1 /*
2 moddatetime.c
3
4 contrib/spi/moddatetime.c
5
6 What is this?
7 It is a function to be called from a trigger for the purpose of updating
8 a modification datetime stamp in a record when that record is UPDATEd.
9
10 Credits
11 This is 95%+ based on autoinc.c, which I used as a starting point as I do
12 not really know what I am doing. I also had help from
13 Jan Wieck <jwieck@debis.com> who told me about the timestamp_in("now") function.
14 OH, me, I'm Terry Mackintosh <terry@terrym.com>
15 */
16 #include "postgres.h"
17
18 #include "access/htup_details.h"
19 #include "catalog/pg_type.h"
20 #include "executor/spi.h"
21 #include "commands/trigger.h"
22 #include "utils/builtins.h"
23 #include "utils/rel.h"
24
25 PG_MODULE_MAGIC;
26
27 PG_FUNCTION_INFO_V1(moddatetime);
28
29 Datum
moddatetime(PG_FUNCTION_ARGS)30 moddatetime(PG_FUNCTION_ARGS)
31 {
32 TriggerData *trigdata = (TriggerData *) fcinfo->context;
33 Trigger *trigger; /* to get trigger name */
34 int nargs; /* # of arguments */
35 int attnum; /* positional number of field to change */
36 Oid atttypid; /* type OID of field to change */
37 Datum newdt; /* The current datetime. */
38 bool newdtnull; /* null flag for it */
39 char **args; /* arguments */
40 char *relname; /* triggered relation name */
41 Relation rel; /* triggered relation */
42 HeapTuple rettuple = NULL;
43 TupleDesc tupdesc; /* tuple description */
44
45 if (!CALLED_AS_TRIGGER(fcinfo))
46 /* internal error */
47 elog(ERROR, "moddatetime: not fired by trigger manager");
48
49 if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
50 /* internal error */
51 elog(ERROR, "moddatetime: must be fired for row");
52
53 if (!TRIGGER_FIRED_BEFORE(trigdata->tg_event))
54 /* internal error */
55 elog(ERROR, "moddatetime: must be fired before event");
56
57 if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
58 /* internal error */
59 elog(ERROR, "moddatetime: cannot process INSERT events");
60 else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
61 rettuple = trigdata->tg_newtuple;
62 else
63 /* internal error */
64 elog(ERROR, "moddatetime: cannot process DELETE events");
65
66 rel = trigdata->tg_relation;
67 relname = SPI_getrelname(rel);
68
69 trigger = trigdata->tg_trigger;
70
71 nargs = trigger->tgnargs;
72
73 if (nargs != 1)
74 /* internal error */
75 elog(ERROR, "moddatetime (%s): A single argument was expected", relname);
76
77 args = trigger->tgargs;
78 /* must be the field layout? */
79 tupdesc = rel->rd_att;
80
81 /*
82 * This gets the position in the tuple of the field we want. args[0] being
83 * the name of the field to update, as passed in from the trigger.
84 */
85 attnum = SPI_fnumber(tupdesc, args[0]);
86
87 /*
88 * This is where we check to see if the field we are supposed to update
89 * even exists.
90 */
91 if (attnum <= 0)
92 ereport(ERROR,
93 (errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
94 errmsg("\"%s\" has no attribute \"%s\"",
95 relname, args[0])));
96
97 /*
98 * Check the target field has an allowed type, and get the current
99 * datetime as a value of that type.
100 */
101 atttypid = SPI_gettypeid(tupdesc, attnum);
102 if (atttypid == TIMESTAMPOID)
103 newdt = DirectFunctionCall3(timestamp_in,
104 CStringGetDatum("now"),
105 ObjectIdGetDatum(InvalidOid),
106 Int32GetDatum(-1));
107 else if (atttypid == TIMESTAMPTZOID)
108 newdt = DirectFunctionCall3(timestamptz_in,
109 CStringGetDatum("now"),
110 ObjectIdGetDatum(InvalidOid),
111 Int32GetDatum(-1));
112 else
113 {
114 ereport(ERROR,
115 (errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
116 errmsg("attribute \"%s\" of \"%s\" must be type TIMESTAMP or TIMESTAMPTZ",
117 args[0], relname)));
118 newdt = (Datum) 0; /* keep compiler quiet */
119 }
120 newdtnull = false;
121
122 /* Replace the attnum'th column with newdt */
123 rettuple = heap_modify_tuple_by_cols(rettuple, tupdesc,
124 1, &attnum, &newdt, &newdtnull);
125
126 /* Clean up */
127 pfree(relname);
128
129 return PointerGetDatum(rettuple);
130 }
131