Wendell wrote:
In the first case, the step 'string(Data)', in the absence of a Data node,
will return '', since string(()) (a string value of nothing) is an empty
string,
i.e. a sequence of one member, ('').
In the second case, the failure of the path to reach any node at Data results
in the comparison () eq '' which should produce a runtime error, since 'eq'
requires two singleton operands.
Ah!
Fantastic explanation!
Thank you Wendell.
/Roger
From: Wendell Piez wapiez(_at_)wendellpiez(_dot_)com
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com>
Sent: Friday, June 18, 2021 12:02 PM
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: [EXT] Re: [xsl] An XPath expression that avoids writing special
casecode?
Roger,
You ask
Question: Below are two XPath expressions. The first is the one that Mukul
recommended and it returns the desired row. The second is the one that I
created and it fails. The only difference between the two XPath expressions
is string(Data) versus Data. Why does the former work whereas the later fails?
/Document/Row[Cell[1]/Data eq 'aviation'][Cell[2]/string(Data) eq '']
/Document/Row[Cell[1]/Data eq 'aviation'][Cell[2]/Data eq '']
In the first case, the step 'string(Data)', in the absence of a Data node, will
return '', since string(()) (a string value of nothing) is an empty string,
i.e. a sequence of one member, ('').
In the second case, the failure of the path to reach any node at Data results
in the comparison () eq '' which should produce a runtime error, since 'eq'
requires two singleton operands.
It is useful to keep in mind the distinction between a test for the existence
of a node, and a test for a node's value. The operators such as '=' have the
nice feature of letting us collapse these things since it permits many-to-many
or many-to-none comparisons. The 'eq' operator has the nice feature of not
letting us collapse these things.
Cheers,
Wendell
On Fri, Jun 18, 2021 at 9:31 AM Roger L Costello
mailto:costello(_at_)mitre(_dot_)org
<mailto:xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
Hi Mukul,
I tried your suggestion. For this XML document:
<Document>
<Row>
<Cell>
<Data>aviation</Data>
</Cell>
<Cell/>
</Row>
</Document>
I evaluated the following XPath expression in Oxygen XML:
/Document/Row[Cell[1]/Data eq 'aviation'][Cell[2]/string(Data) eq '']
Oxygen XML returned the desired row:
<Row>
<Cell>
<Data>aviation</Data>
</Cell>
<Cell/>
</Row>
Fantastic!
Question: Below are two XPath expressions. The first is the one that Mukul
recommended and it returns the desired row. The second is the one that I
created and it fails. The only difference between the two XPath expressions is
string(Data) versus Data. Why does the former work whereas the later fails?
/Document/Row[Cell[1]/Data eq 'aviation'][Cell[2]/string(Data) eq '']
/Document/Row[Cell[1]/Data eq 'aviation'][Cell[2]/Data eq '']
/Roger
From: Mukul Gandhi mailto:mukulg(_at_)softwarebytes(_dot_)org
<mailto:xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com>
Sent: Friday, June 18, 2021 3:28 AM
To: mailto:xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: [EXT] Re: [xsl] An XPath expression that avoids writing special
casecode?
On Thu, Jun 17, 2021 at 7:36 PM Roger L Costello
mailto:mailto:costello(_at_)mitre(_dot_)org
<mailto:mailto:xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
My XML document contains a bunch of <Row> elements, like so:
<Document>
...
<Row>
<Cell>
<Data>airport</Data>
</Cell>
<Cell>
<Data>airports</Data>
</Cell>
</Row>
...
</Document>
I want to fetch the Row whose Cell[1]/Data is 'airport' and whose Cell[2]/Data
is 'airports'. So I created this XPath expression:
/Document/Row[Cell[1]/Data eq 'airport'][Cell[2]/Data eq 'airports']
I do this kind of fetching operation often, so I created a function to fetch
the desired Row:
<xsl:function name="f:getRow">
<xsl:param name="element"/>
<xsl:param name="parent"/>
<xsl:sequence select="$document/Row[Cell[1]/Data eq $element][Cell[2]/Data
eq $parent]" />
</xsl:function>
I call the function this way:
<xsl:sequence select="f:getRow('airport', 'airports')" />
Sometimes there is an element that doesn't have a parent. That is, sometimes
I'd like to fetch a Row in which Cell[2] is empty, like this:
<Row>
<Cell>
<Data>aviation</Data>
</Cell>
<Cell/>
</Row>
Then this call to f:getRow fails:
<xsl:sequence select="f:getRow('aviation', '')" /> <!-- Those are two
apostrophes within the parentheses -->
Clearly I need to modify f:getRow. I could add special case code to test
$parent to see if it is empty (the '' string) and do one thing, and if it's not
empty do another thing. But I wonder if there is a more elegant solution that
doesn't involve special case code? Is there a way to modify the XPath
expression in f:getRow such that it fetches the correct Row regardless of
whether $parent is empty or not?
Testing with XSLT 2.0. Below is an example, for the solution you may be looking
for,
XML input document,
<Document>
<Row>
<Cell>
<Data>airport</Data>
</Cell>
<Cell>
<Data>airports</Data>
</Cell>
</Row>
<Row>
<Cell>
<Data>airport</Data>
</Cell>
<Cell>
<Data>ABC</Data>
</Cell>
</Row>
<Row>
<Cell>
<Data>aviation</Data>
</Cell>
<Cell/>
</Row>
</Document>
XSLT stylesheet,
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
xmlns:f="http://test_fn";
exclude-result-prefixes="f"
version="2.0">
<xsl:output method="xml" indent="yes"/>
<xsl:variable name="document" select="/Document"/>
<xsl:template match="/">
<result>
<xsl:copy-of select="f:getRow('airport', 'airports')"/>
<xsl:copy-of select="f:getRow('aviation', '')"/>
</result>
</xsl:template>
<xsl:function name="f:getRow">
<xsl:param name="element"/>
<xsl:param name="parent"/>
<xsl:sequence select="$document/Row[Cell[1]/Data eq
$element][Cell[2]/string(Data) eq $parent]" />
</xsl:function>
</xsl:stylesheet>
The output of above XSLT transformation is following,
<?xml version="1.0" encoding="UTF-8"?>
<result>
<Row>
<Cell>
<Data>airport</Data>
</Cell>
<Cell>
<Data>airports</Data>
</Cell>
</Row>
<Row>
<Cell>
<Data>aviation</Data>
</Cell>
<Cell/>
</Row>
</result>
--
Regards,
Mukul Gandhi
http://www.mulberrytech.com/xsl/xsl-list
http://lists.mulberrytech.com/unsub/xsl-list/673357 ()
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