在Postgres上使用sqlalchemy创建部分唯一索引

class ScheduledPayment(base):    id = Column(Integer, primary_key=True)    invoice_id = Column(Integer)    is_canceled = Column(Boolean, default=False)    __table_args__ = (        Index('only_one_active_invoice', invoice_id, is_canceled,   unique=True,   postgresql_where=(~is_canceled)),    )