How to copy parent nodes into current node of SimpleXml

Question

I want to split an XML into smaller chunks for further processing. To be self-sufficient for import, each chunk must contain all the information outside their scope.

Let's say I configure < ITEM > as the new, all-containing root:

<ROOT>
    <SUBROOT>
        <MOVEME>moveme</MOVEME>
        <ITEM>
            <AAA>111</AAA>
        </ITEM>
        <ITEM>
            <AAA>111</AAA>
        </ITEM>
    </SUBROOT>
</ROOT>

should become

<NEWROOT>
        <ITEM>
            <MOVEME>moveme</MOVEME>
            <AAA>111</AAA>
        </ITEM>
        <ITEM>
            <MOVEME>moveme</MOVEME>
            <AAA>111</AAA>
        </ITEM>
</NEWROOT>

What would be a high-performance-solution? Thanks!

Answer 1

Consider XSLT (sibling to XPath), the special-purpose language designed to transform XML files into other XML, HTML, even txt files. PHP can run XSLT 1.0 scripts with its php-xsl class (be sure to enable it in .ini file).

For small to medium-sized XML files, XSLT is a performant option as you even avoid foreach loops and if logic and rebuilding tree (i.e., importNode) at the application layer. Specifically, below XSLT parses down to ITEM level and maps over the parent SUBROOT needed item using XPath's ancestor::*. Adjust in script to actual node names.

XSLT (save as .xsl file, a special .xml file)

<xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
    <xsl:output method="xml" indent="yes" />

    <xsl:template match="/ROOT">   
        <NEWROOT>
            <xsl:apply-templates select="SUBROOT"/>
        </NEWROOT>
    </xsl:template>

    <xsl:template match="SUBROOT">      
        <xsl:apply-templates select="ITEM"/>
    </xsl:template>

    <xsl:template match="ITEM">
        <xsl:copy>
            <xsl:copy-of select="ancestor::SUBROOT/MOVEME" />
            <xsl:copy-of select="*"/>
        </xsl:copy>
    </xsl:template>
</xsl:transform>

PHP

# LOAD XML AND XSL FILES
$xml = new DOMDocument;
$xml->load('/path/to/input.xml');

$xsl = new DOMDocument;
$xsl->load('/path/to/xslt_script.xsl');

// CONFIGURE TRANSFORMER
$proc = new XSLTProcessor;
$proc->importStyleSheet($xsl);

// RUN TRANSFORMATION
$newXML = new DOMDocument;
$newXML = $proc->transformToXML($xml);

// OUTPUT NEW XML
echo $newXML;

// SAVE NEW DOM TREE TO FILE
file_put_contents('/path/to/output.xml', $newXML);

XSLT Demo