Datagridview - prevent duplicates in comboboxcell - vb.net

Question

I have a ComboboxCell in first cell of Datagridview. This combobox has Datasource from my DB. When I select Item from It, all other cells in a row gets populated by a record from my DB. Now I want to prevent duplicate row entries, based on Comboboxcell selected item. After that I want to clear that Comboboxcell, and keep code running. I managed to do almost everything, but problem is that after msgbox is displayed, code stops working - so when I select ComboboxCell Item again, nothing happens, even in a new row. Here is my whole code:
Private Sub My_DGV_CellValueChanged(sender As Object, e As DataGridViewCellEventArgs) Handles My_DGV.CellValueChanged
If My_DGV.Columns(e.ColumnIndex).Name = "Column1" Then
'Prevent duplicates
For i As Integer = 0 To My_DGV.RowCount - 2
For j As Integer = i + 1 To My_DGV.RowCount - 2
If My_DGV.Rows(i).Cells(0).Value = My_DGV.Rows(j).Cells(0).Value Then
MsgBox("You allready selected this item. Duplicates are not allowed.", MsgBoxStyle.Information, "Warning")
My_DGV.Rows(j).Cells(0).Value = " "
Dim cbx As ComboBox = DGV_APO.EditingControl
cbx.SelectedIndex = -1
Exit Sub
End If
Next
Next
OracleconnOpen()
Using cmd As New OracleCommand()
Dim SQL As String = "Select NAMES,SURNAMES,STATE FROM My_Table"
Dim Concat_SQL As String = " Where "
SQL = String.Concat(SQL, Concat_SQL, " ID_NUMBER = :id")
cmd.Parameters.Add(New OracleParameter("id", My_DGV.CurrentRow.Cells(0).Value))
cmd.Connection = OracleconnOpen()
cmd.CommandText = SQL
cmd.CommandType = CommandType.Text
Dim dr As OracleDataReader = cmd.ExecuteReader()
Dim dt As New DataTable
dt.Load(dr)
My_DGV.CurrentRow.Cells(1).Value = dt.Rows(0)("NAMES").ToString()
My_DGV.CurrentRow.Cells(2).Value = dt.Rows(0)("SURNAMES").ToString()
My_DGV.CurrentRow.Cells(3).Value = dt.Rows(0)("STATE").ToString()
End Using
OracleconnClose()
End If
End Sub
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'SELECT from my DB
Dim SQL As String = "SELECT ID_NUMBER from My_Table"
Dim dtb As New DataTable()
Try
OracleconnOpen() 'Open my connection
Using dad As New OracleDataAdapter(SQL, OracleconnOpen)
dad.Fill(dtb)
End Using
Column1.DisplayMember = "ID_NUMBER"
Column1.DataSource = dtb
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
OracleconnClose() 'Close my connection
End Try
End Sub
Private Sub My_DGV_CurrentCellDirtyStateChanged(sender As Object, e As EventArgs) Handles My_DGV.CurrentCellDirtyStateChanged
If My_DGV.IsCurrentCellDirty Then My_DGV.CommitEdit(DataGridViewDataErrorContexts.Commit)
End Sub
Private Sub My_DGV_DataError(sender As Object, e As DataGridViewDataErrorEventArgs) Handles DGV_APO.DataError
e.ThrowException = False
End Sub
So, what am I doing wrong ? Any help appreciated.

Answer 1

You have an Exit Sub call within your loop that will always execute so nothing after the exit sub will ever be run when you change this value. If you want to exit the loop and continue running the code after a duplicate is found, that should be done within the If statement. This code should stop working after the first row is compared even if it is not a match.