PHP appendChild to XML root - php

Question

I know this should be simple, but I'm new to PHP and just do not understand the documentation I've come across. I need a simple explanation.
I have an XML document that I would like to add nodes to. I can add nodes to the document, they only appear outside of the root node and cause errors to happen on subsequent attempts.
Here is my XML:
<?xml version="1.0" encoding="UTF-8"?>
<root>
</root>
and here is my PHP:
$playerID = "id_" . $_POST['player'];
//load xml file to edit
$xml = new DOMDocument();
$xml->load('../../saves/playerPositions.xml') or die("Error: Cannot load file.");
//check if the player is already in the database
if(isset($xlm->$playerID)){
echo "Player ID was found.";
}
else{
echo "Player ID was not found.";
//so we want to create a new node with this player information
$playerElement = $xml->createElement($playerID, "");
$playerName = $xml->createElement("name", "John Doe");
//add the name to the playerElement
$playerElement->appendChild($playerName);
//add the playerElement to the document
//THIS IS WHERE THE ERROR OCCURS
$xml->root->appendChild($playerElement);
//save and close the document
$xml->formatOutput = true;
$xml->save("../../saves/playerPositions.xml");
}
echo "done";
If I just use $xml->appendChild() then I can modify the document, but the new text appears outside of <root></root>.
The exact error is:
Notice: Undefined property: DOMDocument::$root

Answer 1

$xml->root isn't the correct way to access root element in this context, since $xml is an instance of DOMDocument (It will work if $xml were SimpleXMLElement instead). You can get root element of a DOMDocument object from documentElement property :
$xml->documentElement->appendChild($playerElement);
eval.in demo 1
Or, more generally, you can get element by name using getElementsByTagName() :
$xml->getElementsByTagName("root")->item(0)->appendChild($playerElement);
eval.in demo 2
Further reading : PHP DOM: How to get child elements by tag name in an elegant manner?
That said, this part of your code is also not correct for the same reason (plus a typo?):
if(isset($xlm->$playerID)){
echo "Player ID was found.";
}
Replace with getElementsByTagName() :
if($xml->getElementsByTagName($playerID)->length > 0){
echo "Player ID was found.";
}

Answer 2

You are trying to handle the dom like a Standar Object, but is not.
To look for elements, you need to use the function getElementsByTagName, and handle the dom like a collection of nodes, like this:
$xml = new DOMDocument();
$xml->loadXML('<?xml version="1.0" encoding="UTF-8"?>
<root>
</root>') or die("Error: Cannot load file.");
$len = $xml->getElementsByTagName('player')->length;
if ( $len > 0 ) {
} else {
$player = $xml->createElement('player', '');
$playerName = $xml->createElement('playerName', "Jhon Doe");
$player->appendChild( $playerName );
$root = $xml->getElementsByTagName('root');
if ( $root->length > 0 ) {
$root[0]->appendChild( $player );
}
$xml->formatOutput = true;
echo $xml->saveXML();
}
This code produces:
<?xml version="1.0" encoding="UTF-8"?>
<root>
<player><playerName>Jhon Doe</playerName></player></root>