SQLAlchemy 如何定义与类的对象实例的primaryjoin 关系？

如何解决SQLAlchemy 如何定义与类的对象实例的primaryjoin 关系？

使用 sqlAlchemy 1.3 我有关系表的多对多映射：

at = Table('asstable',Metadata,Column('number',db.Numeric(38,0),ForeignKey('mynumber.objectid')),Column('list',ForeignKey('mylist.objectid'))
)

class MyList(Base):
    __tablename__ = 'mylist'
    objectid =  Column(Numeric(38,primary_key=True)
    ...
    numbers = relationship('MyList',secondary=at,primaryjoin = "MyList.objectid == at.list")


class MyNumber(Base):
    __tablename__ = 'mynumber'
    objectid =  Column(Numeric(38,primary_key=True)
    ...
    lists = relationship('MyList',primaryjoin = "MyNumber.objectid == at.number")

错误是：

 Could not determine join condition between parent/child tables on relationship Mylist.numbers - there are no foreign keys linking these tables via secondary table

如果关系中有对象不是类，如何定义primaryjoin？