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XSLT supports conditional statements. It is based on a very special construct which includes three XSL tags: xsl:choose, xsl:where, and xsl:otherwise. The <xsl:choose> and </xsl:choose> are the outer tag pair. They embrace the where tags, <xsl:where> and </xsl:where>, followed by the pair <xsl:otherwise> and </xsl:otherwise>.
Let's see an example. Suppose we want to color numbers in a report according to their magnitude. We want them red if they are below a certain limit, green otherwise. The following section chooses the style attribute for one <td> cell in a table. The XML data we compare is dvds_rented, and the limit is weekly_quota:
<td>
<xsl:attribute name="style">
<xsl:choose>
<xsl:when test="number(@dvds_rented <= $weekly_quota)">color:red;</xsl:when>
<xsl:otherwise>color:green;</xsl:otherwise>
</xsl:choose>
text-align:right;
</xsl:attribute>
<xsl:value-of select="format-number(@dvds_rented, '###,###')"/>
</td>
The following XSLT file converts the XML file at the bottom of this tip (try it):
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:output method="html"/>
<xsl:param name="forecast" select="50000"/>
<xsl:param name="weekly_quota" select="12000"/>
<xsl:template match="/">
<HTML>
<HEAD>
<TITLE><xsl:value-of select="//summary/heading"/></TITLE>
</HEAD>
<BODY>
<H1><xsl:value-of select="//summary/heading"/></H1>
<H2><xsl:value-of select="//summary/subhead"/></H2>
<P><xsl:value-of select="//summary/description"/></P>
<TABLE>
<TR>
<TH>Month\Week</TH>
<xsl:for-each select="//data/month[1]/week">
<TH>W<xsl:value-of select="@number"/></TH>
</xsl:for-each>
<TH>Total</TH>
<TH>Forecast</TH>
</TR>
<xsl:for-each select="//data/month">
<tr>
<th style="text-align:left"><xsl:value-of select="name"/></th>
<xsl:for-each select="week">
<td>
<xsl:attribute name="style">
<xsl:choose>
<xsl:when test="number(@dvds_rented <= $weekly_quota)">color:red;</xsl:when>
<xsl:otherwise>color:green;</xsl:otherwise>
</xsl:choose>
text-align:right;
</xsl:attribute>
<xsl:value-of select="format-number(@dvds_rented, '###,###')"/>
</td>
</xsl:for-each>
<td style="text-align:right;font-weight:bold">
<xsl:value-of select="format-number(sum(week/@dvds_rented), '###,###')"/>
</td>
<td style="text-align:right;font-weight:bold">
<xsl:value-of select="format-number($forecast, '###,###')"/>
</td>
</tr>
</xsl:for-each>
</TABLE>
</BODY>
</HTML>
</xsl:template>
</xsl:stylesheet>
Here is the colorful report:
Here is the XML file:
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="020103.xsl"?>
<sales>
<summary>
<heading>MyDVD Rental Store</heading>
<subhead>Periodical Sales Report</subhead>
<description>Sales Report for January, February, and March of 2001</description>
</summary>
<data>
<month>
<name>January 2001</name>
<week number="1" dvds_rented="12000" />
<week number="2" dvds_rented="15000" />
<week number="3" dvds_rented="18000" />
<week number="4" dvds_rented="11800" />
</month>
<month>
<name>February 2001</name>
<week number="1" dvds_rented="11500" />
<week number="2" dvds_rented="12390" />
<week number="3" dvds_rented="19050" />
<week number="4" dvds_rented="11200" />
</month>
<month>
<name>March 2001</name>
<week number="1" dvds_rented="15300" />
<week number="2" dvds_rented="12390" />
<week number="3" dvds_rented="10050" />
<week number="4" dvds_rented="11230" />
</month>
</data>
</sales>
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