Thread.php

<?php

namespace Drupal\comment\Plugin\views\sort;

use Drupal\views\Plugin\views\sort\SortPluginBase;

/**
 * Sort handler for ordering by thread.
 *
 * @ingroup views_sort_handlers
 *
 * @ViewsSort("comment_thread")
 */
class Thread extends SortPluginBase {
    public function query() {
        $this->ensureMyTable();
        // See \Drupal\comment\CommentStorage::loadThread() for an explanation of
        // the thinking behind this sort.
        if ($this->options['order'] == 'DESC') {
            $this->query
                ->addOrderBy($this->tableAlias, $this->realField, $this->options['order']);
        }
        else {
            $alias = $this->tableAlias . '_' . $this->realField . 'asc';
            // @todo is this secure?
            $this->query
                ->addOrderBy(NULL, "SUBSTRING({$this->tableAlias}.{$this->realField}, 1, (LENGTH({$this->tableAlias}.{$this->realField}) - 1))", $this->options['order'], $alias);
        }
    }

}