trigfuncs.c

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/*-------------------------------------------------------------------------
 *
 * trigfuncs.c
 *    Builtin functions for useful trigger support.
 *
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/backend/utils/adt/trigfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "commands/trigger.h"
#include "utils/builtins.h"
#include "utils/rel.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);
}