how to do Serial Number check

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VB

Hi,
I have a program that generate serial numbers and then adds them to a database.

The serial numbers are generated within a for next loop which is based on the number of serials a user needs.


I have no problem checking if the code alread exists in the database but I'm having issues in how to create a new code and to check that one also. So if the code exists it will create another new code and check it again against the records in the database etc. until it has reached the number of all new codes needed.

'For Loop 
 Dim i As Integer = Convert.ToInt32(OrderQuantity.Trim)
                Dim FinalSN As String = ""
                For sn As Integer = 1 To i
                   
                    FinalSN = GenSerial()

                    Dim SW1 As StreamWriter
                    Dim FS1 As FileStream
                    FS1 = New FileStream("c:\Temp\" & PO & ".txt", FileMode.Append)
                    SW1 = New StreamWriter(FS1)
                    SW1.WriteLine(Part.Trim & ":" & Description.Trim & ":" & "SN:" & FinalSN.Trim)
                    SW1.Close()
                    SerialArray.Add(FinalSN)
                    con2.Close()
                    Dim strCommand3 As String = "INSERT INTO SerialNo (SerialNumbers) values ('" & FinalSN & "')"
                    Dim cm3 As New SqlClient.SqlCommand(strCommand3, con2)
                    con2.Open()
                    Try

                        cm3.ExecuteNonQuery()
                    Catch ex As Exception
                        MessageBox.Show(ex.Message, "Error")

                    End Try
                    FinalSN = ""


                Next

'Function for creating codes
Public Function GenSerial() As String
        Dim xCharArray() As Char = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray
        Dim xNoArray() As Char = "0123456789".ToCharArray
        Dim xGenerator As System.Random = New System.Random()
        Dim xStr As String = String.Empty

        While xStr.Length < 15

            If xGenerator.Next(0, 2) = 0 Then
                xStr &= xCharArray(xGenerator.Next(0, xCharArray.Length))
            Else
                xStr &= xNoArray(xGenerator.Next(0, xNoArray.Length))
            End If

        End While
        Return xStr

    End Function