新手请问一个关于PHP从数据库取得数据后怎么填充到XML文件中

// 引用数据库处理文件
require_once "../../DBHandle/DBHandle/DBUser.php";

$lefNav = $_REQUEST ["lefNav"];
$action = $_REQUEST ["action"];
if ($lefNav == "userinfo") {
    if (action == "init") {
        $userId = $_REQUEST ['user_id'];
        $rs = DBUser::getUserInfoByID ( $userId );
        if ($rs) {
            
            // 将查询出来的用户信息结果放置到XML中传到前段
            $doc = new DOMDocument ( "1.0", "utf-8" );
            $doc->appendChild ( $doc->createElement ( "xml" ) );
            
                $userNode = $doc->createElement ( "rs" );
                
                $userId = $doc->createElement ( "userId" );
                $userIdTx = $doc->createTextNode($rs[0]);
                $userId->appendChild($userIdTx);
                
                $name = $doc->createElement ( "name" );
                $nameTx = $doc->createTextNode($rs[1]);
                $name->appendChild($nameTx);
                
                $rname = $doc->createElement ( "rname" );
                $rnameTx = $doc->createTextNode($rs[2]);
                $rname->appendChild($rnameTx);
                
                $gname = $doc->createElement ( "gname" );
                $gnameTx = $doc->createTextNode($rs[3]);
                $gname->appendChild($gnameTx);
                
                $userNode->appendChild($userId);
                $userNode->appendChild($name);
                $userNode->appendChild($rname);
                $userNode->appendChild($gname);
                
                $doc->documentElement->appendChild($userNode);
                echo $doc->saveXML();
            
        } else {
            echo "FAIL";
        }
    }
}
   

include(dirname(__FILE__)."/xmlparse.php");
$listtags = explode(" ","2 name");
$arr = array(1,"name"=>"SOM","admin",100,array("name"=>"TOM","Lily"));
$contXML = dump_xml_config($arr, "xml", "utf-8");
//放入文件
//file_put_contents_safe("/path/test.xml",$contXML,"w");
echo $contXML;
#源码
#
#
#    <0>1
#    SOM
#    <1>admin
#    <2>100
#    <3>
#        TOM
#        <0>Lily
#    
#