在SQLAlchemy中使用关联对象自引用多对多关系

from sqlalchemy import Column, Integer, String, Table
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

association_table = Table('association', Base.metadata,
    Column('left_id', Integer, ForeignKey('entity.id')),
    Column('right_id', Integer, ForeignKey('entity.id'))
)

class Entity(Base):
    __tablename__ = 'entity'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    related_entities = relationship('Entity',
                                    secondary=association_table,
                                    primaryjoin=id==association_table.c.left_id,
                                    secondaryjoin=id==association_table.c.right_id,
                                    backref='related_to')

entity1 = session.query(Entity).get(1)
related_entities = entity1.related_entities