XSL Basics (part 2) - A Node By Any Other Name (
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XSLT also comes with a bunch of instructions designed to help authors
create nodes in the result tree using XSLT instructions, rather than literal character
data. These come in particularly handy when elements, attributes, PIs or text
strings need to be generated dynamically.
In order to illustrate this, let's consider a small snippet from the stock data
you just saw:
<?xml version="1.0"?>
<portfolio>
<stock>
<symbol>HHDT</symbol>
<oprice>100</oprice>
<cprice>25</cprice>
</stock>
<stock>
<symbol>NHSJ</symbol>
<oprice>20</oprice>
<cprice>1000</cprice>
</stock>
</portfolio>
Now, let's suppose that, for some twisted reason of my own, I wanted to convert
this source tree into the following result tree:
<portfolio>
<HHDT oprice="100" cprice="25" />
<NHSJ oprice="20" cprice="1000" />
</portfolio>
Here's how I could accomplish it with XSLT:
<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template
match="/">
<xsl:element name="portfolio">
<xsl:apply-templates />
</xsl:element>
</xsl:template>
<xsl:template
match="//stock">
<xsl:element name="{symbol}">
<xsl:attribute name="oprice">
<xsl:value-of
select="oprice" />
</xsl:attribute>
<xsl:attribute name="cprice">
<xsl:value-of
select="cprice" />
</xsl:attribute>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
The <xsl:element> instruction is used to create a new element in the result
tree; the name of the element to be created is specified via the "name" attribute.
In case the element name needs to be generated dynamically - as in the above example,
where the element name depends on the stock symbol - an expression can be used,
enclosed within curly braces.
In the example above, the elements to be created are "empty" elements - that
is, they do not enclose any content. In case I wanted to add some content between
the opening and closing tags, I would use the following instruction:
<xsl:element name="{symbol}">
I rock!
</xsl:element>
If you take a close look at the first template rule above, you'll see that I've
actually used this technique when creating the outermost "portfolio" element.
Once an element has been created, it may be necessary to assign it some attributes
- this is accomplished via the <xsl:attribute> instruction. The syntax here
is similar to that of <xsl:element>, although <xsl:attribute> instructions
must always be contained within either literal or dynamically-created parent elements.
As you may have guessed, XSLT doesn't just restrict you to creating elements
and attributes dynamically - you can also create text nodes, PIs and comments,
using the <xsl:text>, <xsl:processing-instruction> and <xsl:comment>
instructions respectively. Take a look at the following examples, which demonstrate
how this works:
<xsl:template match="/node">
<xsl:comment>
Superman was here!
</xsl:comment>
</xsl:template>
<xsl:template
match="/node">
<xsl:text>
Mary had a little lamb
</xsl:text>
</xsl:template>
<xsl:template
match="/node">
<xsl:processing-instruction name="bite_me" />
</xsl:template>
Obviously, text, comments and PIs can also be generated dynamically, as previously
demonstrated with elements and attributes.
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