How to Properly Read Colon Tags (<p:id>) in google_merchant.xml in PHP

There is no easy way to read the <p:id> tag in xml. You should analyze the xml for a description of the xmlns:g="http://base.google.com/ns/1.0" space. If such a line is present, you can use xpath, and if not, there is an easier way to read such a tag.

Example xml:

<rss version="2.0" xmlns:g="http://base.google.com/ns/1.0">
  <channel>
    <title>Example of a store</title>
    <link>https://example.com</link>
    <description>Product feed</description>

    <item>
      <g:id>12345</g:id>
      <g:title>Product 1</g:title>
      <g:price>199.00 UAH</g:price>
    </item>

    <item>
      <g:id>12346</g:id>
      <g:title>Product 2</g:title>
      <g:price>299.00 UAH</g:price>
    </item>
  </channel>
</rss>

There is xmlns:g="http://base.google.com/ns/1.0", then we use xpath:

<?php
$xml = simplexml_load_string($xmlString);
// Register the namespace for working via xpath
$xml->registerXPathNamespace('g', 'http://base.google.com/ns/1.0');

// Move item to variable
$items = $xml->xpath('//item');
$result = [];

foreach ($items as $item) {
    $id    = (string) $item->xpath('g:id')[0];
    $title = (string) $item->xpath('g:title')[0];
    $price = (string) $item->xpath('g:price')[0];

    $result[] = [
        'id'    => $id,
        'title' => $title,
        'price' => $price,
    ];
}
var_dump($result);

The construction for accessing the required tag is defined as "$item->xpath('g:id')[0]".

When there is no xmlns:g="http://base.google.com/ns/1.0":

<?php
$xml = simplexml_load_string($xmlString);

$result = [];
foreach ($xml->channel->item as $item) {
    $result[] = [
        'id'    = (string) $item->{'g:id'};
        'title' = (string) $item->{'g:title'};
        'price' = (string) $item->{'g:price'};
    ];
    // OR
    // $result['id'] = (string)$item->children('g', true)->id;
}
var_dump($result);

You can use the $item->children('g', true)->id construction, or you can make it even shorter and more readable, for example, accessing the class via a property$item->{'g:id'}. This is the same as accessing a regular class.

<?php
$obj = new stdClass();
$obj->{'g:field'} = 'value';
var_dump($obj->{'g:field'});