知道生产日期和保质期来计算有效期至的方法和代码

//VS中Add方法中知道 保质期和生产日期来计算有效期至的方法和代码

if (r.Success)
            {
                r.Data = entities.ToExtJsAddResultData<CaiGouDanShangPin, Guid>();   // 返回增加的实体的ID和Timestamp集合
                r.Messages.Add($"新增{entities.Count}条记录成功！");

                var baozhiQi = entities.FirstOrDefault();
                if (baozhiQi != null)
                {
                    if (baozhiQi.BaoZhiQiDanWei == "年")
                    {

                        var t = Convert.ToInt32(baozhiQi.BaoZhiQi);
                        DateTime dt = DateTime.Parse(baozhiQi.ShengChanRiQi.ToString("yyyy-MM-dd"));
                        baozhiQi.YouXiaoQiZhi = dt.AddYears(t);
                        baozhiQi.Update().OnlySaveFields(e => e.YouXiaoQiZhi).SaveToDBAsync().Wait();
                    }
                    if (baozhiQi.BaoZhiQiDanWei == "月")
                    {
                        var t = Convert.ToInt32(baozhiQi.BaoZhiQi);
                        DateTime dt = DateTime.Parse(baozhiQi.ShengChanRiQi.ToString("yyyy-MM-dd"));
                        baozhiQi.YouXiaoQiZhi = dt.AddMonths(t);
                        baozhiQi.Update().OnlySaveFields(e => e.YouXiaoQiZhi).SaveToDBAsync().Wait();
                    }
                    if (baozhiQi.BaoZhiQiDanWei == "日")
                    {
                        var t = Convert.ToInt32(baozhiQi.BaoZhiQi);
                        DateTime dt = DateTime.Parse(baozhiQi.ShengChanRiQi.ToString("yyyy-MM-dd"));
                        baozhiQi.YouXiaoQiZhi = dt.AddDays(t);
                        baozhiQi.Update().OnlySaveFields(e => e.YouXiaoQiZhi).SaveToDBAsync().Wait();
                    }


                }


            }