在linq select中将yyyyMMdd转换为日期时间

我不确定这是否会起作用，但尝试在您的ProcessAccountViewModel中添加一些逻辑来为您处理这个问题。像这样:

class ProcessAccountViewModel()
{
   ...
   DateTime TransactionEffectiveDate { get; set; } // you already have this
   string TransactionEffectiveDateAsString // add this
   {
       set
       {
           TransactionEffectiveDate = DateTime.ParseExact(value,
                      "yyyyMMdd", CultureInfo.InvariantCulture);
       }
   }
}

然后，不要在LINQ查询中直接设置transactioneffecvedate，而是使用字符串版本:

所以，而不是:

TransactionEffectiveDate = DateTime.ParseExact(p.TransactionEffectiveDate,
                                "yyyyMMdd", CultureInfo.InvariantCulture),

TransactionEffectiveDateAsString = p.TransactionEffectiveDate,

LINQ to entities不支持DateTime。ParseExact方法，这样您就可以尝试使用AsEnumerable()将所需的集合带入内存，然后使用LINQ to Objects进行所有解析。

也许这能行?

var exchangeDatas = from p in db.ExchangeDatas
                    where p.ExchangeDataSeqid == entity.ExchangeDataSeqid
                    select p;
return (from p in exchangeDatas.AsEnumerable() 
                  select new ProcessAccountViewModel()
                  {
                      ExchangeCode = p.ExchangeCode,
                      UtilityCompany = p.UtilityCompanySeqid,
                      InvoiceBillingGroup = p.AccountBillingGroupSeqid,
                      AccountNumber = p.CurrentAccountNumber,
                      TurnOnDate = DateTime.ParseExact(p.AccountEffectiveTurnOn, "yyyyMMdd", CultureInfo.InvariantCulture),
                      SalesType = p.SalesType,
                      BillingCycle = p.BillingCycle,
                      TripNumber = p.TripNumber,
                      IsTimeOfDay = p.TODAccount == "Y" ? true : false,
                      IsExcessDistribution = p.ExcessDistributionAccount == "Y" ? true : false,
                      EnergyDeliverType = p.EnergyDeliveryType ?? 0,
                      Name = p.AccountName,
                      Address = p.AccountAddress,
                      Borough = p.Borough,
                      Facility = p.FacilitySeqid == null ? "" : p.FacilitySeqid.Value.ToString(),
                      Agency = p.AgencySeqid == null ? "" : p.AgencySeqid.Value.ToString(),
                      ServiceClass = p.DeliveryServiceClass,
                     AuthenticatedUserID = p.authenticatedUserID ?? 0,
                     ApprovedForCreation = p.ApprovedForCreation,
                     TransactionEffectiveDate = DateTime.ParseExact(p.TransactionEffectiveDate, "yyyyMMdd", CultureInfo.InvariantCulture),
                     ActivityTime = DateTime.ParseExact(p.ActivityTime, "yyyyMMdd", CultureInfo.InvariantCulture),
                     DateAdded = p.DateAdded,
                     LastUpdate = p.LastUpdate,
                     Exclude = p.Exclude,
                     IsProcessed = p.IsProcessed,
                     BillingPeriod = p.BillingPeriod
                 }).FirstOrDefault();