Re: xpath improvement suggestion

Robert Haas wrote:

On Tue, Jan 5, 2010 at 6:09 PM, Arie Bikker <arie@abikker.nl> wrote: 

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   

Hi,

Could you please resend this as a context diff and add it to our patch
management application?

http://wiki.postgresql.org/wiki/Submitting_a_Patch
https://commitfest.postgresql.org/action/commitfest_view/open

Thanks!

...Robert 

Hope this is the right attachement type (I'm new at this)
BTW. here a some nice examples:

- Get the number of attributes of the first childnode:
select ( xpath('count(@*)',(xpath('*[1]','<a b="c"><d e="f" g="j"/></a>'))[1]))[1];

- an alternative for xpath_exist('/a/d')
select (xpath('boolean(/a/d)','<a b="c"><d e="f" g="j"/></a>'))[1];

- fixes bug 4206
select xpath('//text()',xmlparse(document '<?xml version="1.0"?><elem1><elem2>one</elem2><elem2>two</elem2><elem2>three</elem2><elem3att="2"/></elem1>'));

- fixes bug 4294
select xpath('name(/my:a/*[last()])', '<a xmlns="http://myns.com/ns"><b>text1</b><c>text2</c></a>', ARRAY[ARRAY['my','http://myns.com/ns']]);

kind regards, Arie Bikker