This patch implements a different "relkind"

for views. Views are now have a "relkind" of
RELKIND_VIEW instead of RELKIND_RELATION.

Also, views no longer have actual heap storage
files.

The following changes were made

1. CREATE VIEW sets the new relkind

2. The executor complains if a DELETE or
        INSERT references a view.

3. DROP RULE complains if an attempt is made
        to delete a view SELECT rule.

4. CREATE RULE "_RETmytable" AS ON SELECT TO mytable DO INSTEAD ...
        1. checks to make sure mytable is empty.
        2. sets the relkind to RELKIND_VIEW.
        3. deletes the heap storage files.
5. LOCK myview is not allowed. :)


6. the regression test type_sanity was changed to
        account for the new relkind value.

7. CREATE INDEX ON myview ... is not allowed.

8. VACUUM myview is not allowed.
        VACUUM automatically skips views when do the entire
        database.

9. TRUNCATE myview is not allowed.


THINGS LEFT TO THINK ABOUT

o pg_views

o pg_dump

o pgsql (\d \dv)
o Do we really want to be able to inherit from views?

o Is 'DROP TABLE myview' OK?

--
Mark Hollomon

src/backend/rewrite/rewriteDefine.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteDefine.c,v 1.50 2000/09/12 04:15:57 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteDefine.c,v 1.51 2000/09/12 04:49:09 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -23,6 +23,8 @@
 #include "parser/parse_relation.h"
 #include "rewrite/rewriteDefine.h"
 #include "rewrite/rewriteSupport.h"
+#include "utils/syscache.h"
+#include "storage/smgr.h"
 #include "commands/view.h"
 
 
@@ -162,6 +164,7 @@ DefineQueryRewrite(RuleStmt *stmt)
 			   *event_qualP;
 	List	   *l;
 	Query	   *query;
+	bool		RelisBecomingView = false;
 
 	/*
 	 * If we are installing an ON SELECT rule, we had better grab
@@ -207,6 +210,30 @@ DefineQueryRewrite(RuleStmt *stmt)
 			elog(ERROR, "rule actions on NEW currently not supported"
 				 "\n\tuse triggers instead");
 		}
+
+		if (event_relation->rd_rel->relkind != RELKIND_VIEW)
+		{
+			HeapScanDesc  scanDesc;
+			HeapTuple	  tuple;
+			/*
+			 * A relation is about to become a view.
+			 * check that the relation is empty because
+			 * the storage for the relation is going to
+			 * be deleted.
+			 */
+
+			scanDesc = heap_beginscan(event_relation, 0, SnapshotNow, 0, NULL);
+			tuple = heap_getnext(scanDesc, 0);
+			if (HeapTupleIsValid(tuple))
+				elog(ERROR, "relation %s is not empty. Cannot convert to view", event_obj->relname);
+
+			/* don't need heap_freetuple because we never got a valid tuple */
+			heap_endscan(scanDesc);
+
+
+			RelisBecomingView = true;
+		}
+
 	}
 
 	/*
@@ -338,6 +365,10 @@ DefineQueryRewrite(RuleStmt *stmt)
 	/* discard rule if it's null action and not INSTEAD; it's a no-op */
 	if (action != NULL || is_instead)
 	{
+		Relation	relationRelation;
+		HeapTuple	tuple;
+		Relation	idescs[Num_pg_class_indices];
+
 		event_qualP = nodeToString(event_qual);
 		actionP = nodeToString(action);
 
@@ -351,14 +382,50 @@ DefineQueryRewrite(RuleStmt *stmt)
 
 		/*
 		 * Set pg_class 'relhasrules' field TRUE for event relation.
+		 * Also modify the 'relkind' field to show that the relation is
+		 * now a view.
 		 *
 		 * Important side effect: an SI notice is broadcast to force all
 		 * backends (including me!) to update relcache entries with the new
 		 * rule.
+		 *
+		 * NOTE : Used to call setRelhasrulesInRelation. The code
+		 * was inlined so that two updates were not needed. mhh 31-aug-2000
 		 */
-		setRelhasrulesInRelation(ev_relid, true);
+
+		/*
+		 * Find the tuple to update in pg_class, using syscache for the lookup.
+		 */
+		relationRelation = heap_openr(RelationRelationName, RowExclusiveLock);
+		tuple = SearchSysCacheTupleCopy(RELOID,
+									ObjectIdGetDatum(ev_relid),
+									0, 0, 0);
+		Assert(HeapTupleIsValid(tuple));
+
+		/* Do the update */
+		((Form_pg_class) GETSTRUCT(tuple))->relhasrules = true;
+		if (RelisBecomingView)
+			((Form_pg_class) GETSTRUCT(tuple))->relkind = RELKIND_VIEW;
+
+		heap_update(relationRelation, &tuple->t_self, tuple, NULL);
+
+		/* Keep the catalog indices up to date */
+		CatalogOpenIndices(Num_pg_class_indices, Name_pg_class_indices, idescs);
+		CatalogIndexInsert(idescs, Num_pg_class_indices, relationRelation, tuple);
+		CatalogCloseIndices(Num_pg_class_indices, idescs);
+
+		heap_freetuple(tuple);
+		heap_close(relationRelation, RowExclusiveLock);
 	}
 
+	/*
+	 * IF the relation is becoming a view, delete the storage
+	 * files associated with it.
+	 */
+	if (RelisBecomingView)
+		smgrunlink(DEFAULT_SMGR, event_relation);
+
+
 	/* Close rel, but keep lock till commit... */
 	heap_close(event_relation, NoLock);
 }

src/backend/rewrite/rewriteRemove.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteRemove.c,v 1.38 2000/06/30 07:04:23 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteRemove.c,v 1.39 2000/09/12 04:49:09 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -103,6 +103,11 @@ RemoveRewriteRule(char *ruleName)
 	 */
 	event_relation = heap_open(eventRelationOid, AccessExclusiveLock);
 
+	/* do not allow the removal of a view's SELECT rule */
+	if (event_relation->rd_rel->relkind == RELKIND_VIEW &&
+			((Form_pg_rewrite) GETSTRUCT(tuple))->ev_type == '1' )
+		elog(ERROR, "Cannot remove a view's SELECT rule");
+
 	hasMoreRules = event_relation->rd_rules != NULL &&
 		event_relation->rd_rules->numLocks > 1;