The XPath 2.0 functions take the same view: 29 Feb plus one year is 28 Feb.
You can't avoid surprises with date arithmetic. It's not only leap years: 31
March plus 6 months minus 6 months is 30 March.
Michael Kay
http://www.saxonica.com/
-----Original Message-----
From: Fraser Goffin [mailto:goffinf(_at_)hotmail(_dot_)com]
Sent: 16 January 2006 10:58
To: mail(_at_)jenitennison(_dot_)com
Cc: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: [xsl] eXSLT date:add template
I recently had a need to do some date calculations in XSLT
(1.0) and I
thought it would be a good opportunity to take a look at the
eXSLT function
and template library.
What I wanted to do was, given a start date (lets call it startDate),
calculate a new date (lets call it endDate) to be startDate +
1 year - 1
day.
I settled on calling the date:add template twice, the first
time to add the
duration P1Y and the second time to subtract the day from the
result of the
first call (duration -P1D).
This works fine until we get to those pesky leap year dates
(and even for
these I'm not saying the implementation is wrong - I am just
looking for
clarification of the design). The date that I have a question
over is (not
surprisingly) the 29th February !. An example :-
Note: 2004 is a leap year.
The input doc looks like this :-
<eXLST_dateAdd_Test1>
<startDate>2004-02-29</startDate>
</eXLST_dateAdd_Test1>
and the output like this :-
<eXLST_dateAdd_Test1>
<startDate>2004-02-29</startDate>
<currentDatePlus1Year>2005-02-28</currentDatePlus1Year>
<endDate>2005-02-27</endDate>
</eXLST_dateAdd_Test1>
Here endDate is shown as the 27th Feb. One might expect this
to be the 28th,
but it all depends on whether adding 1 year to the 29th Feb
should be 28th
Feb in the following year or 01 March. The implementation
takes the position
that it should be 28th Feb and therefore, subtracting 1 day
yields 27th.
This seems reasonable.
BUT, if I use a startDate of 2004-2-28 I will also get the
same result. H'mm
now I'm not so sure, maybe adding 1 year to 29th February
SHOULD be 01 March
after all ??
Comments
Fraser.
Here's the simple XSLT I was using to test with :-
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
xmlns:date="http://exslt.org/dates-and-times";
extension-element-prefixes="date">
<xsl:import href="../functions/add/date.add.template.xsl"/>
<xsl:output method="xml" version="1.0" encoding="UTF-8"
indent="yes"/>
<xsl:template match="*|@*|text()">
<xsl:copy>
<xsl:apply-templates select="*|@*|text()|comment()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="/">
<xsl:apply-templates/>
</xsl:template>
<xsl:template match="startDate">
<xsl:copy-of select="."/>
<!-- TASK: Add 1 Year minus 1 day -->
<!-- Add 1 Year -->
<xsl:variable name="currentDatePlus1Year">
<xsl:call-template name="date:add">
<xsl:with-param name="date-time" select="."/>
<xsl:with-param name="duration" select="'P1Y'"/>
</xsl:call-template>
</xsl:variable>
<currentDatePlus1Year><xsl:value-of
select="$currentDatePlus1Year"/></currentDatePlus1Year>
<!-- Subtract 1 Day -->
<xsl:variable name="endDate">
<xsl:call-template name="date:add">
<xsl:with-param name="date-time"
select="$currentDatePlus1Year"/>
<xsl:with-param name="duration" select="'-P1D'"/>
</xsl:call-template>
</xsl:variable>
<endDate>
<xsl:value-of select="$endDate"/>
</endDate>
</xsl:template>
</xsl:stylesheet>
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