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From: Arie Bikker on 5 Jan 2010 18:09
Hi all,

Well I had to burn some midnight oil trying to figure out why a
construct like
SELECT xpath('name()','<a/>');
doesn't give the expected result. Kept getting an empty array:
xpath
-------------
{}
instead of the expected "{a}"
BugID 4294 and the TODO item "better handling of XPath data types"
pointed in the right direction.
whithin src/backend/utils/adt/xml.c in the function xpath the result of
the call to xmlXPathCompiledEval is not handled optimally. In fact, the
result is assumed to be a nodeset without consulting the ->type member
of the result. I've made some minor changes to xml.c to handle some
non-nodeset results of xmlXPathCompiledEval.
Essentially, the revised code makes an array of all the nodes in the
xpathobj result in case this is a nodeset, or an array with a single
element in case the reult is a number/string/boolean. The problem cases
mentioned in
http://archives.postgresql.org/pgsql-hackers/2008-06/msg00616.php now
work as expected.
Revision of the code involves:
- A switch statement to handle the result type of xmlXPathCompiledEval.
- an additional function xmlpathobjtoxmltype.

diff of the revisioned code with respect to original is in attached file.

kind regards, Arie Bikker
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