在自定义路由中访问WP自定义REST字段

Question

I have created custom fields to display in WordPress rest api. I want the same data to be fetched into a custom route api. How it is possible?

That is, I have some custom rest fields in the path example.com/wp-json/wp/v2/posts/

have the following rest fields I need to show in the another route. ie at example.com/wp-json/mycustom/route/v2

How can I do it?

function list_subpages() {

   $data = array();
   $request = array();
  $my_column = array();
   global $wpdb;
        $save_table = $wpdb->prefix.'saved_post';
        $regid = $_REQUEST['save_key'] ;
        $sql1 = "select postid FROM ".$save_table." WHERE regid='".$regid."';";
        $result1 = $wpdb->get_results($sql1);
        foreach ($result1 as $p)
        {
        $id[]=$p->postid;
        }


  $args = array(
    'post__in' => $id,
    'per_page' => $per_page,
);

   $subpages = get_posts( $args );

   if ( empty( $subpages ) ) {
       return null;
   }

   foreach ($subpages as $p) {

       $request[] = $data;
   }

   return new WP_REST_Response($request, 200);
}
add_action('rest_api_init', function () {
   $namespace = 'savedpost/v2';
   $base = 'user';
   register_rest_route($namespace, '/' . $base, array(
       'methods' => 'GET',
       'callback' => 'list_subpages',
   ));
});