sqlalchemy相关知识

 #!/usr/bin/env python3.5
 # -*- coding:utf8 -*-
 # 多对多关联
 from sqlalchemy import Table, Column, Integer, ForeignKey,String,create_engine,and_,or_,func
 from sqlalchemy.orm import relationship,sessionmaker
 from sqlalchemy.ext.declarative import declarative_base
 Base = declarative_base() #生成一个SqlORM 基类
 engine = create_engine("mysql+pymysql://python:123456@192.168.1.190:3306/python",echo=True)
 # 1、创建一个关联表，关联两个对象 组和主机
 Host2Group = Table('host_2_group',Base.metadata,
                     Column('host_id',ForeignKey('hosts.id'),primary_key=True),
                     Column('group_id',ForeignKey('group.id'),primary_key=True),
                     )

 class Host(Base):
     __tablename__ = 'hosts'
     id = Column(Integer,primary_key=True,autoincrement=True)
     hostname = Column(String(64),unique=True,nullable=False)
     ip_addr = Column(String(128),unique=True,nullable=False)
     port = Column(Integer,default=22)
     groups = relationship("Group",
                           secondary=Host2Group, # 指定中间表的实例
                           backref ='host_list') # backref参数则对关系提供反向引用的声明。
     def __repr__(self):
          return "<id =%s,hostname=%s,ip_addr =%s>"%\
                (self.id,
                 self.hostname,
                 self.ip_addr)
 class Group(Base):
     __tablename__ ="group"
     id = Column(Integer,primary_key=True)
     name = Column(String(64),unique=True,nullable=False)
     def __repr__(self):
         return "<group_id =%s,group_name=%s>"%\
                 (self.id,
                 self.name)

 Base.metadata.create_all(engine) #创建所有表结构
 #
 if __name__ == '__main__':
     SessionCls = sessionmaker(bind=engine) #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
     session = SessionCls()  # 这才是连接的实例
     # g1 = Group(name = "g1")
     # g2 = Group(name = "g2")
     # g3 = Group(name = "g3")
     # g4 = Group(name = "g4")
     '''
     h1 = Host(hostname='h1',ip_addr='192.168.2.242',port = 2000)
     h2 = Host(hostname='h2',ip_addr='192.168.2.243',port=20000)
     h3 = Host(hostname='h3',ip_addr='192.168.2.244',port=20000)
     session.add_all([h1,h2,h3])
     '''
     # 关联主机
     # 找组
     g1 = session.query(Group).first()
     # groups = session.query(Group).all()
     # h1 = session.query(Host).filter(Host.hostname == "h1").first()
     # 找主机
     h2 = session.query(Host).filter(Host.hostname == "h2").first()
     # h3 = session.query(Host).filter(Host.hostname == "h3").first()
     # # h1.groups = groups
     # # h1.groups.pop()
     # 关联，使一个主机属于多个组
     # h2.groups = groups[1:-1]
     # 查询
     print("======>",h2.groups)
     print("=====>",g1.host_list)
     # update
     # obj = session.query(Host).filter(Host.hostname == "test_localhost").first()
     # print("++>",obj)
     # #obj.hostname = "test_localhost"  # 更改
     # session.delete(obj)
     # objs = session.query(Host).filter(and_(Host.hostname.like("ubun%"),Host.port > 20)).all()
     # print("+++>",objs)

     session.commit()

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