PHP XML Feed - How to print value of specific child within parent. Parent has same name as other nodes

Question

I'm trying to figure out how to grab and print a specific IDValue in the code below, but the number and order of ProductIdentifier nodes varies per Product, so I can't always get the correct value by using:

<?php print $productXML[0]->ProductIdentifier[2]->IDValue; ?>

Is there a way to do something like: "If ProductIDType is 03, then print IDValue of that child node"?

<Product>
  <RecordReference>PublishingGroup</RecordReference>
  <NotificationType>03</NotificationType>
  <RecordSourceType>01</RecordSourceType>
  <RecordSourceName>Publishing Group</RecordSourceName>
  <ProductIdentifier>
    <ProductIDType>01</ProductIDType>
    <IDTypeName>ID</IDTypeName>
    <IDValue>28831</IDValue>
  </ProductIdentifier>
  <ProductIdentifier>
    <ProductIDType>02</ProductIDType>
    <IDValue>0163668869</IDValue>
  </ProductIdentifier>
  <ProductIdentifier>
    <ProductIDType>03</ProductIDType>
    <IDValue>9180763668860</IDValue>
  </ProductIdentifier>
  <ProductIdentifier>
    <ProductIDType>15</ProductIDType>
    <IDValue>9180763668860</IDValue>
  </ProductIdentifier>

UPDATE:

I tried using xpath, as suggested by the very helpful comments below, but it simply returned "Array" when trying to print via php. I tried several ways to fix it, taking note from other questions here on SO and on W3C docs and other places, but no luck.

Here's what I ultimately ended up doing:

<?php
  foreach($productXML[0]->ProductIdentifier as $value) {
    if($value->ProductIDType=='03')
      {
      print ($value->IDValue);
      }
  }
?>

Not the most elegant of solutions, but it outputs the proper value now.

Answer 1

First of all there is the operation to extract the node (-value) from the document. As the whole document is kind of a tree of nodes, running an xpath query helps a lot in getting things done here, especially as you have a condition to obtain a specific node (-value).

However using Xpath also introduces a new language. So there is the xpath-part and there is also the PHP-part. Let's do it Xpath only first (like with pseudo-code). You want:

Is there a way to do something like: "If ProductIDType is 03, then print IDValue of that child node"?

As with every programming question that is asking for possibilities, there is the answer "most certainly yes" ;) - so here it is:

//*[ProductIDType = "03"]/IDValue

This is pure Xpath and reads as the following: Give me the element named IDValue that is a child-node of any element (* is a wildcard for any name) within the whole document (// is root or deeper) which has another child-node named ProductIDType with the string-value "03" (so called predicate).

In your case you know the name of the parent element already, so instead of * you can use the element-name directly (ProductIdentifier). And you also can say what the parent-element name is (Product), so you can use it as well (this makes things more specific, so you show that you've understood exactly what you're looking for):

//Product/ProductIdentifier[ProductIDType = "03"]/IDValue

Many words for some more or less simple pseudo-code that on it's own doesn't run. But it's worth to understand as it's a valid Xpath expression.

Now back to PHP and SimpleXML. As SimpleXML can only query Xpath expressions, it always returns an array (and not a single value). But this is no problem. If you're looking for a single value, it's the first member (value) of the array. Which is accessed by [0] on zero-indexed arrays (which are returned by SimpleXMLElement::xpath() unless there was an error (or there was no element at all)).

In case of your XML fragment:

<?php

$buffer = <<<XML
<Product>
  <RecordReference>PublishingGroup</RecordReference>
  <NotificationType>03</NotificationType>
  <RecordSourceType>01</RecordSourceType>
  <RecordSourceName>Publishing Group</RecordSourceName>
  <ProductIdentifier>
    <ProductIDType>01</ProductIDType>
    <IDTypeName>ID</IDTypeName>
    <IDValue>28831</IDValue>
  </ProductIdentifier>
  <ProductIdentifier>
    <ProductIDType>02</ProductIDType>
    <IDValue>0163668869</IDValue>
  </ProductIdentifier>
  <ProductIdentifier>
    <ProductIDType>03</ProductIDType>
    <IDValue>9180763668860</IDValue>
  </ProductIdentifier>
  <ProductIdentifier>
    <ProductIDType>15</ProductIDType>
    <IDValue>9180763668860</IDValue>
  </ProductIdentifier>
</Product>
XML;

There is an result for the xpath query discussed so far:

$xml = simplexml_load_string($buffer);

$first = $xml->xpath('//Product/ProductIdentifier[ProductIDType = "03"]/IDValue')[0];

echo $first, "\n"; # prints: "9180763668860\n"

This is also the example (see it in full as online-demo).

So until this very line, this should show the whole picture unless I've rushed too much at the end. Please leave some feedback if it helped you and what is missing from your point of view.