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Sourcecode: postgresql-8.4 version File versions  Download package

trigfuncs.c

/*-------------------------------------------------------------------------
 *
 * trigfuncs.c
 *      Builtin functions for useful trigger support.
 *
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/backend/utils/adt/trigfuncs.c,v 1.7 2009/06/11 14:49:04 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup.h"
#include "commands/trigger.h"
#include "utils/builtins.h"


/*
 * suppress_redundant_updates_trigger
 *
 * This trigger function will inhibit an update from being done
 * if the OLD and NEW records are identical.
 */
Datum
suppress_redundant_updates_trigger(PG_FUNCTION_ARGS)
{
      TriggerData *trigdata = (TriggerData *) fcinfo->context;
      HeapTuple   newtuple,
                        oldtuple,
                        rettuple;
      HeapTupleHeader newheader,
                        oldheader;

      /* make sure it's called as a trigger */
      if (!CALLED_AS_TRIGGER(fcinfo))
            ereport(ERROR,
                        (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                         errmsg("suppress_redundant_updates_trigger: must be called as trigger")));

      /* and that it's called on update */
      if (!TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
            ereport(ERROR,
                        (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                         errmsg("suppress_redundant_updates_trigger: must be called on update")));

      /* and that it's called before update */
      if (!TRIGGER_FIRED_BEFORE(trigdata->tg_event))
            ereport(ERROR,
                        (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                         errmsg("suppress_redundant_updates_trigger: must be called before update")));

      /* and that it's called for each row */
      if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
            ereport(ERROR,
                        (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                         errmsg("suppress_redundant_updates_trigger: must be called for each row")));

      /* get tuple data, set default result */
      rettuple = newtuple = trigdata->tg_newtuple;
      oldtuple = trigdata->tg_trigtuple;

      newheader = newtuple->t_data;
      oldheader = oldtuple->t_data;

      /*
       * We are called before the OID, if any, has been transcribed from the old
       * tuple to the new (in heap_update).  To avoid a bogus compare failure,
       * copy the OID now.  But check that someone didn't already put another
       * OID value into newtuple.  (That's not actually possible at present, but
       * maybe someday.)
       */
      if (trigdata->tg_relation->rd_rel->relhasoids &&
            !OidIsValid(HeapTupleHeaderGetOid(newheader)))
            HeapTupleHeaderSetOid(newheader, HeapTupleHeaderGetOid(oldheader));

      /* if the tuple payload is the same ... */
      if (newtuple->t_len == oldtuple->t_len &&
            newheader->t_hoff == oldheader->t_hoff &&
            (HeapTupleHeaderGetNatts(newheader) ==
             HeapTupleHeaderGetNatts(oldheader)) &&
            ((newheader->t_infomask & ~HEAP_XACT_MASK) ==
             (oldheader->t_infomask & ~HEAP_XACT_MASK)) &&
            memcmp(((char *) newheader) + offsetof(HeapTupleHeaderData, t_bits),
                     ((char *) oldheader) + offsetof(HeapTupleHeaderData, t_bits),
                     newtuple->t_len - offsetof(HeapTupleHeaderData, t_bits)) == 0)
      {
            /* ... then suppress the update */
            rettuple = NULL;
      }

      return PointerGetDatum(rettuple);
}

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