Get the path to a category in opencart 1.5.*

opencart.php

<?php

/**
 * Returns the path to a category in the format 1_2_3
 * @param int $category_id
 * @return string the path to the category
 */
public function getCategoryPath($category_id){
	$path = '';

	$category = $this->db->query("SELECT * FROM " . DB_PREFIX . "category c WHERE c.category_id = " .(int)($category_id));
	if($category->row['parent_id'] != 0){
		$path .= $this->getCategoryPath($category->row['parent_id']) . '_';
	}

	$path .= $category->row['category_id'];

	return $path;
}