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I have just started learning XSL(T) and I wonder how apply-templates work? I do not understand the recursively applies templates part of it as it is written in my book.
I understand the XPath-part of XSL(T) and so on but not what apply-templates is doing and why I write it multiple times.
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The <xsl:apply-templates> element applies a template to the current element or to the current element's child nodes. If we add a "select" attribute to the <xsl:apply-templates> element, it will process only the child elements that matches the value of the attribute.
With <xsl:apply-templates> the current node moves on with every iteration, whereas <xsl:call-template> does not change the current node. I.e. the . within a called template refers to the same node as the .
XSLT Template defines a way to set rules to generate the desired Output in a proper structure for a particular context and to build a template. The template tells the XSLT processor how to format a particular output from the XML source document.
The <xsl:apply-templates> element first selects a set of nodes using the expression specified in the select attribute. If this attribute is left unspecified, all children of the current node are selected.
You use <xsl:apply-templates> to invoke the <xsl:template>:s you have defined.
<xsl:apply-templates> calls a matching template for each node in the set.
You can control processing order by specifying a select attribute on apply-templates.
See this example from w3schools:
<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<html>
<body>
<h2>My CD Collection</h2>
<xsl:apply-templates/>
</body>
</html>
</xsl:template>
<xsl:template match="cd">
<p>
<xsl:apply-templates select="title"/>
<xsl:apply-templates select="artist"/>
</p>
</xsl:template>
<xsl:template match="title">
Title: <span style="color:#ff0000">
<xsl:value-of select="."/></span>
<br />
</xsl:template>
<xsl:template match="artist">
Artist: <span style="color:#00ff00">
<xsl:value-of select="."/></span>
<br />
</xsl:template>
</xsl:stylesheet>
The first apply-templates calls the cd template each time an element named "cd" is encountered.
The cd template, in turn calls the title and artist templates to process the children elements of <cd>.
title is processed before artist. Note, that the order of artist and title elements in the source XML makes no difference.
You could think of apply-templates as analoguous to a subroutine call in procedural languages.
104
answered Oct 03 '22 23:10
If you've read about apply-templates in a book but haven't understood it, then it's not clear that a few words here will help. Perhaps you need a different book: different tutorial styles appeal to different people. Or perhaps an online tutorial such as http://vimeo.com/15234803 will get the ideas across.
The essence of the template mechanism is that there are two parties involved. The xsl:apply-templates instruction selects some nodes for processing, and the template rules (between them) decide what that processing should be. This gives very loose coupling and great separation of concerns; it's rather like object-oriented message/method despatch, but much more flexible.
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