postgresql dfs preorder tree traversal

CategoryRepository.php

    public function findCategories(): array
    {
        // dfs preorder tree traversal

        $sql = <<<'SQL'
WITH RECURSIVE preorder_categories_traversal
                   AS (SELECT category.id,
                              category.parent_id,
                              ARRAY [ROW (category.sort_order,category.id)] AS path
                       FROM categories category
                       WHERE category.parent_id IS NULL
                       UNION ALL
                       SELECT category.id,
                              category.parent_id,
                              preorder_categories_traversal.path || ROW (category.sort_order,category.id) AS path
                       FROM preorder_categories_traversal
                                INNER JOIN categories category
                                           ON preorder_categories_traversal.id = category.parent_id)
SELECT category.*
FROM categories category
         INNER JOIN preorder_categories_traversal tree ON category.id = tree.id
WHERE category.template_id = :template_id
ORDER BY tree.path ASC;
SQL;

        $query = $this
            ->getEntityManager()
            ->createNativeQuery($sql, $this->buildRsm())
            ->setParameter('template_id', 123);

        /** @var SurveyTemplateSection[] $results */
        $results = $query->execute();

        return $results;
    }

    private function buildRsm(): ResultSetMappingBuilder
    {
        $rsm = new ResultSetMappingBuilder($this->getEntityManager());

        $rsm->addRootEntityFromClassMetadata(Category::class, 'category');

        return $rsm;
    }