根据php中的特定属性更新xml文件中的单个节点

Question

I have a xml file named test.xml with the following structure.

<?xml version="1.0"?>
    <markers>
       <marker id="1" name="12" signal="23"/>
       <marker id="2" name="12" signal="5"/>
       <marker id="3" name="12" signal="6"/>
       <marker id="4" name="12" signal="0"/>
</markers>

I make an ajax request to my server code where I sent an ID and want to increase the signal attribute in test.xml by 1.

For example if I send id=3 then the signal attribute of the marker node with id of 3 should get 7 and the file should be saved. I don't want to rewrite the whole file due to some issues but only update an attribute.

I tried this but I think it's far away from the right answer. Can anyone help?

$id=$_POST['id'];

$xml = new SimpleXMLElement('test.xml');

foreach( $xml->xpath( 'marker' ) as $xml_row ){
    if( $xml_row->attributes( 'id' ) == $id ){
        $xml_row->attr( 'signals ') = $xml_row->attributes( 'signals' ) + 1;

    }
}
$xml->saveXML( 'test.xml' );

Answer 1

I figured out the answer myself:

$xmldoc = new DOMDocument();
$xmldoc->load('test.xml');
foreach ($xmldoc->getElementsByTagName('marker') as $feeditem) {
    if($feeditem->getAttribute('id')==$id){
        $sig=$feeditem->getAttribute('signal');
        $sig++;
        $feeditem->setAttribute('signal',$sig);
    }


}
$xmldoc->save('test.xml');