Check if a string is null or empty in XSLT

Question

How can I check if a value is null or empty with XSL?

For example, if categoryName is empty? I\'m using a when choosing construct.

For

Answer 1

How can I check if a value is null or empty with XSL?

For example, if categoryName is empty?

This is probably the simplest XPath expression (the one in accepted answer provides a test for the opposite, and would be longer, if negated):

not(string(categoryName))

Explanation:

The argument to the not() function above is false() exactly when there is no categoryName child ("null") of the context item, or the (single such) categoryName child has string value -- the empty string.

I'm using a when choosing construct.

For example:

<xsl:choose>
    <xsl:when test="categoryName !=null">
        <xsl:value-of select="categoryName " />
    </xsl:when>
    <xsl:otherwise>
        <xsl:value-of select="other" />
    </xsl:otherwise>
</xsl:choose>

In XSLT 2.0 use:

<xsl:copy-of select="concat(categoryName,  $vOther[not(string(current()/categoryName))])"/>

Here is a complete example:

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
     <xsl:output omit-xml-declaration="yes" indent="yes"/>

 <xsl:variable name="vOther" select="'Other'"/>

 <xsl:template match="/">
  <xsl:copy-of select="concat(categoryName,$vOther[not(string(current()/categoryName))])"/>
 </xsl:template>
</xsl:stylesheet>

When this transformation is applied on the following XML document:

<categoryName>X</categoryName>

the wanted, correct result is produced:

X

When applied on this XML document:

<categoryName></categoryName>

or on this:

<categoryName/>

or on this

<somethingElse>Y</somethingElse>

the correct result is produced:

Other

---

Similarly, use this XSLT 1.0 transformation:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>

 <xsl:variable name="vOther" select="'Other'"/>

  <xsl:template match="/">
    <xsl:copy-of select=
    "concat(categoryName,  substring($vOther, 1 div not(string(categoryName))))"/>
  </xsl:template>
</xsl:stylesheet>

Do note: No conditionals are used at all. Learn more about the importance of avoiding conditional constructs in this nice Pluralsight course:

"Tactical Design Patterns in .NET: Control Flow"

Answer 2

If there is a possibility that the element does not exist in the XML I would test both that the element is present and that the string-length is greater than zero:

<xsl:choose>
    <xsl:when test="categoryName and string-length(categoryName) &gt; 0">
        <xsl:value-of select="categoryName " />
    </xsl:when>
    <xsl:otherwise>
        <xsl:value-of select="other" />
    </xsl:otherwise>
</xsl:choose>

Answer 3

test="categoryName != ''"

Edit: This covers the most likely interpretation, in my opinion, of "[not] null or empty" as inferred from the question, including it's pseudo-code and my own early experience with XSLT. I.e., "What is the equivalent of the following Java?":

!(categoryName == null || categoryName.equals(""))

For more details e.g., distinctly identifying null vs. empty, see johnvey's answer below and/or the XSLT 'fiddle' I've adapted from that answer, which includes the option in Michael Kay's comment as well as the sixth possible interpretation.

Answer 4

What about?

test="not(normalize-space(categoryName)='')"

Answer 5

Absent of any other information, I'll assume the following XML:

<group>
    <item>
        <id>item 1</id>
        <CategoryName>blue</CategoryName>
    </item>
    <item>
        <id>item 2</id>
        <CategoryName></CategoryName>
    </item>
    <item>
        <id>item 3</id>
    </item>
    ...
</group>

A sample use case would look like:

<xsl:for-each select="/group/item">
    <xsl:if test="CategoryName">
        <!-- will be instantiated for item #1 and item #2 -->
    </xsl:if>
    <xsl:if test="not(CategoryName)">
        <!-- will be instantiated for item #3 -->
    </xsl:if>
    <xsl:if test="CategoryName != ''">
        <!-- will be instantiated for item #1 -->
    </xsl:if>
    <xsl:if test="CategoryName = ''">
        <!-- will be instantiated for item #2 -->
    </xsl:if>
</xsl:for-each>

Answer 6

If a node has no value available in the input xml like below xpath,

<node>
    <ErrorCode/>
</node>

string() function converts into empty value. So this works fine:

string(/Node/ErrorCode) =''