association_table = Table('association', Base.metadata, Column('left_id', Integer, ForeignKey('left.id')), Column('right_id', Integer, ForeignKey('right.id')) ) class Parent(Base): __tablename__ = 'left' id = Column(Integer, primary_key=True) children = relationship("Child", secondary="association", backref="parents") class Child(Base): __tablename__ = 'right' id = Column(Integer, primary_key=True)