編輯實體框架代碼中的數據第一個模型

Question

在下面的代碼中，我有country = 1，school = 2和course = 3。 但之後，當我試圖分配這樣的， userdata.UserCountry.CountryId = Convert.ToInt32（country）。它表示「對象引用未設置爲......對象實例」表示空值。

[HttpPost] 
    public ActionResult Settings(FormCollection frm) 
    { 

      UsersContext db = new UsersContext(); 

      var userdata = db.UserDetails.Where(k => k.UserId == WebSecurity.CurrentUserId).FirstOrDefault(); 

      string country = frm["UserCountry"]; // here I have 1. 
      string school = frm["UserSchool"]; 
      string course = frm["UserCourse"]; 

      userdata.UserCountry.CountryId= Convert.ToInt32(country); // Here i have the null reference error.. !! 
      userdata.UserSchool.SchoolId = Convert.ToInt32(school); 
      userdata.UserCourse.CourseId = Convert.ToInt32(course); 
      userdata.Link = frm["Link"]; 
      userdata.FullName = frm["FullName"]; 
      userdata.Email = frm["Email"]; 
      userdata.About = frm["About"]; 

      db.SaveChanges(); 

      return Content(Boolean.TrueString); 
    } 

這是模型：

public class UserDetail 
{ 
    public int Id { get; set; } 
    public int UserId { get; set; } 
    [Required] 
    [Display(Name="Full name")] 
    public string FullName { get; set; } 
    public string Link { get; set; } 
    public bool? Verified { get; set; } 

    [Required] 
    [Display(Name="Email")] 
    public string Email { get; set; } 

    [Display(Name="About")] 
    public string About { get; set; } 
    public virtual School UserSchool { get; set; } 
    public virtual Course UserCourse { get; set; } 

    [Display(Name = "Country")] 
    public virtual Country UserCountry { get; set; } 

} 

誰能幫我如何解決這個問題？PLZ。

Answer 1

儘量在查詢結果中相關實體：

var userdata = db.UserDetails 
        .Include("UserCountry") 
        .Include("UserSchool") 
        .Include("UserCourse") 
        .Where(k => k.UserId == WebSecurity.CurrentUserId) 
        .FirstOrDefault(); 

BTW驗證你真的有用戶ID您搜索的UserDetails。