Testing if XML element exists in XSLT

Question

This is probably a really easy answer, but for the life of me I can't figure it out.

I want to display certain content depending on which child element is being displayed but I don't know how to test for the element I want. I want to see if the start, stop, and note elements exist

<xsl:template match="protocol[@id=$protocolNumber]">
<h4><xsl:value-of select="$sectionNumber"/>.<xsl:value-of select="@id"/>&nbsp;<xsl:value-of select="@title"/></h4>
<p>
     <xsl:for-each select="child::*"> 
        <xsl:choose>
            <xsl:when test="start">
                <span id="start"><xsl:value-of select="start[@level]" /></span>
            </xsl:when>
            <xsl:when test="stop">
                <span id="stop"><xsl:value-of select="stop[@level]" /></span>
            </xsl:when>
            <xsl:when test="note">
                <span id="note"><xsl:value-of select="note[@title]" />:&nbsp;<xsl:value-of select="note/text()" /></span>
            </xsl:when>
            <xsl:otherwise>
             <xsl:value-of select="text()"/><br/>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:for-each>
</p>

<protocol id="2" title="Post-Conversion Of VF / VT">
   <note title="criteria">Post-conversion treatment of VF or VT should only be started if the patient has regained a pulse of adequate rate, and has a supraventricular rhythm.  If not, refer to other cardiac protocols as appropriate.  All antiarrhythmics are  contraindicated if ventricular escape rhythm is present.</note>
   <start level="All Levels"/>
   <step>Routine medical care.</step>
   <stop level="EMT"/>
   <stop level="EMT-I"/>
   <start level="EMT-CC &amp; P"/>
   <step>
    If conversion results from defibrillation without any drug therapy:<br/><br/>
    Amiodarone (Cordarone) 150 mg IV/IO Slow IV
   </step>
   <step>If Amiodarone was the drug resulting in conversion from VF/VT, no additional antiarrhythmic is required.</step>
   <step>
    If Lidocaine (Xylocaine) was the drug resulting in conversion from VF/VT:<br/><br/>
    Repeat Lidocaine bolus 0.75 mg/kg IV/IO every 10 minutes up to a total cumulative dose of 3 mg/kg.
   </step>
   <step>If more than above listed doses are needed because of length of transport time, contact Medical Control.</step>
  </protocol>

Answer 1

I'm not sure what you're trying to do, but I see a few likely problems:

First, you use <xsl:choose /> construct, which means that if you have "start" no "stop" and "note" will be handled (you may want to use plain <xsl:if />s instead, or whatever the desired logic suggests.

Second, when you use start@level, I believe you really mean start/@level.

Answer 2

Inside xsl:for-each, the context element . is the current element you're iterating over. When you write an XPath expression like start, it really is the same as child::start. What you want here is self::start. Also note that child::* is redundant - just * will do.

A more idiomatic XSLT approach is to refactor this into a separate set of templates, and let pattern matching do its job:

<xsl:template match="protocol[@id=$protocolNumber]">
  <h4><xsl:value-of select="$sectionNumber"/>.<xsl:value-of select="@id"/>&nbsp;<xsl:value-of select="@title"/></h4>
  <p>
    <!-- Applies templates to all child elements -->
    <xsl:apply-templates/>
  </p>
</xsl:template>

<xsl:template match="protocol/start">
  <span id="start"><xsl:value-of select="start/@level" /></span>
</xsl:template>

<xsl:template match="protocol/stop">
  <span id="stop"><xsl:value-of select="stop/@level" /></span>
</xsl:template>

<xsl:template match="protocol/note">
  <span id="note"><xsl:value-of select="note/@title" />:&nbsp;<xsl:value-of select="note" /></span>
</xsl:template>

<xsl:template match="protocol/*">
   <xsl:value-of select="."/>
</xsl:template>