如何在没有PHP数据的情况下克隆不同的XML结构？

Question

I have an XML document that looks like this:

<root>

  <node/>

  <node>
    <sub>more</sub>
  </node>

  <node>
    <sub>another</sub>
  </node>

  <node>value</node>

</root>

Here's my pseudo-code:

import xml.

create empty-xml.

foreach child of imported-xml-root-node,

    recursively clone node structure without data.

    if clone does not match one already in empty-xml,
        then add clone to empty-xml.

I'm trying to get a result that looks like this:

<root>

  <node/>

  <node>
    <sub/>
  </node>

</root>

Note that my piddly example data is only 3 nodes deep. In production, there will be an unknown number of descendants, so an acceptable answer needs to handle variable node depths.

---

Failed Approaches

I have reviewed The DOMNode class which has a cloneNode method with a recursive option that I would like to use, although it would take some extra work to purge the data. But while the class contains a hasChildNodes function which returns a boolean, I can't find a way to actually return the collection of children.

$doc = new DOMDocument();
$doc->loadXML($xml);

$root_node = $doc->documentElement;

if ( $root_node->hasChildNodes() ) {

  // looking for something like this:
  // foreach ($root_node->children() as $child)
  //   $doppel = $child->cloneNode(true);

}

---

Secondly, I have tried my hand with the The SimpleXMLElement class which does have an awesome children method. Although it's lacking the recursive option, I built a simple function to surmount that. But the class is missing a clone/copyNode method, and my function is bloating into something nasty to compensate. Now I'm considering combining usage of the two classes so I've got access to both SimpleXMLElement::children and DOMDocument::cloneNode, but I can tell this is not going cleanly and surely this problem can be solved better.

$sxe = new SimpleXMLElement($xml);

$indentation = 0;

function getNamesRecursive( $xml, &$indentation )
{
    $indentation++;
    foreach($xml->children() as $child) {
        for($i=0;$i<$indentation;$i++)
          echo "\t";
        echo $child->getName() . "
";
        getNamesRecursive($child,$indentation);
    }
    $indentation--;
}

getNamesRecursive($sxe,$indentation);

Answer 1

well here's my stinky solution. suggestions for improvements or completely new better answers are still very welcome.

$xml = '
<root>
  <node/>
  <node>
    <sub>more</sub>
  </node>
  <node>
    <sub>another</sub>
  </node>
  <node>value</node>
</root>
';
$doc = new DOMDocument();
$doc->loadXML($xml);


// clone without data
$empty_xml = new DOMDocument();
$empty_xml->appendChild($empty_xml->importNode($doc->documentElement));
function clone_without_data(&$orig, &$clone, &$clonedoc){
  foreach ($orig->childNodes as $child){
    if(get_class($child) === "DOMElement")
      $new_node = $clone->appendChild($clonedoc->importNode($child));
    if($child->hasChildNodes())
      clone_without_data($child,$new_node,$clonedoc);
  }
}
clone_without_data($doc->documentElement, $empty_xml->documentElement, $empty_xml);


// remove all duplicates
$distinct_structure = new DOMDocument();
$distinct_structure->appendChild($distinct_structure->importNode($doc->documentElement));
foreach ($empty_xml->documentElement->childNodes as $child){
  $match = false;
  foreach ($distinct_structure->documentElement->childNodes as $i => $element){
    if ($distinct_structure->saveXML($element) === $empty_xml->saveXML($child)) {
      $match = true;
      break;
    }
  }
  if (!$match)
    $distinct_structure->documentElement->appendChild($distinct_structure->importNode($child,true));
}
$distinct_structure->formatOutput = true;
echo $distinct_structure->saveXML();

Which results in this output:

<?xml version="1.0"?>
<root>
  <node/>
  <node>
    <sub/>
  </node>
</root>