portgresql中触发器的写法
时间：2010-06-23 来源：chenweiming507
postgresql数据库中触发器的小结
最近因工作需要,需要在postgresql中写个触发器,经过几天的看手册, 查资料,写代码,对代码的测试,终于对触发器有了一定的了解, 为了防止自己忘记,同时希望能给需要的朋友一定的帮助,写下了这篇文章.(感悟: 看书到了一定程度,如果能写个功能类似但不完全一样的代码,那个时候自己的理解会加深很多....哈哈...).好了开始正题.....
一个触发器是一种声明，告诉数据库应该在执行特定的操作的时候执行特定的函数。触发器可以定义在一个 INSERT, UPDATE, DELETE 命令之前或者之后执行，要么是对每行执行一次，要么是对每条 SQL 语句执行一次。如果发生触发器事件，那么将在合适的时刻调用触发器函数以处理该事件。触发器函数必须在创建触发器之前，作为一个没有参数并且返回 trigger 类型的函数定义。触发器函数通过特殊的 TriggerData 结构接收其输入，而不是用普通的函数参数方式.
PostgreSQL 提供按行与按语句触发的触发器。按行触发的触发器函数为触发语句影响的每一行执行一次；按语句触发的触发器函数为每条触发语句执行一次，而不管影响的行数。特别是，一个影响零行的语句将仍然导致按语句触发的触发器执行。这两种类型的触发器有时候分别叫做行级触发器和语句级触发器。触发器还通常分成 before 触发器和 after 触发器。语句级别的"before"触发器通常在语句开始做任何事情之前触发，而语句级别的"after"触发器在语句结束时触发。行级别的"before"触发器在对特定行进行操作之前触发，而行级别的"after"触发器在语句结束的时候触发(但是在任何语句级别的"after"触发器之前)。
注意:
一.按语句触发的触发器应该总是返回 NULL.
二.如果必要，按行触发的触发器函数可以给调用它的执行者返回一行数据(一个类型为 HeapTuple 的数值)，那些在操作之前触发的触发器有以下选择
1. 它可以返回 NULL 以忽略对当前行的操作。这就指示执行器不要执行调用该触
发器的行级别操作(对特定行的插入或者更改)。
2.只用于 INSERT 和 UPDATE 行触发器：返回的行将成为被插入的行或者是成为
将要更新的行。这样就允许触发器函数修改将要被插入或者更新的行。
一个无意导致任何这类行为的在操作之前触发的行级触发器必须仔细返回那个被当作新行传进来的行。也就是说，对于 INSERT 和 UPDATE 触发器而言，是 NEW 行，对于 DELETE触发器而言，是 OLD 行。
三. 对于在操作之后触发的行级触发器，其返回值会被忽略，因此可以回NULL。
下面通过具体的例子来说明在postgresql中触发器的建立和使用(老规矩先写代码然后讲解)
#include <postgres.h>
#include <executor/spi.h>
#include <funcapi.h>
#include <commands/trigger.h>
#include <fmgr.h> extern Datum pg_trigf(PG_FUNCTION_ARGS); #ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif PG_FUNCTION_INFO_V1(pg_trigf); Datum
pg_trigf(PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *)fcinfo->context;
HeapTuple rettuple = NULL;
int ret;
int proc; /* to store the value of SPI_processed (actual row number)*/
/* to be sure this function will be called by trigger */
if (!(CALLED_AS_TRIGGER(fcinfo))) {
elog(ERROR, "trigf: not called by trigger manager");
}
/* should be fired by statement */
if (TRIGGER_FIRED_FOR_ROW(trigdata->tg_event)) {
elog(ERROR, "cannot process row events");
}
/* should be fired before event */
if (TRIGGER_FIRED_AFTER(trigdata->tg_event)) {
elog(ERROR, "must be fired before event");
} /* connect spi manager */
if ((ret = SPI_connect()) < 0) {
elog(INFO, "SPI_connect failed: SPI_connect returned: %d", ret);
return PointerGetDatum(rettuple);
} /* check the permanent table name(perm_user) exists or not*/
ret = SPI_exec("SELECT tablename FROM pg_tables WHERE tablename LIKE 'perm!_user' ESCAPE '!';", 1);
proc = SPI_processed;
if (ret != SPI_OK_SELECT) {
elog(INFO, "SPI_exec execute error: user table.");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* create the permanent table(perm_user) if it does not exist */
if (proc < 1) {
/* create permanent table: perm_user */
ret = SPI_exec("CREATE TABLE perm_user AS SELECT * FROM tbl_user;", 0);
if (ret != SPI_OK_SELINTO ) {
elog(INFO, "SPI_exec execute error: fail to create perm_user");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* set attribute to perm_user */
ret = SPI_exec("ALTER TABLE perm_user ADD PRIMARY KEY (user_name);", 0);
if (ret != SPI_OK_SELINTO) {
elog(INFO, "SPI_exec execute error: fail to add primary key to perm_user");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* set attribute to perm_user*/
ret = SPI_exec("ALTER TABLE perm_user ALTER user_passwd SET NOT NULL;", 0);
if (ret != SPI_OK_SELINTO) {
elog(INFO, "SPI_exec execute error: fail to set attribute to password.");
SPI_finish();
return PointerGetDatum(rettuple);
}
} .....
/* check the permanent table name(perm_member) exists or not */
ret = SPI_exec("SELECT tablename FROM pg_tables WHERE tablename LIKE 'perm!_member' ESCAPE '!';", 1);
proc = SPI_processed;
if (ret != SPI_OK_SELECT) {
elog(INFO, "SPI_exec execute error tbl_member");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* create the permanent table(perm_member) if it does not exist */
if (proc < 1) {
/* create permanent table: perm_member */
ret = SPI_exec("CREATE TABLE perm_member AS SELECT * FROM tbl_member;", 0);
if (ret != SPI_OK_SELINTO) {
elog(INFO, "SPI_exec execute error");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* set attribute to perm_member */
ret = SPI_exec("ALTER TABLE perm_member ADD CONSTRAINT user_fk FOREIGN KEY (user_name) REFERENCES perm_user(user_name) ON DELETE CASCADE ON UPDATE CASCADE;", 0);
if (ret != SPI_OK_UTILITY) {
elog(INFO, "SPI_exec execute error: fail to set attribute to user_name.");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* set attribute to perm_member */
ret = SPI_exec("ALTER TABLE perm_member ADD CONSTRAINT group_fk FOREIGN KEY (grp_name) REFERENCES perm_group(grp_name) ON DELETE CASCADE ON UPDATE CASCADE;", 0);
if (ret != SPI_OK_UTILITY) {
elog(INFO, "SPI_exec execute error: fail to set attribute to grp_name.");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* add primary key to perm_member */
ret = SPI_exec("ALTER TABLE perm_member ADD PRIMARY KEY (user_name, grp_name);", 0);
if (ret != SPI_OK_UTILITY) {
elog(INFO, "SPI_exec execute error: fail to add primary key to perm_member.");
SPI_finish();
return PointerGetDatum(rettuple);
}
}
/*close connect with SPI manager */
SPI_finish();
/* return back must be NULL*/
return PointerGetDatum(rettuple);
} 这个函数写法与postgresql服务端函数的写法很相似, 但是不完全相同.具体需要注意的地方是: 1. 需要多添加头文件:#include <commands/trigger.h> 2. 这个函数的返回值一定是trigger类型的. 3. 函数的开始最好确认我们这个函数是供触发器调用的并且明确一下自己要写的触发器的类型是什么,然后做一下判断,以免别的语句也触发我们的触发器. 二. 接下来的事情是编译: gcc -fpic -c trigger.c -I/usr/local/postgreSQL/include/postgresql/server
gcc -shared -o trigger.so trigger.o 如果不明白可以参考手册(说句题外话,手册的作用实在是太大了,在手册中也提供了一例子). 三. 在数据库中创建函数和触发器: /* create a trigger used to write memory and config memory */
CREATE OR REPLACE FUNCTION pg_trigf() RETURNS trigger
AS 'filename' LANGUAGE C IMMUTABLE STRICT; CREATE TRIGGER tbuser BEFORE INSERT OR UPDATE OR DELETE
ON tbl_user FOR EACH STATEMENT
EXECUTE PROCEDURE pg_trigf(); CREATE TRIGGER tbgroup BEFORE INSERT OR UPDATE OR DELETE 我创建的触发器是语句触发器,这个和手册上的不一样, 手册上的是行触发器. 然后在数据库中使用SQL语句就可以看到触发器的效果了. 哈哈... 大功终于告成...... 我上面写的代码是测试过了的,可以使用. 如果你有什么问题,我很希望你能来和我讨论, 这样我们就可以共同进步. 如果你要转载我的这篇文章,麻烦你注明出处.(因为这个花了我不少的心血,为了写个触发器,我花了好几天啊.....).
#include <executor/spi.h>
#include <funcapi.h>
#include <commands/trigger.h>
#include <fmgr.h> extern Datum pg_trigf(PG_FUNCTION_ARGS); #ifdef PG_MODULE_MAGIC
PG_MODULE_MAGIC;
#endif PG_FUNCTION_INFO_V1(pg_trigf); Datum
pg_trigf(PG_FUNCTION_ARGS)
{
TriggerData *trigdata = (TriggerData *)fcinfo->context;
HeapTuple rettuple = NULL;
int ret;
int proc; /* to store the value of SPI_processed (actual row number)*/
/* to be sure this function will be called by trigger */
if (!(CALLED_AS_TRIGGER(fcinfo))) {
elog(ERROR, "trigf: not called by trigger manager");
}
/* should be fired by statement */
if (TRIGGER_FIRED_FOR_ROW(trigdata->tg_event)) {
elog(ERROR, "cannot process row events");
}
/* should be fired before event */
if (TRIGGER_FIRED_AFTER(trigdata->tg_event)) {
elog(ERROR, "must be fired before event");
} /* connect spi manager */
if ((ret = SPI_connect()) < 0) {
elog(INFO, "SPI_connect failed: SPI_connect returned: %d", ret);
return PointerGetDatum(rettuple);
} /* check the permanent table name(perm_user) exists or not*/
ret = SPI_exec("SELECT tablename FROM pg_tables WHERE tablename LIKE 'perm!_user' ESCAPE '!';", 1);
proc = SPI_processed;
if (ret != SPI_OK_SELECT) {
elog(INFO, "SPI_exec execute error: user table.");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* create the permanent table(perm_user) if it does not exist */
if (proc < 1) {
/* create permanent table: perm_user */
ret = SPI_exec("CREATE TABLE perm_user AS SELECT * FROM tbl_user;", 0);
if (ret != SPI_OK_SELINTO ) {
elog(INFO, "SPI_exec execute error: fail to create perm_user");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* set attribute to perm_user */
ret = SPI_exec("ALTER TABLE perm_user ADD PRIMARY KEY (user_name);", 0);
if (ret != SPI_OK_SELINTO) {
elog(INFO, "SPI_exec execute error: fail to add primary key to perm_user");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* set attribute to perm_user*/
ret = SPI_exec("ALTER TABLE perm_user ALTER user_passwd SET NOT NULL;", 0);
if (ret != SPI_OK_SELINTO) {
elog(INFO, "SPI_exec execute error: fail to set attribute to password.");
SPI_finish();
return PointerGetDatum(rettuple);
}
} .....
/* check the permanent table name(perm_member) exists or not */
ret = SPI_exec("SELECT tablename FROM pg_tables WHERE tablename LIKE 'perm!_member' ESCAPE '!';", 1);
proc = SPI_processed;
if (ret != SPI_OK_SELECT) {
elog(INFO, "SPI_exec execute error tbl_member");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* create the permanent table(perm_member) if it does not exist */
if (proc < 1) {
/* create permanent table: perm_member */
ret = SPI_exec("CREATE TABLE perm_member AS SELECT * FROM tbl_member;", 0);
if (ret != SPI_OK_SELINTO) {
elog(INFO, "SPI_exec execute error");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* set attribute to perm_member */
ret = SPI_exec("ALTER TABLE perm_member ADD CONSTRAINT user_fk FOREIGN KEY (user_name) REFERENCES perm_user(user_name) ON DELETE CASCADE ON UPDATE CASCADE;", 0);
if (ret != SPI_OK_UTILITY) {
elog(INFO, "SPI_exec execute error: fail to set attribute to user_name.");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* set attribute to perm_member */
ret = SPI_exec("ALTER TABLE perm_member ADD CONSTRAINT group_fk FOREIGN KEY (grp_name) REFERENCES perm_group(grp_name) ON DELETE CASCADE ON UPDATE CASCADE;", 0);
if (ret != SPI_OK_UTILITY) {
elog(INFO, "SPI_exec execute error: fail to set attribute to grp_name.");
SPI_finish();
return PointerGetDatum(rettuple);
}
/* add primary key to perm_member */
ret = SPI_exec("ALTER TABLE perm_member ADD PRIMARY KEY (user_name, grp_name);", 0);
if (ret != SPI_OK_UTILITY) {
elog(INFO, "SPI_exec execute error: fail to add primary key to perm_member.");
SPI_finish();
return PointerGetDatum(rettuple);
}
}
/*close connect with SPI manager */
SPI_finish();
/* return back must be NULL*/
return PointerGetDatum(rettuple);
} 这个函数写法与postgresql服务端函数的写法很相似, 但是不完全相同.具体需要注意的地方是: 1. 需要多添加头文件:#include <commands/trigger.h> 2. 这个函数的返回值一定是trigger类型的. 3. 函数的开始最好确认我们这个函数是供触发器调用的并且明确一下自己要写的触发器的类型是什么,然后做一下判断,以免别的语句也触发我们的触发器. 二. 接下来的事情是编译: gcc -fpic -c trigger.c -I/usr/local/postgreSQL/include/postgresql/server
gcc -shared -o trigger.so trigger.o 如果不明白可以参考手册(说句题外话,手册的作用实在是太大了,在手册中也提供了一例子). 三. 在数据库中创建函数和触发器: /* create a trigger used to write memory and config memory */
CREATE OR REPLACE FUNCTION pg_trigf() RETURNS trigger
AS 'filename' LANGUAGE C IMMUTABLE STRICT; CREATE TRIGGER tbuser BEFORE INSERT OR UPDATE OR DELETE
ON tbl_user FOR EACH STATEMENT
EXECUTE PROCEDURE pg_trigf(); CREATE TRIGGER tbgroup BEFORE INSERT OR UPDATE OR DELETE 我创建的触发器是语句触发器,这个和手册上的不一样, 手册上的是行触发器. 然后在数据库中使用SQL语句就可以看到触发器的效果了. 哈哈... 大功终于告成...... 我上面写的代码是测试过了的,可以使用. 如果你有什么问题,我很希望你能来和我讨论, 这样我们就可以共同进步. 如果你要转载我的这篇文章,麻烦你注明出处.(因为这个花了我不少的心血,为了写个触发器,我花了好几天啊.....).
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