public Order(SP_Get_ItemListResult itemResult)
    {
        DBDataContext dbContext = new DBDataContext();

        orderItemID = itemResult.orderItemID;
        itemName    = itemResult.ItemName;
        quantity    = itemResult.quantity;
        // other properties ...
        var additionals = dbContext.SP_Get_AdditionalsList(orderItemID);

        Additionals = new ObservableCollection <string>();
        foreach (var item in additionals)
        {
            Additionals.Add(item.Additionals);
        }
    }