Walkthrough: Debug an XSLT Style Sheet

Article
02/20/2011

The steps in this walkthrough demonstrate how to use the XSLT debugger. Steps include viewing variables, setting breakpoints, and stepping through the code. The style sheet finds all books that cost below the average book price.

To prepare for this walkthrough

Close any open solutions.
Copy the two sample files to your local computer.

Start Debugging

To start debugging

From the File menu, point to Open, and click File.
Locate the belowAvg.xsl file and click Open.

The style sheet is opened in the XML Editor.
Click the browse button (...) on the Input field of the document properties window.
Locate the books.xml file and click Open.

This sets the source document file that is used for the XSLT transformation.
Right-click the xsl:if start tag, point to Breakpoint, and click Insert Breakpoint.
Click the Debug XSL button on the XML Editor toolbar.

This starts the debugging process and opens several new windows that are used by the debugger.

There are two windows that display the input document and styles sheet. The debugger uses these windows to show the current execution state. The debugger is positioned on the xsl:if element of the style sheet and on the first book node in the books.xml file.

The Locals window displays all the local variables and their current values. This includes variables defined in the style sheet and also variables that the debugger uses to track the nodes that are currently in context.

The XSL Output window displays the output of the XSL transformation. This window is separate from the Visual Studio Output window.

Watch Window

To use the Watch window

From the Debug menu, point to Windows, point to Watch, and click Watch 1.

This makes the Watch 1 window visible.
Type $bookAverage in the Name field and press ENTER.

The value of the $bookAverage variable is displayed in the window.
Type self::node() in the Name field and press ENTER.

self::node() is an XPath expression that evaluates to the current context node. The value of the self::node() XPath expression is the first book node. This changes as we progress through the transformation.
Expand the self::node() node, and then expand the price node.

This allows you to see the value of the book price and you can easily compare it to the $bookAverage value. Because the book price is below the average, the xsl:if condition should succeed.

Step Through the Code

The debugger enables you to execute code one line at a time.

To step through the code

Press F5 to continue.

Because the first book node satisfied the xsl:if condition, the book node is added to the XSL output window. The debugger continues to execute until it is positioned again on the xsl:if element in the style sheet. The debugger is now positioned on the second book node in the books.xml file.

In the Watch1 window the self::node() value changes to the second book node. By examining the value of the price element, you can determine that the price is above the average, thus the xsl:if condition should fail.
Press F5 to continue.

Because the second book node does not meet the xsl:if condition, the book node is not added to the XSL output window. The debugger continues to execute until it is positioned again on the xsl:if element in the style sheet. The debugger is now positioned on the third book node in the books.xml file.

In the Watch1 window the self::node() value changes to the third book node. By examining the value of the price element, you can determine that the price is below the average, thus the xsl:if condition should succeed.
Press F5 to continue.

Because the xsl:if condition was satisfied, the third book is added to the XSL Output window. All books in the XML document have been processed and the debugger stops.

Sample Files

The following two files are used by the walkthrough.

belowAvg.xsl

<?xml version='1.0'?>
<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" encoding="utf-8"/>
  <xsl:template match="/">
    <xsl:variable name="bookCount" select="count(/bookstore/book)"/>
    <xsl:variable name="bookTotal" select="sum(/bookstore/book/price)"/>
    <xsl:variable name="bookAverage" select="$bookTotal div $bookCount"/>
    <books>
      <!--Books That Cost Below Average-->
      <xsl:for-each select="/bookstore/book">
        <xsl:if test="price &lt; $bookAverage">
          <xsl:copy-of select="."/>
        </xsl:if>
      </xsl:for-each>
    </books>
  </xsl:template>
</xsl:stylesheet>

books.xml

<?xml version='1.0'?>
<!-- This file represents a fragment of a book store inventory database -->
<bookstore>
  <book genre="autobiography" publicationdate="1981" ISBN="1-861003-11-0">
    <title>The Autobiography of Benjamin Franklin</title>
    <author>
      <first-name>Benjamin</first-name>
      <last-name>Franklin</last-name>
    </author>
    <price>8.99</price>
  </book>
  <book genre="novel" publicationdate="1967" ISBN="0-201-63361-2">
    <title>The Confidence Man</title>
    <author>
      <first-name>Herman</first-name>
      <last-name>Melville</last-name>
    </author>
    <price>11.99</price>
  </book>
  <book genre="philosophy" publicationdate="1991" ISBN="1-861001-57-6">
    <title>The Gorgias</title>
    <author>
      <name>Plato</name>
    </author>
    <price>9.99</price>
  </book>
</bookstore>

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