Check for duplicate entries

[DryGoldFish]

Hi all,
I'm trying to make a form wich can make new users in a Access database. However, usernames can't be duplicate, but I can't seem to get the code to work so users can't enter 2 of the same entries. Can anyone help?

    Private Sub btnAanmaken_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnAanmaken.Click
        Dim strNaam As String
        Dim blnZoeken As Boolean
        strNaam = txtNaam.Text
        GebruikersDataGridView.SelectionMode = DataGridViewSelectionMode.FullRowSelect
        Dim intcount As Integer = 0
        For Each Row As DataGridViewRow In GebruikersDataGridView.Rows
            If GebruikersDataGridView.Rows(intcount).Cells(1).Value.ToString = strNaam Then
                GebruikersDataGridView.Rows(intcount).Selected = True
                blnZoeken = True
                Exit For
            End If
            intcount += 1
        Next Row
        If blnZoeken = True Then
            MessageBox.Show("Naam bestaat al", "", MessageBoxButtons.OK, MessageBoxIcon.Error)
        Else
            If txtWachtwoord.Text = txtWachtwoordHerhaal.Text Then
                MessageBox.Show(strNaam & " is met succes aangemaakt!", "Succes", MessageBoxButtons.OK, MessageBoxIcon.Information)
                Me.Validate()
                Me.GebruikersBindingSource.EndEdit()
                Me.TableAdapterManager.UpdateAll(Me.EasybyteDataSet)
                Me.Close()
                Hoofdmenu.Show()
            Else
                MessageBox.Show("Wachtwoord is fout", "Fout", MessageBoxButtons.OK, MessageBoxIcon.Error)
            End If
        End If
    End Sub

[Reverend Jim]

The typical way is to do something like

select the count of records with the requested username
if count > 0 then
    that name is already taken
else
    add the name to the database
end if

The select would look like

"SELECT COUNT(*) FROM mytable WHERE Username = 'newuser'"

which with parameters would be

Dim con As New OleDbConnection(your connection string here)
Dim cmd As New OleDbCommand("", con)

cmd.CommandText = "SELECT COUNT(*) FROM mytable WHERE Username = ?"
cmd.Parameters.AddWithValue("@username", txtUserName.Text)

If cmd.ExecuteNonQuery() > 0 ...

[DryGoldFish]

But i added my .mdb file in my project so the connection string isn't needed anymore. Is there a way to use this without connection string?

[ShahanDev]

AFAIK, you are using TYPED dataset. What you need to do is, in the table inside you dataset, you need to perform a check with the username you take as an input from user and if it exists display an error message. On the other hand insert an entry in database.