SQLAlchemy. Добавить запись, ссылающуюся на две родительские

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from sqlalchemy.orm import relationship

from sqlalchemy.ext.declarative import declarative_base

from sqlalchemy import Column
from sqlalchemy import Integer
from sqlalchemy import String
from sqlalchemy import ForeignKey

Base = declarative_base()
engine = create_engine('sqlite://')
Session = sessionmaker(engine)


class Parent(Base):
    __tablename__ = 'Parent'

    link = Column('link', Integer, primary_key=True, autoincrement=True)
    name = Column('c_name', String)

    child = relationship('Child')


class Parent2(Base):

    __tablename__ = 'Parent2'

    link = Column('link', Integer, primary_key=True, autoincrement=True)
    name = Column('c_name', String)

    child = relationship('Child')


class Child(Base):
    __tablename__ = 'Child'

    link = Column('link', Integer, primary_key=True, autoincrement=True)
    parent = Column('f_parent', Integer, ForeignKey('Parent.link'), nullable=False)
    parent2 = Column('f_parent2', Integer, ForeignKey('Parent2.link'), nullable=False)
    name = Column('c_name', String)


Base.metadata.create_all(engine)
session = Session()


parent = Parent(name='qwe')
parent2 = Parent2(name='qwerty')

session.add(parent)
session.add(parent2)
session.commit()

child = Child(name='child')

parent.child.append(child)
parent2.child.append(child)

session.add_all([parent, parent2])

session.commit()