Linq on datatable no datasource exception - linq

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);
}
}
When I try to do this datatableInprogress may not have any rows all the time. At run time, I get an exception saying "no datasource". Why? And what should I do to fix this issue?

Answer 1

Just clone DataTable structure if there is no rows for your condition:
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 why you need DataTable? You can get ids!
var pendingIds =
from r in dataSet.Tables[0].AsEnumerable()
where r.Field<string>("Status") == MailStatus.Pending.ToString()
select r.Field<int>("Id");
Sorry, I don't know why are you assigning dataSet in a loop, but here is code which reproduces yours:
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);
}