LINQ to Entities not supported

Question

在Asp.net Web API我有以下模型。

public class User 
    { 
     [Required, Key] 
     public long Id { get; set; } 
     public string Name { get; set; } 
     public Company Employer { get; set; } 
     [Required] 
     public DateTime DateAdded { get; set; } 
    } 

這是一個控制器的摘錄。

// GET api/Company/5 
    public Object GetCompany(int id) 
    { 
     var query = from user in db.Users 
        join company in db.Companies on user.Employer.Id equals company.Id 
        where company.Id == id 
        orderby user.Name 
        select new { Id = user.Id, Name = user.Name, EmailAddress = user.EmailAddress, Version = user.DateAdded.ToString("dd.MM.yyyy"), Employer = company.Name }; 
     return query.AsEnumerable<Object>(); 
    } 

我想要的是格式化DateAdded屬性。但是，當我嘗試調用某個用戶屬性的方法或調用用戶的方法時，EF會引發NotSupportedException。我怎樣才能格式化日期？

Answer 1

EF無法將user.DateAdded.ToString("dd.MM.yyyy")方法轉換爲SQL代碼。您應該搬遷日期格式以客戶端（與AsEnumerable()或ToList()電話），或使用SqlFunctions建立在服務器端的日期字符串：

Version = 
    SqlFunctions.DateName("dd", user.DateAdded) + "." + 
    SqlFunctions.StringConvert(
     (decimal?)SqlFunctions.DatePart("MM", user.DateAdded)).Trim() + "." + 
    SqlFunctions.DateName("yyyy", user.DateAdded)