How do you avoid entering duplicate data in xml file?

Hi,

How do I modify the code below to avoid duplicate NSC in my xml file, part  B is an example of NSC.xml. For example when I enter
3333-33-3333-3333 a second time in the Grid, it should not save it again.


Thanks,

Victor

Part A:

Private Sub Save_Click(sender As System.Object, e As System.EventArgs) Handles Save.Click

        Dim NSC_ID As String = Nothing
        xdNSC.Load((Application.StartupPath + "\Data\LinkFiles\NSC.xml"))
        Dim num As Integer
        Dim numx As Integer
        Dim numy As Integer
        Dim num1 As String
        Dim num2 As String
        Dim xyz() As String = New String() {"NSC"}
        'Multiple rows in Grid
        If C1NSC.RowCount <> 0 Then
            For i = 0 To 1
                num1 = ""
                num2 = ""
                num = 0
                numx = 0
                numy = 0
                searchIdNSC = ""
                Dim xid As String
                Dim xtable As String
                ' Dim i As String = "NSC"
                Dim curXYZ = xyz(i)
                Dim MyFix As XDocument = XDocument.Load(Application.StartupPath + "\Data\LinkFiles\" & curXYZ & ".xml")
                xid = curXYZ & "_ID"
                xtable = curXYZ & "Table"
                'Sort ID in each xml file
                Dim LargestFixID = (From el In MyFix.Descendants(curXYZ & "Table") Select CInt(el.<xid>.Value)).ToList
                LargestFixID.Sort()
                num = (LargestFixID.Count() + 1)
                Dim domFix As New XmlDocument()
                domFix.Load(Application.StartupPath + "\Data\LinkFiles\" & curXYZ & ".xml")
                Dim listFix As XmlNodeList = domFix.SelectNodes("//" & xtable)
                Dim CheckForNSCFix = (From el In MyFix.Descendants(xtable).Elements(curXYZ) Select el.Value).ToList
                Dim u As Integer = 0
                Dim uu As Integer = 0
                'Look for data already in NSC.xml
                For x As Integer = 0 To C1NSC.RowCount - 1
                    If CheckForNSCFix.Contains(C1NSC.Row) Then
                        For Each xnLink As Xml.XmlNode In xdNSC.SelectNodes("/Root/NSCTable[NSC='" & C1NSC.Item(x)("NSC") & "']")
                            NSC_ID = xnLink.SelectSingleNode("NSC_ID").InnerText
                            If NSC_ID <> "" Then
                                CD = NSC_ID
                                If u > 0 Then
                                    num1 = num1 & "" & CD & ","
                                Else
                                    num1 = CD & ","
                                    ' num1 = CD '& ","
                                End If
                                u = u + 1
                            End If
                        Next
                    End If
                Next
                'Assign ID to data not already in XML file
                If C1NSC.RowCount <> 0 Then
                    For x As Integer = 0 To C1NSC.RowCount - 1
                        Dim theString As String
                        theString = C1NSC.Item(x)("NSC")
                        If theString <> "" Then
                            If System.Text.RegularExpressions.Regex.IsMatch(theString, "^\d{13}$") Then
                                theString = theString.Insert(9, "-").Insert(6, "-").Insert(4, "-")
                            ElseIf Not System.Text.RegularExpressions.Regex.IsMatch(theString, "^\d{4}-\d{2}-\d{3}-\d{4}$") Then
                                MsgBox("NSC(s) must be in the follwoing format [xxx-xx-xxx-xxxx]")
                                Exit Sub
                            End If
                        End If
                        Dim xNew As XElement = New XElement(xtable)
                        xNew.Add(New XElement(xid, num))
                        xNew.Add(New XElement(curXYZ, theString))
                        MyFix.Root.Add(xNew)
                        MyFix.Save(Application.StartupPath + "\Data\LinkFiles\" & curXYZ & ".xml")
                        If uu > 0 Then
                            num2 += num & ","
                        Else
                            num2 = num & ","
                        End If
                        uu = uu + 1
                        num = num + 1
                    Next
                End If
                searchIdNSC = num1 & num2
                Exit For
            Next
        End If
        MsgBox("NSC value " & searchIdNSC)

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Part B:
       
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<Root>
  <NSCTable>
    <NSC_ID>0</NSC_ID>
    <NSC></NSC>
  </NSCTable>
  <NSCTable>
    <NSC_ID>2</NSC_ID>
    <NSC>1111-11-111-1111</NSC>
  </NSCTable>
  <NSCTable>
    <NSC_ID>3</NSC_ID>
    <NSC>2222-22-222-2222</NSC>
  </NSCTable>
  <NSCTable>
    <NSC_ID>4</NSC_ID>
    <NSC>3333-33-3333-3333</NSC>
  </NSCTable>
  <NSCTable>
    <NSC_ID>4</NSC_ID>
    <NSC>3333-33-3333-3333</NSC>
  </NSCTable>

</Root>