class Subscription(db.Model):
    id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(255))
secret = db.Column(postgresql.BYTEA)
type = db.Column(SubscriptionType.db_type())
status = db.Column(StatusType.db_type())
subscription_id = db.Column(db.Integer)
billing_system_id = db.Column(db.Integer, db.ForeignKey(
    'public.billing_system.id'))
billing_system = db.relationship('BillingSystem', backref='subscriptions')
Наследование + внешние ключи