For each loop to execute LINQ query failed without going through the loop?

Dim tiu As DataTable = ds.Tables(tblname)
        Dim dy As New dDataSet()
        Dim Th As DataTable = dy.Tables("th")
        Console.WriteLine("{0}", Me.ID.ToString)
        Console.WriteLine("{0}", ds.Tables(tblname).TableName.ToString)
 
        Dim thquery = From f In Th Where f.Field(Of String)("voc") = tiu.Rows(0).ToString Select New With {.v = f.Field(Of String)("voc"), .g = f.Field(Of String)("gP"), .s = f.Field(Of String)("subHead"), .ke = f.Field(Of String)("key")}
 For Each f In thquery
            Console.WriteLine("{0}", f.v)
            myrowTh = _vDtTh.NewRow()
            myrowTh(mycol) = f.v
            myrowTh(mycolgP) = f.g
            myrowTh(mycolsubHead) = f.s
            myrowTh(mycolkey) = f.ke
            _vDt.Rows.Add(myrowTh)
        Next