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Standard English uses "may", "can", and "might" in different ways:
may - permission, "You may borrow my rake."
can - ability, "I can lift that log."
might - possibility, "It might rain today."
Unfortunately, in conversational English, their use is often mixed, as
in, "You may use this variable to do X", when in fact, "can" is a better
choice. Similarly, "It may crash" is better stated, "It might crash".
128 lines
3.8 KiB
C
128 lines
3.8 KiB
C
/*
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moddatetime.c
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$PostgreSQL: pgsql/contrib/spi/moddatetime.c,v 1.14 2007/02/01 19:10:23 momjian Exp $
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What is this?
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It is a function to be called from a trigger for the purpose of updating
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a modification datetime stamp in a record when that record is UPDATEd.
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Credits
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This is 95%+ based on autoinc.c, which I used as a starting point as I do
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not really know what I am doing. I also had help from
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Jan Wieck <jwieck@debis.com> who told me about the timestamp_in("now") function.
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OH, me, I'm Terry Mackintosh <terry@terrym.com>
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*/
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#include "executor/spi.h" /* this is what you need to work with SPI */
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#include "commands/trigger.h" /* -"- and triggers */
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PG_MODULE_MAGIC;
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extern Datum moddatetime(PG_FUNCTION_ARGS);
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PG_FUNCTION_INFO_V1(moddatetime);
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Datum
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moddatetime(PG_FUNCTION_ARGS)
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{
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TriggerData *trigdata = (TriggerData *) fcinfo->context;
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Trigger *trigger; /* to get trigger name */
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int nargs; /* # of arguments */
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int attnum; /* positional number of field to change */
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Datum newdt; /* The current datetime. */
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char **args; /* arguments */
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char *relname; /* triggered relation name */
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Relation rel; /* triggered relation */
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HeapTuple rettuple = NULL;
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TupleDesc tupdesc; /* tuple description */
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if (!CALLED_AS_TRIGGER(fcinfo))
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/* internal error */
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elog(ERROR, "moddatetime: not fired by trigger manager");
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if (TRIGGER_FIRED_FOR_STATEMENT(trigdata->tg_event))
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/* internal error */
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elog(ERROR, "moddatetime: cannot process STATEMENT events");
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if (TRIGGER_FIRED_AFTER(trigdata->tg_event))
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/* internal error */
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elog(ERROR, "moddatetime: must be fired before event");
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if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
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/* internal error */
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elog(ERROR, "moddatetime: must be fired before event");
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else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
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rettuple = trigdata->tg_newtuple;
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else
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/* internal error */
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elog(ERROR, "moddatetime: cannot process DELETE events");
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rel = trigdata->tg_relation;
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relname = SPI_getrelname(rel);
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trigger = trigdata->tg_trigger;
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nargs = trigger->tgnargs;
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if (nargs != 1)
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/* internal error */
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elog(ERROR, "moddatetime (%s): A single argument was expected", relname);
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args = trigger->tgargs;
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/* must be the field layout? */
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tupdesc = rel->rd_att;
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/* Get the current datetime. */
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newdt = DirectFunctionCall3(timestamp_in,
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CStringGetDatum("now"),
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ObjectIdGetDatum(InvalidOid),
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Int32GetDatum(-1));
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/*
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* This gets the position in the tuple of the field we want. args[0] being
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* the name of the field to update, as passed in from the trigger.
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*/
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attnum = SPI_fnumber(tupdesc, args[0]);
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/*
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* This is were we check to see if the field we are supposed to update
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* even exits. The above function must return -1 if name not found?
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*/
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if (attnum < 0)
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ereport(ERROR,
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(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
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errmsg("\"%s\" has no attribute \"%s\"",
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relname, args[0])));
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/*
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* OK, this is where we make sure the timestamp field that we are
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* modifying is really a timestamp field. Hay, error checking, what a
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* novel idea !-)
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*/
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if (SPI_gettypeid(tupdesc, attnum) != TIMESTAMPOID)
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ereport(ERROR,
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(errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
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errmsg("attribute \"%s\" of \"%s\" must be type TIMESTAMP",
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args[0], relname)));
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/* 1 is the number of items in the arrays attnum and newdt.
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attnum is the positional number of the field to be updated.
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newdt is the new datetime stamp.
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NOTE that attnum and newdt are not arrays, but then a 1 ellement array
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is not an array any more then they are. Thus, they can be considered a
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one element array.
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*/
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rettuple = SPI_modifytuple(rel, rettuple, 1, &attnum, &newdt, NULL);
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if (rettuple == NULL)
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/* internal error */
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elog(ERROR, "moddatetime (%s): %d returned by SPI_modifytuple",
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relname, SPI_result);
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/* Clean up */
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pfree(relname);
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return PointerGetDatum(rettuple);
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}
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