ASP.NET MVC 4，EF和LINQ：爲多對多關係創建特定的LINQ查詢

Question

在我的應用程序中，我試圖編寫一個ListStudents ActionResult，它只顯示一個列表，其中的ClassroomID等於當前登錄的教師創建的ClassroomID之一。

我相信我需要使用一些LINQ查詢來獲得所需的結果，但是我被卡住了，因爲當教師實體擁有教室ICollection時，我不知道如何處理它。

ListStudents & CreateClassroom我TeacherController

public ActionResult ListStudents() 
{ 
     //This gets the current teachers UserProfile as only users with the teacher role have access to this controller 

     var teacherProfile = db.UserProfiles.Local.SingleOrDefault(u => u.UserName == User.Identity.Name) 
      ?? db.UserProfiles.SingleOrDefault(u => u.UserName == User.Identity.Name); 

     var teacher = db.Teachers.Find(teacherProfile.UserId); 

     //Need query where students ClassroomID needs to be one of the current teachers ClassroomID's 

     return View(students); 
} 

public ActionResult CreateClassroom(Classroom model) 
    { 
     if (ModelState.IsValid) 
     { 
      try 
      { 
       var userProfile = db.UserProfiles.Local.SingleOrDefault(u => u.UserName == User.Identity.Name) 
        ?? db.UserProfiles.SingleOrDefault(u => u.UserName == User.Identity.Name); 

       var classroom = new Classroom 
       { 
        ClassroomName = model.ClassroomName, 
        TeacherID = userProfile.UserId 

       }; 
       db.Classrooms.Add(classroom); 
       db.SaveChanges(); 
      } 
      catch (DataException) 
      { 
       ModelState.AddModelError("", "Something went wrong, try again."); 
      } 
     } 
     return RedirectToAction("ListClassrooms"); 
    }  

模式對於用戶，學生，教師和課堂

public class User 
{ 
    [Key] 
    [Editable(false)] 
    [ForeignKey("UserProfile")] 
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.None)] 
    public int UserId { get; set; } 

    public virtual UserProfile UserProfile { get; set; } 

    [Display(Name = "First Name")] 
    [Required(ErrorMessage = "First name is required.")] 
    [MaxLength(50)] 
    public virtual string FirstName { get; set; } 

    [Display(Name = "Last Name")] 
    [Required(ErrorMessage = "Last name is required.")] 
    [MaxLength(50)] 
    public virtual string LastName { get; set; } 
} 

學生

public class Student : User 
{ 
    [ForeignKey("Account")] 
    [Editable(false)] 
    public virtual int AccountID { get; set; } 

    public virtual Account Account { get; set; } 

    [Column("ClassroomID")] 
    [ForeignKey("Classroom")] 
    public virtual int ClassroomID { get; set; } 

    public virtual Classroom Classroom { get; set; } 
} 

教師

public class Teacher : User 
{ 
    public virtual ICollection<Classroom> Classrooms { get; set; } 
} 

課堂

public class Classroom 
{ 
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)] 
    public virtual int ClassroomID { get; set; } 

    [Display(Name = "Classroom Name")] 
    [MaxLength(50)] 
    public virtual string ClassroomName { get; set; } 

    public virtual ICollection<Student> Students { get; set; } 

    [Column("TeacherID")] 
    [ForeignKey("Teacher")] 
    public virtual int TeacherID { get; set; } 

    public virtual Teacher Teacher { get; set; } 
} 

感謝您抽出時間來幫我解決這個問題，我是很新的MVC和我試圖儘可能多的學習，因爲我能夠。

Answer 1

分成幾行，使其更容易理解。

var classrooms = db.Classrooms.Where(x => x.TeacherID == teacher.Id).Select(x => x.ClassroomID); 
var students = db.Students.Where(x => classrooms.Contains(x.ClassroomID);