SQLALchemy 学习理解

orm对象关系模型,将数据与程序对象建议一个映射关系,首推此框架
http://docs.sqlalchemy.org/en/latest/orm/tutorial.html

#建立数据库引擎
from sqlalchemy import create_engine
create_engine包含有多个数据库连接配置等参数,并通过懒连接的方式建立连接
engine = create_engin(mysql://scott:tiger@hostname/dbname",encoding='latin1',echo=True)


# 创建会话
from sqlalchemy.orm import sessionmaker
or
from sqlalchemy.orm import create_session
#sessionmaker(bind=None)
#create_session(bind=None)
绑定的是db对象
以上两种方法都是创建的 sqlalchemy.orm.session.Session对象

session的正确用法

#介绍session相关的问题
#http://docs.sqlalchemy.org/en/latest/orm/session_basics.html#what-does-the-session-do
# 非线程安全的

class ThingOne(object):
    def go(self, session):
        session.query(FooBar).update({"x": 5})

class ThingTwo(object):
    def go(self, session):
        session.query(Widget).update({"q": 18})

def run_my_program():
    session = Session()
    try:
        ThingOne().go(session)
        ThingTwo().go(session)

        session.commit()
    except:
        session.rollback()
        raise
    finally:
        session.close()

#close 关闭所有的transaction

创建对象实例 declare a mapping

>>> 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)
...     fullname = Column(String)
...     password = Column(String)
...
...     def __repr__(self):
...        return "" % (
...                             self.name, self.fullname, self.password)

增加

>>> ed_user = User(name='ed', fullname='Ed Jones', password='edspassword')
>>> session.add(ed_user)
>>> session.commit()

查询

>>> for instance in session.query(User).order_by(User.id):
...     print(instance.name, instance.fullname)
ed Ed Jones
wendy Wendy Williams
mary Mary Contrary
fred Fred Flinstone

>>> for name, fullname in session.query(User.name, User.fullname):
...     print(name, fullname)
ed Ed Jones
wendy Wendy Williams
mary Mary Contrary
fred Fred Flinstone

>>> for row in session.query(User, User.name).all():
...    print(row.User, row.name)
 ed
 wendy
 mary
 fred

修改

直接修改对象之后，commit即可

删除

session.delete(obj)