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Make xpath() do something useful with XPath expressions that return scalars.

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Previously, xpath() simply returned an empty array if the expression did
not yield a node set.  This is useless for expressions that return scalars,
such as one with name() at the top level.  Arrange to return the scalar
value as a single-element xml array, instead.  (String values will be
suitably escaped.)

This change will also cause xpath_exists() to return true, not false,
for such expressions.

Florian Pflug, reviewed by Radoslaw Smogura
This commit is contained in:
Tom Lane
2011-07-21 11:32:46 -04:00
parent aaf15e5c1c
commit 0ce7676aa0
5 changed files with 198 additions and 22 deletions
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114
src/backend/utils/adt/xml.c
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@ -126,6 +126,8 @@ static bool print_xml_decl(StringInfo buf, const xmlChar *version,
static xmlDocPtr xml_parse(text *data, XmlOptionType xmloption_arg,
bool preserve_whitespace, int encoding);
static text *xml_xmlnodetoxmltype(xmlNodePtr cur);
static int xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
ArrayBuildState **astate);
#endif /* USE_LIBXML */
static StringInfo query_to_xml_internal(const char *query, char *tablename,
@ -3503,6 +3505,7 @@ SPI_sql_row_to_xmlelement(int rownum, StringInfo result, char *tablename,
*/
#ifdef USE_LIBXML
/*
* Convert XML node to text (dump subtree in case of element,
* return value otherwise)
@ -3554,20 +3557,100 @@ xml_xmlnodetoxmltype(xmlNodePtr cur)
return result;
}
#endif
/*
* Convert an XML XPath object (the result of evaluating an XPath expression)
* to an array of xml values, which is returned at *astate. The function
* result value is the number of elements in the array.
*
* If "astate" is NULL then we don't generate the array value, but we still
* return the number of elements it would have had.
*
* Nodesets are converted to an array containing the nodes' textual
* representations. Primitive values (float, double, string) are converted
* to a single-element array containing the value's string representation.
*/
static int
xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
ArrayBuildState **astate)
{
int result = 0;
Datum datum;
Oid datumtype;
char *result_str;
if (astate != NULL)
*astate = NULL;
switch (xpathobj->type)
{
case XPATH_NODESET:
if (xpathobj->nodesetval != NULL)
{
result = xpathobj->nodesetval->nodeNr;
if (astate != NULL)
{
int i;
for (i = 0; i < result; i++)
{
datum = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
*astate = accumArrayResult(*astate, datum,
false, XMLOID,
CurrentMemoryContext);
}
}
}
return result;
case XPATH_BOOLEAN:
if (astate == NULL)
return 1;
datum = BoolGetDatum(xpathobj->boolval);
datumtype = BOOLOID;
break;
case XPATH_NUMBER:
if (astate == NULL)
return 1;
datum = Float8GetDatum(xpathobj->floatval);
datumtype = FLOAT8OID;
break;
case XPATH_STRING:
if (astate == NULL)
return 1;
datum = CStringGetDatum((char *) xpathobj->stringval);
datumtype = CSTRINGOID;
break;
default:
elog(ERROR, "xpath expression result type %d is unsupported",
xpathobj->type);
return 0; /* keep compiler quiet */
}
/* Common code for scalar-value cases */
result_str = map_sql_value_to_xml_value(datum, datumtype, true);
datum = PointerGetDatum(cstring_to_xmltype(result_str));
*astate = accumArrayResult(*astate, datum,
false, XMLOID,
CurrentMemoryContext);
return 1;
}
/*
* Common code for xpath() and xmlexists()
*
* Evaluate XPath expression and return number of nodes in res_items
* and array of XML values in astate.
* and array of XML values in astate. Either of those pointers can be
* NULL if the corresponding result isn't wanted.
*
* 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.
*/
#ifdef USE_LIBXML
static void
xpath_internal(text *xpath_expr_text, xmltype *data, ArrayType *namespaces,
int *res_nitems, ArrayBuildState **astate)
@ -3711,26 +3794,13 @@ xpath_internal(text *xpath_expr_text, xmltype *data, ArrayType *namespaces,
xml_ereport(xmlerrcxt, 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;
/*
* Extract the results as requested.
*/
if (res_nitems != NULL)
*res_nitems = xml_xpathobjtoxmlarray(xpathobj, astate);
else
*res_nitems = xpathobj->nodesetval->nodeNr;
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);
}
}
(void) xml_xpathobjtoxmlarray(xpathobj, astate);
}
PG_CATCH();
{