關係 事物等高級操做就參考官方文檔了.