多对多表结构创建
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
engine = create_engine("mysql+pymysql://root:[email protected]:3306/web", max_overflow=5)
Base = declarative_base(engine)
Session = sessionmaker(bind=engine)
dbSession = Session()
# 多对多
class HostToHostUser(Base):
__tablename__ = ‘host_to_hostuser‘
nid = Column(Integer, primary_key=True, autoincrement=True)
host_id = Column(Integer, ForeignKey(‘host.nid‘))
hostuser_id = Column(Integer, ForeignKey(‘hostuser.nid‘))
# 多对多操作
host = relationship(‘Host‘, backref=‘h‘)
hostuser = relationship(‘HostUser‘, backref=‘hu‘)
class Host(Base):
__tablename__ = ‘host‘
nid = Column(Integer, primary_key=True, autoincrement=True)
hostname = Column(String(32))
port = Column(String(32))
ip = Column(String(32))
#创建到关联表的虚拟关系
###############################################
host_user = relationship(‘HostUser‘, secondary=HostToHostUser.__table__, backref=‘h‘)
class HostUser(Base):
__tablename__ = ‘hostuser‘
nid = Column(Integer, primary_key=True, autoincrement=True)
username = Column(String(32))
def init_db():
Base.metadata.create_all(engine)
def drop_db():
Base.metadata.drop_all(engine)
# 向表内插入数据
# ##################################################################
# dbSession.add_all([
# Host(hostname=‘lala1‘, port=‘22‘, ip=‘1.1.1.1‘),
# Host(hostname=‘lala2‘, port=‘22‘, ip=‘1.1.1.2‘),
# Host(hostname=‘lala3‘, port=‘22‘, ip=‘1.1.1.3‘),
# HostToHostUser(host_id=1, hostuser_id=1),
# HostToHostUser(host_id=1, hostuser_id=2),
# HostToHostUser(host_id=1, hostuser_id=3),
# ])
# dbSession.commit()
##################################################################
查询数据
# 首先查询hostname 为 lala1 的 host
host_obj = dbSession.query(Host).filter(Host.hostname==‘lala1‘).first()
print host_obj
# 通过反向查询，查到hostuser 的对象
for item in host_obj.h:
print (item.hostuser.username)
最后总结：
多对多表结构，只需在主表上创建到子表的虚拟关系：
host_user = relationship(‘HostUser‘, secondary=HostToHostUser.__table__, backref=‘h‘)
然后在中间表中，关联两张表的外键，再通过relationship + backref参数创建虚拟关系，实现正反向查询