LINQ to Entities无法识别方法

Question

我有一个很长的Linq To Entities查询: -

reports = db.CallProfileDailies
    .Join(db.ReportDailyTotals, 
          cpd => cpd.Date, 
          rdt => rdt.Date, 
          (cpd, rdt) => new { cpd = cpd, rdt = rdt })
    .Where(a => a.cpd.Skill == a.rdt.Skill)
    .Join(db.SummaryIntervalTotals, 
          a => a.rdt.Date, 
          sit => sit.Date,
          (a, sit) => new { cpd = a.cpd, rdt = a.rdt, sit = sit })
    .Where(a => a.rdt.Skill == a.sit.Skill)
    .Select((a, i) => new ReportModel
    {
        AverageAbandonDelay = a.sit.AvgAbanTime,
        AverageAfterCallWorkTime = a.sit.AvgAcwTime,
        AverageHandleTime = (a.sit.AvgAcwTime + a.sit.AvgAcdTime),
        AverageSpeedOfAnswer = a.sit.AvgSpeedAns,
        AverageTalkTime = a.sit.AvgAcdTime,
        CallsAnswered = a.sit.AcdCalls,
        Date = a.sit.Date.ToString(),
        MaximumDelay = a.sit.MaxDelay,
        PercentageAbandon = (a.sit.AbanCalls / (a.sit.AcdCalls + a.sit.AbanCalls)),
        TotalCallsAbandon = a.sit.AbanCalls,
        TotalCallsOffered = (a.sit.AcdCalls + a.sit.AbanCalls),
        TotalHandleTime = (a.rdt.HoldTime + a.rdt.AcdTime + a.rdt.AcwTime)
    }).Take(5).ToList();

我在运行时收到以下错误: -

LINQ to Entities无法识别方法'System.Linq.IQueryable`1 [ExpediaReports.Models.ReportModel]选择[<> f_ AnonymousType1`3,ReportModel](System.Linq.IQueryable`1 [<> f _AnonymousType1`3 [ ExpediaReports.CallProfileDaily,ExpediaReports.ReportDailyTotal,ExpediaReports.SummaryIntervalTotal]],System.Linq.Expressions.Expression`1 [System.Func`3 [<> f__AnonymousType1`3 [ExpediaReports.CallProfileDaily,ExpediaReports.ReportDailyTotal,ExpediaReports.SummaryIntervalTotal],System .Int32,ExpediaReports.Models.ReportModel]])'方法,并且此方法无法转换为商店表达式.

我只是想了解这个错误意味着什么.我甚至无法读取它(Linq To Entities)无法识别的方法.

如何阅读此错误并识别无法识别的方法,以便我可以相应地更改我的查询？

这些字符在这里是什么意思:`<>'等.

Answer 1

"此方法无法转换为商店表达式"意味着Linq to Entities无法将您的查询转换为SQL.

当您在.Select()函数中有某些东西尝试以无法直接转换为SQL的方式操作结果时(例如运行函数时),通常会发生这种情况.我敢打赌,"a.sit.Date.ToString()"行导致了这个问题.在你调用.ToList()之后,只需返回日期并格式化它,我敢打赌问题就会消失.

令人沮丧的是 - Linq to SQL在运行这样的查询方面要好得多,你在.Select()函数中有复杂的函数.请记住,Linq to Entities在将其转换为SQL的功能上非常有限.