LINQ to Entities 无法识别方法 'System.String get_Item(Int32)' 方法，并且此方法无法转换为存储表达式答案

【问题标题】：LINQ to Entities does not recognize the method 'System.String get_Item(Int32)' method, and this method cannot be translated into a store expressionLINQ to Entities 无法识别方法 'System.String get_Item(Int32)' 方法，并且此方法无法转换为存储表达式
【发布时间】：2016-12-19 16:52:33
【问题描述】：

当我执行这个查询时，我得到这个错误：

return (from i in _ctx.TestPackages
   where i.Id==TestPackageId

   select new  ViewTestPackageState
   {
       Id = i.Id,
       PackageNumber = i.PackageNumber,
       ReInstatement = ReturnTestPackageState(i.Id, "Reinstatment")[0],
       ReInstatementReportNumber = ReturnTestPackageState(i.Id, "Reinstatment")[1],
       ReInstatementSubmitDateTime = ReturnTestPackageState(i.Id, "Reinstatment")[2],

       TestReportNumber = ReturnTestPackageState(i.Id, "Test")[1],
       TestState = ReturnTestPackageState(i.Id, "Test")[0],
       TestSubmitDateTime = ReturnTestPackageState(i.Id, "Test")[2],

       CleanReportNumber = ReturnTestPackageState(i.Id, "Clean")[1],
       CleanSubmitDateTime = ReturnTestPackageState(i.Id, "Clean")[2],
       CleaningState = ReturnTestPackageState(i.Id, "Clean")[0],

       Drying = ReturnTestPackageState(i.Id, "Drying")[0],
       DryingReportNumber = ReturnTestPackageState(i.Id, "Drying")[1],
       DryingSubmitDateTime = ReturnTestPackageState(i.Id, "Drying")[2],

       Flushing = ReturnTestPackageState(i.Id, "Flushing")[0],
       FlushingReportNumber = ReturnTestPackageState(i.Id, "Flushing")[1],
       FlushingSubmitDateTime = ReturnTestPackageState(i.Id, "Flushing")[2],

       LineCheckReportNumber = ReturnTestPackageState(i.Id, "LineCheck")[1],
       LineCheckState = ReturnTestPackageState(i.Id, "LineCheck")[0],
       LineCheckSubmitDateTime = ReturnTestPackageState(i.Id, "LineCheck")[2],

       Size = i.Size.ToString(),
       TestPackageOrder = i.TestPackageOrder,

   }).ToList();

错误：LINQ to Entities 无法识别方法 'System.String get_Item(Int32)' 方法，并且此方法无法转换为存储表达式

我知道问题是因为查询和查询应该在 select 语句之前执行，所以我的问题是如何在 select 之前执行这个查询？

【问题讨论】：

评论否决票

标签： c# entity-framework linq

【解决方案1】：

执行查询，然后从结果中选择对象

var result = (from i in _ctx.TestPackages
   where i.Id==TestPackageId).ToList();

return(result.Select( new ViewTestPackageState{...}));

【讨论】：

【解决方案2】：

var rawList = (from i in _ctx.TestPackages where i.Id==TestPackageId).ToList();

return rawList.Select(i => new ViewTestPackageState
       {
           Id = i.Id,
           PackageNumber = i.PackageNumber,
           ReInstatement = ReturnTestPackageState(i.Id, "Reinstatment")[0],
           // etc

【讨论】：