private void cmbBoxBooks_SelectedIndexChanged(object sender, EventArgs e)
{
if (cmbBoxBooks.Items.Count == 0)
{
return;
}
ReservationsService reservationsService = new ReservationsService();
Book selectedBook = (Book)cmbBoxBooks.SelectedItem;
List <Reservation> reservations = reservationsService.getByBook(selectedBook);
reservedByList.Items.Clear();
foreach (Reservation reservation in reservations)
{
reservedByList.Items.Add(reservation.customer.ToString());
}
}