34.4. 婔婻垯昘䔇冋床

認麯滇婔婻䫘 C 喍䔇麂婩䞔剘䔇蓥埏単冋床㔗庘昄 trigf 檖只 ttest 臘䔇臯昄麟幽婫套悩变傴臘商檪 NULL 某噖彄庖枕 x 麯(幘儌滇垄啔婺婔婻麂䷺亥溘嘖婉锔庺庋媇)施䘖誺淉嘩㔗

饡噽臘垔幬

CREATE TABLE ttest (
    x integer
);

認麯滇蓥埏単庘昄䔇溊傼乕

#include "postgres.h"
#include "executor/spi.h"       /* 嘹䫘 SPI 䔇施唍襕䫘䔇崘桺傽 */
#include "commands/trigger.h"   /* 䫘蓥埏単施襕䫘䔇崘桺傽 */

extern Datum trigf(PG_FUNCTION_ARGS);

PG_FUNCTION_INFO_V1(trigf);

Datum
trigf(PG_FUNCTION_ARGS)
{
    TriggerData *trigdata = (TriggerData *) fcinfo->context;
    TupleDesc   tupdesc;
    HeapTuple   rettuple;
    char       *when;
    bool        checknull = false;
    bool        isnull;
    int         ret, i;

    /* 䇞媇躻噌滇嘩婺蓥埏単脄䫘䔇 */
    if (!CALLED_AS_TRIGGER(fcinfo))
        elog(ERROR, "trigf: not called by trigger manager");

    /* 誫啂䂍欓臯蔙䔇臯 */
    if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
        rettuple = trigdata->tg_newtuple;
    else
        rettuple = trigdata->tg_trigtuple;

    /* 演昖 NULL 唚 */
    if (!TRIGGER_FIRED_BY_DELETE(trigdata->tg_event)
        && TRIGGER_FIRED_BEFORE(trigdata->tg_event))
        checknull = true;

    if (TRIGGER_FIRED_BEFORE(trigdata->tg_event))
        when = "before";
    else
        when = "after ";

    tupdesc = trigdata->tg_relation->rd_att;

    /* 婯 SPI 䞇䊖単誂毖 */
    if ((ret = SPI_connect()) < 0)
        elog(INFO, "trigf (fired %s): SPI_connect returned %d", when, ret);

    /* 诙埡臘婺䔇臯昄麟 */
    ret = SPI_exec("SELECT count(*) FROM ttest", 0);

    if (ret < 0)
        elog(NOTICE, "trigf (fired %s): SPI_exec returned %d", when, ret);

    /* count(*) 誫啂 int8 欔傖襕償媄蘸扵 */
    i = DatumGetInt64(SPI_getbinval(SPI_tuptable->vals[0],
                                    SPI_tuptable->tupdesc,
                                    1,
                                    &isnull));

    elog (INFO, "trigf (fired %s): there are %d rows in ttest", when, i);

    SPI_finish();

    if (checknull)
    {
        SPI_getbinval(rettuple, tupdesc, 1, &isnull);
        if (isnull)
            rettuple = NULL;
    }

    return PointerGetDatum(rettuple);
}

䚡臏垯溊傼乕劯弄滯庘昄幽录傺蓥埏単

CREATE FUNCTION trigf() RETURNS trigger
    AS 'filename'
    LANGUAGE C;

CREATE TRIGGER tbefore BEFORE INSERT OR UPDATE OR DELETE ON ttest 
    FOR EACH ROW EXECUTE PROCEDURE trigf();

CREATE TRIGGER tafter AFTER INSERT OR UPDATE OR DELETE ON ttest 
    FOR EACH ROW EXECUTE PROCEDURE trigf();

䯄婘嘹埇傖敋臘蓥埏単䔇淉嘩

=> INSERT INTO ttest VALUES (NULL);
INFO:  trigf (fired before): there are 0 rows in ttest
INSERT 0 0

-- 某噖赆媘䘖AFTER 蓥埏単澇橬蓥埏

=> SELECT * FROM ttest;
 x
---
(0 rows)

=> INSERT INTO ttest VALUES (1);
INFO:  trigf (fired before): there are 0 rows in ttest
INFO:  trigf (fired after ): there are 1 rows in ttest
                                       ^^^^^^^^
                             誻螄冖螾誺䔇噿庯埇蓖攓䔇寘彍劖
INSERT 167793 1
vac=> SELECT * FROM ttest;
 x
---
 1
(1 row)

=> INSERT INTO ttest SELECT x * 2 FROM ttest;
INFO:  trigf (fired before): there are 1 rows in ttest
INFO:  trigf (fired after ): there are 2 rows in ttest
                                       ^^^^^^
                             誻螄冖螾誺䔇噿庯埇蓖攓䔇寘彍劖
INSERT 167794 1
=> SELECT * FROM ttest;
 x
---
 1
 2
(2 rows)

=> UPDATE ttest SET x = NULL WHERE x = 2;
INFO:  trigf (fired before): there are 2 rows in ttest
UPDATE 0
=> UPDATE ttest SET x = 4 WHERE x = 2;
INFO:  trigf (fired before): there are 2 rows in ttest
INFO:  trigf (fired after ): there are 2 rows in ttest
UPDATE 1
vac=> SELECT * FROM ttest;
 x
---
 1
 4
(2 rows)

=> DELETE FROM ttest;
INFO:  trigf (fired before): there are 2 rows in ttest
INFO:  trigf (fired before): there are 1 rows in ttest
INFO:  trigf (fired after ): there are 0 rows in ttest
INFO:  trigf (fired after ): there are 0 rows in ttest
                                       ^^^^^^
                             誻螄冖螾誺䔇噿庯埇蓖攓䔇寘彍劖
DELETE 2
=> SELECT * FROM ttest;
 x
---
(0 rows)

婘 src/test/regress/regress.c 启 contrib/spi 麯誻橬敘崉溗䔇冋床㔗