src/test/regress/regress.c と contrib/spi にはもっと複雑な例があ ります。
トリガーの使い方に関するとても簡単な例をここに示します。trigf 関 数はトリガーを発行した ttest リレーション内にあるタプル数を報告し、 問い合わせが x に NULL を挿入しようとしていた場合はその操作をとば します。(つまり、この関数は、トランザクションを中断させない NOT NULL 制約のような動作をします。)
#include "executor/spi.h" /* これはSPI を使用する場合に必要なものです。*/ #include "commands/trigger.h" /* SPI とトリガーを、以下同文 */ HeapTuple trigf(void); HeapTuple trigf() { TupleDesc tupdesc; HeapTuple rettuple; char *when; bool checknull = false; bool isnull; int ret, i; if (!CurrentTriggerData) elog(WARN, "trigf: triggers are not initialized"); /* エグゼキュータに返すタプル */ if (TRIGGER_FIRED_BY_UPDATE(CurrentTriggerData->tg_event)) rettuple = CurrentTriggerData->tg_newtuple; else rettuple = CurrentTriggerData->tg_trigtuple; /* NULLに関する点検を行なうかどうか */ if (!TRIGGER_FIRED_BY_DELETE(CurrentTriggerData->tg_event) && TRIGGER_FIRED_BEFORE(CurrentTriggerData->tg_event)) checknull = true; if (TRIGGER_FIRED_BEFORE(CurrentTriggerData->tg_event)) when = "before"; else when = "after "; tupdesc = CurrentTriggerData->tg_relation->rd_att; CurrentTriggerData = NULL; /* SPIマネージャに接続します */ if ((ret = SPI_connect()) < 0) elog(WARN, "trigf (fired %s): SPI_connect returned %d", when, ret); /* リレーション中のタプル数を取得します */ ret = SPI_exec("select count(*) from ttest", 0); if (ret < 0) elog(WARN, "trigf (fired %s): SPI_exec returned %d", when, ret); i = SPI_getbinval(SPI_tuptable->vals[0], SPI_tuptable->tupdesc, 1, &isnull); elog (NOTICE, "trigf (fired %s): there are %d tuples in ttest", when, i); SPI_finish(); if (checknull) { i = SPI_getbinval(rettuple, tupdesc, 1, &isnull); if (isnull) rettuple = NULL; } return (rettuple); }
ここでコンパイルを行ない、そして次を行ないます。 create table ttest (x int4); create function trigf () returns opaque as '...path_to_so' language 'c';
vac=> create trigger tbefore before insert or update or delete on ttest for each row execute procedure trigf(); CREATE vac=> create trigger tafter after insert or update or delete on ttest for each row execute procedure trigf(); CREATE vac=> insert into ttest values (null); NOTICE:trigf (fired before): there are 0 tuples in ttest INSERT 0 0 -- 挿入操作はとばされ、また、AFTER トリガーも発行されません。 vac=> select * from ttest; x - (0 rows) vac=> insert into ttest values (1); NOTICE:trigf (fired before): there are 0 tuples in ttest NOTICE:trigf (fired after ): there are 1 tuples in ttest ^^^^^^^^ 可視性について述べたことを思い出して下さい。 INSERT 167793 1 vac=> select * from ttest; x - 1 (1 row) vac=> insert into ttest select x * 2 from ttest; NOTICE:trigf (fired before): there are 1 tuples in ttest NOTICE:trigf (fired after ): there are 2 tuples in ttest ^^^^^^^^ 可視性について述べたことを思い出して下さい。 INSERT 167794 1 vac=> select * from ttest; x - 1 2 (2 rows) vac=> update ttest set x = null where x = 2; NOTICE:trigf (fired before): there are 2 tuples in ttest UPDATE 0 vac=> update ttest set x = 4 where x = 2; NOTICE:trigf (fired before): there are 2 tuples in ttest NOTICE:trigf (fired after ): there are 2 tuples in ttest UPDATE 1 vac=> select * from ttest; x - 1 4 (2 rows) vac=> delete from ttest; NOTICE:trigf (fired before): there are 2 tuples in ttest NOTICE:trigf (fired after ): there are 1 tuples in ttest NOTICE:trigf (fired before): there are 1 tuples in ttest NOTICE:trigf (fired after ): there are 0 tuples in ttest ^^^^^^^^ 可視性について述べたことを思い出して下さい。 DELETE 2 vac=> select * from ttest; x - (0 rows)