collectioncontroller.js

  _arrangedObjects: [],
  
  arrangedObjects: function( key, value ) { 
      if ( value ) {
         /* adjust for incoming array, store internally, e.g. this._aryToReturn */ 
         var newList = [];
         value.each(function(s){ 
               newList.push(s.get('ID_from_the_linking_table')); 
               });
         this.set('_arrangedObjects',newList);
      }
      // our model:
      //else return (this._aryToReturn) ? this._aryToReturn: []; 
      else return (this._arrangedObjects) ? this._arrangedObjects: []; 
  }.property()

exam_teacher.js

AdmissionExam.AEExamTeacher = SC.Record.extend(
/** @scope Admissionexam.AEExamTeacher.prototype */ {

  // TODO: Add your own code here.
  properties: ['id','examId','teacherId'],
  
  teacherIdType: 'OrionFw.Teacher'
  
}) ;