contrib/spi/moddatetime.c

   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
  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 }