sort by expression

ronisc · December 17th, 2006, 04:23 AM

Hi,

I am developing a report generator based on xslt.
I am trying to sort by expression.
To make it simple I have wrote an example of what I am trying to do.

I need to sort by date.
In order to do so I am taking the date (dd/mm/yyyy) and changing it to yyyymmdd and then sorting this expression by regular number sort.

this can be easily done with the following expression (assuming @th is the date):

<xsl:sort select="concat(substring(@th,7,4),substring(@th,4, 2),substring(@th,1,2))" data-type="number"/>

here is the full example:

xml
-----------------------------------

<?xml version="1.0"?>
<root>
  <Chanich FullName="firstName1 lastName1" id="29152485" th="15/11/1999" />
  <Chanich FullName="firstName2 lastName2" id="32036758" th="01/10/2003" />
  <Chanich FullName="firstName3 lastName3" id="32273716" th="15/08/2000" />
  <Chanich FullName="firstName4 lastName4" id="27425586" th="15/11/1999" />
  <Chanich FullName="firstName5 lastName5" id="58829979" th="14/08/1994" />
  <Chanich FullName="firstName6 lastName6" id="24354292" th="13/02/2000" />
</root>

xslt
-----------------------------------
<xsl:template match="/">
    <html>
    <body>
      <table border="1">
      <xsl:for-each select="root/Chanich">
        <xsl:sort select="concat(substring(@th,7,4),substring(@th,4, 2),substring(@th,1,2))" data-type="number"/>
        <tr>
          <td><xsl:value-of select="@FullName"/></td>
          <td><xsl:value-of select="@id"/></td>
          <td><xsl:value-of select="@th"/></td>
        </tr>
      </xsl:for-each>
      </table>
    </body>
    </html>
</xsl:template>
</xsl:stylesheet>

It is working fine.

my problem is that the sorting expression needs to come dynamically form variable.
so lets say that I want to rewrite the xslt that the sorting expression will come from a variable.
it will look like this:

<xsl:template match="/">
    <html>
    <body>
      <table border="1">
      <xsl:variable name="sortSelect" select="concat(substring(@th,7,4),substring(@th,4, 2),substring(@th,1,2))"/>
      <xsl:for-each select="root/Chanich">
        <xsl:sort select="$sortSelect"/>
        <tr>
          <td><xsl:value-of select="@FullName"/></td>
          <td><xsl:value-of select="@id"/></td>
          <td><xsl:value-of select="@th"/></td>
        </tr>
      </xsl:for-each>
      </table>
    </body>
    </html>
</xsl:template>
</xsl:stylesheet>

1. How can I make it Work ???
2. Is there any "elegant" way to sort by dates?

I am writing xslt ver 2.0 using saxon.

thanx,
Roni.

mhkay · December 17th, 2006, 02:36 PM

A number of products have an extension function that allows you to construct an expression dynamically as a string (or read it from a source document) and then evaluate it. In Saxon it's called saxon:evaluate(). You need to read the rules carefully concerning the static and dynamic context for the expression. You can't do this in standard XSLT, even in 2.0.

I would recommend always storing dates in XML in the standard international YYYY-MM-DD format. YOu'll then be able to sort them directly, simply by casting to the xs:date data type.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference