理解sqlalchemy与ORM

 1 __author__ = ‘lizheng‘
 2 # !/usr/bin/env python
 3 #-*- coding:utf-8 -*-
 4 
 5 
 6 from sqlalchemy import create_engine
 7 from sqlalchemy.ext.declarative import declarative_base
 8 from sqlalchemy import Column, Integer, String, ForeignKey, and_, or_ , func
 9 from sqlalchemy.orm import sessionmaker, relationship
10 
11 Base = declarative_base()   # 生成一个sqlORM 基类
12 
13 engine = create_engine(‘mysql+pymysql://root:root@localhost:3306/test?charset=utf8‘, echo=False)  # echo显示执行过程
14 
15 class Host(Base):
16     __tablename__ = ‘hosts‘
17     id = Column(Integer, primary_key=True, autoincrement=True)
18     hostname = Column(String(64), unique=True, nullable=False)
19     ip_addr = Column(String(128), unique=True, nullable=False)
20     port = Column(Integer, default=22)
21     group_id = Column(Integer, ForeignKey(‘group.id‘))
22 #backref为Group关联Host时用的对象名
23     group = relationship(‘Group‘, backref=‘host_list‘)
24 
25 class Group(Base):
26     __tablename__ = ‘group‘
27     id = Column(Integer, primary_key=True)
28     name = Column(String(64), unique=True, nullable=False)
29 
30 Base.metadata.create_all(engine)    # 创建所有表结构
31 if __name__ == ‘__main__‘:
32     # 创建与数据库的会话session class，注意：这里返回给session的是个class，不是实例
33     SessionCls = sessionmaker(bind=engine)
34     session = SessionCls()      # 创建实例
35     h = session.query(Host).filter(Host.hostname==‘server‘).first()   # first 结果为class属性
36     print(‘host group name -->‘, h.group.name)
37     g = session.query(Group).filter(Group.name==‘g2‘).first()
38 #g.host_list为Host对象
39     for i in g.host_list:
40         print(‘group 2 hostname -->‘, g.host_list.hostname)
41     # h1 = Host(hostname=‘localhost‘, ip_addr=‘127.0.0.1‘)
42     # h2 = Host(hostname=‘ubuntu‘, ip_addr=‘192.168.1.1‘, port=8888)
43     # h3 = Host(hostname=‘server2‘, ip_addr=‘192.168.2.22‘, port=1234,group_id = 2)
44     # session.add_all([h3,])
45     # session.commit()
46     # g1 = Group(name=‘g1‘)
47     # g2 = Group(name=‘g2‘)
48     # g3 = Group(name=‘g3‘)
49     # session.add_all([g1,g2,g3])
50     # session.commit()
51     # res = session.query(Host).filter(Host.hostname==‘server‘).all()   # all 结果为列表
52     # res = session.query(Host).filter(Host.hostname==‘server‘).first()   # first 结果为class属性
53     # print(‘host group name -->‘, res.group.name)
54     # print(‘res type-->‘, type(res))
55     # g = session.query(Group).filter(Group.name==‘g2‘).first()
56     # print(‘group 2 hostname -->‘, g.host_list)
57     # print(‘group name to hostname -->‘, g.host_list.hostname)
58     # print(‘group-->‘, g)
59     # obj = session.query(Host, func.count()).group_by(Host.group_id).all()
60     # print(obj)
61     # session.commit()