savechanges（）保存一个实体而不是其他实体

Question

一个奇怪的情况让我感到震惊，这个代码在两天前成功运行，但我不知道它为什么不像以前一样运行：

public static void ChangeStatus(int sessionID, int? participantID, Guid? temporaryParticipantID, int statustypeID)
{
    using (EMSEntities entities = new EMSEntities())
    using (TransactionScope ts = new TransactionScope())
    {
        try
        {
            SessionParticipant sessionParticipant = null;
            CurrentSessionSeatsStatu sessionCurrentStatus = null;
            if (participantID != null)
            {
                sessionParticipant = entities.SessionParticipants
                                             .Where(a => a.SessionID == sessionID && a.ParticipantID == participantID)
                                             .FirstOrDefault();
            }
            else if (temporaryParticipantID != null)
            {
                sessionParticipant = entities.SessionParticipants
                                             .Where(a => a.SessionID == sessionID && a.TemporaryParticipantID == temporaryParticipantID)
                                             .FirstOrDefault();
            }
            if (sessionParticipant != null)
            {
                sessionParticipant.StatusTypeID = statustypeID; // Status Changed here
            }
            **if (sessionParticipant.StatusTypeID == 2) // verified status
            {
                sessionCurrentStatus = entities.CurrentSessionSeatsStatus
                                               .Where(a => a.SessionID == sessionID)
                                               .FirstOrDefault();
                if (sessionCurrentStatus.SeatsLeft > 0)
                {
                    sessionCurrentStatus.SeatsLeft = sessionCurrentStatus.SeatsLeft - 1;
                }
            }**
            entities.SaveChanges();
            ts.Complete();
        }
        catch (Exception ex)
        {
            ts.Dispose();
        }
    }
}

问题是sessionParticipant的更改（在StatusTypeID中）没有保存在数据库中，但sessionCurrentStatus更改了！

没有任何错误！

编辑：我发现sessionparticipant的更改在所有情况下都会发生，除非状态更改为已验证。
即。当另一张表即。 sessioncurrentstatus在if块中更新 无论何时进入if block(bold in code)问题都会发生。

最后我发现了问题并且我认为它是因为下面的代码然而如果有人可以解释确切的原因会很好：

EMS.DAL.DALHelper.AttachAndSaveChanges(sessionParticipant, System.Data.EntityState.Modified); // the position of this code line can be found in the below code

下面是调用ChangesStatus方法的代码：

protected void ddlStatuses_SelectedIndexChanged(object sender, EventArgs e)
{
    for (int i = 0; i < gridViewEvents.VisibleRowCount; i++)
    {
        if (gridViewEvents.Selection.IsRowSelected(i))
        {
            EMS.DAL.SessionParticipant sessionParticipant = (EMS.DAL.SessionParticipant)gridViewEvents.GetRow(i);
            EMS.DAL.Session session = EMS.DAL.DALHelper.GetSessionById(sessionParticipant.SessionID);
            EMS.DAL.DALHelper.ChangeStatus(sessionParticipant.SessionID, sessionParticipant.ParticipantID, sessionParticipant.TemporaryParticipantID, Convert.ToInt32(ddlStatuses.SelectedItem.Value));
            if (ddlStatuses.SelectedItem.Value == "2" || ddlStatuses.SelectedItem.Value == "3") // if accepted or rejected
            {
                if (ddlStatuses.SelectedItem.Value == "2")  // verified/accepted
                {
                    EMS.DAL.DALHelper.SendMail("Congratulations! your participation for " + session.Name + " event has been confirmed.", "", sessionParticipant.Email, "");
// AT THIS POINT THE 'sessionParticipant' did not have the changed status which was set in the ChangeStatus method
                    sessionParticipant.IsNotified = true;
                    EMS.DAL.DALHelper.AttachAndSaveChanges(sessionParticipant, System.Data.EntityState.Modified);  // culprit as per me

                    List<EMS.DAL.SessionAttendanceList> attendanceList = EMS.DAL.DALHelper.GetSessionAttendanceList(session.ID);
                    attendanceList.ForEach(a =>
                    {
                        EMS.DAL.AttendanceListDetail attendanceListDetail = a.AttendanceListDetails.Where(p => p.ParticipantID == sessionParticipant.ParticipantID).FirstOrDefault();
                        if (attendanceListDetail == null)
                        {
                            attendanceListDetail.AttendanceListID = a.ID;
                            attendanceListDetail.ParticipantID = sessionParticipant.ParticipantID.Value;
                            attendanceListDetail.IsPresent = false;
                            EMS.DAL.DALHelper.AttachAndSaveChanges(attendanceListDetail, System.Data.EntityState.Added);
                        }
                    });
                }
                else if (ddlStatuses.SelectedItem.Value == "3") // denied/rejected
                {
                    EMS.DAL.DALHelper.SendMail("Your participation for " + session.Name + " event has been denied.", "", sessionParticipant.Email, "");
                    sessionParticipant.IsNotified = true;
                    EMS.DAL.DALHelper.AttachAndSaveChanges(sessionParticipant, System.Data.EntityState.Modified);
                    List<EMS.DAL.SessionAttendanceList> attendanceList = EMS.DAL.DALHelper.GetSessionAttendanceList(session.ID);
                    attendanceList.ForEach(a =>
                    {
                        EMS.DAL.AttendanceListDetail attendanceListDetail = a.AttendanceListDetails.Where(p => p.ParticipantID == sessionParticipant.ParticipantID).FirstOrDefault();
                        if (attendanceListDetail != null)
                        {
                            EMS.DAL.DALHelper.AttachAndSaveChanges(attendanceListDetail, System.Data.EntityState.Deleted);
                        }
                    });
                }
            }
            else
            {
                List<EMS.DAL.SessionAttendanceList> attendanceList = EMS.DAL.DALHelper.GetSessionAttendanceList(session.ID);
                attendanceList.ForEach(a =>
                {
                    EMS.DAL.AttendanceListDetail attendanceListDetail = a.AttendanceListDetails.Where(p => p.ParticipantID == sessionParticipant.ParticipantID).FirstOrDefault();
                    if (attendanceListDetail != null)
                    {
                        EMS.DAL.DALHelper.DeleteAttendanceListDetail(attendanceListDetail);
                    }
                });
                attendanceList.ForEach(a =>
                {
                    EMS.DAL.DALHelper.DeleteSessionAttendanceList(a);
                });
            }
        }
    }
    gridViewEvents.DataBind();
    RefreshSeats();
}