Yii2 cant sort in calculated values - sorting

Question

In my model i have
public function getRating(){
$rating=ShopRating::getRating($this->id);
if($rating)
return $rating->rating;
else
return 0;
}
And in search model i have created a virtual column like
public $rating;
and marked it as safe
[['rating'], 'safe']
And in the controller defined my sort
private function getSort(){
$sort = new Sort([
'attributes' => [
'date-asc' => [
'asc' => ['date' => SORT_ASC],
'label' => Inflector::camel2words('Old to New'),
],
'date-desc' => [
'desc' => ['date' => SORT_DESC],
'label' => Inflector::camel2words('New to Old'),
'default' => SORT_DESC,
],
'rating-desc' => [
'desc' => ['rating' => SORT_DESC],
'default' => SORT_DESC,
],
'rating-desc' => [
'desc' => ['rating' => SORT_DESC],
'default' => SORT_DESC,
],
],
]);
return $sort;
}
like this.
$sort=$this->getSort();
And my date-wise sort is working perfectly.But the sorting on the calculated value doesn't work. Meaning sorting with the rating asc and desc is not working. How to can I make it to work