Cannot add child to XML node in PHP - php

Question

I am trying to add a child note to an XML file using PHP. I have used the same method about 5 times before and each one works as expected, however this method is using a different XML structure on a new file (which I think might be part of the problem).
The method causing me the problem is this:
function addCourseToProject($name, $project){
$projects = self::getRoles();
$theProject = $projects->xpath('project[name = "'.$project.'"]');
echo $theProject->name;
$theCourses = $theProject[0]->courses->addchild("course", $name);
$projects->asXml("projects.xml");
}
The XML file looks like this:
<projects>
<project>
<name>Alpha</name>
<courses>
<course>Beta</course>
<course>Charlie</course>
</courses>
</project>
</project>
And getRoles() looks like this:
function getRoles(){
$roles = simplexml_load_file("projects.xml") or die("ERROR: Unable to read file");
return $roles;
}
I'm at a loss here, I have no idea why this is different from the other adding functions (see below).
Should you need it, here is an example of what my other methods look like:
function addModule($courseName, $name, $link){
$xml = self::getXml();#get the xml file
$course = $xml->xpath('course[name = "'.$courseName.'"]');
$module = $course[0]->addChild("module");
$module->addChild("name", $name);
$module->addChild("link", $link);
$xml->asXml("data.xml");
echo self::toJSON($course);
}
and the getXML() method:
function getXml(){
$xml=simplexml_load_file("data.xml") or die("ERROR: Unable to read file");
return $xml;
}

Answer 1

Turned out that the problem was caused by the fact that <project> element is nested within the XML document. You can use descendant-or-self axis (// for the abbreviated syntax) to get nested element like so :
$theProject = $projects->xpath('//project[name = "'.$project.'"]');
or specify the complete path :
$theProject = $projects->xpath('/projects/project[name = "'.$project.'"]');