We are using Saxon EE 12.x to transform large (multi-GB) XML files into a much smaller internal XML-structure. We would like to reduce memory-consumption and burst-streaming on each <Document>-node seems to be a prefect match for our application. It works - but we struggle with some seemingly simple construct: How to get the information like the <PrintDate> of the <ExportHeader>-Branch and add it to each output <Doc>-element as an attribute in a streaming-mode?
The source XML contains 1000s of <Document>-nodes, each <Document>-node contains 1000s of lines of XML, the <ExportHeader>-node is very small, just contains some Meta-info. A reduced example source-XML looks like this:
<Export>
<ExportHeader>
<PrintDate>2024-12-24</PrintDate>
</ExportHeader>
<ExportContent>
<Document>
<LotsOfXml></LotsOfXml>
</Document>
<Document>
<LotsOfXml></LotsOfXml>
</Document>
<Document>
<LotsOfXml></LotsOfXml>
</Document>
</ExportContent>
</Export>
our target XML should look like this:
<Exp>
<Doc PrintDate="???">
<LotsOfTransformedXML></LotsOfTransformedXML>
</Doc>
<Doc PrintDate="???">
<LotsOfTransformedXML></LotsOfTransformedXML>
</Doc>
<Doc PrintDate="???">
<LotsOfTransformedXML></LotsOfTransformedXML>
</Doc>
</Exp>
A very simple XSLT would look like this, but we don't know a way to get the <PrintDate> into the <Doc>-node attribute without breaking streamability... Can an <xsl:accumulator> be used to store/get the value, if yes, how?
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:math="http://www.w3.org/2005/xpath-functions/math"
exclude-result-prefixes="xs math"
version="3.0">
<xsl:mode streamable="yes" on-no-match="shallow-skip"/>
<xsl:mode name="insideDoc" streamable="no" on-no-match="shallow-copy "/>
<xsl:template match="Export">
<xsl:element name="Exp">
<xsl:apply-templates></xsl:apply-templates>
</xsl:element>
</xsl:template>
<xsl:template match="PrintDate">
<!-- how to keep/store this PrintDate, so we can add it to the Doc elements as an attribute later... -->
</xsl:template>
<xsl:template match="ExportContent">
<xsl:apply-templates select="copy-of(Document)" mode="insideDoc"/>
</xsl:template>
<xsl:template match="Document" mode="insideDoc">
<xsl:element name="Doc">
<xsl:attribute name="PrintDate" select="'???'"/>
<xsl:apply-templates select="*" mode="insideDoc"/>
</xsl:element>
</xsl:template>
<xsl:template match="LotsOfXml" mode="insideDoc">
<xsl:element name="LotsOfTransformedXML">
</xsl:element>
</xsl:template>
</xsl:stylesheet>
Use a capturing accumulator https://www.saxonica.com/html/documentation12/extensions/attributes/capture.html e.g.
<xsl:mode streamable="yes" on-no-match="shallow-skip" use-accumulators="PrintDate"/>
<xsl:accumulator name="PrintDate" as="element(PrintDate)*" initial-value="()" streamable="yes">
<xsl:accumulator-rule saxon:capture="yes" match="ExportHeader/PrintDate"
phase="end" select="$value, ."/>
</xsl:accumulator>
Declare xmlns:saxon="http://saxon.sf.net/".
...
<xsl:attribute name="PrintDate" select="accumulator-before('PrintDate')"/>