Replace Ember.ArrayController.create() will not resolve belongTo relationships | ember upgrade 3.x

Im in the process of upgrade and im facing issues on ArrayController is being depreciated

in my old Ember 1.13 route im using

model/announcement.js

export default DS.Model.extend( {


  id:DS.attr('string'),
  title: DS.attr( 'string' ),
  description: DS.attr( 'string' ),
  published: DS.attr( 'boolean' ),
  publishedAt: DS.attr( 'date' ),

  course: DS.belongsTo( 'course' ),
  author: DS.belongsTo( 'profile', { async: true } ),

  viewed: false,
  isNew: true,

}

serializer/announcement.js

import DS from 'ember-data';
import ApplicationSerializer from 'mim/serializers/application';

export default ApplicationSerializer.extend( DS.EmbeddedRecordsMixin, {

  keyForRelationship: function( key ) {

    return key !== 'author' ? key : 'id';
  }
} );

routes/announcement.js

 setupController: function( controller, model ) {

    this._super( ...arguments );

     var announcements = Ember.ArrayController.create( {

          model: model,
          sortProperties: [ 'publishedAt' ],
          sortAscending: false
        } );

        controller.set( 'model', announcements );
  },

in controller of route announcement as follow

controller/announcement.js

publishedAnnouncements: Ember.computed( 'model.[]', 'model.@each.published', 'model.@each.viewed', function() {

    var published = this.get( 'model' ).filterBy( 'published', true ),
        announcements = Ember.A();

    announcements.pushObjects( published.filterBy( 'viewed', false ) );
    announcements.pushObjects( published.filterBy( 'viewed' ) );

    return announcements;
  } ),

so in the template im running a for each loop to render all announcements like

templates/announcements.hbs

In ember upgrade 3.5 i have changed these to following

model/announcement.js

export default DS.Model.extend( {

  id:DS.attr('string'),
  title: DS.attr( 'string' ),
  description: DS.attr( 'string' ),
  published: DS.attr( 'boolean' ),
  publishedAt: DS.attr( 'date' ),

  course: DS.belongsTo( 'course' ),

// remove async true from profile

  author: DS.belongsTo( 'profile'),

  viewed: false,
  isNew: true,

}

serializer/announcement.js

import DS from 'ember-data';
import ApplicationSerializer from 'mim/serializers/application';

export default ApplicationSerializer.extend( DS.EmbeddedRecordsMixin, {

  keyForRelationship: function( key ) {

    return key !== 'author' ? key : 'id';
  }
} );

routes/announcement.js

setupController: function( controller, model ) {

    this._super( ...arguments );

     //removed arrayController from here and assigned model

        controller.set( 'model', model );
  },

controller/announcement.js

sortProperties: ['publishedAt:desc'], sortedModel: computed.sort('model', 'sortProperties'),

publishedAnnouncements: Ember.computed( 'model.[]', 'model.@each.published', 'model.@each.viewed', function() {

   //getting model by local computed property defined above.arrayController sort is doing with above method by sortPropteries 
   var published =this.get('sortedModel').filterBy( 'published', true);
        announcements = Ember.A();

    announcements.pushObjects( published.filterBy( 'viewed', false ) );
    announcements.pushObjects( published.filterBy( 'viewed' ) );

    return announcements;
  } ),

templates/announcements.hbs

then the announcement.author.firstname is undefined in ember 3.5 but when if it is not a belongsTo relationship it will be there (example announcement.publishedAt)

i have no clue what i missed or what i did wrong here.

im here attaching screenshot of a console log which i did in controller published variable.

ember 1.13

ember 3.5