From: Joe Halpin <jhalpin100@gmail.com>
To: pgsql-interfaces@postgresql.org
Subject: Problem with trigger function in C
Date: Tue, 28 Oct 2008 14:34:41 -0500
Message-ID: <4dc28b160810281234g1292831awf4b8716d64f7f405@mail.gmail.com> (raw)
I'm new at this and I apologize if I got the wrong list, but I'm
trying to write a trigger function in C which is linked in with
libxqilla and is supposed to run an xquery against some xml we have
stored in a column. I find that when the function is entered fcinfo is
null, which causes a segfault.
I copied the example trigger function from the documentation at
http://www.postgresql.org/docs/8.3/static/trigger-example.html. I
added some debug output to tell that fcinfo is null.
I built the function by copying the makefile in the contrib directory
for the xml2 demo and modifying it a bit. Here's what I wound up with:
--- start ---
MODULE_big = xqueryTrigger
PG_CPPFLAGS = -I$(libpq_srcdir)
OBJS = xqueryTrigger.o
DATA = libxqueryTrigger.so
SHLIB_LINK = -L/usr/local/lib -lxqilla -lxerces-c-3.0 -lcrypto -lssl
ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = contrib/xml2
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif
--- stop ---
Here's the trigger function (or at least as far as it gets)
--- start ---
#include "postgres.h"
#include "executor/spi.h" /* this is what you need to work with SPI */
#include "commands/trigger.h" /* ... and triggers */
#include <fmgr.h>
#ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif
typedef void*(*memFunc)(unsigned int sz);
extern int runQuery(const char *qry, const char *xml, char **result,
memFunc allocator);
extern Datum xqueryTrigger(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(xqueryTrigger);
void *memAllocator(unsigned int);
Datum xquerytrigger(PG_FUNCTION_ARGS);
void *memAllocator(unsigned int sz)
{
return palloc(sz);
}
Datum
xquerytrigger(PG_FUNCTION_ARGS)
{
TriggerData *trigdata;
TupleDesc tupdesc;
HeapTuple rettuple;
char *when;
bool checknull;
bool isnull;
int ret, i;
char *status;
elog(INFO, "Entering xquerytrigger()");
elog(INFO, "getting TriggerData...");
elog(INFO, "fcinfo = %p", fcinfo);
elog(INFO, "fcinfo->context = %p", fcinfo->context);
trigdata = (TriggerData *) fcinfo->context;
--- stop ---
Any advice would be appreciated.
Thanks
Joe
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Cc: jhalpin100@gmail.com
Subject: Re: Problem with trigger function in C
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