XSLT Reference

current-merge-key()

XSLT 3.0 node function

Returns the current merge key value inside an xsl:merge-action block.

Syntax

current-merge-key()

Description

current-merge-key() returns the value of the merge key for the current group being processed inside an xsl:merge-action block. When xsl:merge groups items from one or more sources by their computed key, current-merge-key() provides the key value shared by all items in the current group.

The returned value is an atomic value or a sequence of atomic values corresponding to the xsl:merge-key expressions declared in the merge sources. When multiple keys are declared (composite keys), the function returns a sequence of values — one per key component — in declaration order.

current-merge-key() is the merge equivalent of current-grouping-key() from xsl:for-each-group.

Parameters

This function takes no parameters.

Return value

xs:anyAtomicType+ — the merge key value(s) for the current group.

Examples

Displaying the merge key in output

Input XML (employees.xml):

<?xml version="1.0" encoding="UTF-8"?>
<employees>
  <emp dept="HR" name="Alice"/>
  <emp dept="IT" name="Bob"/>
  <emp dept="HR" name="Carol"/>
</employees>

Input XML (salaries.xml):

<?xml version="1.0" encoding="UTF-8"?>
<salaries>
  <sal dept="HR" amount="50000"/>
  <sal dept="IT" amount="75000"/>
</salaries>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="3.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/">
    <departments>
      <xsl:merge>
        <xsl:merge-source name="emps"
          select="doc('employees.xml')/employees/emp">
          <xsl:merge-key select="@dept" order="ascending"/>
        </xsl:merge-source>
        <xsl:merge-source name="sals"
          select="doc('salaries.xml')/salaries/sal">
          <xsl:merge-key select="@dept" order="ascending"/>
        </xsl:merge-source>
        <xsl:merge-action>
          <dept name="{current-merge-key()}">
            <xsl:for-each select="current-merge-group('emps')">
              <employee name="{@name}"/>
            </xsl:for-each>
            <xsl:for-each select="current-merge-group('sals')">
              <salary amount="{@amount}"/>
            </xsl:for-each>
          </dept>
        </xsl:merge-action>
      </xsl:merge>
    </departments>
  </xsl:template>
</xsl:stylesheet>

Output:

<departments>
  <dept name="HR">
    <employee name="Alice"/>
    <employee name="Carol"/>
    <salary amount="50000"/>
  </dept>
  <dept name="IT">
    <employee name="Bob"/>
    <salary amount="75000"/>
  </dept>
</departments>

Using the key in a conditional

Stylesheet snippet:

<xsl:merge-action>
  <xsl:if test="current-merge-key() = 'IT'">
    <tech-dept>
      <xsl:copy-of select="current-merge-group()"/>
    </tech-dept>
  </xsl:if>
</xsl:merge-action>

Notes

current-merge-key() is only valid inside the xsl:merge-action element.
For composite merge keys (multiple xsl:merge-key declarations), the function returns a sequence of atomic values in declaration order.
The key type is determined by the key expression; string, numeric, date, and other atomic types are all supported.
This function is the merge counterpart to current-grouping-key() used with xsl:for-each-group.