PHP で無段階再帰分類を実装する 2 つの方法の詳細な説明

/**
*   无级递归分类 TP框架
*   @param   int     $assortPid   要查询分类的父级id
*   @param   mixed   $tag         上下级分类之间的分隔符
*   @return  string  $tree        返回的分类树型结构结果 
*
*/
function recursiveAssort($assortPid, $tag = '')
{   
    $assort = M('goods_class')->where("class_pid = $assortPid")->field('class_id, class_name')->select();
    foreach ($assort as $value) {
        $tree .= &#39;<option value="&#39; . $value[&#39;class_id&#39;] . &#39;">&#39; . $tag . $value[&#39;class_name&#39;] . &#39;</option>&#39;;
        $tree .= recursiveAssort($value[&#39;class_id&#39;], $tag . &#39;&emsp;&#39;);
    }
    return $tree;
}

/**
    *   利用php的引用传递 CI框架
    *
    */
    public function get_access()
    {
        $access = array();
        $field = 'id, pid, method, name, description';
        $q_access = $this->db->select($field)->get('access');
        $q_result = $q_access->result_array();

        if (!empty($q_result)) {
            $items = array();
            foreach ($q_result as $value) {
                $items[$value['id']] = $value;
            }
            foreach ($items as $key => $item) {
                if ($item['pid'] == 0) {
                    $access[] = &$items[$key];
                } else {
                    $items[$item['pid']]['sub_access'][] = &$items[$key];
                }
            }
        }
        return $access;
    }