public static List<CompleteOrder> GeneriereOrders(List<Order> orders, List<OrderLine> lines) { var ret = new List<CompleteOrder>(); foreach (var order1 in orders) { var order = new CompleteOrder(order1, new List<OrderLine>()); ret.Add(order); foreach (var orderLine in lines) { if (orderLine.Order.Id == order1.Id) { order.Orderlines.Add(orderLine); } } } return ret; }