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[转贴]已经过了两年了，不知道结论还正确吗？
当创建一个引用关系时候，会在引用表上自动创建一个触发器，当向这个引用表插入修改数据时候，由这个触发器去查询被引用表。以此来知道是否违反了约束。
/*-------------------------------------------------------------------------
*
* trigger.c
* PostgreSQL TRIGGERs support code.
*
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql-server/src/backend/commands/trigger.c,v 1.136 2002/10/21 19:55:49 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/genam.h"
#include "access/heapam.h"
#include "catalog/catalog.h"
#include "catalog/catname.h"
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/pg_language.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_trigger.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "commands/trigger.h"
#include "executor/executor.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "parser/parse_func.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"
static void InsertTrigger(TriggerDesc *trigdesc, Trigger *trigger, int indx);
static HeapTuple GetTupleForTrigger(EState *estate,
ResultRelInfo *relinfo,
ItemPointer tid,
TupleTableSlot **newSlot);
static HeapTuple ExecCallTriggerFunc(TriggerData *trigdata,
FmgrInfo *finfo,
MemoryContext per_tuple_context);
static void DeferredTriggerSaveEvent(ResultRelInfo *relinfo, int event,
HeapTuple oldtup, HeapTuple newtup);
static void DeferredTriggerExecute(DeferredTriggerEvent event, int itemno,
Relation rel, TriggerDesc *trigdesc, FmgrInfo *finfo,
MemoryContext per_tuple_context);
/*
* Create a trigger. Returns the OID of the created trigger.
*
* forConstraint, if true, says that this trigger is being created to
* implement a constraint. The caller will then be expected to make
* a pg_depend entry linking the trigger to that constraint (and thereby
* to the owning relation(s)).
*/
/* 创建触发器
第一个参数是语法树结构
第二个是是否是约束触发器
*/
Oid
CreateTrigger(CreateTrigStmt *stmt, bool forConstraint)
{
int16 tgtype;
int16 tgattr[FUNC_MAX_ARGS];
Datum values[Natts_pg_trigger];
char nulls[Natts_pg_trigger];
Relation rel;
AclResult aclresult;
Relation tgrel;
SysScanDesc tgscan;
ScanKeyData key;
Relation pgrel;
HeapTuple tuple;
Oid fargtypes[FUNC_MAX_ARGS];
Oid funcoid;
Oid funcrettype;
Oid trigoid;
int found = 0;
int i;
char constrtrigname[NAMEDATALEN];
char *trigname;
char *constrname;
Oid constrrelid = InvalidOid;
ObjectAddress myself,
referenced;
rel = heap_openrv(stmt->;relation, AccessExclusiveLock);
if (stmt->;constrrel != NULL)
constrrelid = RangeVarGetRelid(stmt->;constrrel, false);
/*判断是否一个约束触发器 */
else if (stmt->;isconstraint)
{
/*
* If this trigger is a constraint (and a foreign key one)
* then we really need a constrrelid. Since we don't have one,
* we'll try to generate one from the argument information.
*
* This is really just a workaround for a long-ago pg_dump bug
* that omitted the FROM clause in dumped CREATE CONSTRAINT TRIGGER
* commands. We don't want to bomb out completely here if we can't
* determine the correct relation, because that would prevent loading
* the dump file. Instead, NOTICE here and ERROR in the trigger.
*/
bool needconstrrelid = false;
void *elem = NULL;
/* 那么起一个特定规则的名字 */
if (strncmp(strVal(llast(stmt->;funcname)), "RI_FKey_check_", 14) == 0)
{
/* A trigger on FK table. */
needconstrrelid = true;
if (length(stmt->;args) >; RI_PK_RELNAME_ARGNO)
elem = nth(RI_PK_RELNAME_ARGNO, stmt->;args);
}
else if (strncmp(strVal(llast(stmt->;funcname)), "RI_FKey_",  == 0)
{
/* A trigger on PK table. */
needconstrrelid = true;
if (length(stmt->;args) >; RI_FK_RELNAME_ARGNO)
elem = nth(RI_FK_RELNAME_ARGNO, stmt->;args);
}
if (elem != NULL)
{
RangeVar *rel = makeRangeVar(NULL, strVal(elem));
constrrelid = RangeVarGetRelid(rel, true);
}
if (needconstrrelid && constrrelid == InvalidOid)
elog(NOTICE, "Unable to find table for constraint \"%s\"",
stmt->;trigname);
}
if (rel->;rd_rel->;relkind != RELKIND_RELATION)
elog(ERROR, "CreateTrigger: relation \"%s\" is not a table",
stmt->;relation->;relname);
if (!allowSystemTableMods && IsSystemRelation(rel))
elog(ERROR, "CreateTrigger: can't create trigger for system relation %s",
stmt->;relation->;relname);
/* permission checks */
if (stmt->;isconstraint)
{
/* foreign key constraint trigger */
/* 进行权限检查 */
aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(), ACL_REFERENCES);
if (aclresult != ACLCHECK_OK)
aclcheck_error(aclresult, RelationGetRelationName(rel));
if (constrrelid != InvalidOid)
{
aclresult = pg_class_aclcheck(constrrelid, GetUserId(), ACL_REFERENCES);
if (aclresult != ACLCHECK_OK)
aclcheck_error(aclresult, get_rel_name(constrrelid));
}
}
else
{
/* real trigger */
aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(), ACL_TRIGGER);
if (aclresult != ACLCHECK_OK)
aclcheck_error(aclresult, RelationGetRelationName(rel));
} |
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发表于 2003-01-29 10:44
发表于 2003-01-30 23:39
