contrib/spi/moddatetime.c

   1 /*
   2 moddatetime.c
   3
   4 $PostgreSQL$
   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
  17 #include "executor/spi.h"               /* this is what you need to work with SPI */
  18 #include "commands/trigger.h"   /* -"- and triggers */
  19
  20 PG_MODULE_MAGIC;
  21
  22 extern Datum moddatetime(PG_FUNCTION_ARGS);
  23
  24 PG_FUNCTION_INFO_V1(moddatetime);
  25
  26 Datum
  27 moddatetime(PG_FUNCTION_ARGS)
  28 {
  29         TriggerData *trigdata = (TriggerData *) fcinfo->context;
  30         Trigger    *trigger;            /* to get trigger name */
  31         int                     nargs;                  /* # of arguments */
  32         int                     attnum;                 /* positional number of field to change */
  33         Datum           newdt;                  /* The current datetime. */
  34         char      **args;                       /* arguments */
  35         char       *relname;            /* triggered relation name */
  36         Relation        rel;                    /* triggered relation */
  37         HeapTuple       rettuple = NULL;
  38         TupleDesc       tupdesc;                /* tuple description */
  39
  40         if (!CALLED_AS_TRIGGER(fcinfo))
  41                 /* internal error */
  42                 elog(ERROR, "moddatetime: not fired by trigger manager");
  43
  44         if (TRIGGER_FIRED_FOR_STATEMENT(trigdata->tg_event))
  45                 /* internal error */
  46                 elog(ERROR, "moddatetime: cannot process STATEMENT events");
  47
  48         if (TRIGGER_FIRED_AFTER(trigdata->tg_event))
  49                 /* internal error */
  50                 elog(ERROR, "moddatetime: must be fired before event");
  51
  52         if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
  53                 /* internal error */
  54                 elog(ERROR, "moddatetime: must be fired before event");
  55         else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
  56                 rettuple = trigdata->tg_newtuple;
  57         else
  58                 /* internal error */
  59                 elog(ERROR, "moddatetime: cannot process DELETE events");
  60
  61         rel = trigdata->tg_relation;
  62         relname = SPI_getrelname(rel);
  63
  64         trigger = trigdata->tg_trigger;
  65
  66         nargs = trigger->tgnargs;
  67
  68         if (nargs != 1)
  69                 /* internal error */
  70                 elog(ERROR, "moddatetime (%s): A single argument was expected", relname);
  71
  72         args = trigger->tgargs;
  73         /* must be the field layout? */
  74         tupdesc = rel->rd_att;
  75
  76         /* Get the current datetime. */
  77         newdt = DirectFunctionCall3(timestamp_in,
  78                                                                 CStringGetDatum("now"),
  79                                                                 ObjectIdGetDatum(InvalidOid),
  80                                                                 Int32GetDatum(-1));
  81
  82         /*
  83          * This gets the position in the tuple of the field we want. args[0] being
  84          * the name of the field to update, as passed in from the trigger.
  85          */
  86         attnum = SPI_fnumber(tupdesc, args[0]);
  87
  88         /*
  89          * This is were we check to see if the field we are supposed to update
  90          * even exits.  The above function must return -1 if name not found?
  91          */
  92         if (attnum < 0)
  93                 ereport(ERROR,
  94                                 (errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
  95                                  errmsg("\"%s\" has no attribute \"%s\"",
  96                                                 relname, args[0])));
  97
  98         /*
  99          * OK, this is where we make sure the timestamp field that we are
 100          * modifying is really a timestamp field. Hay, error checking, what a
 101          * novel idea !-)
 102          */
 103         if (SPI_gettypeid(tupdesc, attnum) != TIMESTAMPOID)
 104                 ereport(ERROR,
 105                                 (errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
 106                                  errmsg("attribute \"%s\" of \"%s\" must be type TIMESTAMP",
 107                                                 args[0], relname)));
 108
 109 /* 1 is the number of items in the arrays attnum and newdt.
 110         attnum is the positional number of the field to be updated.
 111         newdt is the new datetime stamp.
 112         NOTE that attnum and newdt are not arrays, but then a 1 ellement array
 113         is not an array any more then they are.  Thus, they can be considered a
 114         one element array.
 115 */
 116         rettuple = SPI_modifytuple(rel, rettuple, 1, &attnum, &newdt, NULL);
 117
 118         if (rettuple == NULL)
 119                 /* internal error */
 120                 elog(ERROR, "moddatetime (%s): %d returned by SPI_modifytuple",
 121                          relname, SPI_result);
 122
 123 /* Clean up */
 124         pfree(relname);
 125
 126         return PointerGetDatum(rettuple);
 127 }