PHP递归函数从DB获取文件夹和文件

Question

我正在尝试使用递归函数将mysql表转换为POO数组以获取所有目录并将它们推送到每个目录中。但是我有一些实现问题，因为我的代码不起作用（只有一半）。我编辑了一些代码，因为它很长（对于stackoverflow帖子）所以如果缺少某些东西警告我。

示例文件夹表：

id | parent_id | foldername
1  | 0         | folder1
2  | 0         | folder2
3  | 1         | folder3
4  | 2         | folder4
5  | 3         | folder5

示例文件表：

id | folderid | filename | filepath
 1 | 1        | file1    | serverpath
 2 | 1        | file2    | serverpath
 3 | 2        | file3    | serverpath
 4 | 5        | file4    | serverpath
 5 | 4        | file5    | serverpath

folderid引用文件夹表中的id

示例文件系统映像：

我的PHP课程：

class Root
{
    public $root = array();

    public function __construct($object)
    {
        $this->root = $object;
    }
}

class Folder
{
    public $folderid;
    public $foldername;
    public $files = array();
    public $folders = array();

    public function __construct($folderid, $foldername)
    {
        $this->folderid = $folderid;
        $this->foldername = $foldername;
    }

    public function addFile($file)
    {
        if ($file instanceof File) {
            $this->files[] = $file;
        }
    }

    public function addFolder($folder)
    {
        if ($folder instanceof Folder) {
            $this->folders[]=$folder;
        }
    }
}

class File
{
    public $filename;
    public $filepath;

    public function __construct($filename, $filepath)
    {
        $this->filename = $filename;
        $this->filepath = $filepath;
    }
}

PHP代码（GetFileSystem.php）：

<?php
$config = require_once('config.php');

function getRootContent()
{
    $root = array();
    $conn = new mysqli($config->host, $config->user, $config->password, $config->db);
    if ($conn->connect_error) {
        die('Connection failed:' . $conn->connect_error);
    }
    if ($stmt = $conn->prepare('SELECT id,foldername FROM foldertable WHERE parent_id=? AND published=1')) {
        //I only want to get specific folders so there for each id (folderid)) 
        foreach ($config->parentid as $id) {
            $root[] = getSubFolders($stmt, $id);
        }
    } else {
        die('Query/Statement Error:' . $conn->error);
    }
}

function getSubFolders($stmt, $id)
{
    $stmt->reset();
    $stmt->bind_param('i', $id);
    $stmt->execute();
    $stmt->store_result();
    $stmt->bind_result($folderid, $foldername);

    $data = array();
    if ($stmt->num_rows > 0) {
        while ($stmt->fetch()) {
            $data[] = new Folder($folderid, $foldername);
            //TO DO $data[] = new File();
        }

        foreach ($data as $row) {
            $row[$folderid] = getSubFolders($stmt, $row['folderid']);
        }
    }
    return $data;
}

    $root = new Root(getRootContent());

    var_dump($root);

我正在尝试将我的java代码转换为php，因此有些东西可能编码错误（我不是php专家所以任何帮助都会很好）。