How to sort data by array of category ids in drupal 8?

Sometime we have a case of sort data with array of categories So we can't use direct 'orderBy' in drupal 8 query. We have to use 'addExpression' in query. Here we have an example for better clear this article.
Example:
In a way of query:

    $products = db_query("select gfd.entity_id from node__field_category as gfd inner join node_field_data as nfd on nfd.nid=gfd.entity_id ORDER BY FIELD(gfd.field_category_target_id, 675, 676, 677), nfd.title ASC");

    OR
    Other way of Query:

    $products = \Drupal::database()->select('node__field_category', 'gfd');
    $products->join('node_field_data', 'nfd', 'nfd.nid=gfd.entity_id');       
    $products->fields('gfd', array('entity_id'));       
    $products->addExpression('FIELD(gfd.field_category_target_id, 675, 676, 677)', 'order_field');
    $products->orderBy('order_field', 'ASC');   
    $product_ids = $products->execute()->fetchAll();
   
Description: Here we are using '$products->addExpression' for add special type of sorting so we will pass the field alias and field name then category id which you want for sort data and then 'order_field' is some kind of alias and we will pass in this way for ASC or DESC:
$products->orderBy('order_field', 'ASC');
So this is the simple way to sort data by array ASC/DESC in Drupal 8 query.


Note: How to sort data by array of category ids in drupal 8?

How we can Url Alias in Drupal 8?

If you want to path alias in drupal 8 then we have different syntax in drupal 8, Please follow this.
Syntax:
$alias = \Drupal::service('path.alias_manager')->getAliasByPath($tid or $nid);

Example: like if we have taxonomy term and we want to path alias so first we create URL path as given exmaple..

$tid = '/taxonomy/term/'.$term_id;
$alias = \Drupal::service('path.alias_manager')->getAliasByPath($tid); or \Drupal::service('path.alias_manager')->getAliasByPath('/taxonomy/term/'.$term_id),

OR

$nid = '/node/'.$node_id;
$alias = \Drupal::service('path.alias_manager')->getAliasByPath($nid); or \Drupal::service('path.alias_manager')->getAliasByPath('/node/'.$node_id),


Simple then we can use this alias to send or redirect using
$response = new Symfony\Component\HttpFoundation\RedirectResponse($alias);
$response->send();
return; 


Note: If have any suggestions or issue regarding 'How we can Url Alias in Drupal 8?' then you can ask by comments.