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Simple Postgres audit trigger written in C. Tested with PG 10.4
#include "postgres.h"
#include "access/htup_details.h"
#include "catalog/pg_type.h"
#include "commands/trigger.h"
#include "executor/spi.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/rel.h"
#include "utils/datetime.h"
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(set_audit_columns_if_empty);
Datum
set_audit_columns_if_empty(PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *) fcinfo->context;
Trigger *trigger; /* to get trigger name */
int nargs; /* # of arguments */
bool newnull = false; /* null flag */
char **args; /* arguments */
char *relname; /* triggered relation name */
char *valbuf;
Relation rel; /* triggered relation */
HeapTuple rettuple = NULL;
TupleDesc tupdesc; /* tuple description */
int attnum;
Datum newval; /* for new timestamp */
/* sanity checks from autoinc.c */
if (!CALLED_AS_TRIGGER(fcinfo))
/* internal error */
elog(ERROR, "set_audit_columns_if_empty: not fired by trigger manager");
if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
/* internal error */
elog(ERROR, "set_audit_columns_if_empty: must be fired for row");
if (!TRIGGER_FIRED_BEFORE(trigdata->tg_event))
/* internal error */
elog(ERROR, "set_audit_columns_if_empty: must be fired before event");
if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
rettuple = trigdata->tg_trigtuple;
else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
rettuple = trigdata->tg_newtuple;
else
/* internal error */
elog(ERROR, "set_audit_columns_if_empty: cannot process DELETE events");
rel = trigdata->tg_relation;
tupdesc = rel->rd_att;
// audit field #1 - last_modified_on
attnum = SPI_fnumber(tupdesc, "last_modified_on");
if (attnum <= 0)
ereport(ERROR,
(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
errmsg("relation \"%d\" has no attribute \"%s\"", rel->rd_id, "last_modified_on")));
valbuf = (char*)SPI_getvalue(rettuple, tupdesc, attnum);
if (valbuf == NULL) {
newval = GetCurrentTimestamp();
rettuple = heap_modify_tuple_by_cols(rettuple, tupdesc,
1, &attnum, &newval, &newnull);
}
// audit field #2 - last_modified_by
attnum = SPI_fnumber(tupdesc, "last_modified_by");
if (attnum <= 0)
ereport(ERROR,
(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
errmsg("relation \"%d\" has no attribute \"%s\"", rel->rd_id, "last_modified_by")));
valbuf = (char*)SPI_getvalue(rettuple, tupdesc, attnum);
if (valbuf == NULL) {
newval = CStringGetTextDatum(GetUserNameFromId(GetUserId(), false));
rettuple = heap_modify_tuple_by_cols(rettuple, tupdesc,
1, &attnum, &newval, &newnull);
}
return PointerGetDatum(rettuple);
}
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