Re: XPath string comparison of two strings representin

On Wed, Aug 16, 2017 at 04:09:15PM -0000, Costello, Roger L. costello@xxxxxxxxx scripsit:
> Note that I am doing mere string comparison. I am comparing the string '20170817' against the string '20170816'.
> 
> Will the XPath always work? 

If and only if you've got a guarantee that the date format is always
correct.  That strikes me as rash.  (2017817 is going to mess things up,
for example.)  Trusting input isn't a good plan in general and dates
represented in strings in particular.

The below works; I'd be inclined to inclined to do something more
sensible with the date parsing in a production environment.

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:local="http://www.example.com/local"
    exclude-result-prefixes="xs local" version="2.0">
    <xsl:output method="text" />
    <xsl:variable as="element(Test)" name="input">
        <Test>
            <Date1>20170816</Date1>
            <Date2>20170817</Date2>
        </Test>
    </xsl:variable>
    <xsl:function name="local:error">
        <xsl:message>Something, somewhere, has gone wrong.</xsl:message>
    </xsl:function>
    <xsl:function name="local:makeDate" as="xs:date">
        <xsl:param name="in" as="xs:string" />
        <xsl:choose>
            <xsl:when test="matches($in, '^(19|20)[0-9][0-9][01][1-9][0123][1-9]$')">
                <xsl:variable name="year" select="substring($in, 1, 4)" />
                <xsl:variable name="month" select="substring($in, 5, 2)" />
                <xsl:variable name="day" select="substring($in, 7, 2)" />
                <xsl:sequence select="xs:date(concat($year, '-', $month, '-', $day))" />
            </xsl:when>
            <xsl:otherwise>
                <xsl:sequence select="local:error()" />
            </xsl:otherwise>
        </xsl:choose>
    </xsl:function>
    <xsl:template match="/">
        <xsl:variable name="date1" as="xs:date*" select="local:makeDate($input/Date1)" />
        <xsl:variable name="date2" as="xs:date*" select="local:makeDate($input/Date2)" />
        <xsl:choose>
            <xsl:when test="$date1 instance of xs:date and $date2 instance of xs:date">
                <xsl:sequence
                    select="
                        if ($date2 gt $date1) then
                            'dates are sequential'
                        else
                            'first date may be after second date'"
                 />
            </xsl:when>
            <xsl:otherwise>
                <xsl:message>Trying to compare non-dates.</xsl:message>
            </xsl:otherwise>
        </xsl:choose>
    </xsl:template>
</xsl:stylesheet>


-- Graydon