public static void SelectAllById(string id, List <ShoppingCart> idList) { Database db = new Database(); OleDbDataReader reader; db.Open(); reader = db.Read("select * from shopping_cart where session_id = '" + id + "'"); while (reader.Read()) { ShoppingCart tmpCart = new ShoppingCart(); List <Book> tmpBookList = new List <Book>(); tmpCart.sessionId = reader.GetString(0).Trim(); tmpCart.isbn = reader.GetString(1).Trim(); tmpCart.quantity = Convert.ToInt32(reader.GetValue(2)); Book.SelectAllByAttr(tmpCart.isbn, "isbn", tmpBookList); tmpCart.book = tmpBookList.ElementAt(0); idList.Add(tmpCart); } db.Close(); }