Retrieving a subset of XML nodes with PHP

Question

Using PHP, how do I get an entire subset of nodes from an XML document? I can retrieve something like:

<?xml version="1.0" encoding="utf-8"?>
<people>
  <certain>
    <name>Jane Doe</name>
    <age>21</age>
  </certain>
  <certain>
  <certain>
    <name>John Smith</name>
    <age>34</age>
  </certain>
</people>

But what if I only want to return the child nodes of like this?

  <certain>
    <name>Jane Doe</name>
    <age>21</age>
  </certain>
  <certain>
  <certain>
    <name>John Smith</name>
    <age>34</age>
  </certain>

EDIT: I'm trying to get a subset of XML and pass that directly, not an object like simplexml would give me. I am basically trying to get PHP to do what .NET's OuterXml does... return literally the above subset of XML as is... no interpreting or converting or creating a new XML file or anything... just extract those nodes in situ and pass them on. Am I going to have to get the XML file, parse out what I need and then rebuild it as a new XML file? If so then I need to get rid of the <?xml version="1.0" encoding="utf-8"?> bit... ugh.

Answer 1

See http://www.php.net/manual/en/domdocument.getelementsbytagname.php

Answer 2

You could use DOMDocument.GetElementsByTagName or you could:

Use XPath?

<?php
$xml = simplexml_load_file("test.xml");

$result = $xml->xpath("//certain");

print_r($result);
?>

Answer 3

The answer would be to use XPath.

$people = simplexml_load_string(
    '<?xml version="1.0" encoding="utf-8"?>
    <people>
      <certain>
        <name>Jane Doe</name>
        <age>21</age>
      </certain>
      <certain>
        <name>John Smith</name>
        <age>34</age>
      </certain>
    </people>'
);

// get all <certain/> nodes
$people->xpath('//certain');

// get all <certain/> nodes whose <name/> is "John Smith"
print_r($people->xpath('//certain[name = "John Smith"]'));

// get all <certain/> nodes whose <age/> child's value is greater than 21
print_r($people->xpath('//certain[age > 21]'));

---

Take 2

So apparently you want to copy some nodes from a document into another document? SimpleXML doesn't support that. DOM has methods for that but they're kind of annoying to use. Which one are you using? Here's what I use: SimpleDOM. In fact, it's really SimpleXML augmented with DOM's methods.

include 'SimpleDOM.php';
$results = simpledom_load_string('<results/>');

foreach ($people->xpath('//certain') as $certain)
{
    $results->appendChild($certain);
}

That routine finds all <certain/> node via XPath, then appends them to the new document.

Answer 4

The answer turned out to be a combination of the xpath suggestion and outputting with asXML().

Using the example given by Josh Davis:

$people = simplexml_load_string(
      <?xml version="1.0" encoding="utf-8"?>
        <people>
          <certain>
            <name>Jane Doe</name>
            <age>21</age>
          </certain>
          <certain>
            <name>John Smith</name>
            <age>34</age>
          </certain>
        </people>'
    );

    // get all <certain/> nodes
    $nodes = $people->xpath('/people/certain');

    foreach ( $nodes as $node ) {
      $result .= $node->asXML()."\n";
    }
    echo $result;