ASP.NET :: ObjectContext實例已配置

Question

我是新的實體框架和ASP.NET。我正在嘗試訪問導航屬性的屬性。但我面臨着「ObjectContext實例已被處置」的錯誤。比我做了一些谷歌，發現它可以通過data = db.tblCourses.Include(c => c.tblSection).ToList();修復，但我仍然面臨這個問題。 型號：

using System.Data.Entity; 
public List<tblCourse> editedCoursesView() 
{ 
    List<tblCourse> data; 
    using (enrolmentsystemEntities db = new enrolmentsystemEntities()) 
    { 
     data = db.tblCourses.ToList(); 
     data = db.tblCourses.Include(c => c.tblSection).ToList(); 
     return data; 
    } 
} 

tblCourse：

namespace enrolmentSystem.Models 
{ 
    using System; 
    using System.Collections.Generic; 

    public partial class tblCourse 
    { 
     public tblCourse() 
     { 
      this.tblenrolments = new HashSet<tblenrolment>(); 
     } 

     public int CourseId { get; set; } 
     public string CourseName { get; set; } 
     public int departmentID { get; set; } 
     public int TeacherId { get; set; } 
     public int CreditHours { get; set; } 
     public int SectionId { get; set; } 

     public virtual tbldepartment tbldepartment { get; set; } 
     public virtual tblteacher tblteacher { get; set; } 
     public virtual ICollection<tblenrolment> tblenrolments { get; set; } 
     public virtual tblSection tblSection { get; set; } 
    } 
} 

tblRoom：

namespace enrolmentSystem.Models 
{ 
    using System; 
    using System.Collections.Generic; 

    public partial class tblRoom 
    { 
     public tblRoom() 
     { 
      this.tblSections = new HashSet<tblSection>(); 
     } 

     public int RoomNo { get; set; } 
     public string Block { get; set; } 
     public int Capacity { get; set; } 

     public virtual ICollection<tblSection> tblSections { get; set; } 
    } 
} 

控制器：

[HttpGet] 
public ActionResult editCourse() 
{ 
    course c = new course(); 
    List<tblCourse> data = c.editedCoursesView(); 
    return View("editCourse", data);  
} 

檢視：

@model List<enrolmentSystem.Models.tblCourse> 
@{ 
    ViewBag.Title = "editCourse"; 

} 

<h2>Edit Course</h2> 
<table border="1"> 
    <tr style="text-align:center;"> 
     <td>Course ID</td> 
     <td>Course Name</td> 
     <td> Course Department ID</td> 
     <td> Course Teacher ID</td> 
     <td> Course CreditHours</td> 
     <td> Course StartTime</td> 
     <td> Course EndTime</td> 
     <td> MaxCapacity </td> 
     <td> Course RoomNo </td> 


    </tr> 
    @if (Model != null) 
    { 

     foreach (var i in Model) 
     { 
      <form action="~/Enrolment/editCourse" method="post"> 
       <tr> 


        <td>@i.CourseId <input name="id" type="hidden" value="@i.CourseId" /> </td> 
        <td><input type="text" name="name" value="@i.CourseName" required /></td> 
        <td><input type="number" name="dpId" value="@i.departmentID" required /></td> 
        <td><input type="number" name="teacherId" value="@i.TeacherId" required /></td> 


        <td><input type="number" name="creditHours" value="@i.CreditHours" required /></td> 
        <td><input type="text" name="startTime" value="@i.tblSection.startTime" required /></td> 
        <td><input type="text" name="endTime" value="@i.tblSection.endTime" required /></td> 
        <td><input type="number" name="capacity" value="@i.tblSection.tblRoom.Capacity" required /></td> 
        <td><input type="number" name="roomNo" value="@i.tblSection.RoomNo" required /></td> 
        <td> <input type="submit" value="Update Course" /> </td> 


       </tr> 
      </form> 
     } 
    } 
</table> 

Answer 1

tblRoom可能會導致問題，因爲它不包含但在視圖中引用。一般來說，這個錯誤意味着你正在嘗試延遲加載一些屬性，但上下文已經處理完畢。

使用.Include(x => x.ApplicationsWithOverrideGroup.NestedProp)或.Include(x => x.Collection.Select(y => y.Property))來包含嵌套屬性或集合。

在你的情況下使用：

public List<tblCourse> editedCoursesView() 
{ 
    List<tblCourse> data; 
    using (enrolmentsystemEntities db = new enrolmentsystemEntities()) 
    { 
     data = db.tblCourses 
      .Include(c => c.tblSection) 
      .Include(c => c.tblSection.tblRoom) 
      .ToList(); 
     return data; 
    } 
}