Prevent table partitions from being turned into views.

A table partition must be a table, not a view, so don't allow a
"_RETURN" rule to be added that would convert an existing table
partition into a view.

Amit Langote

Discussion: https://postgr.es/m/CAEZATCVzFcAjZwC1bTFvJ09skB_sgkF4SwPKMywev-XTnimp9Q%40mail.gmail.com

src/backend/rewrite/rewriteDefine.c

@@ -428,6 +428,12 @@ DefineQueryRewrite(char *rulename,
 				errmsg("could not convert partitioned table \"%s\" to a view",
 					   RelationGetRelationName(event_relation))));
 
+			if (event_relation->rd_rel->relispartition)
+				ereport(ERROR,
+						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				errmsg("could not convert partition \"%s\" to a view",
+					   RelationGetRelationName(event_relation))));
+
 			snapshot = RegisterSnapshot(GetLatestSnapshot());
 			scanDesc = heap_beginscan(event_relation, snapshot, 0, NULL);
 			if (heap_getnext(scanDesc, ForwardScanDirection) != NULL)

src/test/regress/expected/rules.out

@@ -2572,6 +2572,11 @@ create table fooview (x int, y text) partition by list (x);
 create rule "_RETURN" as on select to fooview do instead
   select 1 as x, 'aaa'::text as y;
 ERROR:  could not convert partitioned table "fooview" to a view
+-- nor can one convert a partition to view
+create table fooview_part partition of fooview for values in (1);
+create rule "_RETURN" as on select to fooview_part do instead
+  select 1 as x, 'aaa'::text as y;
+ERROR:  could not convert partition "fooview_part" to a view
 --
 -- check for planner problems with complex inherited UPDATES
 --

src/test/regress/sql/rules.sql

@@ -903,6 +903,11 @@ create table fooview (x int, y text) partition by list (x);
 create rule "_RETURN" as on select to fooview do instead
   select 1 as x, 'aaa'::text as y;
 
+-- nor can one convert a partition to view
+create table fooview_part partition of fooview for values in (1);
+create rule "_RETURN" as on select to fooview_part do instead
+  select 1 as x, 'aaa'::text as y;
+
 --
 -- check for planner problems with complex inherited UPDATES
 --