Каким образом составить правильное выражение?

Question

[Павел]

@hybrid_property
    def balance(self):
        
        plus = sum(op.amount for op in self.operations if op.operation_type in BALANCE_PLUS_OPERATIONS)
        minus = sum(op.amount for op in self.operations if op.operation_type in BALANCE_MINUS_OPERATIONS)

        return plus - minus

    @balance.expression
    def balance(cls):

        p = select([func.sum(Operation.amount).label('BALANCE_PLUS_OPERATIONS')]) \
                    .where(Operation.operation_type.in_(BALANCE_PLUS_OPERATIONS)) \
                    .where(User.id == cls.id) \
                    .as_scalar()
        m = select([func.sum(Operation.amount).label('BALANCE_MINUS_OPERATIONS')]) \
                    .where(Operation.operation_type.in_(BALANCE_MINUS_OPERATIONS)) \
                    .where(User.id == cls.id) \
                    .as_scalar()

        return select([p - m]).label('BALANCE')

balance.expression def balance(cls):
работает некорректно

users = User.query.filter_by(balance=51).all()
<User([e-mail])> 51
<User([e-mail])> 0