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Add xmlexists function
by Mike Fowler, reviewed by Peter Eisentraut
1 parent 26e47ef commit 641459f

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10 files changed

+312
-31
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10 files changed

+312
-31
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‎doc/src/sgml/func.sgml

Lines changed: 53 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.522 2010/07/29 19:34:40 petere Exp $ -->
1+
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.523 2010/08/05 04:21:53 petere Exp $ -->
22

33
<chapter id="functions">
44
<title>Functions and Operators</title>
@@ -8554,10 +8554,19 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
85548554
]]></screen>
85558555
</para>
85568556
</sect3>
8557+
</sect2>
85578558

8558-
<sect3>
8559+
<sect2>
85598560
<title>XML Predicates</title>
85608561

8562+
<para>
8563+
The expressions described in this section check properties
8564+
of <type>xml</type> values.
8565+
</para>
8566+
8567+
<sect3>
8568+
<title>IS DOCUMENT</title>
8569+
85618570
<indexterm>
85628571
<primary>IS DOCUMENT</primary>
85638572
</indexterm>
@@ -8574,6 +8583,48 @@ SELECT xmlagg(x) FROM (SELECT * FROM test ORDER BY y DESC) AS tab;
85748583
between documents and content fragments.
85758584
</para>
85768585
</sect3>
8586+
8587+
<sect3>
8588+
<title>XMLEXISTS</title>
8589+
8590+
<indexterm>
8591+
<primary>XMLEXISTS</primary>
8592+
</indexterm>
8593+
8594+
<synopsis>
8595+
<function>XMLEXISTS</function>(<replaceable>text</replaceable> PASSING <optional>BY REF</optional> <replaceable>xml</replaceable> <optional>BY REF</optional>)
8596+
</synopsis>
8597+
8598+
<para>
8599+
The function <function>xmlexists</function> returns true if the
8600+
XPath expression in the first argument returns any nodes, and
8601+
false otherwise. (If either argument is null, the result is
8602+
null.)
8603+
</para>
8604+
8605+
<para>
8606+
Example:
8607+
<screen><![CDATA[
8608+
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Toronto</town><town>Ottawa</town></towns>');
8609+
8610+
xmlexists
8611+
------------
8612+
t
8613+
(1 row)
8614+
]]></screen>
8615+
</para>
8616+
8617+
<para>
8618+
The <literal>BY REF</literal> clauses have no effect in
8619+
PostgreSQL, but are allowed for SQL conformance and compatibility
8620+
with other implementations. Per SQL standard, the
8621+
first <literal>BY REF</literal> is required, the second is
8622+
optional. Also note that the SQL standard specifies
8623+
the <function>xmlexists</function> construct to take an XQuery
8624+
expression as first argument, but PostgreSQL currently only
8625+
supports XPath, which is a subset of XQuery.
8626+
</para>
8627+
</sect3>
85778628
</sect2>
85788629

85798630
<sect2 id="functions-xml-processing">

‎src/backend/parser/gram.y

Lines changed: 44 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
*
1212
*
1313
* IDENTIFICATION
14-
* $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.714 2010/07/25 23:21:21 rhaas Exp $
14+
* $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.715 2010/08/05 04:21:53 petere Exp $
1515
*
1616
* HISTORY
1717
* AUTHOR DATE MAJOR EVENT
@@ -425,6 +425,7 @@ static TypeName *TableFuncTypeName(List *columns);
425425
%type <target> xml_attribute_el
426426
%type <list> xml_attribute_list xml_attributes
427427
%type <node> xml_root_version opt_xml_root_standalone
428+
%type <node> xmlexists_argument
428429
%type <ival> document_or_content
429430
%type <boolean> xml_whitespace_option
430431

@@ -511,13 +512,13 @@ static TypeName *TableFuncTypeName(List *columns);
511512
OBJECT_P OF OFF OFFSET OIDS ON ONLY OPERATOR OPTION OPTIONS OR
512513
ORDER OUT_P OUTER_P OVER OVERLAPS OVERLAY OWNED OWNER
513514

514-
PARSER PARTIAL PARTITION PASSWORD PLACING PLANS POSITION
515+
PARSER PARTIAL PARTITION PASSING PASSWORD PLACING PLANS POSITION
515516
PRECEDING PRECISION PRESERVE PREPARE PREPARED PRIMARY
516517
PRIOR PRIVILEGES PROCEDURAL PROCEDURE
517518

518519
QUOTE
519520

520-
RANGE READ REAL REASSIGN RECHECK RECURSIVE REFERENCES REINDEX
521+
RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REINDEX
521522
RELATIVE_P RELEASE RENAME REPEATABLE REPLACE REPLICA RESET RESTART
522523
RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROW ROWS RULE
523524

@@ -539,7 +540,7 @@ static TypeName *TableFuncTypeName(List *columns);
539540

540541
WHEN WHERE WHITESPACE_P WINDOW WITH WITHOUT WORK WRAPPER WRITE
541542

542-
XML_P XMLATTRIBUTES XMLCONCAT XMLELEMENT XMLFOREST XMLPARSE
543+
XML_P XMLATTRIBUTES XMLCONCAT XMLELEMENT XMLEXISTS XMLFOREST XMLPARSE
543544
XMLPI XMLROOT XMLSERIALIZE
544545

545546
YEAR_P YES_P
@@ -9839,6 +9840,21 @@ func_expr: func_name '(' ')' over_clause
98399840
{
98409841
$$ = makeXmlExpr(IS_XMLELEMENT, $4, $6, $8, @1);
98419842
}
9843+
| XMLEXISTS '(' c_expr xmlexists_argument ')'
9844+
{
9845+
/* xmlexists(A PASSING [BY REF] B [BY REF]) is
9846+
* converted to xmlexists(A, B)*/
9847+
FuncCall *n = makeNode(FuncCall);
9848+
n->funcname = SystemFuncName("xmlexists");
9849+
n->args = list_make2($3, $4);
9850+
n->agg_order = NIL;
9851+
n->agg_star = FALSE;
9852+
n->agg_distinct = FALSE;
9853+
n->func_variadic = FALSE;
9854+
n->over = NULL;
9855+
n->location = @1;
9856+
$$ = (Node *)n;
9857+
}
98429858
| XMLFOREST '(' xml_attribute_list ')'
98439859
{
98449860
$$ = makeXmlExpr(IS_XMLFOREST, NULL, $3, NIL, @1);
@@ -9929,6 +9945,27 @@ xml_whitespace_option: PRESERVE WHITESPACE_P { $$ = TRUE; }
99299945
| /*EMPTY*/ { $$ = FALSE; }
99309946
;
99319947

9948+
/* We allow several variants for SQL and other compatibility. */
9949+
xmlexists_argument:
9950+
PASSING c_expr
9951+
{
9952+
$$ = $2;
9953+
}
9954+
| PASSING c_expr BY REF
9955+
{
9956+
$$ = $2;
9957+
}
9958+
| PASSING BY REF c_expr
9959+
{
9960+
$$ = $4;
9961+
}
9962+
| PASSING BY REF c_expr BY REF
9963+
{
9964+
$$ = $4;
9965+
}
9966+
;
9967+
9968+
99329969
/*
99339970
* Window Definitions
99349971
*/
@@ -10999,6 +11036,7 @@ unreserved_keyword:
1099911036
| PARSER
1100011037
| PARTIAL
1100111038
| PARTITION
11039+
| PASSING
1100211040
| PASSWORD
1100311041
| PLANS
1100411042
| PRECEDING
@@ -11015,6 +11053,7 @@ unreserved_keyword:
1101511053
| REASSIGN
1101611054
| RECHECK
1101711055
| RECURSIVE
11056+
| REF
1101811057
| REINDEX
1101911058
| RELATIVE_P
1102011059
| RELEASE
@@ -11148,6 +11187,7 @@ col_name_keyword:
1114811187
| XMLATTRIBUTES
1114911188
| XMLCONCAT
1115011189
| XMLELEMENT
11190+
| XMLEXISTS
1115111191
| XMLFOREST
1115211192
| XMLPARSE
1115311193
| XMLPI

‎src/backend/utils/adt/xml.c

Lines changed: 66 additions & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.98 2010/07/06 19:18:58 momjian Exp $
10+
* $PostgreSQL: pgsql/src/backend/utils/adt/xml.c,v 1.99 2010/08/05 04:21:54 petere Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -3295,24 +3295,20 @@ xml_xmlnodetoxmltype(xmlNodePtr cur)
32953295

32963296

32973297
/*
3298-
* Evaluate XPath expression and return array of XML values.
3298+
* Common code for xpath() and xmlexists()
32993299
*
3300-
* As we have no support of XQuery sequences yet, this function seems
3301-
* to be the most useful one (array of XML functions plays a role of
3302-
* some kind of substitution for XQuery sequences).
3300+
* Evaluate XPath expression and return number of nodes in res_items
3301+
* and array of XML values in astate.
33033302
*
33043303
* It is up to the user to ensure that the XML passed is in fact
33053304
* an XML document - XPath doesn't work easily on fragments without
33063305
* a context node being known.
33073306
*/
3308-
Datum
3309-
xpath(PG_FUNCTION_ARGS)
3310-
{
33113307
#ifdef USE_LIBXML
3312-
text *xpath_expr_text = PG_GETARG_TEXT_P(0);
3313-
xmltype *data = PG_GETARG_XML_P(1);
3314-
ArrayType *namespaces = PG_GETARG_ARRAYTYPE_P(2);
3315-
ArrayBuildState *astate = NULL;
3308+
static void
3309+
xpath_internal(text *xpath_expr_text, xmltype *data, ArrayType *namespaces,
3310+
int *res_nitems, ArrayBuildState **astate)
3311+
{
33163312
xmlParserCtxtPtr ctxt = NULL;
33173313
xmlDocPtr doc = NULL;
33183314
xmlXPathContextPtr xpathctx = NULL;
@@ -3324,7 +3320,6 @@ xpath(PG_FUNCTION_ARGS)
33243320
xmlChar *string;
33253321
xmlChar *xpath_expr;
33263322
int i;
3327-
int res_nitems;
33283323
int ndim;
33293324
Datum *ns_names_uris;
33303325
bool *ns_names_uris_nulls;
@@ -3339,7 +3334,7 @@ xpath(PG_FUNCTION_ARGS)
33393334
* ARRAY[ARRAY['myns', 'http://example.com'], ARRAY['myns2',
33403335
* 'http://example2.com']].
33413336
*/
3342-
ndim = ARR_NDIM(namespaces);
3337+
ndim = namespaces ? ARR_NDIM(namespaces) : 0;
33433338
if (ndim != 0)
33443339
{
33453340
int *dims;
@@ -3439,28 +3434,36 @@ xpath(PG_FUNCTION_ARGS)
34393434
xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
34403435
"invalid XPath expression");
34413436

3437+
/*
3438+
* Version 2.6.27 introduces a function named
3439+
* xmlXPathCompiledEvalToBoolean, which would be enough for
3440+
* xmlexists, but we can derive the existence by whether any
3441+
* nodes are returned, thereby preventing a library version
3442+
* upgrade and keeping the code the same.
3443+
*/
34423444
xpathobj = xmlXPathCompiledEval(xpathcomp, xpathctx);
34433445
if (xpathobj == NULL) /* TODO: reason? */
34443446
xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
34453447
"could not create XPath object");
34463448

34473449
/* return empty array in cases when nothing is found */
34483450
if (xpathobj->nodesetval == NULL)
3449-
res_nitems = 0;
3451+
*res_nitems = 0;
34503452
else
3451-
res_nitems = xpathobj->nodesetval->nodeNr;
3453+
*res_nitems = xpathobj->nodesetval->nodeNr;
34523454

3453-
if (res_nitems)
3455+
if (*res_nitems && astate)
34543456
{
3457+
*astate = NULL;
34553458
for (i = 0; i < xpathobj->nodesetval->nodeNr; i++)
34563459
{
34573460
Datum elem;
34583461
bool elemisnull = false;
34593462

34603463
elem = PointerGetDatum(xml_xmlnodetoxmltype(xpathobj->nodesetval->nodeTab[i]));
3461-
astate = accumArrayResult(astate, elem,
3462-
elemisnull, XMLOID,
3463-
CurrentMemoryContext);
3464+
*astate = accumArrayResult(*astate, elem,
3465+
elemisnull, XMLOID,
3466+
CurrentMemoryContext);
34643467
}
34653468
}
34663469
}
@@ -3485,6 +3488,28 @@ xpath(PG_FUNCTION_ARGS)
34853488
xmlXPathFreeContext(xpathctx);
34863489
xmlFreeDoc(doc);
34873490
xmlFreeParserCtxt(ctxt);
3491+
}
3492+
#endif /* USE_LIBXML */
3493+
3494+
/*
3495+
* Evaluate XPath expression and return array of XML values.
3496+
*
3497+
* As we have no support of XQuery sequences yet, this function seems
3498+
* to be the most useful one (array of XML functions plays a role of
3499+
* some kind of substitution for XQuery sequences).
3500+
*/
3501+
Datum
3502+
xpath(PG_FUNCTION_ARGS)
3503+
{
3504+
#ifdef USE_LIBXML
3505+
text *xpath_expr_text = PG_GETARG_TEXT_P(0);
3506+
xmltype *data = PG_GETARG_XML_P(1);
3507+
ArrayType *namespaces = PG_GETARG_ARRAYTYPE_P(2);
3508+
int res_nitems;
3509+
ArrayBuildState *astate;
3510+
3511+
xpath_internal(xpath_expr_text, data, namespaces,
3512+
&res_nitems, &astate);
34883513

34893514
if (res_nitems == 0)
34903515
PG_RETURN_ARRAYTYPE_P(construct_empty_array(XMLOID));
@@ -3495,3 +3520,24 @@ xpath(PG_FUNCTION_ARGS)
34953520
return 0;
34963521
#endif
34973522
}
3523+
3524+
/*
3525+
* Determines if the node specified by the supplied XPath exists
3526+
* in a given XML document, returning a boolean.
3527+
*/
3528+
Datum xmlexists(PG_FUNCTION_ARGS)
3529+
{
3530+
#ifdef USE_LIBXML
3531+
text *xpath_expr_text = PG_GETARG_TEXT_P(0);
3532+
xmltype *data = PG_GETARG_XML_P(1);
3533+
int res_nitems;
3534+
3535+
xpath_internal(xpath_expr_text, data, NULL,
3536+
&res_nitems, NULL);
3537+
3538+
PG_RETURN_BOOL(res_nitems > 0);
3539+
#else
3540+
NO_XML_SUPPORT();
3541+
return 0;
3542+
#endif
3543+
}

‎src/include/catalog/catversion.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -37,7 +37,7 @@
3737
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
3838
* Portions Copyright (c) 1994, Regents of the University of California
3939
*
40-
* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.588 2010/07/16 02:15:54 tgl Exp $
40+
* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.589 2010/08/05 04:21:54 petere Exp $
4141
*
4242
*-------------------------------------------------------------------------
4343
*/
@@ -53,6 +53,6 @@
5353
*/
5454

5555
/* yyyymmddN */
56-
#define CATALOG_VERSION_NO 201007151
56+
#define CATALOG_VERSION_NO 201008051
5757

5858
#endif

‎src/include/catalog/pg_proc.h

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.573 2010/07/29 20:09:25 tgl Exp $
10+
* $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.574 2010/08/05 04:21:54 petere Exp $
1111
*
1212
* NOTES
1313
* The script catalog/genbki.pl reads this file and generates .bki
@@ -4391,6 +4391,9 @@ DESCR("evaluate XPath expression, with namespaces support");
43914391
DATA(insert OID = 2932 ( xpath PGNSP PGUID 14 1 0 0 f f f t f i 2 0 143 "25 142" _null_ _null_ _null_ _null_ "select pg_catalog.xpath($1, $2, ''{}''::pg_catalog.text[])" _null_ _null_ _null_ ));
43924392
DESCR("evaluate XPath expression");
43934393

4394+
DATA(insert OID = 2614 ( xmlexists PGNSP PGUID 12 1 0 0 f f f t f i 2 0 16 "25 142" _null_ _null_ _null_ _null_ xmlexists _null_ _null_ _null_ ));
4395+
DESCR("test XML value against XPath expression");
4396+
43944397
/* uuid */
43954398
DATA(insert OID = 2952 ( uuid_in PGNSP PGUID 12 1 0 0 f f f t f i 1 0 2950 "2275" _null_ _null_ _null_ _null_ uuid_in _null_ _null_ _null_ ));
43964399
DESCR("I/O");

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