Change previous sibling value with php xPath - php

Question

I have a situation that's driving me crazy. I want to search my feed for an element with a certain value (deriving from an array) and if that value is found, change the value of it's previous sibling element.
My feed looks like this
<products>
<product>
<properties>
<property name="category">
<value>Fruits</value>
</property>
<property name="item">
<value>Banana</value>
</property>
</properties>
</product>
<product>
<properties>
<property name="category">
<value>Fruits</value>
</property>
<property name="item">
<value>Apple</value>
</property>
</properties>
</product>
<product>
<properties>
<property name="category">
<value>Fruits</value>
</property>
<property name="item">
<value>Carrot</value>
</property>
</properties>
</product>
</products>
As you can see, there can be some errors in the feed. For these instances i made an array with the appropriate value, like so:
$replacements = Array(
"Carrot" => "Vegetable"
);
Now i thought to select every property with the attribute item that has the value as in $replacements's key, then select the previous sibling element with the attribute category and change this value with the matching $replacements's value.
I came up with this, but that only gives me a white screen with no output at all
$xml_src = 'feed.xml';
$document = new DOMDocument();
$document->load($xml_src);
$xpath = new DOMXpath($document);
$query = '//property[#name = "item"]';
$entries = $xpath->query($query);
foreach ($entries as $entry) {
if(array_key_exists($entry->nodeValue,$replacements)){
$entry->previousSibling->previousSibling->nodeValue = $replacements[$entries->nodeValue];
}
}
But i don't understand why it doesn't output anything

Answer 1

There's a couple things a bit off here:
array_key_exists($entry->nodeValue,$replacements)
The nodeValue is going to contain all the text content within the property element and its descendants - including newlines and spaces.
... = $replacements[$entries->nodeValue];
You're likely looking for $replacements[$entry->nodeValue] but again you've got the same problem as above with the white space. Not only that but you'd be replacing the entirety of the prior property's nodeValue with text so:
<property name="category">
<value>Fruits</value>
</property>
would become just:
<property name="category">Vegetable</property>
To fix it all up I'd recommend adjusting the query, as well as how you're addressing the target value to replace in order to get rid of the ->previousSibling->previousSibling chaining and be a bit more explicit.
Example:
foreach ($xpath->query('//property[#name="item"]/value') as $node) {
if (array_key_exists(trim($node->textContent), $replacements)) {
$target = $xpath->query(
'preceding-sibling::property/value/text()',
$node->parentNode
)->item(0);
$target->parentNode->replaceChild(
$dom->createTextNode($replacements[trim($node->textContent)]),
$target
);
}
}
echo $dom->saveXML();
Output:
...
<product>
<properties>
<property name="category">
<value>Vegetable</value>
</property>
<property name="item">
<value>Carrot</value>
</property>
</properties>
</product>
</products>

Answer 2

You need to return Value and in order to do that you need to correct your query to this
$query = '//property[#name = "item"]/value';

Answer 3

You can try to use the complete path, so:
$query = '//products/product/properties/property[#name = "item"]/value';
$entries = $xpath->query($query);
foreach ($entries as $entry) {
if(array_key_exists($entry->nodeValue,$replacements)){
$entry->previousSibling->previousSibling->nodeValue = $replacements[$entries->nodeValue];
}
}
Also, you can try to use a context (Manual):
$context = $document->getElementsByTagName('products')->item(0);
$query = './/property[#name = "item"]/value';//add a '.' before the query to make it relative to the context
$entries = $xpath->query($query, $context);
foreach ($entries as $entry) {
if(array_key_exists($entry->nodeValue,$replacements)){
$entry->previousSibling->previousSibling->nodeValue = $replacements[$entries->nodeValue];
}
}
Both solutions work for me in very similar situations.