Simplexml Object Node Iteration - php

Question

I have an XML file that I'm parsing with PHP's Simplexml, but I'm having an issue with an iteration through nodes.
The XML:
<channel>
<item>
<title>Title1</title>
<category>Cat1</category>
</item>
<item>
<title>Title2</title>
<category>Cat1</category>
</item>
<item>
<title>Title3</title>
<category>Cat2</category>
</item>
</channel>
My counting function:
public function cat_count($cat) {
$count = 0;
$items = $this->xml->channel->item;
$size = count($items);
for ($i=0; $i<$size; $i++) {
if ($items[$i]->category == $cat) {
$count++;
}
}
return $count;
}
Am I overlooking an error in my code, or is there another preferred method for iterating through the nodes? I've also used a foreach and while statement with no luck, so I'm at a loss. Any suggestions?
EDIT: while using the xpath method below, I noticed that using
foreach ($this->xml->channel->item as $item) {
echo $item->category;
}
will print all the category name, but, using
foreach ($this->xml->channel->item as $item) {
if ($item->category == $cat) {
echo $item->category;
}
}
will only print one instance of the doubled categories. Even when I have copy and pasted the lines, only one shows. Does this mean the XML structure could be invalid somehow?

Answer 1

An easy way to count elements with a given name in an XML file is to use xpath. Try this:
private function categoryCount($categoryName) {
$categoryName = $this->sanitize($categoryName); // easy xpath injection protection
return count($this->xml->xpath("//item[category='$categoryName']"));
}
The sanitize() function should remove single and double quotes in your $categoryName to prevent xpath injection. To also get queries for a category name containing quotes to work, you need to build your xpath query string depending on wheather it contains single or double quotes:
// xpath in case of single quotes in category name
$xpath = '//item[category="' . $categoryName . '"]';
// xpath in case of double quotes in category name
$xpath = "//item[category='" . $categoryName . "']";
If you don't have full control over the xml data (for example if is created out of user generated content), you should take this into account. Unfortunately there is no simple way to this in php like parametrized queries.
see here for the php xpath function docs: http://php.net/manual/en/simplexmlelement.xpath.php
see here for an xpath reference: http://www.w3schools.com/xpath/xpath_syntax.asp