pg_constraint.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

 *
 * name1, name2, and label are used the same way as for makeObjectName(),
 * except that the label can't be NULL; digits will be appended to the label
 * if needed to create a name that is unique within the specified namespace.
 *
 * 'others' can be a list of string names already chosen within the current
 * command (but not yet reflected into the catalogs); we will not choose
 * a duplicate of one of these either.
 *
 * Note: it is theoretically possible to get a collision anyway, if someone
 * else chooses the same name concurrently.  This is fairly unlikely to be
 * a problem in practice, especially if one is holding an exclusive lock on
 * the relation identified by name1.
 *
 * Returns a palloc'd string.
 */
char *
ChooseConstraintName(const char *name1, const char *name2,
					 const char *label, Oid namespace,
					 List *others)
{
	int			pass = 0;
	char	   *conname = NULL;
	char		modlabel[NAMEDATALEN];
	Relation	conDesc;
	SysScanDesc conscan;
	ScanKeyData skey[2];
	bool		found;
	ListCell   *l;

	conDesc = heap_open(ConstraintRelationId, AccessShareLock);

	/* try the unmodified label first */
	StrNCpy(modlabel, label, sizeof(modlabel));

	for (;;)
	{
		conname = makeObjectName(name1, name2, modlabel);

		found = false;

		foreach(l, others)
		{
			if (strcmp((char *) lfirst(l), conname) == 0)
			{
				found = true;
				break;
			}
		}

		if (!found)
		{
			ScanKeyInit(&skey[0],
						Anum_pg_constraint_conname,
						BTEqualStrategyNumber, F_NAMEEQ,
						CStringGetDatum(conname));

			ScanKeyInit(&skey[1],
						Anum_pg_constraint_connamespace,
						BTEqualStrategyNumber, F_OIDEQ,
						ObjectIdGetDatum(namespace));

			conscan = systable_beginscan(conDesc, ConstraintNameNspIndexId, true,
										 SnapshotNow, 2, skey);

			found = (HeapTupleIsValid(systable_getnext(conscan)));

			systable_endscan(conscan);
		}

		if (!found)
			break;

		/* found a conflict, so try a new name component */
		pfree(conname);
		snprintf(modlabel, sizeof(modlabel), "%s%d", label, ++pass);
	}

	heap_close(conDesc, AccessShareLock);

	return conname;
}

/*
 * Delete a single constraint record.
 */
void
RemoveConstraintById(Oid conId)
{
	Relation	conDesc;
	ScanKeyData skey[1];
	SysScanDesc conscan;
	HeapTuple	tup;
	Form_pg_constraint con;

	conDesc = heap_open(ConstraintRelationId, RowExclusiveLock);

	ScanKeyInit(&skey[0],
				ObjectIdAttributeNumber,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(conId));

	conscan = systable_beginscan(conDesc, ConstraintOidIndexId, true,
								 SnapshotNow, 1, skey);

	tup = systable_getnext(conscan);
	if (!HeapTupleIsValid(tup))
		elog(ERROR, "could not find tuple for constraint %u", conId);
	con = (Form_pg_constraint) GETSTRUCT(tup);

	/*
	 * Special processing depending on what the constraint is for.
	 */
	if (OidIsValid(con->conrelid))
	{
		Relation	rel;

		/*
		 * If the constraint is for a relation, open and exclusive-lock the
		 * relation it's for.
		 */
		rel = heap_open(con->conrelid, AccessExclusiveLock);

		/*
		 * We need to update the relcheck count if it is a check constraint
		 * being dropped.  This update will force backends to rebuild relcache
		 * entries when we commit.
		 */
		if (con->contype == CONSTRAINT_CHECK)
		{
			Relation	pgrel;
			HeapTuple	relTup;
			Form_pg_class classForm;

			pgrel = heap_open(RelationRelationId, RowExclusiveLock);
			relTup = SearchSysCacheCopy(RELOID,
										ObjectIdGetDatum(con->conrelid),
										0, 0, 0);
			if (!HeapTupleIsValid(relTup))
				elog(ERROR, "cache lookup failed for relation %u",
					 con->conrelid);
			classForm = (Form_pg_class) GETSTRUCT(relTup);

			if (classForm->relchecks == 0)		/* should not happen */
				elog(ERROR, "relation \"%s\" has relchecks = 0",
					 RelationGetRelationName(rel));
			classForm->relchecks--;

			simple_heap_update(pgrel, &relTup->t_self, relTup);

			CatalogUpdateIndexes(pgrel, relTup);

			heap_freetuple(relTup);

			heap_close(pgrel, RowExclusiveLock);
		}

		/* Keep lock on constraint's rel until end of xact */
		heap_close(rel, NoLock);
	}
	else if (OidIsValid(con->contypid))
	{
		/*
		 * XXX for now, do nothing special when dropping a domain constraint
		 *
		 * Probably there should be some form of locking on the domain type,
		 * but we have no such concept at the moment.
		 */
	}
	else
		elog(ERROR, "constraint %u is not of a known type", conId);

	/* Fry the constraint itself */
	simple_heap_delete(conDesc, &tup->t_self);

	/* Clean up */
	systable_endscan(conscan);
	heap_close(conDesc, RowExclusiveLock);
}

/*
 * GetConstraintNameForTrigger
 *		Get the name of the constraint owning a trigger, if any
 *
 * Returns a palloc'd string, or NULL if no constraint can be found
 */
char *
GetConstraintNameForTrigger(Oid triggerId)
{
	char	   *result;
	Oid			constraintId = InvalidOid;
	Relation	depRel;
	Relation	conRel;
	ScanKeyData key[2];
	SysScanDesc scan;
	HeapTuple	tup;

	/*
	 * We must grovel through pg_depend to find the owning constraint. Perhaps
	 * pg_trigger should have a column for the owning constraint ... but right
	 * now this is not performance-critical code.
	 */
	depRel = heap_open(DependRelationId, AccessShareLock);

	ScanKeyInit(&key[0],
				Anum_pg_depend_classid,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(TriggerRelationId));
	ScanKeyInit(&key[1],
				Anum_pg_depend_objid,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(triggerId));
	/* assume we can ignore objsubid for a trigger */

	scan = systable_beginscan(depRel, DependDependerIndexId, true,
							  SnapshotNow, 2, key);

	while (HeapTupleIsValid(tup = systable_getnext(scan)))
	{
		Form_pg_depend foundDep = (Form_pg_depend) GETSTRUCT(tup);

		if (foundDep->refclassid == ConstraintRelationId &&
			foundDep->deptype == DEPENDENCY_INTERNAL)
		{
			constraintId = foundDep->refobjid;
			break;
		}
	}

	systable_endscan(scan);

	heap_close(depRel, AccessShareLock);

	if (!OidIsValid(constraintId))
		return NULL;			/* no owning constraint found */

	conRel = heap_open(ConstraintRelationId, AccessShareLock);

	ScanKeyInit(&key[0],
				ObjectIdAttributeNumber,
				BTEqualStrategyNumber, F_OIDEQ,
				ObjectIdGetDatum(constraintId));

	scan = systable_beginscan(conRel, ConstraintOidIndexId, true,
							  SnapshotNow, 1, key);

	tup = systable_getnext(scan);

	if (HeapTupleIsValid(tup))
	{
		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tup);

		result = pstrdup(NameStr(con->conname));
	}
	else
	{
		/* This arguably should be an error, but we'll just return NULL */
		result = NULL;
	}

	systable_endscan(scan);

	heap_close(conRel, AccessShareLock);

	return result;
}

/*
 * AlterConstraintNamespaces
 *		Find any constraints belonging to the specified object,
 *		and move them to the specified new namespace.
 *
 * isType indicates whether the owning object is a type or a relation.
 */
void
AlterConstraintNamespaces(Oid ownerId, Oid oldNspId,
						  Oid newNspId, bool isType)
{
	Relation	conRel;
	ScanKeyData key[1];
	SysScanDesc scan;
	HeapTuple	tup;

	conRel = heap_open(ConstraintRelationId, RowExclusiveLock);

	if (isType)
	{
		ScanKeyInit(&key[0],
					Anum_pg_constraint_contypid,
					BTEqualStrategyNumber, F_OIDEQ,
					ObjectIdGetDatum(ownerId));

		scan = systable_beginscan(conRel, ConstraintTypidIndexId, true,
								  SnapshotNow, 1, key);
	}
	else
	{
		ScanKeyInit(&key[0],
					Anum_pg_constraint_conrelid,
					BTEqualStrategyNumber, F_OIDEQ,
					ObjectIdGetDatum(ownerId));

		scan = systable_beginscan(conRel, ConstraintRelidIndexId, true,
								  SnapshotNow, 1, key);
	}

	while (HeapTupleIsValid((tup = systable_getnext(scan))))
	{
		Form_pg_constraint conform = (Form_pg_constraint) GETSTRUCT(tup);

		if (conform->connamespace == oldNspId)
		{
			tup = heap_copytuple(tup);
			conform = (Form_pg_constraint) GETSTRUCT(tup);

			conform->connamespace = newNspId;

			simple_heap_update(conRel, &tup->t_self, tup);
			CatalogUpdateIndexes(conRel, tup);

			/*
			 * Note: currently, the constraint will not have its own
			 * dependency on the namespace, so we don't need to do
			 * changeDependencyFor().
			 */
		}
	}

	systable_endscan(scan);

	heap_close(conRel, RowExclusiveLock);
}