Linq on datatable no datasource exception

Question

dataSet = clsDb.MailData("SELECT * FROM CM_Mail cm WHERE cm.[ActualTime] < '" + DateTimeOffset.UtcNow + "' ", CommandType.Text); 
     DataTable datatablepending = (from ds in dataSet.Tables[0].AsEnumerable() where ds.Field<string>("Status") == MailStatus.Pending.ToString() select ds).CopyToDataTable(); 
     DataTable datatableInprogress = (from ds in dataSet.Tables[0].AsEnumerable() where ds.Field<string>("Status") == MailStatus.Inprogress.ToString() select ds).CopyToDataTable(); 

     if (datatablepending.Rows.Count != 0) 
     { 
      for (int i = 0; i < datatablepending.Rows.Count; i++) 
      { 

       dataSet = clsDb.MailData("UPDATE CM_Mail SET [Status] = '" + updateStatus + "',LastProccessedTime = '" + DateTimeOffset.UtcNow.ToString() + "' WHERE Id='" + datatablepending.Rows[i]["Id"].ToString() + "'", CommandType.Text); 
      } 

     } 
     if (datatableInprogress.Rows.Count != 0) 
     { 
      for (int i = 0; i < datatableInprogress.Rows.Count; i++) 
      { 
       dataSet = clsDb.MailData("UPDATE CM_Mail SET [Status] = '" + updateStatus + "',SentTime = '" + DateTimeOffset.UtcNow + "',LastProccessedTime = '" + DateTimeOffset.UtcNow.ToString() + "' WHERE Id='" + datatableInprogress.Rows[i]["Id"].ToString() + "'", CommandType.Text); 
      } 



     } 

当我尝试这样做时datatableInprogress可能一直没有任何行。在运行时，我得到一个异常说“没有数据源”。为什么？我该如何解决这个问题？

Answer 1

只是clone DataTable structure如果你的病情没有行：

var pendingRows = 
    dataSet.Tables[0].AsEnumerable() 
     .Where(r => r.Field<string>("Status") == MailStatus.Pending.ToString()); 

DataTable datatablepending = pendingRows.Any() ? pendingRows.CopyToDataTable() : 
               dataSet.Tables[0].Clone(); 

BTW，为什么你需要的DataTable？你可以得到ids！

var pendingIds = 
    from r in dataSet.Tables[0].AsEnumerable() 
    where r.Field<string>("Status") == MailStatus.Pending.ToString() 
    select r.Field<int>("Id"); 

对不起，我不知道为什么你在一个循环中分配数据集，但这里是再现你的代码：

string updateStringFormat = 
"UPDATE CM_Mail SET [Status] = '{0}',LastProccessedTime = '{1}' WHERE Id='{2}'"; 

foreach(var id in pendingIds) 
{ 
    var commandText = String.Format(updateStringFormat, updateStatus, DateTimeOffset.UtcNow, id); 
    dataSet = clsDb.MailData(commandText, CommandType.Text); 
}