Question

I have a problem, I can’t figure out the XSL code for “transforming” an xml into another xml

This is the input xml:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<output>
  <cars>
    <car>
      <id>1</id>
      <brand>Audi</brand>
      <type>A3</type>
      <license>B-01-TST</license>
    </car>
    <car>
      <id>2</id>
      <brand>Volkwagen</brand>
      <type>Golf</type>
      <license>IF-02-TST</license>
    </car>
  </cars>
  <distances>
    <distance>
      <id_car>1</id_car>
      <date>20110901</date>
      <distance>111</distance>
    </distance>
    <distance>
      <id_car>1</id_car>
      <date>20110902</date>
      <distance>23</distance>
    </distance>
    <distance>
      <id_car>1</id_car>
      <date>20110903</date>
      <distance>0</distance>
    </distance>
    <distance>
      <id_car>2</id_car>
      <date>20110901</date>
      <distance>92</distance>
    </distance>
    <distance>
      <id_car>2</id_car>
      <date>20110902</date>
      <distance>87</distance>
    </distance>
    <distance>
      <id_car>2</id_car>
      <date>20110903</date>
      <distance>132</distance>
    </distance>
  </distances>
</output>

This is the output xml:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<cars>
  <car>
    <id>1</id> 
    <brand>Audi</brand>
    <type>A3</type>
    <license>B-01-TST</license>
    <distances>
      <distance day="20110901">111</distance>
      <distance day="20110902">23</distance>
      <distance day="20110903">0</distance>
    </distances>
  </car>
  <car>
    <id>2</id>
    <brand>Volkwagen</brand>
    <type>Golf</type>
    <license>IF-02-TST</license>
    <distances>
      <distance day="20110901">92</distance>
      <distance day="20110902">87</distance>
      <distance day="20110903">132</distance>
    </distances>
  </car>
</cars>

and the end for the element cars at the end I forgot.

Thank you.

Answer 1

This is actually quite easy to do using XSLT; the hardest part is the use of keys. Here’s the code you need:

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:key name="distances" match="distance" use="id_car" />

  <xsl:template match="output">
    <xsl:apply-templates select="cars" />
  </xsl:template>

  <xsl:template match="car">
    <xsl:copy>
      <xsl:apply-templates />
      <distances>
        <xsl:apply-templates select="key('distances', id)" />
      </distances>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="distance">
    <distance day="{date}">
      <xsl:value-of select="distance" />
    </distance>
  </xsl:template>

  <xsl:template match="@* | node()">
    <xsl:copy>
      <xsl:apply-templates select="@* | node()"/>
    </xsl:copy>
  </xsl:template>
</xsl:stylesheet>

The key essentially allows you to use the key function to get a list of all distance elements with an id_car of a given value.

The first template handles the root and outputs only the cars element.

The second template handles any car elements, outputting them exactly as they are, but adding in a distances element, and with the use of the key function, processes any distance elements with the correct ID.

The last template is the ‘identity’ template that copies any elements that we haven’t already accounted for exactly as they are; this handles the brand, type, license elements, and so on.