one-or-more()

Description

one-or-more() is a cardinality assertion function. It returns its argument unchanged when the sequence contains at least one item, and raises a dynamic error (FORG0004) if the sequence is empty. The function has no effect on sequences of two or more items.

Use one-or-more() to document and enforce the assumption that a set of nodes must not be empty — for example when deriving a result from a required configuration element, or when a stylesheet would produce meaningless output if no input nodes matched. Asserting this explicitly makes the stylesheet self-documenting and avoids silent failures.

Parameters

Return value

item()+ — the original sequence, unchanged. Raises FORG0004 if the sequence is empty.

Examples

Enforcing required configuration

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<config>
  <endpoint>https://api.example.com</endpoint>
  <endpoint>https://backup.example.com</endpoint>
</config>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/config">
    <urls>
      <xsl:for-each select="one-or-more(endpoint)">
        <url><xsl:value-of select="."/></url>
      </xsl:for-each>
    </urls>
  </xsl:template>
</xsl:stylesheet>

Output:

<urls>
  <url>https://api.example.com</url>
  <url>https://backup.example.com</url>
</urls>

Combining with string-join

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<tags>
  <tag>xslt</tag>
  <tag>xml</tag>
  <tag>xpath</tag>
</tags>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="text"/>

  <xsl:template match="/tags">
    <xsl:value-of select="string-join(one-or-more(tag), ', ')"/>
  </xsl:template>
</xsl:stylesheet>

Output:

xslt, xml, xpath

Notes

• The error code raised for an empty sequence is err:FORG0004.
• one-or-more() is the XPath equivalent of a database NOT NULL or EXISTS constraint applied at transformation time.
• When the stylesheet is intended to run against schema-validated documents, one-or-more() duplicates validation that the schema already performs; its value is greatest in schema-free environments.
• Use zero-or-one() when zero items is acceptable, and exactly-one() when the count must be precisely one.

See also

• exactly-one()
• zero-or-one()
• error()
• empty()