//定义一个静态方法

public static function del($id)
{
    $document = Document::find($id);
    if (!$document) {
        return false;
    }
    $documentOne = Document::where('parent_id', $id)->get();
    if (count($documentOne) != 0) {
        $document->delete();
        foreach ($documentOne as $item){
            self::del($item->id);
        }
        return true;
    } else {
        $document->delete();
        return true;
    }

public function deleteDocument(Request $request, $id)
{
    self::del($id);
    return response()->json(['code' => 200, 'msg' => '删除成功']);
}