下面详细说明为什么使用单例模式：
问题：业务类在使用时不得不单例，不然无法使用transactionscope。
举例如下：业务类A，需要做一个a操作，而这个操作包括了业务类B的一个b操作，然后再执行A中的c操作，需要transactionscope，此时，如果不单例数据库的话，业务类A实例化时，需要业务类A内部读取数据库数据并实例化，然后业务类B实例化时，需要业务类B内部读取数据库并实例化，那么这两个业务类是分别实例化的，自然也是分别两个数据库连接，此时执行业务类A的a操作，并NEW一个transactionscope，因为涉及到B中的b，所以会弹出错误，错误原因很简单，就是一个过程却是两个线程执行的，无法执行存储过程。
下面附上业务类A中的代码，和业务B的代码，请教一下，我这样实例化是否正确
业务类
public class ExamBatchInfo
{
DataBaseControl _DBControl = DataBaseControl.getSingleton();
public virtual IEnumerable<ExamRoomInfo> ExamRoomList
{
get
{
var query = from r in _DBControl.ExamRoom_GetList(YearTermID, CourID, BatchOrder).AsEnumerable()
select ExamRoomInfo.GetInfo(r);
return query;
}
}
#region 初始化与转换
private void InitClass(exam_Batch dbtable)
{
if (dbtable != null)
{
this.YearTermID = dbtable.YearTermID;
this.CourID = dbtable.CourID;
this.BatchOrder = dbtable.BatchOrder;
this.ExamWeek = dbtable.ExamWeek;
this.ExamDate = dbtable.ExamDate;
this.BatchName = dbtable.BatchName;
this.TeachList = dbtable.TeachList;
this.SelectedNum = dbtable.SelectedNum;
this.WeekSection = dbtable.WeekSection;
this.WeekTime = dbtable.WeekTime;
this.TimeExplain = dbtable.TimeExplain;
this.BatchType = dbtable.BatchType;
this.BatchFlag = dbtable.BatchFlag;
this.Inspector1 = dbtable.Inspector1;
this.Inspector1Name = dbtable.Inspector1Name;
this.Inspector2 = dbtable.Inspector2;
this.Inspector2Name = dbtable.Inspector2Name;
this.Inspector3 = dbtable.Inspector3;
this.Inspector3Name = dbtable.Inspector3Name;
this.Operator = dbtable.Operator;
this.LastDate = dbtable.LastDate;
}
}
public ExamBatchInfo()
{
this.YearTermID = string.Empty;
this.CourID = string.Empty;
this.BatchOrder = 0;
this.ExamWeek = 0;
this.ExamDate = null;
this.WeekSection = string.Empty;
this.WeekTime = 3;
this.TimeExplain = string.Empty;
this.BatchFlag = 0;
this.Inspector1 = string.Empty;
this.Inspector1Name = string.Empty;
this.Inspector2 = string.Empty;
this.Inspector2Name = string.Empty;
this.Inspector3 = string.Empty;
this.Inspector3Name = string.Empty;
this.Operator = string.Empty;
this.LastDate = DateTime.Now;
}
public ExamBatchInfo(exam_Batch dbtable)
{
InitClass(dbtable);
}
}
}
/// <summary>
/// 重置批次（包括删除考场、删除学生、任务还原为未安排状态、批次删除）
/// </summary>
public void Reset()
{
if (BatchOrder > 0)
{
using (System.Transactions.TransactionScope transactionScope = new System.Transactions.TransactionScope(System.Transactions.TransactionScopeOption.Required))
{
#region 更新考试任务
foreach (var examTaskInfo in ExamTaskList)
{
examTaskInfo.ExamTask_BatchOrder = 0;
examTaskInfo.Update();
}
#endregion
#region 删除批次
exam_Batch batch = ConvertDBModel();
_DBControl.ExamBatch_Delete(batch);
#endregion
transactionScope.Complete();
}
}
else
throw new Exception("不存在批次，无法重置！");
}
从上述代码中可以看到，在 Reset()方法中，有两个操作，examTaskInfo.Update();是对另一个业务类进行的操作，_DBControl.ExamBatch_Delete(batch);是对本业务类进行操作。
下面是业务类B
public class ExamTaskInfo
{
DataBaseControl _DBControl = DataBaseControl.getSingleton();
#region 属性
public string ExamTask_YearTermID { get; set; }
public string ExamTask_CourID { get; set; }
public short ExamTask_CourOrder { get; set; }
public int ExamTask_BatchOrder { get; set; }
public string ExamTask_ArrangeType { get; set; }
public Enum_ExamTaskType ExamTask_ArrangeTypeEnum { get; set; }
public DateTime? ExamTask_GradeEndTime { get; set; }
public string ExamTask_Operator { get; set; }
public DateTime? ExamTask_LastDate { get; set; }
#endregion
#region 初始化
private void InitClass(exam_Task dbTable)
{
this.ExamTask_YearTermID = dbTable.YearTermID;
this.ExamTask_BatchOrder = dbTable.BatchOrder;
this.ExamTask_CourID = dbTable.CourID;
this.ExamTask_CourOrder = dbTable.CourOrder;
this.ExamTask_ArrangeType = dbTable.ArrangeType;
this.ExamTask_GradeEndTime = dbTable.GradeEndTime;
this.ExamTask_Operator = dbTable.Operator;
this.ExamTask_LastDate = dbTable.LastDate;
}
private exam_Task ConvertDBModel()
{
exam_Task task = new exam_Task();
task.YearTermID = ExamTask_YearTermID;
task.BatchOrder = this.ExamTask_BatchOrder;
task.CourID = ExamTask_CourID;
task.CourOrder = ExamTask_CourOrder;
task.ArrangeType = EnumUtil.GetEnumShowName(typeof(ClEas.Model.Exam.ExamTaskInfo.Enum_ExamTaskType), (int)ExamTask_ArrangeTypeEnum);
task.GradeEndTime = ExamTask_GradeEndTime;
task.Operator = ExamTask_Operator;
task.LastDate = ExamTask_LastDate;
return task;
}
public ExamTaskInfo()
{
this.ExamTask_YearTermID = string.Empty;
this.ExamTask_BatchOrder = 0;
this.ExamTask_CourID = string.Empty;
this.ExamTask_CourOrder = 0;
this.ExamTask_ArrangeTypeEnum = Enum_ExamTaskType.SchoolType;
this.ExamTask_GradeEndTime = null;
this.ExamTask_Operator = string.Empty;
this.ExamTask_LastDate = DateTime.Now;
}
public ExamTaskInfo(exam_Task dbTable)
{
if (dbTable != null)
{
InitClass(dbTable);
}
}
#endregion
#region 方法
public void Update()
{
exam_Task task = ConvertDBModel();
_DBControl.ExamTask_Update(task);
}
#endregion
}
总之，就是两个业务类在实例化的过程中，分别需要使用数据库，如果每次NEW则会出现使用存储过程时造成线程不一致，所以不得不使用单例模式解决问题。
但如果单例模式，则会出现下面的问题，不知道是否是我的问题，回滚时无法执行，导致上下文数据存在。
代码如下：
using (System.Transactions.TransactionScope transactionScope = new System.Transactions.TransactionScope(System.Transactions.TransactionScopeOption.Required))
{
foreach (System.Data.DataRow dr in dt.Rows)
{
//这里将来切换为MODEL，不应该直接读取数据库
string studid = dr["学号"].ToString().Trim();
string name = dr["姓名"].ToString().Trim();
string grade = string.Empty;
if (dt.Columns.Contains("成绩"))
{
grade = dr["成绩"].ToString().Trim();
}
e_Student student = _DBControl.Student_GetInfo(studid);
if (student != null && student.StudName == name)
{
ECItemTempGradeInfo tempGrade = new ECItemTempGradeInfo();
tempGrade.ECGroupID = ECGroupID;
tempGrade.StudID = studid;
tempGrade.ECGrade = grade;
tempGrade.Operator = Operator;
tempGrade.Insert();
}
else
throw new Exception(studid + "学号与姓名无法对应！请检查是否有误！");
}
SelectedNum = _DBControl.ECItemGrade_GetList(ECGroupID).Count();
Update();
}
当这句执行时throw new Exception(studid + "学号与姓名无法对应！请检查是否有误！");，抛出错误，可以看到数据库确实没有变化 ，但是上下文却发生了变化，再次调用本函数时，就会发生主键冲突的错误。原因是因为tempGrade.Insert()时 使用AddObject，将该对象添加进了上下文。而回滚似乎是不回滚上下文的，这样就导致了数据库与上下文不一致的现象。
求教大神，该如何解决这个问题，到底是应该单例模式还是不应该单例，如果应该单例的话，如何解决上下文的问题？
