Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Quoting Peter Eisentraut :
It would be nice to make XMLEXISTS work as in the standard, seeing how
many others are providing the same interface.
...
I think providing XPath is enough, at least for now.
Hi Peter,
From piecing together sections 8.4 () and 6.18
(), I believe the full call signature would be (apologies
if my bracketing isn't right):
XMLEXISTS
(
xquery_expression
[
PASSING {BY REF|BY VALUE}
{ (xml_expression [BY REF|BY VALUE])
| (xml_expression AS identifier)
}
[, ...]
]
)
Seeing as we're only intereseted in XPath for the moment and most of
the syntax above is only really relevant to XQuery, I would suggest
the following as accepatable until full XQuery support comes:
XMLEXISTS
(
xpath_expression
[
PASSING BY REF xml_expression [BY REF]
]
)
There is one drawback in this approach, namely xml namespace support.
I think borrowing the solution used in the xpath() (i.e. passing a
nsarray) is out of the question as it won't be future proofed against
full XQuery support. This is because the declaration of namespaces in
XQuery is actually part of the query itself. I also think it
inappropriate to attempt to parse the xpath_expression looking for
XQuery style namespace declartions. So I think we ignore declared
namespace support for the moment and just get the syntax correct ready
for XQuery support in the hopefully near future.
Do you agree with what I have proposed?
Regards,
--
Mike Fowler
--
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Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Mike Fowler wrote: > Tom Lane wrote: > > Robert Haas writes: > > > >> On Tue, May 25, 2010 at 1:09 PM, Mike Fowler wrote: > >> > We're unlikely to accept this patch if it changes the minimum version > of libxml2 required to compile PostgreSQL > > >>> Why? 2.6.27 is almost 4 years old. > >> At a minimum, I think it's fair to say that the burden is on you to > >> justify what it's worth bumping the version number. > >> > > > > Yes. Increasing the minimum required version of some library is a Big > > Deal, we don't do it on a whim. And we definitely don't do it just > > because it's old. > > > > regards, tom lane > > > > > > OK, I consider myself suitably educated/chastised. I now understand why > a version bump is such a big deal. Your objections are all reasonable, I > suppose I'm just used to living on the bleeding edge of everything. > Consequently I have changed the code to produce the same result in a > different way without using the new function. I've down-graded my > version to 2.6.26 and it all compiles cleanly. Please find attached my > revised patch, and thanks all for your advise. FYI, it is often good to add a comment in the C code about why you didn't use the new XML function so if the issue comes up again, we know why, and in 10 years, we can use it. ;-) -- Bruce Momjian http://momjian.us EnterpriseDB http://enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Peter Eisentraut wrote: On ons, 2010-05-26 at 11:47 +0100, Mike Fowler wrote: The XMLEXISTS function works with XQuery expressions and doesn't have the call signature that your patch implements Looking at the manuals of Oracle, Derby and DB2 I see how the call signature differs. I also note that Oracle's implementation is XPath only, Derby's is partial XQuery and DB2 appears to be full XQuery. What do people prefer me to do? I see the options as: 1) Change the call signature to match the standard 2) Change the function name back to xpath_exists It would be nice to make XMLEXISTS work as in the standard, seeing how many others are providing the same interface. Should option one be the more popular there's further choices: 1) Integrate XQuery support to completely match the standard, however this will require the addition of a new library libxquery 2) Leave the XPath as is, inline with Oracle's implementation 3) Hybrid approach. Since XML is a comple time option, add XQuery as another. Conditional completion gives the full XQuery support when available or just the XPath when not I think providing XPath is enough, at least for now Agreed. I'll get another patch together in the next day or two. Regards, -- Mike Fowler Registered Linux user: 379787 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
On ons, 2010-05-26 at 11:47 +0100, Mike Fowler wrote: > > The XMLEXISTS function works with XQuery expressions and doesn't have > > the call signature that your patch implements > > Looking at the manuals of Oracle, Derby and DB2 I see how the call > signature differs. I also note that Oracle's implementation is XPath > only, Derby's is partial XQuery and DB2 appears to be full XQuery. > > What do people prefer me to do? I see the options as: > > 1) Change the call signature to match the standard > 2) Change the function name back to xpath_exists It would be nice to make XMLEXISTS work as in the standard, seeing how many others are providing the same interface. > Should option one be the more popular there's further choices: > > 1) Integrate XQuery support to completely match the standard, however > this will require the addition of a new library libxquery > 2) Leave the XPath as is, inline with Oracle's implementation > 3) Hybrid approach. Since XML is a comple time option, add XQuery as > another. Conditional completion gives the full XQuery support when > available or just the XPath when not I think providing XPath is enough, at least for now. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Peter Eisentraut wrote: On tis, 2010-05-25 at 15:31 +0100, Mike Fowler wrote: I've been reading the SQL/XML standard and discovered that it defines a function named XMLEXISTS that does exactly what the todo item xpath_exists defines. My original patch named the function as per the todo but I think using the function name from the standard is a better idea. So this patch is the same as before, but the function is now named XMLEXISTS instead of xpath_exists. The XMLEXISTS function works with XQuery expressions and doesn't have the call signature that your patch implements Looking at the manuals of Oracle, Derby and DB2 I see how the call signature differs. I also note that Oracle's implementation is XPath only, Derby's is partial XQuery and DB2 appears to be full XQuery. What do people prefer me to do? I see the options as: 1) Change the call signature to match the standard 2) Change the function name back to xpath_exists Should option one be the more popular there's further choices: 1) Integrate XQuery support to completely match the standard, however this will require the addition of a new library libxquery 2) Leave the XPath as is, inline with Oracle's implementation 3) Hybrid approach. Since XML is a comple time option, add XQuery as another. Conditional completion gives the full XQuery support when available or just the XPath when not Thoughts? -- Mike Fowler Registered Linux user: 379787 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard (was: Add xpath_exists Function)
On tis, 2010-05-25 at 15:31 +0100, Mike Fowler wrote: > I've been reading the SQL/XML standard and discovered that it defines a > function named XMLEXISTS that does exactly what the todo item > xpath_exists defines. My original patch named the function as per the > todo but I think using the function name from the standard is a better > idea. So this patch is the same as before, but the function is now named > XMLEXISTS instead of xpath_exists. The XMLEXISTS function works with XQuery expressions and doesn't have the call signature that your patch implements. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Tom Lane wrote:
Robert Haas writes:
On Tue, May 25, 2010 at 1:09 PM, Mike Fowler wrote:
We're unlikely to accept this patch if it changes the minimum version
of libxml2 required to compile PostgreSQL
Why? 2.6.27 is almost 4 years old.
At a minimum, I think it's fair to say that the burden is on you to
justify what it's worth bumping the version number.
Yes. Increasing the minimum required version of some library is a Big
Deal, we don't do it on a whim. And we definitely don't do it just
because it's old.
regards, tom lane
OK, I consider myself suitably educated/chastised. I now understand why
a version bump is such a big deal. Your objections are all reasonable, I
suppose I'm just used to living on the bleeding edge of everything.
Consequently I have changed the code to produce the same result in a
different way without using the new function. I've down-graded my
version to 2.6.26 and it all compiles cleanly. Please find attached my
revised patch, and thanks all for your advise.
Regards,
--
Mike Fowler
Registered Linux user: 379787
Index: src/backend/utils/adt/xml.c
===
RCS file: /home/mfowler/cvsrepo/pgrepo/pgsql/src/backend/utils/adt/xml.c,v
retrieving revision 1.97
diff -c -r1.97 xml.c
*** src/backend/utils/adt/xml.c 3 Mar 2010 17:29:45 - 1.97
--- src/backend/utils/adt/xml.c 26 May 2010 09:36:50 -
***
*** 3495,3497
--- 3495,3678
return 0;
#endif
}
+
+ /*
+ * Determines if the node specified by the supplied XPath exists
+ * in a given XML document, returning a boolean.
+ *
+ * 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
+ xmlexists(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);
+ xmlParserCtxtPtr ctxt = NULL;
+ xmlDocPtr doc = NULL;
+ xmlXPathContextPtr xpathctx = NULL;
+ xmlXPathCompExprPtr xpathcomp = NULL;
+ xmlXPathObjectPtr xpathobj = NULL;
+ char *datastr;
+ int32 len;
+ int32 xpath_len;
+ xmlChar*string;
+ xmlChar*xpath_expr;
+ int i;
+ int ndim;
+ Datum *ns_names_uris;
+ bool *ns_names_uris_nulls;
+ int ns_count;
+ int result;
+
+ /*
+ * Namespace mappings are passed as text[]. If an empty array is passed
+ * (ndim = 0, "0-dimensional"), then there are no namespace mappings.
+ * Else, a 2-dimensional array with length of the second axis being equal
+ * to 2 should be passed, i.e., every subarray contains 2 elements, the
+ * first element defining the name, the second one the URI. Example:
+ * ARRAY[ARRAY['myns', 'http://example.com'], ARRAY['myns2',
+ * 'http://example2.com']].
+ */
+ ndim = ARR_NDIM(namespaces);
+ if (ndim != 0)
+ {
+ int *dims;
+
+ dims = ARR_DIMS(namespaces);
+
+ if (ndim != 2 || dims[1] != 2)
+ ereport(ERROR,
+ (errcode(ERRCODE_DATA_EXCEPTION),
+ errmsg("invalid array for XML namespace mapping"),
+ errdetail("The array must be two-dimensional with length of the second axis equal to 2.")));
+
+ Assert(ARR_ELEMTYPE(namespaces) == TEXTOID);
+
+ deconstruct_array(namespaces, TEXTOID, -1, false, 'i',
+ &ns_names_uris, &ns_names_uris_nulls,
+ &ns_count);
+
+ Assert((ns_count % 2) == 0); /* checked above */
+ ns_count /= 2; /* count pairs only */
+ }
+ else
+ {
+ ns_names_uris = NULL;
+ ns_names_uris_nulls = NULL;
+ ns_count = 0;
+ }
+
+ datastr = VARDATA(data);
+ len = VARSIZE(data) - VARHDRSZ;
+ xpath_len = VARSIZE(xpath_expr_text) - VARHDRSZ;
+ if (xpath_len == 0)
+ ereport(ERROR,
+ (errcode(ERRCODE_DATA_EXCEPTION),
+ errmsg("empty XPath expression")));
+
+ string = (xmlChar *) palloc((len + 1) * sizeof(xmlChar));
+ memcpy(string, datastr, len);
+ string[len] = '\0';
+
+ xpath_expr = (xmlChar *) palloc((xpath_len + 1) * sizeof(xmlChar));
+ memcpy(xpath_expr, VARDATA(xpath_expr_text), xpath_len);
+ xpath_expr[xpath_len] = '\0';
+
+ pg_xml_init();
+ xmlInitParser();
+
+ PG_TRY();
+ {
+ /*
+ * redundant XML parsing (two parsings for the same value during one
+ * command execution are possible)
+ */
+ ctxt = xmlNewParserCtxt();
+ if (ctxt == NULL)
+ xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
+ "could not allocate parser context");
+ doc = xmlCtxtReadMemory(ctxt, (char *) string, len, NULL, NULL, 0);
+ if (doc == NULL)
+ xml_ereport(ERROR, ERRCODE_INVALID_XML_DOCUMENT,
+ "could not parse XML document");
+ xpathctx = xmlXPathNewContext(doc);
+ if (xpathctx == NULL)
+ xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
+ "could not allocate XPath context");
+ xpathctx->node = xmlDocGetRootElement(doc);
+ if (xpathctx->node == NULL)
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Robert Haas writes: > On Tue, May 25, 2010 at 1:09 PM, Mike Fowler wrote: >>> We're unlikely to accept this patch if it changes the minimum version >>> of libxml2 required to compile PostgreSQL >> >> Why? 2.6.27 is almost 4 years old. > Because we work hard to minimize our dependencies and make them as > non-onerous as possible. > At a minimum, I think it's fair to say that the burden is on you to > justify what it's worth bumping the version number. Yes. Increasing the minimum required version of some library is a Big Deal, we don't do it on a whim. And we definitely don't do it just because it's old. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Robert Haas wrote: On Tue, May 25, 2010 at 1:09 PM, Mike Fowler wrote: We're unlikely to accept this patch if it changes the minimum version of libxml2 required to compile PostgreSQL Why? 2.6.27 is almost 4 years old. Because we work hard to minimize our dependencies and make them as non-onerous as possible. At a minimum, I think it's fair to say that the burden is on you to justify what it's worth bumping the version number. If there is some major speed or performance advantage to using the newer API, maybe we'll consider it. But if it's just a few extra lines of code to work around it, then it's better to write those extra lines of code rather than potentially force users to upgrade packages they're otherwise happy with. The real issue is what's going to be available on most of the platforms we build on. Unfortunately, 2.6.26 is what's on my CentOS 5.4 boxes, for example. I'm sure we don't want to make 9.1 not buildable with the installed libraries on still fairly current RedHat-derived platforms. cheers andrew -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
On 05/25/2010 01:09 PM, Mike Fowler wrote: Why? 2.6.27 is almost 4 years old. RHEL 5 ships with 2.6.26. I imagine that supporting it is very desirable, regardless of its age, since that is unfortunately still the latest version of RHEL. -- m. tharp -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
On Tue, May 25, 2010 at 1:09 PM, Mike Fowler wrote: >> We're unlikely to accept this patch if it changes the minimum version >> of libxml2 required to compile PostgreSQL > > Why? 2.6.27 is almost 4 years old. Because we work hard to minimize our dependencies and make them as non-onerous as possible. At a minimum, I think it's fair to say that the burden is on you to justify what it's worth bumping the version number. If there is some major speed or performance advantage to using the newer API, maybe we'll consider it. But if it's just a few extra lines of code to work around it, then it's better to write those extra lines of code rather than potentially force users to upgrade packages they're otherwise happy with. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Robert Haas wrote:
On Tue, May 25, 2010 at 12:04 PM, Mike Fowler wrote:
Erik Rijkers wrote:
libxml2.x86_64 2.6.26-2.1.2.8 installed
libxml2-devel.x86_642.6.26-2.1.2.8 installed
Thanks for testing my patch Erik. It turns out I've got libxml2 installed at
version 2.7.5. Searching the gnome mailing lists, it turns out
xmlXPathCompiledEvalToBoolean was added (unbelievably) in the very next
version from yours, 2.6.27 (see:
http://mail.gnome.org/archives/xml/2006-October/msg00119.html).
We're unlikely to accept this patch if it changes the minimum version
of libxml2 required to compile PostgreSQL
Why? 2.6.27 is almost 4 years old.
I realise that my patch didn't update configure and configure.in, and
indeed I didn't think of it when I responded to Erik (I'm too used to
the Java world where people manage their own dependencies). I've now
attached the updated patch which ups the check from version 2.6.23 to
2.6.27.
Regards,
--
Mike Fowler
Registered Linux user: 379787
Index: configure
===
RCS file: /home/mfowler/cvsrepo/pgrepo/pgsql/configure,v
retrieving revision 1.679
diff -c -r1.679 configure
*** configure 13 May 2010 22:07:40 - 1.679
--- configure 25 May 2010 16:57:49 -
***
*** 9079,9087
if test "$with_libxml" = yes ; then
! { $as_echo "$as_me:$LINENO: checking for xmlSaveToBuffer in -lxml2" >&5
! $as_echo_n "checking for xmlSaveToBuffer in -lxml2... " >&6; }
! if test "${ac_cv_lib_xml2_xmlSaveToBuffer+set}" = set; then
$as_echo_n "(cached) " >&6
else
ac_check_lib_save_LIBS=$LIBS
--- 9079,9087
if test "$with_libxml" = yes ; then
! { $as_echo "$as_me:$LINENO: checking for xmlXPathCompiledEvalToBoolean in -lxml2" >&5
! $as_echo_n "checking for xmlXPathCompiledEvalToBoolean in -lxml2... " >&6; }
! if test "${ac_cv_lib_xml2_xmlXPathCompiledEvalToBoolean+set}" = set; then
$as_echo_n "(cached) " >&6
else
ac_check_lib_save_LIBS=$LIBS
***
*** 9099,9109
#ifdef __cplusplus
extern "C"
#endif
! char xmlSaveToBuffer ();
int
main ()
{
! return xmlSaveToBuffer ();
;
return 0;
}
--- 9099,9109
#ifdef __cplusplus
extern "C"
#endif
! char xmlXPathCompiledEvalToBoolean ();
int
main ()
{
! return xmlXPathCompiledEvalToBoolean ();
;
return 0;
}
***
*** 9129,9140
test "$cross_compiling" = yes ||
$as_test_x conftest$ac_exeext
}; then
! ac_cv_lib_xml2_xmlSaveToBuffer=yes
else
$as_echo "$as_me: failed program was:" >&5
sed 's/^/| /' conftest.$ac_ext >&5
! ac_cv_lib_xml2_xmlSaveToBuffer=no
fi
rm -rf conftest.dSYM
--- 9129,9140
test "$cross_compiling" = yes ||
$as_test_x conftest$ac_exeext
}; then
! ac_cv_lib_xml2_xmlXPathCompiledEvalToBoolean=yes
else
$as_echo "$as_me: failed program was:" >&5
sed 's/^/| /' conftest.$ac_ext >&5
! ac_cv_lib_xml2_xmlXPathCompiledEvalToBoolean=no
fi
rm -rf conftest.dSYM
***
*** 9142,9150
conftest$ac_exeext conftest.$ac_ext
LIBS=$ac_check_lib_save_LIBS
fi
! { $as_echo "$as_me:$LINENO: result: $ac_cv_lib_xml2_xmlSaveToBuffer" >&5
! $as_echo "$ac_cv_lib_xml2_xmlSaveToBuffer" >&6; }
! if test "x$ac_cv_lib_xml2_xmlSaveToBuffer" = x""yes; then
cat >>confdefs.h <<_ACEOF
#define HAVE_LIBXML2 1
_ACEOF
--- 9142,9150
conftest$ac_exeext conftest.$ac_ext
LIBS=$ac_check_lib_save_LIBS
fi
! { $as_echo "$as_me:$LINENO: result: $ac_cv_lib_xml2_xmlXPathCompiledEvalToBoolean" >&5
! $as_echo "$ac_cv_lib_xml2_xmlXPathCompiledEvalToBoolean" >&6; }
! if test "x$ac_cv_lib_xml2_xmlXPathCompiledEvalToBoolean" = x""yes; then
cat >>confdefs.h <<_ACEOF
#define HAVE_LIBXML2 1
_ACEOF
***
*** 9152,9159
LIBS="-lxml2 $LIBS"
else
! { { $as_echo "$as_me:$LINENO: error: library 'xml2' (version >= 2.6.23) is required for XML support" >&5
! $as_echo "$as_me: error: library 'xml2' (version >= 2.6.23) is required for XML support" >&2;}
{ (exit 1); exit 1; }; }
fi
--- 9152,9159
LIBS="-lxml2 $LIBS"
else
! { { $as_echo "$as_me:$LINENO: error: library 'xml2' (version >= 2.6.27) is required for XML support" >&5
! $as_echo "$as_me: error: library 'xml2' (version >= 2.6.27) is required for XML support" >&2;}
{ (exit 1); exit 1; }; }
fi
Index: configure.in
===
RCS file: /home/mfowler/cvsrepo/pgrepo/pgsql/configure.in,v
retrieving revision 1.627
diff -c -r1.627 configure.in
*** configure.in 13 May 2010 22:07:42 - 1.627
--- configure.in 25 May 2010 16:22:32 -
***
*** 940,946
fi
if test "$with_libxml" = yes ; then
! AC_CHECK_LIB(xml2, xmlSaveToBuffer, [], [AC_MSG_ERROR([library 'xml2' (version >= 2.6.23) is required for XML support])])
fi
if test "$with_libxslt" = yes ; then
--- 940,946 ---
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
On Tue, May 25, 2010 at 12:04 PM, Mike Fowler wrote: > Erik Rijkers wrote: >> >> libxml2.x86_64 2.6.26-2.1.2.8 installed >> libxml2-devel.x86_64 2.6.26-2.1.2.8 installed >> > > Thanks for testing my patch Erik. It turns out I've got libxml2 installed at > version 2.7.5. Searching the gnome mailing lists, it turns out > xmlXPathCompiledEvalToBoolean was added (unbelievably) in the very next > version from yours, 2.6.27 (see: > http://mail.gnome.org/archives/xml/2006-October/msg00119.html). We're unlikely to accept this patch if it changes the minimum version of libxml2 required to compile PostgreSQL. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise Postgres Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard
Erik Rijkers wrote: libxml2.x86_64 2.6.26-2.1.2.8 installed libxml2-devel.x86_642.6.26-2.1.2.8 installed Thanks for testing my patch Erik. It turns out I've got libxml2 installed at version 2.7.5. Searching the gnome mailing lists, it turns out xmlXPathCompiledEvalToBoolean was added (unbelievably) in the very next version from yours, 2.6.27 (see: http://mail.gnome.org/archives/xml/2006-October/msg00119.html). Regards, -- Mike Fowler Registered Linux user: 379787 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard (was: Add xpath_exists Function)
On Tue, May 25, 2010 16:31, Mike Fowler wrote: > I've been reading the SQL/XML standard and discovered that it defines a > function named XMLEXISTS that does exactly what the todo item > xpath_exists defines. My original patch named the function as per the > todo but I think using the function name from the standard is a better > idea. So this patch is the same as before, but the function is now named > XMLEXISTS instead of xpath_exists. > I tried this path (cvs HEAD, applies without error), but get this error: [...] utils/adt/xml.o: In function `xmlexists': /var/data1/pg_stuff/pg_sandbox/pgsql.xmlexists/src/backend/utils/adt/xml.c:3639: undefined reference to `xmlXPathCompiledEvalToBoolean' collect2: ld returned 1 exit status make[2]: *** [postgres] Error 1 make[2]: Leaving directory `/var/data1/pg_stuff/pg_sandbox/pgsql.xmlexists/src/backend' make[1]: *** [all] Error 2 make[1]: Leaving directory `/var/data1/pg_stuff/pg_sandbox/pgsql.xmlexists/src' make: *** [all] Error 2 ./configure --prefix=/var/data1/pg_stuff/pg_installations/pgsql.xmlexists --with-pgport=6548 --quiet --enable-depend --enable-cassert --enable-debug --with-openssl --with-perl --with-libxml --with-libxslt centos 5.4 2.6.18-164.el5 x86_64 GNU/Linux libxml2.x86_64 2.6.26-2.1.2.8 installed libxml2-devel.x86_642.6.26-2.1.2.8 installed Erik Rijkers -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] [PATCH] Add XMLEXISTS function from the SQL/XML standard (was: Add xpath_exists Function)
I've been reading the SQL/XML standard and discovered that it defines a
function named XMLEXISTS that does exactly what the todo item
xpath_exists defines. My original patch named the function as per the
todo but I think using the function name from the standard is a better
idea. So this patch is the same as before, but the function is now named
XMLEXISTS instead of xpath_exists.
Regards,
--
Mike Fowler
Registered Linux user: 379787
Index: src/backend/utils/adt/xml.c
===
RCS file: /home/mfowler/cvsrepo/pgrepo/pgsql/src/backend/utils/adt/xml.c,v
retrieving revision 1.97
diff -c -r1.97 xml.c
*** src/backend/utils/adt/xml.c 3 Mar 2010 17:29:45 - 1.97
--- src/backend/utils/adt/xml.c 25 May 2010 14:02:33 -
***
*** 3495,3497
--- 3495,3668
return 0;
#endif
}
+
+ /*
+ * Determines if the node specified by the supplied XPath exists
+ * in a given XML document, returning a boolean.
+ *
+ * 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
+ xmlexists(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);
+ xmlParserCtxtPtr ctxt = NULL;
+ xmlDocPtr doc = NULL;
+ xmlXPathContextPtr xpathctx = NULL;
+ xmlXPathCompExprPtr xpathcomp = NULL;
+ char *datastr;
+ int32 len;
+ int32 xpath_len;
+ xmlChar*string;
+ xmlChar*xpath_expr;
+ int i;
+ int ndim;
+ Datum *ns_names_uris;
+ bool *ns_names_uris_nulls;
+ int ns_count;
+ int result;
+
+ /*
+ * Namespace mappings are passed as text[]. If an empty array is passed
+ * (ndim = 0, "0-dimensional"), then there are no namespace mappings.
+ * Else, a 2-dimensional array with length of the second axis being equal
+ * to 2 should be passed, i.e., every subarray contains 2 elements, the
+ * first element defining the name, the second one the URI. Example:
+ * ARRAY[ARRAY['myns', 'http://example.com'], ARRAY['myns2',
+ * 'http://example2.com']].
+ */
+ ndim = ARR_NDIM(namespaces);
+ if (ndim != 0)
+ {
+ int *dims;
+
+ dims = ARR_DIMS(namespaces);
+
+ if (ndim != 2 || dims[1] != 2)
+ ereport(ERROR,
+ (errcode(ERRCODE_DATA_EXCEPTION),
+ errmsg("invalid array for XML namespace mapping"),
+ errdetail("The array must be two-dimensional with length of the second axis equal to 2.")));
+
+ Assert(ARR_ELEMTYPE(namespaces) == TEXTOID);
+
+ deconstruct_array(namespaces, TEXTOID, -1, false, 'i',
+ &ns_names_uris, &ns_names_uris_nulls,
+ &ns_count);
+
+ Assert((ns_count % 2) == 0); /* checked above */
+ ns_count /= 2; /* count pairs only */
+ }
+ else
+ {
+ ns_names_uris = NULL;
+ ns_names_uris_nulls = NULL;
+ ns_count = 0;
+ }
+
+ datastr = VARDATA(data);
+ len = VARSIZE(data) - VARHDRSZ;
+ xpath_len = VARSIZE(xpath_expr_text) - VARHDRSZ;
+ if (xpath_len == 0)
+ ereport(ERROR,
+ (errcode(ERRCODE_DATA_EXCEPTION),
+ errmsg("empty XPath expression")));
+
+ string = (xmlChar *) palloc((len + 1) * sizeof(xmlChar));
+ memcpy(string, datastr, len);
+ string[len] = '\0';
+
+ xpath_expr = (xmlChar *) palloc((xpath_len + 1) * sizeof(xmlChar));
+ memcpy(xpath_expr, VARDATA(xpath_expr_text), xpath_len);
+ xpath_expr[xpath_len] = '\0';
+
+ pg_xml_init();
+ xmlInitParser();
+
+ PG_TRY();
+ {
+ /*
+ * redundant XML parsing (two parsings for the same value during one
+ * command execution are possible)
+ */
+ ctxt = xmlNewParserCtxt();
+ if (ctxt == NULL)
+ xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
+ "could not allocate parser context");
+ doc = xmlCtxtReadMemory(ctxt, (char *) string, len, NULL, NULL, 0);
+ if (doc == NULL)
+ xml_ereport(ERROR, ERRCODE_INVALID_XML_DOCUMENT,
+ "could not parse XML document");
+ xpathctx = xmlXPathNewContext(doc);
+ if (xpathctx == NULL)
+ xml_ereport(ERROR, ERRCODE_OUT_OF_MEMORY,
+ "could not allocate XPath context");
+ xpathctx->node = xmlDocGetRootElement(doc);
+ if (xpathctx->node == NULL)
+ xml_ereport(ERROR, ERRCODE_INTERNAL_ERROR,
+ "could not find root XML element");
+
+ /* register namespaces, if any */
+ if (ns_count > 0)
+ {
+ for (i = 0; i < ns_count; i++)
+ {
+ char *ns_name;
+ char *ns_uri;
+
+ if (ns_names_uris_nulls[i * 2] ||
+ ns_names_uris_nulls[i * 2 + 1])
+ ereport(ERROR,
+ (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
+ errmsg("neither namespace name nor URI may be null")));
+ ns_name = TextDatumGetCString(ns_names_uris[i * 2]);
+ ns_uri = TextDatumGetCString(ns_names_uris[i * 2 + 1]);
+ if (xmlXPathRegisterNs(xpathctx,
+ (xmlChar *) ns_name,
+ (xmlChar *) ns_uri) != 0)
+ e
