Question

所以我正在做的是从一个员工（通过他的身份证）获得特定年份（在这种情况下为2015年）的查询。

这是数据库模型，这些是类：

[Serializable] 
public class Absence
{
    public Int32 IDAbsence;
    public Int32 IDEmployee;
    public Int32 Period;
    public DateTime BeginDate;
    public DateTime? EndDate;
    public AbsenceType AbsenceType;
    public AbsenceStatus AbsenceStatus;
    public List<Justification> Justifications;
    public List<Notification> Notifications;

    public Absence() { }

    public Absence(Int32 IDAbsence, Int32 IDEmployee, Int32 Period, DateTime BeginDate, DateTime? EndDate, AbsenceType AbsenceType, AbsenceStatus AbsenceStatus, List<Justification> Justifications, List<Notification> Notifications)
    {
        this.IDAbsence = IDAbsence;
        this.IDEmployee = IDEmployee;
        this.Period = Period;
        this.BeginDate = BeginDate;
        this.EndDate = EndDate;
        this.AbsenceType = AbsenceType;
        this.AbsenceStatus = AbsenceStatus;
        this.Justifications = Justifications;
        this.Notifications = Notifications;
    }
    }

[Serializable] 
    public class TimePeriod
    {
        public Int32 IDTimePeriod;
        public DateTime StartTime;
        public DateTime EndTime;

        public TimePeriod() { }

        public TimePeriod(Int32 IDTimePeriod, DateTime StartTime, DateTime EndTime)
        {
            this.IDTimePeriod = IDTimePeriod;
            this.StartTime = StartTime;
            this.EndTime = EndTime;
        }
    }

TimePeriod主键（IDTimePeriod）应该是缺勤表中外键Period的引用，但我无法为Period创建外键（是的，DB I'与之合作非常令人困惑......）。

这是我的LINQ查询：

   public static List<Tuple<Absence,TimePeriod>> GetAbsencesByEmployeeIDAndYear(Int32 employeeID, Int32 year) {

                List<Tuple<Absence,TimePeriod>> absences = dataContext.Absences.Join(dataContext.TimePeriods,
                                                           abs => abs.Period,
                                                           tps => tps.IDTimePeriod,
                                                           (abs, tps) => new Tuple<Absence, TimePeriod>(abs, tps))
                                                 .Where(abstps => abstps.Item1.Employee.IDEmployee == employeeID && abstps.Item2.StartTime.Year == year).ToList();

            return absences;
        }

这就是错误：

对象引用未设置为对象的实例。

奇怪的是，因为我查阅了数据库，并且2015年该员工的缺勤条目与各自的TimePeriod相同。在任何情况下，Period都没有找到相应的IDTimePeriod。

我错过了什么？

Answer 1

尝试一下：

public static List<Tuple<Absence,TimePeriod>> GetAbsencesByEmployeeIDAndYear(Int32 employeeID, Int32 year) {

    List<Tuple<Absence,TimePeriod>> absences = dataContext.Absences.Join(dataContext.TimePeriods,
     abs => abs.Period,
     tps => tps.IDTimePeriod,
     (abs, tps) => new { abs, tps})
     .Where(x => x.abs.Employee.IDEmployee == employeeID && x.tps.StartTime.Year == year)
    .Select(t => new Tuple<Absence,TimePeriod>(t.abs, t.tps))
    .ToList();

    return absences;
}

这个LINQ查询不正确吗？

1 个答案: