src/backend/utils/adt/trigfuncs.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * trigfuncs.c
   4  *        Builtin functions for useful trigger support.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/backend/utils/adt/trigfuncs.c
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #include "postgres.h"
  15
  16 #include "access/htup_details.h"
  17 #include "commands/trigger.h"
  18 #include "utils/fmgrprotos.h"
  19
  20
  21 /*
  22  * suppress_redundant_updates_trigger
  23  *
  24  * This trigger function will inhibit an update from being done
  25  * if the OLD and NEW records are identical.
  26  */
  27 Datum
  28 suppress_redundant_updates_trigger(PG_FUNCTION_ARGS)
  29 {
  30         TriggerData *trigdata = (TriggerData *) fcinfo->context;
  31         HeapTuple       newtuple,
  32                                 oldtuple,
  33                                 rettuple;
  34         HeapTupleHeader newheader,
  35                                 oldheader;
  36
  37         /* make sure it's called as a trigger */
  38         if (!CALLED_AS_TRIGGER(fcinfo))
  39                 ereport(ERROR,
  40                                 (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
  41                                  errmsg("suppress_redundant_updates_trigger: must be called as trigger")));
  42
  43         /* and that it's called on update */
  44         if (!TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
  45                 ereport(ERROR,
  46                                 (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
  47                                  errmsg("suppress_redundant_updates_trigger: must be called on update")));
  48
  49         /* and that it's called before update */
  50         if (!TRIGGER_FIRED_BEFORE(trigdata->tg_event))
  51                 ereport(ERROR,
  52                                 (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
  53                                  errmsg("suppress_redundant_updates_trigger: must be called before update")));
  54
  55         /* and that it's called for each row */
  56         if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
  57                 ereport(ERROR,
  58                                 (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
  59                                  errmsg("suppress_redundant_updates_trigger: must be called for each row")));
  60
  61         /* get tuple data, set default result */
  62         rettuple = newtuple = trigdata->tg_newtuple;
  63         oldtuple = trigdata->tg_trigtuple;
  64
  65         newheader = newtuple->t_data;
  66         oldheader = oldtuple->t_data;
  67
  68         /* if the tuple payload is the same ... */
  69         if (newtuple->t_len == oldtuple->t_len &&
  70                 newheader->t_hoff == oldheader->t_hoff &&
  71                 (HeapTupleHeaderGetNatts(newheader) ==
  72                  HeapTupleHeaderGetNatts(oldheader)) &&
  73                 ((newheader->t_infomask & ~HEAP_XACT_MASK) ==
  74                  (oldheader->t_infomask & ~HEAP_XACT_MASK)) &&
  75                 memcmp(((char *) newheader) + SizeofHeapTupleHeader,
  76                            ((char *) oldheader) + SizeofHeapTupleHeader,
  77                            newtuple->t_len - SizeofHeapTupleHeader) == 0)
  78         {
  79                 /* ... then suppress the update */
  80                 rettuple = NULL;
  81         }
  82
  83         return PointerGetDatum(rettuple);
  84 }