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 "commands/trigger.h"
21 #include "executor/spi.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