Working with XSLT variables

Working with variables can get you into any kind of delight or trouble. It brings in many scenarios making it tricky in ways you don't experience with other programming languages.

First of all you need to remember that xsl variables are STATIC. That means that you cannot change them once they are set. Also you need to make sure that they are in the correct scope. If you create a variable inside a template, it will only be available inside the template. However, you can create GLOBAL variables outside a template as well.

Now on to the code examples. This post is using the XML example from an earlier post on XML and XSLT.

1. <!-- The following example creates variables in different ways. -->
2.  
3. <!-- This variable is a simple string, hardcoded inside the variable node. -->
4. <xsl:variable name="myString">
5. <xsl:text>Hello Nerd!</xsl:text>
6. </ xsl:variable >
7. <!-- In order to print the variable we do a simple value-of call. -->
8. <xsl:value-of select="$myString"/>

This will give us the following output:

Hello Nerd!

1. <!-- The next variable is created by looking up the artist 'Michael Jackson' in the example XML, and assigning the record title as value to the variable. -->
2. <xsl:variable name="myArtistAlbum" select="//record/title[../artist='Michael Jackson']"/>
3. <!-- In order to print the variable we do a simple value-of call. -->
4. <xsl:value-of select="$myArtistAlbum"/>

This will give us the following output:

Bad

1. <!-- Sometimes we need to load an intire XML structure into a variable. The following exmaple loads a document by using the document() function and the filepath(./music/recordCollection.xml) as an argument. On load we set the xml files root node as the root node in the variable. -->
2. <xsl:variable name="allArtists" select="document('./music/recordCollection.xml')/recordCollection"/>

When getting the output from this variable, we can do it in two ways.

1. <!-- The following code gives us a result similar to the previous example. -->
2. <xsl:value-of select="ext:node-set($myArtist)//record/title[../artist='Michael Jackson']"/>

This will give us the following output:

Bad

1. <!-- The following example simply outputs the XML as it is inside the variable. -->
2. <!-- <xsl:copy-of select="ext:node-set($finData)"/> -->

This will give us the following output:

1. < recordCollection >
2. <record>
3. <artist>Madonna</artist>
4. <title>Like a prair</title>
5. </record>
6. <record>
7. <artist>Gorillaz</artist>
8. <title>Gorillaz</title>
9. </record>
10. <record>
11. <artist>Madcon</artist>
12. <title>Beggin</title>
13. </record>
14. <record>
15. <artist>Michael Jackson</artist>
16. <title>Bad</title>
17. </record>
18. <record>
19. <artist>Queen</artist>
20. <title>Jazz</title>
21. </record>
22. <record>
23. <artist>Muse</artist>
24. <title>The Resistance</title>
25. </record>
26. <record>
27. <artist>Duffy</artist>
28. <title>Rockferry</title>
29. </record>
30. </ recordCollection >
31.  
32. <!-- Next up we create a new variable containing an XML structure. We want to create a subset of the original XML containing only titles inside a root node. -->
33.  
34. <xsl:variable name="titleCollection">
35. <titleCol>
36. <xsl:for-each select=".//child::title">
37. <xsl:copy-of select="."/>
38. </xsl:for-each>
39. </titleCol>
40. </ xsl:variable >
41.  
42. <!-- Now when running the copy-of call we get the new XML structure printed out in the result. -->
43. <xsl:copy-of select="ext:node-set($titleCollection)"/>

OutPut:

1. < titleCol >
2. <title>Like a prair</title>
3. <title>Gorillaz</title>
4. <title>Beggin</title>
5. <title>Bad</title>
6. <title>Jazz</title>
7. <title>The Resistance</title>
8. <title>Rockferry</title>
9. </ titleCol >