old_contents: import DS from 'ember-data';
  
  export default DS.Model.extend({
    title: DS.attr('string'),
    users: DS.hasMany('user', {async: true}),
  });
  
new_contents: import DS from 'ember-data';
  
  export default DS.Model.extend({
    title: DS.attr('string'),
  });
  
subject: Remove users from UserRole model