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/*
* noup.c -- functions to remove update permission from a column
*/
#include "executor/spi.h" /* this is what you need to work with SPI */
#include "commands/trigger.h" /* -"- and triggers */
#include <ctype.h> /* tolower () */
extern Datum noup(PG_FUNCTION_ARGS);
/*
* noup () -- revoke permission on column
*
* Though it's called without args You have to specify referenced
* table/column while creating trigger:
* EXECUTE PROCEDURE noup ('col').
*/
PG_FUNCTION_INFO_V1(noup);
Datum
noup(PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *) fcinfo->context;
Trigger *trigger; /* to get trigger name */
int nargs; /* # of args specified in CREATE TRIGGER */
char **args; /* arguments: column names and table name */
int nkeys; /* # of key columns (= nargs / 2) */
Datum *kvals; /* key values */
Relation rel; /* triggered relation */
HeapTuple tuple = NULL; /* tuple to return */
TupleDesc tupdesc; /* tuple description */
bool isnull; /* to know is some column NULL or not */
int ret;
int i;
/*
* Some checks first...
*/
/* Called by trigger manager ? */
if (!CALLED_AS_TRIGGER(fcinfo))
/* internal error */
elog(ERROR, "noup: not fired by trigger manager");
/* Should be called for ROW trigger */
if (TRIGGER_FIRED_FOR_STATEMENT(trigdata->tg_event))
/* internal error */
elog(ERROR, "noup: can't process STATEMENT events");
/* Should not be called for INSERT */
if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
/* internal error */
elog(ERROR, "noup: can't process INSERT events");
/* Should not be called for DELETE */
else if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))
/* internal error */
elog(ERROR, "noup: can't process DELETE events");
/* check new Tuple */
tuple = trigdata->tg_newtuple;
trigger = trigdata->tg_trigger;
nargs = trigger->tgnargs;
args = trigger->tgargs;
nkeys = nargs;
rel = trigdata->tg_relation;
tupdesc = rel->rd_att;
/* Connect to SPI manager */
if ((ret = SPI_connect()) < 0)
/* internal error */
elog(ERROR, "noup: SPI_connect returned %d", ret);
/*
* We use SPI plan preparation feature, so allocate space to place key
* values.
*/
kvals = (Datum *) palloc(nkeys * sizeof(Datum));
/* For each column in key ... */
for (i = 0; i < nkeys; i++)
{
/* get index of column in tuple */
int fnumber = SPI_fnumber(tupdesc, args[i]);
/* Bad guys may give us un-existing column in CREATE TRIGGER */
if (fnumber < 0)
/* internal error */
elog(ERROR, "noup: there is no attribute %s in relation %s",
args[i], SPI_getrelname(rel));
/* Well, get binary (in internal format) value of column */
kvals[i] = SPI_getbinval(tuple, tupdesc, fnumber, &isnull);
/*
* If it's NOT NULL then cancel update
*/
if (!isnull)
{
elog(WARNING, "%s: update not allowed", args[i]);
SPI_finish();
return PointerGetDatum(NULL);
}
}
SPI_finish();
return PointerGetDatum(tuple);
}
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