无法使用AngularJs在数字“1”上创建属性“subjects”

我想在一门课程中选择多个科目,但无法选择

我有两个下拉列表,一个用于课程选择,一个用于科目选择。对于多个主题的选择,我使用 angular-chosen 插件,我只能在没有从下拉列表中选择课程的情况下选择多个科目。但当我从下拉列表中选择课程时,我甚至无法从下拉列表中选择一个科目

下面是我的AddCourseController。js和相关HTML

(function() {

  var myApp = angular.module("myApp");

  var AddCourseController = function($scope, CourseService, TeacherService) {

    var onCourses = function(courses) {
      $scope.courses = courses;
    }
    var onError = function(response) {
      $scope.error = true;
      $scope.errors = response.data;
    };
    CourseService.courses().then(onCourses, onError);
    TeacherService.getSubjects().then(function(data) {
      $scope.subjects = data
    });
  };

  myApp.controller("AddCourseController", AddCourseController);
}());

<div class="form-group">
  <label>Select Course</label>
  <select ng-model="course" class="form-control"
          ng-options="course.IdCourse as course.Name for course in courses track by course.IdCourse">
  </select>
</div>
<div class="form-group" ng-class="{ 'has-error' : 
   addCourseForm.subjects.$invalid && !addCourseForm.subjects.$pristine }">
  <label class="pull-left">Select Subjects</label>
  <a class="pull-right btn btn-primary btn-xs" data-toggle="modal" data- target="#add-subject">Add Subject</a>
  <select chosen multiple class="form-control" 
          ng-model="course.subjects"
          ng-options="subject.IdSubject as subject.Name for subject in subjects">
  </select>
  <p ng-show="addCourseForm.subjects.$invalid && 
  !addCourseForm.subjects.$pristine" class="help-block">Subject is required.
  </p>
</div>