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XSLT <xsl:key> Element

The <xsl:key> element specifies a name-value pair assigned to a specific element in an XML document. This key is used with the key() function in XPath expressions to access assigned elements in an XML document.

<xsl:key> Element​

Syntax​

The syntax of <xsl:key> is as follows:

<xsl:key
   name=QName
   match=Pattern
   use=Expression >
</xsl:key>

Attributes​

The table describes the meaning of the attributes of <xsl:key>:

NameDescription
nameName of the key to be used.
matchPatterns used to identify a node that holds this key.
useXPath expression to identify the value of the nodes of xml document.

Example​

Let's see an example:

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

<bookstore>
	<book category="children">
		<title lang="en">Harry Potter</title>
		<author>J K. Rowling</author>
		<year>2005</year>
		<price>29.99</price>
	</book>
	<book category="web">
		<title lang="en">XQuery Tips</title>
		<author>Tom Nolan</author>
		<year>2022</year>
		<price>39.99</price>
	</book>
	<book category="web">
		<title lang="en">Learn XML</title>
		<author>Tutorial Reference</author>
		<year>2022</year>
		<price>9.99</price>
	</book>
</bookstore>
books.xsl
<?xml version="1.0" encoding="UTF-8"?>

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:key name="author-search"  match="book"  use="author"/>

<xsl:template match="/">
	<html>
		<body>
			<h2>The Bookstore</h2>
			<table border="1">
				<tr bgcolor="#6565d5">
					<th>Title</th>
					<th>Author</th>
					<th>Year</th>
					<th>Price</th>
				</tr>  
				<xsl:for-each select="key('author-search', 'Tom Nolan')">
					<tr>
						<td><xsl:value-of select="title"/></td>
						<td><xsl:value-of select="author"/></td>
						<td><xsl:value-of select="year"/></td>
						<td><xsl:value-of select="price"/></td>
					</tr>
				</xsl:for-each>
			</table>
		</body>
	</html>
</xsl:template>

</xsl:stylesheet>
note

In the example, the <xsl:key> element is used to print the book details of all books with author "Tom Nolan".

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