1/*-------------------------------------------------------------------------
2 *
3 * trigfuncs.c
4 * Builtin functions for useful trigger support.
5 *
6 *
7 * Portions Copyright (c) 1996-2019, 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/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 */
28Datum
29suppress_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 /* if the tuple payload is the same ... */
70 if (newtuple->t_len == oldtuple->t_len &&
71 newheader->t_hoff == oldheader->t_hoff &&
72 (HeapTupleHeaderGetNatts(newheader) ==
73 HeapTupleHeaderGetNatts(oldheader)) &&
74 ((newheader->t_infomask & ~HEAP_XACT_MASK) ==
75 (oldheader->t_infomask & ~HEAP_XACT_MASK)) &&
76 memcmp(((char *) newheader) + SizeofHeapTupleHeader,
77 ((char *) oldheader) + SizeofHeapTupleHeader,
78 newtuple->t_len - SizeofHeapTupleHeader) == 0)
79 {
80 /* ... then suppress the update */
81 rettuple = NULL;
82 }
83
84 return PointerGetDatum(rettuple);
85}
86