c# - 从 Controller 在模型中传递 ICollection 时，Ajax 方法将不再起作用

Question

我正在尝试列出特定学生的所有类(class)。但是，我在将 ICollection 列表发送到 Ajax 方法时遇到问题。当我这样做时，没有任何反应，我收到错误消息(在 chrome 中):

http://localhost:25237/Home/Test 500 (Internal Server Error)

如果我评论/删除 Courses = readStudent.Courses(Courses 的ICollection)，我的 Ajax 方法就会按预期工作(没有培训类)。

public ActionResult Test(Guid id) {

        var readStudent = db.Students.SingleOrDefault(x => x.Id == id);

        var results = new StudentVm {

            FirstName = readStudent.FirstName,
            LastName = readStudent.LastName,
            SchoolName = readStudent.School.Name,               
            Courses = readStudent.Courses  //Icollection, works if I remove this line.
        };

        return Json(results);
    }

我的 Ajax 代码:

 $.post("/Home/Test", { "id": id },
     function (data) {
         if (data) {    

             $("#testDiv").append($('<div class=\"studentInfo\"> ' +
             '<br/> ' +
              <b>Student: </b>' + data.FirstName + " " + data.LastName +
              '<br/>' +
              '<b>School: </b>' + data.SchoolName +
              '<br/>' +
              '<b>All courses: </b>' +

               $.each(data.Courses(function(index, item) { allCources += '<b>' + item + '</b>'; })

               +'</div>'));

         }
    });

在 View 中，我需要访问 Course 的 Name 和 Description 属性

有什么想法吗？

编辑:

System.InvalidOperationException: A circular reference was detected while serializing an object of type 'System.Data.Entity.DynamicProxies.Student_32DDE9D84FE99EFF8907954351AD1F1A8162A0B565198DD8C7B4B25E2330BB98'.

学生模型(英孚创建):

public partial class Student {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public Student() {
            this.Courses = new HashSet<Course>();
        }

        public System.Guid Id { get; set; }            
        public System.Guid SchoolId { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public System.DateTime Started { get; set; }
        public Nullable<System.DateTime> Ended { get; set; } 

        public virtual School School { get; set; }    
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<Course> Courses { get; set; }
    }

类(class)模型(英孚创建)

  public partial class Course {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public Course() {
            this.Students = new HashSet<Student>();
        }

        public System.Guid ID { get; set; }
        public string Name { get; set; }
        public string Classroom { get; set; }
        public string Description { get; set; }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<Student> Students { get; set; }
    }

我的 ViewModel 传递给 View:

public class StudentVm {

        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string SchoolName { get; set; }

        public virtual ICollection<Course> Courses { get; set; }

    }

Answer 1

异常被抛出是因为 Course 包含一个 Student 的属性 - JavascriptSerializer 试图序列化 Course包含 Student，其中包含 Course，其中包含 Student 等等(如果继续，您将耗尽内存)。

您只需要返回 View 中需要的Course 属性，因此StudentVM 的Courses 属性应该是一个集合另一个 View 模型仅包含您需要的属性，或者只是将匿名对象传递回客户端

var student = db.Students.SingleOrDefault(x => x.Id == id);
var results = new
{
    FirstName = student.FirstName,
    LastName = student.LastName,
    SchoolName = student.SchoolName,
    Courses = student.Courses.Select(x => new
    {
        Name = x.Name,
        Description = x.Description
    })
};
return Json(results);

或者，如果你想使用 View 模型，那么它们将需要

public class StudentVm
{
    public string FirstName { get; set; }
    ....
    IEnumerable<CourseVM> Courses { get; set; }
}
public class CourseVM
{
    public string Name { get; set; }
    public string Description { get; set; }
}

Controller 代码将是

var student = db.Students.SingleOrDefault(x => x.Id == id);
var results = new StudentVm
{
    FirstName = student.FirstName,
    LastName = student.LastName,
    SchoolName = student.School.Name,               
    Courses = student.Courses.Select(x => new StudentVM
    {
        Name = x.Name,
        Desription = x.Name
    }
};
return Json(results);

然后在 View 中，您需要更改 $.each() 循环中的代码以访问 Courses

的每个属性

$.each(data.Courses(function(index, item) {
    allCources += '<b>' + item.Name + '</b>'; // and item.Description
})

或者，考虑使用更好更强大的 Json.NET用于序列化数据，它具有设置如何处理循环引用的选项。