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

+198
-22
lines changed

5 files changed

+198
-22
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‎doc/src/sgml/func.sgml‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -9275,6 +9275,8 @@ SELECT xml_is_well_formed_document('<pg:foo xmlns:pg="http://postgresql.org/stuf
92759275
against the XML value
92769276
<replaceable>xml</replaceable>. It returns an array of XML values
92779277
corresponding to the node set produced by the XPath expression.
9278+
If the XPath expression returns a scalar value rather than a node set,
9279+
a single-element array is returned.
92789280
</para>
92799281

92809282
<para>

‎src/backend/utils/adt/xml.c‎

Lines changed: 92 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -126,6 +126,8 @@ static bool print_xml_decl(StringInfo buf, const xmlChar *version,
126126
static xmlDocPtr xml_parse(text *data, XmlOptionType xmloption_arg,
127127
bool preserve_whitespace, int encoding);
128128
static text *xml_xmlnodetoxmltype(xmlNodePtr cur);
129+
static int xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
130+
ArrayBuildState **astate);
129131
#endif /* USE_LIBXML */
130132

131133
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,
35033505
*/
35043506

35053507
#ifdef USE_LIBXML
3508+
35063509
/*
35073510
* Convert XML node to text (dump subtree in case of element,
35083511
* return value otherwise)
@@ -3554,20 +3557,100 @@ xml_xmlnodetoxmltype(xmlNodePtr cur)
35543557

35553558
return result;
35563559
}
3557-
#endif
3560+
3561+
/*
3562+
* Convert an XML XPath object (the result of evaluating an XPath expression)
3563+
* to an array of xml values, which is returned at *astate. The function
3564+
* result value is the number of elements in the array.
3565+
*
3566+
* If "astate" is NULL then we don't generate the array value, but we still
3567+
* return the number of elements it would have had.
3568+
*
3569+
* Nodesets are converted to an array containing the nodes' textual
3570+
* representations. Primitive values (float, double, string) are converted
3571+
* to a single-element array containing the value's string representation.
3572+
*/
3573+
static int
3574+
xml_xpathobjtoxmlarray(xmlXPathObjectPtr xpathobj,
3575+
ArrayBuildState **astate)
3576+
{
3577+
int result = 0;
3578+
Datum datum;
3579+
Oid datumtype;
3580+
char *result_str;
3581+
3582+
if (astate != NULL)
3583+
*astate = NULL;
3584+
3585+
switch (xpathobj->type)
3586+
{
3587+
case XPATH_NODESET:
3588+
if (xpathobj->nodesetval != NULL)
3589+
{
3590+
result = xpathobj->nodesetval->nodeNr;
3591+
if (astate != NULL)
3592+
{
3593+
int i;
3594+
3595+
for (i = 0; i < result; i++)
3596+
{
3597+
datum = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
3598+
*astate = accumArrayResult(*astate, datum,
3599+
false, XMLOID,
3600+
CurrentMemoryContext);
3601+
}
3602+
}
3603+
}
3604+
return result;
3605+
3606+
case XPATH_BOOLEAN:
3607+
if (astate == NULL)
3608+
return 1;
3609+
datum = BoolGetDatum(xpathobj->boolval);
3610+
datumtype = BOOLOID;
3611+
break;
3612+
3613+
case XPATH_NUMBER:
3614+
if (astate == NULL)
3615+
return 1;
3616+
datum = Float8GetDatum(xpathobj->floatval);
3617+
datumtype = FLOAT8OID;
3618+
break;
3619+
3620+
case XPATH_STRING:
3621+
if (astate == NULL)
3622+
return 1;
3623+
datum = CStringGetDatum((char *) xpathobj->stringval);
3624+
datumtype = CSTRINGOID;
3625+
break;
3626+
3627+
default:
3628+
elog(ERROR, "xpath expression result type %d is unsupported",
3629+
xpathobj->type);
3630+
return 0; /* keep compiler quiet */
3631+
}
3632+
3633+
/* Common code for scalar-value cases */
3634+
result_str = map_sql_value_to_xml_value(datum, datumtype, true);
3635+
datum = PointerGetDatum(cstring_to_xmltype(result_str));
3636+
*astate = accumArrayResult(*astate, datum,
3637+
false, XMLOID,
3638+
CurrentMemoryContext);
3639+
return 1;
3640+
}
35583641

35593642

35603643
/*
35613644
* Common code for xpath() and xmlexists()
35623645
*
35633646
* Evaluate XPath expression and return number of nodes in res_items
3564-
* and array of XML values in astate.
3647+
* and array of XML values in astate. Either of those pointers can be
3648+
* NULL if the corresponding result isn't wanted.
35653649
*
35663650
* It is up to the user to ensure that the XML passed is in fact
35673651
* an XML document - XPath doesn't work easily on fragments without
35683652
* a context node being known.
35693653
*/
3570-
#ifdef USE_LIBXML
35713654
static void
35723655
xpath_internal(text *xpath_expr_text, xmltype *data, ArrayType *namespaces,
35733656
int *res_nitems, ArrayBuildState **astate)
@@ -3711,26 +3794,13 @@ xpath_internal(text *xpath_expr_text, xmltype *data, ArrayType *namespaces,
37113794
xml_ereport(xmlerrcxt, ERROR, ERRCODE_INTERNAL_ERROR,
37123795
"could not create XPath object");
37133796

3714-
/* return empty array in cases when nothing is found */
3715-
if (xpathobj->nodesetval == NULL)
3716-
*res_nitems = 0;
3797+
/*
3798+
* Extract the results as requested.
3799+
*/
3800+
if (res_nitems != NULL)
3801+
*res_nitems = xml_xpathobjtoxmlarray(xpathobj, astate);
37173802
else
3718-
*res_nitems = xpathobj->nodesetval->nodeNr;
3719-
3720-
if (*res_nitems && astate)
3721-
{
3722-
*astate = NULL;
3723-
for (i = 0; i < xpathobj->nodesetval->nodeNr; i++)
3724-
{
3725-
Datum elem;
3726-
bool elemisnull = false;
3727-
3728-
elem = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
3729-
*astate = accumArrayResult(*astate, elem,
3730-
elemisnull, XMLOID,
3731-
CurrentMemoryContext);
3732-
}
3733-
}
3803+
(void) xml_xpathobjtoxmlarray(xpathobj, astate);
37343804
}
37353805
PG_CATCH();
37363806
{

‎src/test/regress/expected/xml.out‎

Lines changed: 48 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -601,6 +601,42 @@ SELECT xpath('//@value', '<root value="&lt;"/>');
601601
{&lt;}
602602
(1 row)
603603

604+
SELECT xpath('''<<invalid>>''', '<root/>');
605+
xpath
606+
---------------------------
607+
{&lt;&lt;invalid&gt;&gt;}
608+
(1 row)
609+
610+
SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
611+
xpath
612+
-------
613+
{3}
614+
(1 row)
615+
616+
SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
617+
xpath
618+
---------
619+
{false}
620+
(1 row)
621+
622+
SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
623+
xpath
624+
--------
625+
{true}
626+
(1 row)
627+
628+
SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
629+
xpath
630+
--------
631+
{root}
632+
(1 row)
633+
634+
SELECT xpath('/nosuchtag', '<root/>');
635+
xpath
636+
-------
637+
{}
638+
(1 row)
639+
604640
-- Test xmlexists and xpath_exists
605641
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
606642
xmlexists
@@ -614,6 +650,12 @@ SELECT xmlexists('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><town>Bid
614650
t
615651
(1 row)
616652

653+
SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
654+
xmlexists
655+
-----------
656+
t
657+
(1 row)
658+
617659
SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
618660
xpath_exists
619661
--------------
@@ -626,6 +668,12 @@ SELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><town>Bidford-on-Avon
626668
t
627669
(1 row)
628670

671+
SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
672+
xpath_exists
673+
--------------
674+
t
675+
(1 row)
676+
629677
INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
630678
INSERT INTO xmltest VALUES (5, '<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
631679
INSERT INTO xmltest VALUES (6, '<myns:menu xmlns:myns="http://myns.com"><myns:beers><myns:name>Budvar</myns:name><myns:cost>free</myns:cost><myns:name>Carling</myns:name><myns:cost>lots</myns:cost></myns:beers></myns:menu>'::xml);

‎src/test/regress/expected/xml_1.out‎

Lines changed: 48 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -516,6 +516,42 @@ LINE 1: SELECT xpath('//@value', '<root value="&lt;"/>');
516516
^
517517
DETAIL: This functionality requires the server to be built with libxml support.
518518
HINT: You need to rebuild PostgreSQL using --with-libxml.
519+
SELECT xpath('''<<invalid>>''', '<root/>');
520+
ERROR: unsupported XML feature
521+
LINE 1: SELECT xpath('''<<invalid>>''', '<root/>');
522+
^
523+
DETAIL: This functionality requires the server to be built with libxml support.
524+
HINT: You need to rebuild PostgreSQL using --with-libxml.
525+
SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
526+
ERROR: unsupported XML feature
527+
LINE 1: SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
528+
^
529+
DETAIL: This functionality requires the server to be built with libxml support.
530+
HINT: You need to rebuild PostgreSQL using --with-libxml.
531+
SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
532+
ERROR: unsupported XML feature
533+
LINE 1: SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
534+
^
535+
DETAIL: This functionality requires the server to be built with libxml support.
536+
HINT: You need to rebuild PostgreSQL using --with-libxml.
537+
SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
538+
ERROR: unsupported XML feature
539+
LINE 1: SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
540+
^
541+
DETAIL: This functionality requires the server to be built with libxml support.
542+
HINT: You need to rebuild PostgreSQL using --with-libxml.
543+
SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
544+
ERROR: unsupported XML feature
545+
LINE 1: SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
546+
^
547+
DETAIL: This functionality requires the server to be built with libxml support.
548+
HINT: You need to rebuild PostgreSQL using --with-libxml.
549+
SELECT xpath('/nosuchtag', '<root/>');
550+
ERROR: unsupported XML feature
551+
LINE 1: SELECT xpath('/nosuchtag', '<root/>');
552+
^
553+
DETAIL: This functionality requires the server to be built with libxml support.
554+
HINT: You need to rebuild PostgreSQL using --with-libxml.
519555
-- Test xmlexists and xpath_exists
520556
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
521557
ERROR: unsupported XML feature
@@ -529,6 +565,12 @@ LINE 1: ...sts('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><t...
529565
^
530566
DETAIL: This functionality requires the server to be built with libxml support.
531567
HINT: You need to rebuild PostgreSQL using --with-libxml.
568+
SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
569+
ERROR: unsupported XML feature
570+
LINE 1: ...LECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>')...
571+
^
572+
DETAIL: This functionality requires the server to be built with libxml support.
573+
HINT: You need to rebuild PostgreSQL using --with-libxml.
532574
SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
533575
ERROR: unsupported XML feature
534576
LINE 1: ...ELECT xpath_exists('//town[text() = ''Toronto'']','<towns><t...
@@ -541,6 +583,12 @@ LINE 1: ...ELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><t...
541583
^
542584
DETAIL: This functionality requires the server to be built with libxml support.
543585
HINT: You need to rebuild PostgreSQL using --with-libxml.
586+
SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
587+
ERROR: unsupported XML feature
588+
LINE 1: SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
589+
^
590+
DETAIL: This functionality requires the server to be built with libxml support.
591+
HINT: You need to rebuild PostgreSQL using --with-libxml.
544592
INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
545593
ERROR: unsupported XML feature
546594
LINE 1: INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</n...

‎src/test/regress/sql/xml.sql‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -177,12 +177,20 @@ SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><loc
177177
SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
178178
SELECT xpath('//text()', '<root>&lt;</root>');
179179
SELECT xpath('//@value', '<root value="&lt;"/>');
180+
SELECT xpath('''<<invalid>>''', '<root/>');
181+
SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
182+
SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
183+
SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
184+
SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
185+
SELECT xpath('/nosuchtag', '<root/>');
180186

181187
-- Test xmlexists and xpath_exists
182188
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
183189
SELECT xmlexists('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
190+
SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
184191
SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
185192
SELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
193+
SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
186194

187195
INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
188196
INSERT INTO xmltest VALUES (5, '<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);

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