// Get an OrderItem by Id
 public static IO <OrderItemAgg> GetOrderItem(int orderItemId)
 => from orderItem in Database.Query <FindOrderItemQuery, OrderItem>(new FindOrderItemQuery(orderItemId))
 from getResult in RestaurantDomain.GetOrderItem(orderItem)
 let agg = (getResult as GetOrderItemResult.OrderItemFound)?.Agg
           select agg;