[xml] Fwd: Re: xpath exists

[Tomáš Pospíšil <killteck seznam cz>]

I was not clear about idea behind xpath exists. It's not part of XPath specification. The purpose of this 
function is checking XML document if will return values on specified XPath expression. (Only check, not 
evaluate result). But someone was faster and this code will apear in PostgreSQL 9.1.

        xpathobj = xmlXPathCompiledEval(xpathcomp, xpathctx);
                if (xpathobj == NULL)   /* TODO: reason? */
                        xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
                                                "could not create XPath object");

                /* return empty array in cases when nothing is found */
                if (xpathobj->nodesetval == NULL)
                        *res_nitems = 0;
                else
                        *res_nitems = xpathobj->nodesetval->nodeNr;

I am not sure if xmlXPathCompiledEval is best way to check for values. Someone suggest 
xmlXPathCompiledEvalToBoolean so any suggestions are welcome.

 I would like to use xpath exists as core function for a new Index on XML documents. Just now studing 
possibilities of serializing whole xmlDocPtr and reuse it when needed. Is any plan to for indexing in LibXML2?


P.S. http://veillard.com/XML/search.php return private informations about DB, user names etc

# ------------ Původní zpráva ------------
# Od: Daniel Veillard <veillard redhat com>
# Komu: Tomáš Pospíšil<killteck seznam cz>,
# Kopie: <xml gnome org>,
# Předmět: Re: [xml] xpath exists
# Datum: 24.3.2011 16:43:34
# ----------------------------------------
# On Thu, Mar 24, 2011 at 03:48:25PM +0100, Tomáš Pospíšil wrote:
# > I'm going to implement xpath exist function in PostgreSQL, where LibXML
# > is in use. Can anybody suggest how achieve that with LibXML functions
# > (fastest way and in memory) ?
#
#   Hum, what does it do. It's not in XPath 1.0 , seems to be in 2.0
# though but I don't know it...
#
# Daniel
#
# --
# Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
# daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
# http://veillard.com/ | virtualization library  http://libvirt.org/
#
#