List<T> 重复记录合龙 数量相加

public partial class ProductItem    {        /// <summary>        /// 订单编号        /// </summary>        public string orderId { get; set; }        /// <summary>        /// 条形码        /// </summary>        public string barCode { get; set; }        /// <summary>        /// 产品名称        /// </summary>        public string Title { get; set; }        /// <summary>        /// 单价        /// </summary>        public string Price { get; set; }        /// <summary>        /// 订货数量        /// </summary>        public string quantity { get; set; }        /// <summary>        /// 规格        /// </summary>        public string Spec { get; set; }        /// <summary>        /// 优惠价        /// </summary>        public double preferPrice { get; set; }        /// <summary>        /// 原价        /// </summary>        public double costPrice { get; set; }        /// <summary>        /// 审核备注        /// </summary>        public string auditMemo { get; set; }    }

List<Model.ProductItem> listProductItem = new List<Model.ProductItem>();List<Model.SellOrderCart> listOrderCart = SellOrderCart.GetModelList(OrderID);foreach (Model.SellOrderCart item in listOrderCart){                        Model.ProductItem modelProductItem = new Model.ProductItem();                        modelProductItem.orderId = item.OrderID.ToString();                        modelProductItem.barCode = SellOrder.GetSpec(item.Title, item.ItemCode, item.GoodsTypeID, item.GoodsID, item.Specs, "", item.YGD);                        modelProductItem.Title = SellOrder.GetTitle(item.Title, item.SetTableID);                        modelProductItem.Price = item.SalePrice.ToString();                        modelProductItem.quantity = item.Quantity.ToString();                        modelProductItem.Spec = modelProductItem.barCode;                        modelProductItem.preferPrice = Convert.ToDouble(item.SalePrice);                        modelProductItem.costPrice = Convert.ToDouble(item.SalePrice);                        modelProductItem.auditMemo = SellOrder.GetAuditMemo(item.UserRemark, item.YGD);                        //如何判断barCode 条形码相同的情况下合并为一个商品quantity 订货数量相加                        listProductItem.Add(modelProductItem);}

            Dictionary<string, Model.ProductItem> productDic = new Dictionary<string, Model.ProductItem>();            List<Model.SellOrderCart> listOrderCart = SellOrderCart.GetModelList(OrderID);            foreach (Model.SellOrderCart item in listOrderCart)            {                string barCode = SellOrder.GetSpec(item.Title, item.ItemCode, item.GoodsTypeID, item.GoodsID, item.Specs, "", item.YGD);                if (productDic.ContainsKey(barCode))                {                    productDic[barCode].quantity += item.Quantity.ToString();                }                else                {                    Model.ProductItem modelProductItem = new Model.ProductItem();                    modelProductItem.orderId = item.OrderID.ToString();                    modelProductItem.barCode = barCode;                    modelProductItem.Title = SellOrder.GetTitle(item.Title, item.SetTableID);                    modelProductItem.Price = item.SalePrice.ToString();                    modelProductItem.quantity = item.Quantity.ToString();                    modelProductItem.Spec = modelProductItem.barCode;                    modelProductItem.preferPrice = Convert.ToDouble(item.SalePrice);                    modelProductItem.costPrice = Convert.ToDouble(item.SalePrice);                    modelProductItem.auditMemo = SellOrder.GetAuditMemo(item.UserRemark, item.YGD);                    productDic.Add(barCode, modelProductItem);                }            }