Python-сообщество

 menu_horizontal = db.relationship('MenuHorizontal', remote_side=[id], backref='menu_horizontal_this')

 class MenuHorizontal(db.Model):
    __tablename__ = 'menu_horizontal'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(45), nullable=False)
    id_contents = db.Column(db.Integer, db.ForeignKey('contents.id'), nullable=False)
    id_parent = db.Column(db.Integer, db.ForeignKey('menu_horizontal.id'), nullable=False)
    menu_horizontal = db.relationship('MenuHorizontal', remote_side=[id], backref='menu_horizontal_this')

 q = models.MenuHorizontal(name='menu', id_contents=1, id_parent=1)
db.session.add(q)
db.session.commit()
q = models.MenuHorizontal(name='menu1', id_contents=1, id_parent=3)
db.session.add(q)
db.session.commit()

 Table [menu_horizontal]
    Fields: 4
        [id]: INTEGER NOT NULL
        [name]: VARCHAR(45) NOT NULL
        [id_contents]: INTEGER NOT NULL
        [id_parent]: INTEGER NOT NULL
    Foreign Keys: 2
        [] ([id_contents]) REFERENCES [contents]([id])
        [] ([id_parent]) REFERENCES [menu_horizontal]([id])
    Indexes: 1
        [] PRIMARY
            [id] 
    Triggers: 0
    Unique constraints: 0
    Check constraints: 0

 #
q_f = models.MenuHorizontal(name='menu_parent')
db.session.add(q_f)
q_2 = models.MenuHorizontal(name='menu_slave_1')
q_3 = models.MenuHorizontal(name='menu_slave_2')
q_f.menu_horizontal = q_2
q_f.menu_horizontal = q_3
db.session.commit()
#
parent = db.session.query(models.MenuHorizontal).filter(models.MenuHorizontal.name == 'menu_parent').one()
for menu_slave in parent.menu_horizontal_this:
    print(slave.name)