PHP XML DOM Uncaught exception 'DOMException' with message 'Wrong Document Error'

Question

I am trying to learn XML and I know this is a problem with not properly importing the Nodes. But I can't quite figure it out. I've been looking around and most people don't have multiple child elements like I do with the departments.

Here is my XML structure:

<SOT>  
    <DEPARTMENT name="Aviation Technology" id="AT">  
        <EMPLOYEE type="Faculty">  
            <LOGIN>jdoe1</LOGIN>  
            <NAME>John Doe</NAME>   
        </EMPLOYEE>

        <EMPLOYEE type="Faculty">  
            <LOGIN>jdoe2</LOGIN>  
            <NAME>Jane Doe</NAME>   
        </EMPLOYEE>

        <EMPLOYEE type="Faculty">  
            <LOGIN>jdoe3</LOGIN>  
            <NAME>Joe Doe</NAME>  
        </EMPLOYEE> 
    </DEPARTMENT>    

    <DEPARTMENT name="Building and Construction Management" id="BCM">  
    </DEPARTMENT>

    <DEPARTMENT name="Computer Graphics Technology" id="CGT">  
    </DEPARTMENT>  
</SOT>

I understand that SOT is my root element and that departments are "children" of SOT and each department has multiple employee "children". The problem I run into is when I am trying to add a new employee to a certain department. When I try $departmentArray->item($i)->appendChild($employee); I get the Wrong Document Error.

I'm using this PHP code to try and append the child to the departmentNode

<?php

    //grab form data
    $username = $_POST['username'];
    $employeeName = $_POST['employeeName'];
    $department = $_POST['department'];

    //create new DOMDocument to hold current XML data
    $doc = new DOMDocument();
    $doc->load("test.xml");
    $xpath = new DOMXpath($doc);

    //create our new DOMDocument for combining the XML data
    $newDoc = new DOMDocument();
    $newDoc->preserveWhiteSpace = false;

    //create School of Tech Node and append to new doc
    $sotElement = $newDoc->createElement("SOT");
    $newDoc->appendChild($sotElement);
    $root = $newDoc->documentElement;

    //grab the department Nodes
    $departmentArray = $doc->getElementsByTagName("DEPARTMENT");

    //create a new employee and set attribute to faculty
    $employee = $newDoc->createElement("EMPLOYEE");
    $employee->setAttribute("type", "Faculty");

    //counters (might use them later for ->item(counter) function
    $indexCounter = 0;
    $i = 0;

    foreach($departmentArray as $departmentNode){
        if(strcmp($departmentNode->getAttribute('name'),$department) == 0){//check if departments match
            //create login element
            $loginNode = $newDoc->createElement("LOGIN");
            $loginNode->appendChild($newDoc->createTextNode($username));
            $employee->appendChild($loginNode);

            //create name node
            $nameNode = $newDoc->createElement("NAME");
            $nameNode->appendChild($newDoc->createTextNode($employeeName));
            $employee->appendChild($nameNode);

            //append employee onto department node
            //$departmentArray->item($i) = $doc->importNode($departmentArray->item($i), true);
            $departmentArray->item($i)->appendChild($employee);

            //set index of department array (possibly used for appending later)
            $indexCounter = $i;
        }
        $i++;
    }

    #######################################
    /*Write out data to XML file         */
    #######################################
    //$departmentArray = $doc->getElementsByTagName("DEPARTMENT");
    foreach($departmentArray as $departmentNode){
        $tempNode = $newDoc->importNode($departmentNode, true);
        /*if(strcmp($departmentNode->getAttribute('name'),$department) == 0){
            $sotElement->appendChild($employee);

        }*/
        $sotElement->appendChild($tempNode);
    }

    $newDoc->formatOutput = true;
    $newDoc->save("test2.xml");


?>

Any help explaining how to properly import all the department nodes to be able to append onto them would be greatly appreciated. I've tried using arrays.

Answer 1

You need to import any node to append it to another document:

$departmentArray->item($i)->appendChild( $doc->importNode( $employee, true ) );

Answer 2

I'm pretty sure that this is happening because you are trying to append an element from a different document into your output document.

I found this code in a comment on php's site for DOMNode::cloneNode which might be what you want.

<?php 
    $dom1->documentElement->appendChild( 
        $dom1->importNode( $dom2->documentElement, true )
    ); 
?>

Alternatively, you could look at exporting the node's XML and reimporting it into a DOMDocumentFragment, but I'd have to experiment to know for sure.