Linq查询抛出异常

Question

我正在使用linq查询从Appointment表中获取两个最近的约会。距离现在还不到365天。

当约会小于或等于365天时，我得到正确的值，但如果约会超过365天，我会收到错误。

我尝试使用n，但不知道使用它的正确方法。能帮助我在正确的环境中使用它吗？

这是我的班级：

DefaultIfEmpty()

这是我的BO课程：

public SchedulingEligibility(ClassMember member)
{
    int[] excludedStatuses = new int[]
    {
        (int) AppointmentStatusEnum.Cancelled,
        (int) AppointmentStatusEnum.Deleted,
        (int) AppointmentStatusEnum.Rescheduled,
        (int) AppointmentStatusEnum.Missed,
        (int) AppointmentStatusEnum.Pending
    };

    RecentAppointments = (from a in member.Appointments
                          orderby a.StartTime descending
                          where (!excludedStatuses.Contains((int)a.AppointmentStatusID) &
                              DateTime.Now.Subtract(a.StartTime).Days <= 365)
                          select a).Take(2).ToList();

    if (RecentAppointments == null)
    {
        IsEligibleForDisplay = false;
    }
    else
    {
        IsEligibleForDisplay = true;
    }

} 

这是我从服务部门打来的电话：

public static SchedulingEligibility GetEligibility(Guid cmID)
{
    using (PMCContext db = new PMCContext())
    {
        var cm = (from c in db.ClassMembers where c.ID == cmID select c)
            .Include(x => x.Appointments)
            .Include(x => x.Appointments.Select(y => y.lkp_AppointmentStatus))
            .Include(x => x.Appointments.Select(y => y.Facility))
            .Include(x => x.Appointments.Select(y => y.lkp_AppointmentType))
            .Single();

        return new SchedulingEligibility(cm);
    }
}

这是结果的类型：

public SchedulingEligibility GetMemberEligibility(Guid cmID)
{
    return ClassMemberBO.GetEligibility(cmID);
}