public class RoomCheckinRecordsVO {
    private List<CostRecordVO> costRecords;
    private List<RoomRecordSimpleVO> roomRecords;
    private BigDecimal costAmount;
    private BigDecimal payAmount;
    private BigDecimal balance;
    // 新增字段
    private String checkInNo;
    
    // getter和setter方法
    public String getCheckInNo() {
        return checkInNo;
    }
    
    public RoomCheckinRecordsVO setCheckInNo(String checkInNo) {
        this.checkInNo = checkInNo;
        return this;
    }
}

@Override
public RoomCheckinRecordsVO records(Integer checkInId) {
    List<CostRecordVO> costRecords = costQuery.queryByCheckInId(checkInId);
    List<RoomRecordSimpleVO> roomRecords = roomRecordQuery.queryByCheckInId(checkInId);

    // 原有的業(yè)務(wù)邏輯...
    List<CostRecordVO> safeCostRecords = costRecords == null ? Collections.emptyList() : costRecords;
    BigDecimal payAmount = safeCostRecords.stream()
            .filter(Objects::nonNull)
            .filter(v -> CheckinCostRecordConstants.TYPE_INCOME_EXPENSE.equals(v.getType()))
            .map(CostRecordVO::getAmount)
            .filter(Objects::nonNull)
            .reduce(BigDecimal.ZERO, BigDecimal::add);

    BigDecimal costAmount = safeCostRecords.stream()
            .filter(Objects::nonNull)
            .filter(v -> CheckinCostRecordConstants.TYPE_COST.equals(v.getType()))
            .map(CostRecordVO::getAmount)
            .filter(Objects::nonNull)
            .reduce(BigDecimal.ZERO, BigDecimal::add);

    // 查詢?nèi)胱∮涗洬@取checkInNo
    RoomCheckinPO checkin = mapper.selectById(checkInId);
    String checkInNo = checkin != null ? checkin.getCheckInNo() : null;

    return new RoomCheckinRecordsVO()
            .setCostRecords(costRecords)
            .setRoomRecords(roomRecords)
            .setCostAmount(costAmount)
            .setPayAmount(payAmount)
            .setBalance(payAmount.subtract(costAmount))
            .setCheckInNo(checkInNo);  // 設(shè)置新字段
}

mvn compile

// 推薦的做法
String checkInNo = checkin != null ? checkin.getCheckInNo() : null;

// 或者使用Optional（Java 8+）
String checkInNo = Optional.ofNullable(checkin)
    .map(RoomCheckinPO::getCheckInNo)
    .orElse(null);

@Transactional(rollbackFor = Exception.class)

logger.info("查詢?nèi)胱∮涗?，checkInId: {}, checkInNo: {}", checkInId, checkInNo);