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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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2
doc/src/sgml/func.sgml
View File

@ -9275,6 +9275,8 @@ SELECT xml_is_well_formed_document('<pg:foo xmlns:pg="http://postgresql.org/stuf
against the XML value
<replaceable>xml</replaceable>. It returns an array of XML values
corresponding to the node set produced by the XPath expression.
If the XPath expression returns a scalar value rather than a node set,
a single-element array is returned.
</para>
<para>

114
src/backend/utils/adt/xml.c
View File

@ -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();
{

48
src/test/regress/expected/xml.out
View File

@ -601,6 +601,42 @@ SELECT xpath('//@value', '<root value="&lt;"/>');
{&lt;}
(1 row)
SELECT xpath('''<<invalid>>''', '<root/>');
xpath
---------------------------
{&lt;&lt;invalid&gt;&gt;}
(1 row)
SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
xpath
-------
{3}
(1 row)
SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
xpath
---------
{false}
(1 row)
SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
xpath
--------
{true}
(1 row)
SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
xpath
--------
{root}
(1 row)
SELECT xpath('/nosuchtag', '<root/>');
xpath
-------
{}
(1 row)
-- Test xmlexists and xpath_exists
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
xmlexists
@ -614,6 +650,12 @@ SELECT xmlexists('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><town>Bid
t
(1 row)
SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
xmlexists
-----------
t
(1 row)
SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
xpath_exists
--------------
@ -626,6 +668,12 @@ SELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><town>Bidford-on-Avon
t
(1 row)
SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
xpath_exists
--------------
t
(1 row)
INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
INSERT INTO xmltest VALUES (5, '<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
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);

48
src/test/regress/expected/xml_1.out
View File

@ -516,6 +516,42 @@ LINE 1: SELECT xpath('//@value', '<root value="&lt;"/>');
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xpath('''<<invalid>>''', '<root/>');
ERROR: unsupported XML feature
LINE 1: SELECT xpath('''<<invalid>>''', '<root/>');
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
ERROR: unsupported XML feature
LINE 1: SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
ERROR: unsupported XML feature
LINE 1: SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
ERROR: unsupported XML feature
LINE 1: SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
ERROR: unsupported XML feature
LINE 1: SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xpath('/nosuchtag', '<root/>');
ERROR: unsupported XML feature
LINE 1: SELECT xpath('/nosuchtag', '<root/>');
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
-- Test xmlexists and xpath_exists
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
ERROR: unsupported XML feature
@ -529,6 +565,12 @@ LINE 1: ...sts('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><t...
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
ERROR: unsupported XML feature
LINE 1: ...LECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>')...
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
ERROR: unsupported XML feature
LINE 1: ...ELECT xpath_exists('//town[text() = ''Toronto'']','<towns><t...
@ -541,6 +583,12 @@ LINE 1: ...ELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><t...
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
ERROR: unsupported XML feature
LINE 1: SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
^
DETAIL: This functionality requires the server to be built with libxml support.
HINT: You need to rebuild PostgreSQL using --with-libxml.
INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
ERROR: unsupported XML feature
LINE 1: INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</n...

8
src/test/regress/sql/xml.sql
View File

@ -177,12 +177,20 @@ SELECT xpath('//loc:piece/@id', '<local:data xmlns:local="http://127.0.0.1"><loc
SELECT xpath('//b', '<a>one <b>two</b> three <b>etc</b></a>');
SELECT xpath('//text()', '<root>&lt;</root>');
SELECT xpath('//@value', '<root value="&lt;"/>');
SELECT xpath('''<<invalid>>''', '<root/>');
SELECT xpath('count(//*)', '<root><sub/><sub/></root>');
SELECT xpath('count(//*)=0', '<root><sub/><sub/></root>');
SELECT xpath('count(//*)=3', '<root><sub/><sub/></root>');
SELECT xpath('name(/*)', '<root><sub/><sub/></root>');
SELECT xpath('/nosuchtag', '<root/>');
-- Test xmlexists and xpath_exists
SELECT xmlexists('//town[text() = ''Toronto'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
SELECT xmlexists('//town[text() = ''Cwmbran'']' PASSING BY REF '<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>');
SELECT xmlexists('count(/nosuchtag)' PASSING BY REF '<root/>');
SELECT xpath_exists('//town[text() = ''Toronto'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
SELECT xpath_exists('//town[text() = ''Cwmbran'']','<towns><town>Bidford-on-Avon</town><town>Cwmbran</town><town>Bristol</town></towns>'::xml);
SELECT xpath_exists('count(/nosuchtag)', '<root/>'::xml);
INSERT INTO xmltest VALUES (4, '<menu><beers><name>Budvar</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);
INSERT INTO xmltest VALUES (5, '<menu><beers><name>Molson</name><cost>free</cost><name>Carling</name><cost>lots</cost></beers></menu>'::xml);