为什么我的 Linqued 查询不起作用？答案

【问题标题】：why my Linqued query not working?为什么我的 Linqued 查询不起作用？
【发布时间】：2016-06-03 07:29:29
【问题描述】：

我有这个运行良好的 sql 查询

    select u.FirstName,u.LastName,case when ei.Gender=1 then 'Male' else 'Female' end as Gender,t.Name as 'Team Name',ei.MobileNumber,u.Phone as 'Alternative Number',u.EmailAddress,ei.AlternateEmailAddress,ei.GMail,ei.Skype,FORMAT(ei.DateOfBirth,'dd-MMM-yyyy') AS BirthDay,ei.Address1,ei.Address2,ei.City,ei.[State],ei.Country,ei.ZipPostalCode,ei.Designation,ei.MasterLeaves
 from Employee e
inner join [user] u
on e.[User]=u.Id and IsDeleted!=1
inner join Team t 
on e.Team=t.Id
inner join EmployeeInformation ei
on e.AdditionalInformation=ei.Id

什么时候我将相同的查询转换为 linqued 查询，即

    var EmpReport = (from Emp in db.Employees
                 join Usr in db.Users
                 on Emp.User equals Usr.Id
                 join Tm in db.Teams
                on Emp.Team equals Tm.Id
                 join Ei in db.EmployeeInformations
                 on Emp.AdditionalInformation equals Ei.Id
                 where Usr.IsDeleted  != true
                select new { Usr.FirstName, Usr.LastName, Gender = Ei.Gender == 1 ? "Male" : "Female", Team_Name = Tm.Name, Ei.MobileNumber, Alternative_Number = Usr.Phone, Email_Address = Usr.EmailAddress, Alternate_Email_Address = Ei.AlternateEmailAddress, Ei.GMail, Ei.Skype, Birthday = Ei.DateOfBirth.ToString("dd-MMM-yyyy"), Ei.Address1, Ei.Address2, Ei.State, Ei.Country, Ei.ZipPostalCode, Ei.Designation, Ei.MasterLeaves }).ToList();

它给了我这个错误

 LINQ to Entities does not recognize the method 
     'System.String ToString(System.String)' method, and this method cannot
      be translated into a store expression.

错误基本上是在这部分引起的

Birthday = Ei.DateOfBirth.ToString("dd-MMM-yyyy").

我哪里出错了？

【问题讨论】：

标签： mysql sql-server linq linq-to-sql

【解决方案1】：

您收到错误是因为 DateTime.ToString() 是一个 .NET 函数，不能直接转换为 SQL。以本机格式返回您的 DateOfBirth 列，并在您的应用程序中获得结果后更改格式，或使用 Linq-to-Entities 中提供的一些 SQL 函数，请参阅此答案：https://stackoverflow.com/a/16364484/5785878

【讨论】：