MVC CodeFirst計算屬性獲取錯誤「ObjectContext實例處置」

我有一個ASP.NET MVC Code First站點。我有一個型號Teacher，它有一個列表Student s，其中每個都有一個計算屬性CompletedTests。我越來越想包含的Student是清單一個ViewModel內訪問計算財產CompletedTests如果出現以下錯誤：MVC CodeFirst計算屬性獲取錯誤「ObjectContext實例處置」

An exception of type 'System.ObjectDisposedException' occurred in EntityFramework.dll but was not handled in user code 

Additional information: The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

老師：

public class Teacher 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
    public virtual ICollection<Student> Students{ get; set; } 
}

學生：

public class Student 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
    public int TeacherId { get; set; } 

    public virtual Teacher Teacher { get; set; } 

    public int TotalTests 
    { 
     get 
     { 
      return Tests.Count; 
     } 
    } 

    public int CompletedTests 
    { 
     get 
     { 
      return Tests.Count(p => p.IsCompleted); 
     } 
    } 

    public virtual ICollection<Test> Tests{ get; set; } 
}

測試：

public class Test 
{ 
    public int Id { get; set; } 

    public int StudentId { get; set; } 

    public int QuestionsTotal 
    { 
     get 
     { 
      return Questions.Count; 
     } 
    } 

    public bool IsCompleted 
    { 
     get 
     { 
      return Questions.Count(q => q.Completed) >= QuestionsTotal; 
     } 
    } 

    public virtual Student Student { get; set; } 
    public virtual ICollection<Question> Questions{ get; set; } 
}

問：

public class Question 
{ 
    public int Id { get; set; } 
    public int TestId { get; set; } 

    public virtual Question Question { get; set; } 
}

HomeViewModel：

public class HomeViewModel 
{ 
    public string TeacherName { get; set; } 
    public int StudentCount { get; set; } 
    public IEnumerable<Student> Students { get; set; } 
}

首頁控制器：

public ActionResult Index() 
{ 
    var model = new HomeViewModel(); 
    var userId = User.Identity.GetUserId(); 
    using (var context = new ApplicationDbContext()) 
    { 
     var teacher = context.Teachers.FirstOrDefault(c => c.IdentityId == userId); 
     if (teacher != null) 
     { 
      model.TeacherName = teacher.Name; 
      model.Students = teacher.Students.ToList(); 
     } 
     return View(model); 
    } 
}

Index.cshtml部分：

 <tbody> 
      @foreach (var student in Model.Students) 
      { 
       <tr> 
        <td> 
         @student.Name 
        </td> 
        <td> 
         @(student.CompletedTests + "/" + student.TotalTests) 
        </td> 
       </tr> 
      } 
     </tbody>

難道有人請指出爲什麼我在student.CompletedTests部件上收到處置的實例錯誤？

來源

2015-06-21 Marcus

我看不到你在哪裏得到老師或學生的名字。您只有'Test'中的'Name'字段。 –

對不起，有錯的課。它在'Student'上，而不是'Test'。 – Marcus

'teacher.Name'呢？ –

使用包括加載學生的實體時避免延遲加載，包括測試實體：

model.Students = teacher.Students.Include(t => t.Tests).ToList();

這就是所謂的預先加載：

https://msdn.microsoft.com/en-us/data/jj574232.aspx

你得到的錯誤是因爲ObjectContext的（ApplicationDbContext）在您的視圖中不再可用。它已經置於控制器的方法內部。

來源

2015-06-21 22:13:07 Jure

MVC CodeFirst計算屬性獲取錯誤「ObjectContext實例處置」

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