How does xsl:apply-templates work exactly and why does it write the name 2 times?

Question

I am using http://www.freeformatter.com/xsl-transformer.html. Here is my XML document:

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="listacd_es1.xslt"?>

<listacd>
    <artista>
        <nome>Stanley Jordan</nome>
        <albums>
            <album>
                <titolo>Magic Touch</titolo>
                <anno>1985</anno>
                <etichetta>Blue Note</etichetta>
            </album>
            <album>
                <titolo>Stolen Moments</titolo>
                <anno>1991</anno>
                <etichetta>Blue Note</etichetta>
            </album>
        </albums>
    </artista>
    <artista>
        <nome>Nick Drake</nome>
        <albums>
            <album>
                <titolo>Pink Moon</titolo>
                <anno>1972</anno>
                <etichetta>Island</etichetta>
            </album>
            <album>
                <titolo>Bryter Layter</titolo>
                <anno>1970</anno>
                <etichetta>Island</etichetta>
            </album>
            <album>
                <titolo>Five leaves left</titolo>
                <anno>1970</anno>
                <etichetta>Island</etichetta>
            </album>
        </albums>
    </artista>
    <artista>
        <nome>Jeff Buckley</nome>
        <albums>
            <album>
                <titolo>Grace</titolo>
                <anno>1994</anno>
                <etichetta>Columbia</etichetta>
            </album>
            <album>
                <titolo>Mistery white boy</titolo>
                <anno>2000</anno>
                <etichetta>Columbia</etichetta>
            </album>
        </albums>
    </artista>
    <artista>
        <nome>Joe Satriani</nome>
        <albums>
            <album>
                <titolo>Surfing with the alien</titolo>
                <anno>1987</anno>
                <etichetta>Epic</etichetta>
            </album>
            <album>
                <titolo>Not of this earth</titolo>
                <anno>1988</anno>
                <etichetta>Relativity</etichetta>
            </album>
        </albums>
    </artista>
</listacd>

Here is the XSLT file:

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

    <xsl:template match="/">
        <html>
            <xsl:apply-templates />
        </html>
    </xsl:template>

    <xsl:template match="artista">
        <b>
            <xsl:value-of select="nome" /> :
        </b>
        <xsl:apply-templates />
        <br />
        <br />
    </xsl:template>

    <xsl:template match="album">
        <xsl:value-of select="titolo" />
    </xsl:template>

</xsl:stylesheet>

And here is the result:

<?xml version="1.0" encoding="UTF-8"?>
<html>
  <b>Stanley Jordan :</b>
  Stanley JordanMagic TouchStolen Moments
  <br />
  <br />
  <b>Nick Drake :</b>
  Nick DrakePink MoonBryter LayterFive leaves left
  <br />
  <br />
  <b>Jeff Buckley :</b>
  Jeff BuckleyGraceMistery white boy
  <br />
  <br />
  <b>Joe Satriani :</b>
  Joe SatrianiSurfing with the alienNot of this earth
  <br />
  <br />
</html>

I know the result is not very pretty, I don't care much, but I don't understand why the name of the artist gets written 2 times. What do I have to do to make the name appear only once for every artist?

Part of your frustration with XSLT may be because of the freeformatter site that you are using. This provides a front-end to Saxon HE 9.4. However, when you get your code wrong (as you will), it doesn't give you all the diagnostics available from Saxon - it produces messages like "Unable to perform XSL transformation on your XML file. Failed to compile stylesheet. 1 error detected." without telling you what the errors are. I would recommend using KernowforSaxon (free) or oXygen (evaluation version available) for your learning platform. — Michael Kay, Aug 31 '13 at 19:15

score 2 · Accepted Answer · answered Aug 31 '13 at 13:52

This is partial to do with XSLT's built-in templates. These are templates that are used when it can't find a specific template to match a node in your stylesheet. The built-in templates will output the text of any text node is matches, otherwise it will simply skip over the node and carry on processing its children.

The issue arises because of this template

<xsl:template match="artista">
    <b>
        <xsl:value-of select="nome" /> :
    </b>
    <xsl:apply-templates />
    <br />
    <br />
</xsl:template>

In particular, the line <xsl:apply-templates />. This will look for templates that match the child nodes of the current artista element, which in your case are nome and albums, neither of which have matching templates in your XSLT. Thus the built-in templates apply, and in the case of the nome element, the text within it will be output, which is where the duplicate text comes from.

There are two possible, simple, solutions. Firstly, you can this template to your XSLT to match nome in your XSLT, and ignore it, to prevent the built-in template applying:

 <xsl:template match="nome" />

The second solution is to remove the current <xsl:value-of select="." /> from the artista template, and instead have a template matching nome that outputs the value there. Try this XSLT as an example of this

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
        <html>
            <xsl:apply-templates />
        </html>
    </xsl:template>

    <xsl:template match="artista">
        <xsl:apply-templates />
        <br />
        <br />
    </xsl:template>

    <xsl:template match="album">
        <xsl:value-of select="titolo" />
    </xsl:template>

    <xsl:template match="nome">
        <b>
            <xsl:value-of select="." /> :
        </b>
   </xsl:template>
</xsl:stylesheet>

I should avoid comments like "thank you" and the sort but I really have to thank you. I'm learning XSLT right now and I hate it. I hate the fact that the output depends on the processor and it's so verbose to me. Hope to learn it well in these days for my exam. — Ariel, Aug 31 '13 at 15:26
It's natural to be frustrated when you are having problems mastering the key concepts. You're clearly someone (like me) who doesn't like writing code until you fully understand what you are doing, and my advice would be to do a lot more reading - preferably a book (like mine, dare I say!) that goes into the concepts in some depth. You will find that XSLT, while different from languages you have encountered in the past, is uniquely well suited to the task it is designed for. — Michael Kay, Aug 31 '13 at 19:02

How does xsl:apply-templates work exactly and why does it write the name 2 times?

1 Answers1