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Add xmlexists function

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by Mike Fowler, reviewed by Peter Eisentraut
This commit is contained in:
Peter Eisentraut
2010-08-05 04:21:54 +00:00
parent 26e47efb66
commit 641459f269
10 changed files with 312 additions and 31 deletions
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86
src/backend/utils/adt/xml.c
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.98 2010/07/06 19:18:58 momjian Exp $
* $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.99 2010/08/05 04:21:54 petere Exp $
*
*-------------------------------------------------------------------------
*/
@ -3295,24 +3295,20 @@ xml_xmlnodetoxmltype(xmlNodePtr cur)
/*
* Evaluate XPath expression and return array of XML values.
* Common code for xpath() and xmlexists()
*
* As we have no support of XQuery sequences yet, this function seems
* to be the most useful one (array of XML functions plays a role of
* some kind of substitution for XQuery sequences).
* Evaluate XPath expression and return number of nodes in res_items
* and array of XML values in astate.
*
* It is up to the user to ensure that the XML passed is in fact
* an XML document - XPath doesn't work easily on fragments without
* a context node being known.
*/
Datum
xpath(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
text *xpath_expr_text = PG_GETARG_TEXT_P(0);
xmltype *data = PG_GETARG_XML_P(1);
ArrayType *namespaces = PG_GETARG_ARRAYTYPE_P(2);
ArrayBuildState *astate = NULL;
static void
xpath_internal(text *xpath_expr_text, xmltype *data, ArrayType *namespaces,
int *res_nitems, ArrayBuildState **astate)
{
xmlParserCtxtPtr ctxt = NULL;
xmlDocPtr doc = NULL;
xmlXPathContextPtr xpathctx = NULL;
@ -3324,7 +3320,6 @@ xpath(PG_FUNCTION_ARGS)
xmlChar *string;
xmlChar *xpath_expr;
int i;
int res_nitems;
int ndim;
Datum *ns_names_uris;
bool *ns_names_uris_nulls;
@ -3339,7 +3334,7 @@ xpath(PG_FUNCTION_ARGS)
* ARRAY[ARRAY['myns', 'http://example.com'], ARRAY['myns2',
* 'http://example2.com']].
*/
ndim = ARR_NDIM(namespaces);
ndim = namespaces ? ARR_NDIM(namespaces) : 0;
if (ndim != 0)
{
int *dims;
@ -3439,6 +3434,13 @@ xpath(PG_FUNCTION_ARGS)
xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
"invalid XPath expression");
/*
* Version 2.6.27 introduces a function named
* xmlXPathCompiledEvalToBoolean, which would be enough for
* xmlexists, but we can derive the existence by whether any
* nodes are returned, thereby preventing a library version
* upgrade and keeping the code the same.
*/
xpathobj = xmlXPathCompiledEval(xpathcomp, xpathctx);
if (xpathobj == NULL) /* TODO: reason? */
xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
@ -3446,21 +3448,22 @@ xpath(PG_FUNCTION_ARGS)
/* return empty array in cases when nothing is found */
if (xpathobj->nodesetval == NULL)
res_nitems = 0;
*res_nitems = 0;
else
res_nitems = xpathobj->nodesetval->nodeNr;
*res_nitems = xpathobj->nodesetval->nodeNr;
if (res_nitems)
if (*res_nitems && astate)
{
*astate = NULL;
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);
*astate = accumArrayResult(*astate, elem,
elemisnull, XMLOID,
CurrentMemoryContext);
}
}
}
@ -3485,6 +3488,28 @@ xpath(PG_FUNCTION_ARGS)
xmlXPathFreeContext(xpathctx);
xmlFreeDoc(doc);
xmlFreeParserCtxt(ctxt);
}
#endif /* USE_LIBXML */
/*
* Evaluate XPath expression and return array of XML values.
*
* As we have no support of XQuery sequences yet, this function seems
* to be the most useful one (array of XML functions plays a role of
* some kind of substitution for XQuery sequences).
*/
Datum
xpath(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
text *xpath_expr_text = PG_GETARG_TEXT_P(0);
xmltype *data = PG_GETARG_XML_P(1);
ArrayType *namespaces = PG_GETARG_ARRAYTYPE_P(2);
int res_nitems;
ArrayBuildState *astate;
xpath_internal(xpath_expr_text, data, namespaces,
&res_nitems, &astate);
if (res_nitems == 0)
PG_RETURN_ARRAYTYPE_P(construct_empty_array(XMLOID));
@ -3495,3 +3520,24 @@ xpath(PG_FUNCTION_ARGS)
return 0;
#endif
}
/*
* Determines if the node specified by the supplied XPath exists
* in a given XML document, returning a boolean.
*/
Datum xmlexists(PG_FUNCTION_ARGS)
{
#ifdef USE_LIBXML
text *xpath_expr_text = PG_GETARG_TEXT_P(0);
xmltype *data = PG_GETARG_XML_P(1);
int res_nitems;
xpath_internal(xpath_expr_text, data, NULL,
&res_nitems, NULL);
PG_RETURN_BOOL(res_nitems > 0);
#else
NO_XML_SUPPORT();
return 0;
#endif
}