Sorry for the previous NUUUB post, didn't now the mailing list doesn't
support html ;(
Robert Haas wrote:
On Tue, Jan 5, 2010 at 6:09 PM, Arie Bikker <a...@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
*** src/backend/utils/adt/xml.c.old Fri Sep 4 12:49:43 2009
--- src/backend/utils/adt/xml.c Wed Jan 6 21:32:22 2010
***************
*** 111,116 ****
--- 111,117 ----
static xmlDocPtr xml_parse(text *data, XmlOptionType xmloption_arg,
bool preserve_whitespace, int encoding);
static text *xml_xmlnodetoxmltype(xmlNodePtr cur);
+ static text *xml_xmlpathobjtoxmltype(xmlXPathObjectPtr cur);
#endif /* USE_LIBXML */
static StringInfo query_to_xml_internal(const char *query, char *tablename,
***************
*** 3265,3270 ****
--- 3266,3312 ----
return result;
}
+
+ /*
+ * Convert XML pathobject to text for non-nodeset objects
+ */
+ static text *
+ xml_xmlpathobjtoxmltype(xmlXPathObjectPtr cur)
+ {
+ xmltype *result;
+
+ if (cur->type == XPATH_BOOLEAN)
+ {
+ PG_TRY();
+ {
+ result = cstring_to_text((char *)(xmlXPathCastToBoolean(cur)?"t":"f"));
+ }
+ PG_CATCH();
+ {
+ PG_RE_THROW();
+ }
+ PG_END_TRY();
+ }
+ else
+ {
+ xmlChar *str;
+
+ str = xmlXPathCastToString(cur);
+ PG_TRY();
+ {
+ result = (xmltype *) cstring_to_text((char *) str);
+ }
+ PG_CATCH();
+ {
+ xmlFree(str);
+ PG_RE_THROW();
+ }
+ PG_END_TRY();
+ xmlFree(str);
+ }
+
+ return result;
+ }
#endif
***************
*** 3418,3442 ****
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;
!
! if (res_nitems)
! {
! for (i = 0; i < xpathobj->nodesetval->nodeNr; i++)
{
! Datum elem;
! bool elemisnull = false;
!
! elem = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
! astate = accumArrayResult(astate, elem,
! elemisnull, XMLOID,
! CurrentMemoryContext);
}
}
}
PG_CATCH();
{
--- 3460,3504 ----
xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
"could not create XPath object");
! switch (xpathobj->type) {
! case XPATH_NODESET: {
! /* return empty array in cases when nothing is found */
! if (xpathobj->nodesetval == NULL)
! res_nitems = 0;
! else
! res_nitems = xpathobj->nodesetval->nodeNr;
!
! if (res_nitems)
{
! for (i = 0; i < xpathobj->nodesetval->nodeNr; i++)
! {
! Datum elem;
! bool elemisnull = false;
!
! elem = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
! astate = accumArrayResult(astate, elem,
! elemisnull, XMLOID,
! CurrentMemoryContext);
! }
}
+ break;
}
+ case XPATH_BOOLEAN:
+ case XPATH_NUMBER:
+ case XPATH_STRING: {
+ Datum elem;
+ bool elemisnull = false;
+
+ elem = PointerGetDatum(xml_xmlpathobjtoxmltype(xpathobj));
+ astate = accumArrayResult(astate, elem,
+ elemisnull, XMLOID,
+ CurrentMemoryContext);
+ break;
+ }
+ default: {
+ ereport(WARNING, (errmsg("Unknown PathObjectType (%d)", xpathobj->type)));
+ }
+ }
}
PG_CATCH();
{
***************
*** 3460,3466 ****
xmlFreeDoc(doc);
xmlFreeParserCtxt(ctxt);
! if (res_nitems == 0)
PG_RETURN_ARRAYTYPE_P(construct_empty_array(XMLOID));
else
PG_RETURN_ARRAYTYPE_P(makeArrayResult(astate, CurrentMemoryContext));
--- 3522,3528 ----
xmlFreeDoc(doc);
xmlFreeParserCtxt(ctxt);
! if (astate == NULL)
PG_RETURN_ARRAYTYPE_P(construct_empty_array(XMLOID));
else
PG_RETURN_ARRAYTYPE_P(makeArrayResult(astate, CurrentMemoryContext));
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