# Disallow TRUNCATE on tables that are involved in referential

constraints


The issue with finding and removing foreign key constraints is no longer
an issue, so please apply the attached.

It does NOT check for rules or on delete triggers (old style foreign
keys) as those are difficult to deal with (remove, truncate, re-add).

Rod Taylor

1 files changed, 35 insertions, 1 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index c6e8d686d41..1961ca1344a 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.30 2002/08/19 15:08:46 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.31 2002/08/22 04:51:05 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -332,6 +332,10 @@ TruncateRelation(const RangeVar *relation)
 {
 	Relation	rel;
 	Oid			relid;
+ 	ScanKeyData key;
+ 	Relation	fkeyRel;
+ 	SysScanDesc	fkeyScan;
+	HeapTuple	tuple;
 
 	/* Grab exclusive lock in preparation for truncate */
 	rel = heap_openrv(relation, AccessExclusiveLock);
@@ -356,6 +360,36 @@ TruncateRelation(const RangeVar *relation)
 	if (!pg_class_ownercheck(relid, GetUserId()))
 		aclcheck_error(ACLCHECK_NOT_OWNER, RelationGetRelationName(rel));
 
+	/*
+	 * Don't allow truncate on tables which are referenced
+	 * by foreign keys
+	 */
+	fkeyRel = heap_openr(ConstraintRelationName, AccessShareLock);
+
+	ScanKeyEntryInitialize(&key, 0,
+						   Anum_pg_constraint_confrelid,
+						   F_OIDEQ,
+						   ObjectIdGetDatum(relid));
+
+	fkeyScan = systable_beginscan(fkeyRel, 0, false,
+								  SnapshotNow, 1, &key);
+
+	/*
+	 * First foriegn key found with us as the reference
+	 * should throw an error.
+	 */
+	while (HeapTupleIsValid(tuple = systable_getnext(fkeyScan)))
+	{
+		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
+
+		if (con->contype == 'f')
+			elog(ERROR, "TRUNCATE cannot be used as other tables reference this one via foreign key constraint %s",
+				 NameStr(con->conname));
+	}
+
+	systable_endscan(fkeyScan);
+	heap_close(fkeyRel, AccessShareLock);
+
 	/* Keep the lock until transaction commit */
 	heap_close(rel, NoLock);