Question

I have an XSLT 1.0 stylesheet that needs to either output the value of a specific element if that element exists, or output the string “NULL” if it doesn’t. How can I accomplish this?

Update

The document I’m working with looks something like this:

<kanjidic2>
    <header>
        <file_version>4</file_version>
        <database_version>2010-325</database_version>
        <date_of_creation>2010-11-20</date_of_creation>
    </header>
    <character>
        <literal>亜</literal>
        <codepoint>
            <cp_value cp_type="ucs">4e9c</cp_value>
            <cp_value cp_type="jis208">16-01</cp_value>
        </codepoint>
    </character>
    <character>
        <literal></literal>
        <codepoint>
            <cp_value cp_type="ucs">226F3</cp_value>
            <cp_value cp_type="jis213">2-12-48</cp_value>
        </codepoint>
    </character>
    <!-- Plus a few thousand more <character>s -->
</kanjidic2>

I’m writing an XSLT stylesheet to transform the above into a series of MySQL queries. Initially I wanted to output NULL if the character did not have a jis208 codepoint associated with it (hence my initial question), producing a query like this:

INSERT INTO `kanji` (`literal`, `ucs`, `jis208`, ...) VALUES ('亜', '4e9c', '16-01', ...);
INSERT INTO `kanji` (`literal`, `ucs`, `jis208`, ...) VALUES (', '226F3', NULL, ...);

I’ve since realised that I could make the XSLT simpler and produce a shorter query instead:

INSERT INTO `kanji` (`literal`, `ucs`, `jis208`, ...) VALUES ('亜', '4e9c', '16-01', ...);
INSERT INTO `kanji` (`literal`, `ucs`, `jis213`, ...) VALUES ('', '226F3', '2-12-48', ...);

The solution

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

    <template match="/">
        <apply-templates select="kanjidic2/character"/>
    </template>

    <template match="/kanjidic2/character">
        <text>INSERT INTO `kanji` (`literal`</text>
        <apply-templates select="codepoint/cp_value" mode="first"/>
        <text>) VALUES ('</text>
        <value-of select="literal"/>
        <apply-templates select="codepoint/cp_value" mode="second"/>
        <text>);&#10;</text>
    </template>

    <template match="/kanjidic2/character/codepoint/cp_value" mode="first">
        <text>, `</text>
        <value-of select="@cp_type"/>
        <text>`</text>
    </template>
    <template match="/kanjidic2/character/codepoint/cp_value" mode="second">
        <text>, '</text>
        <value-of select="."/>
        <text>'</text>
    </template>
</stylesheet>

I will mark Dimitre Novatchev’s answer as the correct one because it is the most succinct solution to my initial question.

Thanks for your help.

Answer 1

This transformation:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

 <xsl:param name="pDefault">NULL</xsl:param>
 <xsl:variable name="vDefault" select=
  "document('')/*/xsl:param[@name='pDefault']"/>

 <xsl:variable name="vDoc" select="/"/>

 <xsl:template match="/">
     <xsl:value-of select=
      "concat(//myelement[@myattribute='avalue'],
              $vDefault[not($vDoc/*/myelement[@myattribute='avalue'])]
              )"/>
 </xsl:template>
</xsl:stylesheet>

when applied on the provided XML document:

<mydoc>
    <myelement myattribute="avalue">Some text</myelement>
    <myelement myattribute="anothervalue">Some more text</myelement>
</mydoc>

produces the wanted, correct result:

Some text

When applied on this XML document:

<mydoc>
    <myelement myattribute="anothervalue">Some more text</myelement>
</mydoc>

again the wanted, correct result is produced:

NULL

Do note:

No conditional instruction (<xsl:if> or <xsl:choose>/<xsl:when>/<xsl:otherwise>) is used at all.