insert_username.c

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/*
 * contrib/spi/insert_username.c
 *
 * insert user name in response to a trigger
 * usage:  insert_username (column_name)
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "catalog/pg_type.h"
#include "commands/trigger.h"
#include "executor/spi.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/rel.h"

PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(insert_username);

Datum
insert_username(PG_FUNCTION_ARGS)
{
    TriggerData *trigdata = (TriggerData *) fcinfo->context;
    Trigger    *trigger;        /* to get trigger name */
    int         nargs;          /* # of arguments */
    Datum       newval;         /* new value of column */
    bool        newnull;        /* null flag */
    char      **args;           /* arguments */
    char       *relname;        /* triggered relation name */
    Relation    rel;            /* triggered relation */
    HeapTuple   rettuple = NULL;
    TupleDesc   tupdesc;        /* tuple description */
    int         attnum;

    /* sanity checks from autoinc.c */
    if (!CALLED_AS_TRIGGER(fcinfo))
        /* internal error */
        elog(ERROR, "insert_username: not fired by trigger manager");
    if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event))
        /* internal error */
        elog(ERROR, "insert_username: must be fired for row");
    if (!TRIGGER_FIRED_BEFORE(trigdata->tg_event))
        /* internal error */
        elog(ERROR, "insert_username: must be fired before event");

    if (TRIGGER_FIRED_BY_INSERT(trigdata->tg_event))
        rettuple = trigdata->tg_trigtuple;
    else if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
        rettuple = trigdata->tg_newtuple;
    else
        /* internal error */
        elog(ERROR, "insert_username: cannot process DELETE events");

    rel = trigdata->tg_relation;
    relname = SPI_getrelname(rel);

    trigger = trigdata->tg_trigger;

    nargs = trigger->tgnargs;
    if (nargs != 1)
        /* internal error */
        elog(ERROR, "insert_username (%s): one argument was expected", relname);

    args = trigger->tgargs;
    tupdesc = rel->rd_att;

    attnum = SPI_fnumber(tupdesc, args[0]);

    if (attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
                 errmsg("\"%s\" has no attribute \"%s\"", relname, args[0])));

    if (SPI_gettypeid(tupdesc, attnum) != TEXTOID)
        ereport(ERROR,
                (errcode(ERRCODE_TRIGGERED_ACTION_EXCEPTION),
                 errmsg("attribute \"%s\" of \"%s\" must be type TEXT",
                        args[0], relname)));

    /* create fields containing name */
    newval = CStringGetTextDatum(GetUserNameFromId(GetUserId(), false));
    newnull = false;

    /* construct new tuple */
    rettuple = heap_modify_tuple_by_cols(rettuple, tupdesc,
                                         1, &attnum, &newval, &newnull);

    pfree(relname);

    return PointerGetDatum(rettuple);
}