src/backend/utils/adt/trigfuncs.c

   1 /*-------------------------------------------------------------------------
   2  *
   3  * trigfuncs.c
   4  *        Builtin functions for useful trigger support.
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2011, 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.h"
  17 #include "commands/trigger.h"
  18 #include "utils/builtins.h"
  19 #include "utils/rel.h"
  20
  21
  22 /*
  23  * suppress_redundant_updates_trigger
  24  *
  25  * This trigger function will inhibit an update from being done
  26  * if the OLD and NEW records are identical.
  27  */
  28 Datum
  29 suppress_redundant_updates_trigger(PG_FUNCTION_ARGS)
  30 {
  31         TriggerData *trigdata = (TriggerData *) fcinfo->context;
  32         HeapTuple       newtuple,
  33                                 oldtuple,
  34                                 rettuple;
  35         HeapTupleHeader newheader,
  36                                 oldheader;
  37
  38         /* make sure it's called as a trigger */
  39         if (!CALLED_AS_TRIGGER(fcinfo))
  40                 ereport(ERROR,
  41                                 (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
  42                                  errmsg("suppress_redundant_updates_trigger: must be called as trigger")));
  43
  44         /* and that it's called on update */
  45         if (!TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
  46                 ereport(ERROR,
  47                                 (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
  48                                  errmsg("suppress_redundant_updates_trigger: must be called on update")));
  49
  50         /* and that it's called before update */
  51         if (!TRIGGER_FIRED_BEFORE(trigdata->tg_event))
  52                 ereport(ERROR,
  53                                 (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
  54                                  errmsg("suppress_redundant_updates_trigger: must be called before update")));
  55
  56         /* and that it's called for each row */
  57         if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
  58                 ereport(ERROR,
  59                                 (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
  60                                  errmsg("suppress_redundant_updates_trigger: must be called for each row")));
  61
  62         /* get tuple data, set default result */
  63         rettuple = newtuple = trigdata->tg_newtuple;
  64         oldtuple = trigdata->tg_trigtuple;
  65
  66         newheader = newtuple->t_data;
  67         oldheader = oldtuple->t_data;
  68
  69         /*
  70          * We are called before the OID, if any, has been transcribed from the old
  71          * tuple to the new (in heap_update).  To avoid a bogus compare failure,
  72          * copy the OID now.  But check that someone didn't already put another
  73          * OID value into newtuple.  (That's not actually possible at present, but
  74          * maybe someday.)
  75          */
  76         if (trigdata->tg_relation->rd_rel->relhasoids &&
  77                 !OidIsValid(HeapTupleHeaderGetOid(newheader)))
  78                 HeapTupleHeaderSetOid(newheader, HeapTupleHeaderGetOid(oldheader));
  79
  80         /* if the tuple payload is the same ... */
  81         if (newtuple->t_len == oldtuple->t_len &&
  82                 newheader->t_hoff == oldheader->t_hoff &&
  83                 (HeapTupleHeaderGetNatts(newheader) ==
  84                  HeapTupleHeaderGetNatts(oldheader)) &&
  85                 ((newheader->t_infomask & ~HEAP_XACT_MASK) ==
  86                  (oldheader->t_infomask & ~HEAP_XACT_MASK)) &&
  87                 memcmp(((char *) newheader) + offsetof(HeapTupleHeaderData, t_bits),
  88                            ((char *) oldheader) + offsetof(HeapTupleHeaderData, t_bits),
  89                            newtuple->t_len - offsetof(HeapTupleHeaderData, t_bits)) == 0)
  90         {
  91                 /* ... then suppress the update */
  92                 rettuple = NULL;
  93         }
  94
  95         return PointerGetDatum(rettuple);
  96 }