Add Column to DataTable before exporting to Excel file - vb.net

Question

I have a DataTable that is built like this:
Dim dt As New DataTable()
dt = SqlHelper.ExecuteDataset(connString, "storedProcedure", Session("Member"), DBNull.Value, DBNull.Value).Tables(0)
Then it is converted to a DataView and exported to Excel like this:
Dim dv As New DataView()
dv = dt.DefaultView
Export.CreateExcelFile(dv, strFileName)
I want to add another column and fill it with data before I export to Excel. Here's what I'm doing now to add the column:
Dim dc As New DataColumn("New Column", Type.GetType("System.String"))
dc.DefaultValue = "N"
dt.Columns.Add(dc)
Then to populate it:
For Each row As DataRow In dt.Rows
Dim uID As Integer = Convert.ToInt32(dt.Columns(0).ColumnName)
Dim pID As String = dt.Columns(0).ColumnName
Dim qry As String = "SELECT * FROM [MyTable] WHERE [UserID] = " & uID & " AND [PassID] = '" & pID & "'"
Dim myCommand As SqlCommand
Dim myConn As SqlConnection = New SqlConnection(ConfigurationSettings.AppSettings("connString"))
myConn.Open()
myCommand = New SqlCommand(qry, myConn)
Dim reader As SqlDataReader = myCommand.ExecuteReader()
If reader.Read() Then
row.Item("New Column") = "Y"
Else
row.Item("New Column") = "N"
End If
Next row
But I get a "System.FormatException: Input string was not in a correct format." error when I run the app. It doesn't seem to like these lines:
Dim uID As Integer = Convert.ToInt32(dt.Columns(0).ColumnName)
Dim pID As String = dt.Columns(0).ColumnName
I think I have more than one issue here because even if I comment out the loop that fills the data in, the column I created doesn't show up in the Excel file. Any help would be much appreciated. Thanks!
EDIT:
Okay, I was grabbing the column name instead of the actual data in the column... because I'm an idiot. The new column still doesn't show up in the exported Excel file. Here's the updated code:
Dim dt As New DataTable()
dt = SqlHelper.ExecuteDataset(connString, "storedProcedure", Session("Member"), DBNull.Value, DBNull.Value).Tables(0)
Dim dc As New DataColumn("New Column", Type.GetType("System.String"))
dc.DefaultValue = "N"
dt.Columns.Add(dc)
'set the values of the new column based on info pulled from db
Dim myCommand As SqlCommand
Dim myConn As SqlConnection = New SqlConnection(ConfigurationSettings.AppSettings("connString"))
Dim reader As SqlDataReader
For Each row As DataRow In dt.Rows
Dim uID As Integer = Convert.ToInt32(row.Item(0))
Dim pID As String = row.Item(2).ToString
Dim qry As String = "SELECT * FROM [MyTable] WHERE [UserID] = " & uID & " AND [PassID] = '" & pID & "'"
myConn.Open()
myCommand = New SqlCommand(qry, myConn)
reader = myCommand.ExecuteReader()
If reader.Read() Then
row.Item("New Column") = "Y"
Else
row.Item("New Column") = "N"
End If
myConn.Close()
Next row
dt.AcceptChanges()
Dim dv As New DataView()
dv = dt.DefaultView
Export.CreateExcelFile(dv, strFileName)

Answer 1

I suppose that you want to search your MyTable if it contains a record with the uid and the pid for every row present in your dt table.
If this is your intent then your could write something like this
Dim qry As String = "SELECT UserID FROM [MyTable] WHERE [UserID] = #uid AND [PassID] = #pid"
Using myConn = New SqlConnection(ConfigurationSettings.AppSettings("connString"))
Using myCommand = new SqlCommand(qry, myConn)
myConn.Open()
myCommand.Parameters.Add("#uid", OleDbType.Integer)
myCommand.Parameters.Add("#pid", OleDbType.VarWChar)
For Each row As DataRow In dt.Rows
Dim uID As Integer = Convert.ToInt32(row(0))
Dim pID As String = row(1).ToString()
cmd.Parameters("#uid").Value = uID
cmd.Parameters("#pid").Value = pID
Dim result = myCommand.ExecuteScalar()
If result IsNot Nothing Then
row.Item("New Column") = "Y"
Else
row.Item("New Column") = "N"
End If
Next
End Using
End Using
Of course the exporting to Excel of the DataTable changed with the new column should be done AFTER the add of the column and this code that updates it
In this code the opening of the connection and the creation of the command is done before entering the loop over your rows. The parameterized query holds the new values extracted from your ROWS not from your column names and instead of a more expensive ExecuteReader, just use an ExecuteScalar. If the record is found the ExecuteScalar just returns the UserID instead of a full reader.

Answer 2

The issue was in my CreateExcelFile() method. I inherited the app I'm modifying and assumed the method dynamically read the data in the DataTable and built the spreadsheet. In reality, it was searching the DataTable for specific values and ignored everything else.
2 lines of code later, I'm done.