SQLAlchemy多对多

from sqlalchemy.ext.declarative import declarative_base
Base=declarative_base()

from sqlalchemy import Column,String,Integer,ForeignKey
from sqlalchemy.orm import relationship

class Girl(Base):
    __tablename__="girl"
    id = Column(Integer,primary_key=True)
    name=Column(String(32))
#secondary="Hotel" 表示两个表关联Hotel
    girl2boy = relationship("Boy",secondary="hotel",backref="boy2girl" )


class Boy(Base):
    __tablename__ = "boy"
    id = Column(Integer,primary_key=True)
    name = Column(String(32))


class Hotel(Base):
    __tablename__ = "hotel"
    id=Column(Integer,primary_key=True)
    girl_id =Column(Integer,ForeignKey("girl.id"))
    boy_id=Column(Integer,ForeignKey("boy.id"))

from sqlalchemy import create_engine
engine=create_engine("mysql+pymysql://root:@127.0.0.1:3306/day127?charset=utf8")

Base.metadata.create_all(engine)

from sqlalchemy.orm import sessionmaker
from SQL.M_M import engine,Boy

Session=sessionmaker(engine)
db_session=Session()
#反向添加
# boy_obj=Boy(name="kobe")
# boy_obj.boy2girl =[Girl(name="dva"),Girl(name="xiaoemi")]
# db_session.add(boy_obj)
# db_session.commit()
# db_session.close()
#正向添加
# girl_obj=Girl(name="anna",girl2boy=[Boy(name="curry"),Boy(name="green")])
# db_session.add(girl_obj)
# db_session.commit()
# db_session.close()
#正向查询
# g_list=db_session.query(Girl).all()
# for row in g_list:
#     for item in row.girl2boy:
#         print(row.id,row.name,item.name)

#反向查询
b_list=db_session.query(Boy).all()
for row in b_list:
    for item in row.boy2girl:
        print(row.id,row.name,item.name)