使用带有EF的JSON和MVC4的级联下拉列表

Question

我无法更新级联下拉列表中的第二个，我希望能够从第一个下拉列表中选择一个课程，然后根据所选值填充第二个下拉列表和课程部分列表。我有以下两种型号：

public class Course
{
    [Key]
    public int CourseID { get; set; }

    public string CourseTitle { get; set; }

    public virtual ICollection<CourseSection> CourseSections { get; set; }
}

public class CourseSection
{
    [Key]
    public int CourseSectionID { get; set; }

    public int CourseID { get; set; }

    public string Title { get; set; }
}

我对包含两个下拉列表的页面的视图如下：

<h3>Upload Course Section Content</h3>
  <div class="row">
    <div class="nine columns">
      <label for="name">Select Course:</label>
      <select id="coursedd" name="courseid" style="height:40px; font-size:18px;">
      <option value="0" id ="defaultcid" class ="choosefilter" >----Please Select Course----</option>
      @foreach (var course in Model.CourseList)
      {
        <option value="@course.CourseID" id ="courseid" class ="choosefilter" >@course.Name </option>
      }
      </select>
    </div>
  </div>
  <div class="row" style="margin-top:30px;">
    <div class="nine columns">
      <label for="name" id="namelabel">Select Course Section:</label>
      <select id="coursesectiondd" name="coursesectionid" style="height:40px; font-size:18px;">
      <option value="0" id ="defaultcs" class ="choosefilter" >----Please Select Course Section----</option>
      @if(Model.CourseSectionList != null)
          {
      foreach (var courseSection in Model.CourseSectionList)
      {
        <option value="@courseSection.CourseSectionID" id ="coursesectionid" class ="choosefilter" >@courseSection.Title </option>
      }
      }
          else
          {

      }
      </select>
    </div>
  </div>

如果选择了课程下拉列表值，则会调用以下jquery：

$(function () {
    $("#coursedd").change(function () {
        $('#namelabel').show();
        $('#title').show();
        $('#CourseSectionSubmit').show();
        var chosen = document.getElementById("coursedd").value;
        if (chosen == "0") {
            $('#namelabel').hide();
            $('#coursesectiondd').hide();
            $('#file').hide();
            $('#filelabel').hide();
        }
        else {
            GetCourseID()
            $.getJSON('@Url.Action("GetCourseID", "Admin")', { VendorGroup: DistributorID }, function (param) {
                var courseSectionDropdown = $('#coursesectiondd');
                courseSectionDropdown.empty();
                $.each(param, function (index, param) {
                    courseSectionDropdown.append(
                       $('<option/>')
                          .attr('value', param.sectionID)
                          .text(param.sectionTitle)
                    );
                });
            });
        }
    });
});

在这个jquery的else上调用了一个名为GetCourseID（）的javascript方法，其中包含以下代码：

function GetCourseID() {

    var id = document.getElementById("coursedd").value;

    var postData = {
        'CourseID': id
    };

    $('#coursesectiondd').show();

    $.post('/Admin/GetCourseID/', postData, function (data) {
        document.getElementById("coursedd").selectedIndex = id;
    });


};

此链接的控制器操作如下：

 [HttpPost]
    public ActionResult GetCourseID(int courseID)
    {  
        IEnumerable<Course> Courses = avm.GetCourseList();

        var Sections = dbcontext.CourseSection.Where(cs => cs.CourseID.Equals(courseID)).Select(x => new
        {
            sectionID = x.CourseSectionID,
            sectionTitle = x.Title
        });
        return Json(Sections, JsonRequestBehavior.AllowGet);
    }

有人可以帮助我返回Json值并更新我的第二个下拉列表