SQLAlchemy tutorial

重要概念

ORM：数据库对象 <--> class --> 类实例instance
定义数据库连接
session：数据库事务通过session操作，flush()提交到内存但是未提交到数据库，commit()保存到数据库；

commit() flushes whatever remaining changes remain to the database, and commits the transaction. The connection resources referenced by the session are now returned to the connection pool. Subsequent operations with this session will occur in a new transaction, which will again re-acquire connection resources when first needed.

或者 What's the difference between flush() and commit()

The session object registers transaction operations with session.add(), but doesn't yet communicate them to the database until session.flush() is called.

session.flush() communicates a series of operations to the database (insert, update, delete). The database maintains them as pending operations in a transaction. The changes aren't persisted permanently to disk, or visible to other transactions until the database receives a COMMIT for the current transaction (which is what session.commit() does).

session.commit() commits (persists) those changes to the database.

flush() is always called as part of a call to commit()

定义映射

>>> from sqlalchemy import create_engine
>>> engine = create_engine('sqlite:///:memory:', echo=True)
>>> from sqlalchemy.ext.declarative import declarative_base
>>> Base = declarative_base()
>>> from sqlalchemy import Column, Integer, String
>>> class User(Base):
...     __tablename__ = 'users'
...     id = Column(Integer,  primary_key=True)
...     name = Column(String(50))
...     fullname = Column(String(50))
...     password = Column(String(12))
...     def __repr__(self):
...         return "<User(name='%s', fullname='%s', password='%s')>" % (self.nam
e, self.fullname, self.password)
...

class 定义

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer,  primary_key=True)
    name = Column(String(50))
    fullname = Column(String(50))
    password = Column(String(12))
    def __repr__(self):
        return "<User(name='%s', fullname='%s', password='%s')>" % (self.name, self.fullname, self.password)

创建数据库

>>> Base.metadata.create_all(engine)
2015-12-29 15:56:59,029 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS VARCHAR(60)) AS anon_1
2015-12-29 15:56:59,030 INFO sqlalchemy.engine.base.Engine ()
2015-12-29 15:56:59,035 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS VARCHAR(60)) AS anon_1
2015-12-29 15:56:59,036 INFO sqlalchemy.engine.base.Engine ()
2015-12-29 15:56:59,039 INFO sqlalchemy.engine.base.Engine PRAGMA table_info("users")
2015-12-29 15:56:59,039 INFO sqlalchemy.engine.base.Engine ()
2015-12-29 15:56:59,042 INFO sqlalchemy.engine.base.Engine
CREATE TABLE users (
        id INTEGER NOT NULL,
        name VARCHAR(50),
        fullname VARCHAR(50),
        password VARCHAR(12),
        PRIMARY KEY (id)
)

2015-12-29 15:56:59,043 INFO sqlalchemy.engine.base.Engine ()
2015-12-29 15:56:59,046 INFO sqlalchemy.engine.base.Engine COMMIT

添加数据

>>> ed_user = User(name='ed', fullname='Ed Jones', password='edspassword')
>>> str(ed_user.id)
'None'
>>> from sqlalchemy.orm import sessionmaker
>>> Session = sessionmaker(bind=engine)
>>> session = Session()
>>> session.add(ed_user)
>>> our_user = session.query(User).filter_by(name='ed').first()
2015-12-29 15:57:48,361 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2015-12-29 15:57:48,364 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, password) VALUES (?, ?, ?)
2015-12-29 15:57:48,365 INFO sqlalchemy.engine.base.Engine ('ed', 'Ed Jones', 'edspassword')
2015-12-29 15:57:48,369 INFO sqlalchemy.engine.base.Engine 
SELECT users.id AS users_id, users.name AS users_name, users.fullname AS users_fullname, users.password AS users_password
FROM users
WHERE users.name = ?
 LIMIT ? OFFSET ?
2015-12-29 15:57:48,371 INFO sqlalchemy.engine.base.Engine ('ed', 1, 0)
>>> our_user
<User(name='ed', fullname='Ed Jones', password='edspassword')>
>>> ed_user is our_user
True
>>> session.add_all([
...     User(name='wendy', fullname='Wendy Williams', password='foobar'),
...     User(name='mary', fullname='Mary Contrary', password='xxg527'),
...     User(name='fred', fullname='Fred Flinstone', password='blah')])
>>> ed_user.password = 'f8s7ccs'
>>> session.dirty
IdentitySet([<User(name='ed', fullname='Ed Jones', password='f8s7ccs')>])
>>> session.new
IdentitySet([<User(name='wendy', fullname='Wendy Williams', password='foobar')>,
 <User(name='fred', fullname='Fred Flinstone', password='blah')>, <User(name='ma
ry', fullname='Mary Contrary', password='xxg527')>])
>>> session.commit()
2015-12-29 16:05:12,272 INFO sqlalchemy.engine.base.Engine UPDATE users SET password=? WHERE users.id = ?
2015-12-29 16:05:12,273 INFO sqlalchemy.engine.base.Engine ('f8s7ccs', 1)
2015-12-29 16:05:12,275 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, password) VALUES (?, ?, ?)
2015-12-29 16:05:12,276 INFO sqlalchemy.engine.base.Engine ('wendy', 'Wendy Williams', 'foobar')
2015-12-29 16:05:12,278 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, password) VALUES (?, ?, ?)
2015-12-29 16:05:12,279 INFO sqlalchemy.engine.base.Engine ('mary', 'Mary Contrary', 'xxg527')
2015-12-29 16:05:12,280 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, password) VALUES (?, ?, ?)
2015-12-29 16:05:12,282 INFO sqlalchemy.engine.base.Engine ('fred', 'Fred Flinstone', 'blah')
2015-12-29 16:05:12,285 INFO sqlalchemy.engine.base.Engine COMMIT
>>> ed_user.id
2015-12-29 16:06:27,977 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2015-12-29 16:06:27,980 INFO sqlalchemy.engine.base.Engine SELECT users.id AS us
ers_id, users.name AS users_name, users.fullname AS users_fullname, users.passwo
rd AS users_password
FROM users
WHERE users.id = ?
2015-12-29 16:06:27,983 INFO sqlalchemy.engine.base.Engine (1,)
1
>>> ed_user.id
1

事务回滚 Rolling Back

>>> ed_user.name = 'Edwardo'
>>> fake_user = User(name='fakeuser', fullname='Invalid', password='12345')
>>> session.add(fake_user)
>>> session.query(User).filter(User.name.in_(['Edwardo', 'fakeuser'])).all()
2015-12-29 16:10:52,517 INFO sqlalchemy.engine.base.Engine UPDATE users SET name=? WHERE users.id = ?
2015-12-29 16:10:52,519 INFO sqlalchemy.engine.base.Engine ('Edwardo', 1)
2015-12-29 16:10:52,520 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name, fullname, password) VALUES (?, ?, ?)
2015-12-29 16:10:52,522 INFO sqlalchemy.engine.base.Engine ('fakeuser', 'Invalid', '12345')
2015-12-29 16:10:52,528 INFO sqlalchemy.engine.base.Engine 
SELECT users.id AS users_id, users.name AS users_name, users.fullname AS users_fullname, users.password AS users_password
FROM users
WHERE users.name IN (?, ?)
2015-12-29 16:10:52,529 INFO sqlalchemy.engine.base.Engine ('Edwardo', 'fakeuser')
[<User(name='Edwardo', fullname='Ed Jones', password='f8s7ccs')>, <User(name='fa
keuser', fullname='Invalid', password='12345')>]
>>> session.rollback()
2015-12-29 16:11:14,276 INFO sqlalchemy.engine.base.Engine ROLLBACK
>>> ed_user.name
2015-12-29 16:11:20,378 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2015-12-29 16:11:20,381 INFO sqlalchemy.engine.base.Engine 
SELECT users.id AS users_id, users.name AS users_name, users.fullname AS users_fullname, users.password AS users_password
FROM users
WHERE users.id = ?
2015-12-29 16:11:20,384 INFO sqlalchemy.engine.base.Engine (1,)
u'ed'
>>> fake_user in session
False
>>> session.query(User).filter(User.name.in_(['ed', 'fakeuser'])).all()
2015-12-29 16:11:35,526 INFO sqlalchemy.engine.base.Engine 
SELECT users.id AS users_id, users.name AS users_name, users.fullname AS users_fullname, users.password AS users_password
FROM users
WHERE users.name IN (?, ?)
2015-12-29 16:11:35,529 INFO sqlalchemy.engine.base.Engine ('ed', 'fakeuser')
[<User(name='ed', fullname='Ed Jones', password='f8s7ccs')>]