Visual Basic MySQL Datagrid Delete from database

Question

I am making a invoice system in Visual Basic 2010 and i am stuck here

Here is my code

     Private Sub btnDelete_Click(ByVal sender As System.Object, ByVal e As  System.EventArgs) Handles btnDelete.Click

    For Each row As DataGridViewRow In datagrid.SelectedRows
        Dim selectedindex As String = datagrid.CurrentRow.Cells(0).Value.ToString()
        datagrid.Rows.Remove(row)
        If conn.State = ConnectionState.Closed Then
            conn.Open()
        End If
        Dim sql = "DELETE FROM sales WHERE InvoiceNo='" & txtInvoiceNo.Text & "' and id='" & selectedindex & "'"
        Dim cmd As New MySqlCommand(sql, conn)
        Dim reader As MySqlDataReader = cmd.ExecuteReader

        If reader.Read() Then

        End If
        conn.Close()
        reader.Close()
    Next

End Sub

This code is not working well please have a look to my invoice screen shot and suggest me a better code

When i try to delete the selected row the code does not work and if any one can tell me i can delete multiple selected rows? they are deleted from the datagrid but not from database

Answer 1

Try this:

Private Sub btnDelete_Click(ByVal sender As System.Object, ByVal e As  System.EventArgs) Handles btnDelete.Click

    Using cn As New MySqlConnection("Connection string here"), _
          cmd As New MySqlCommand("DELETE sales WHERE InvoiceNo= ?InvoiceNo and id= ?id", cn)

        cmd.Parameters.Add("?InvoiceNo", MySqlDbTypes.VarChar, 10).Value = txtInvoiceNo.Text
        cmd.Parameters.Add("?id", MySqlDbTypes.Int32)

        cn.Open()
        For Each row As DataGridViewRow In datagrid.SelectedRows
            cmd.Parameters(1).Value = row.Cells(0).Value
            cmd.ExecuteNonQuery()
            datagrid.Rows.Remove(row)
        Next row

    End Using

End Sub

It looks like you're trying to save and re-use a single connection object, and just open it as needed. This is misguided: it breaks .Net's ability to do connection pooling. You really do want to create a new connection object for each place where you'll talk to the database. This also let's you do a better job making sure a connection is closed properly after a bad query. Finally, the use of query parameters will guard your app against sql injection attacks.