add as_subselect_rs

lib/DBIx/Class/ResultSet.pm

@@ -2502,7 +2502,7 @@ sub related_resultset {
         ->relname_to_table_alias($rel, $join_count);
 
     # since this is search_related, and we already slid the select window inwards
-    # (the select/as attrs were deleted in the beginning), we need to flip all 
+    # (the select/as attrs were deleted in the beginning), we need to flip all
     # left joins to inner, so we get the expected results
     # read the comment on top of the actual function to see what this does
     $attrs->{from} = $rsrc->schema->storage->_straight_join_to_node ($attrs->{from}, $alias);
@@ -2588,6 +2588,56 @@ sub current_source_alias {
   return ($self->{attrs} || {})->{alias} || 'me';
 }
 
+=head2 as_subselect_rs
+
+=over 4
+
+=item Arguments: none
+
+=item Return Value: $resultset
+
+=back
+
+Act as a barrier to SQL symbols.  The resultset provided will be made into a
+"virtual view" by including it as a subquery within the from clause.  From this
+point on, any joined tables are inaccessible to ->search on the resultset (as if
+it were simply where-filtered without joins).  For example:
+
+ my $rs = $schema->resultset('Bar')->search({'x.name' => 'abc'},{ join => 'x' });
+
+ # 'x' now pollutes the query namespace
+
+ # So the following works as expected
+ my $ok_rs = $rs->search({'x.other' => 1});
+
+ # But this doesn't: instead of finding a 'Bar' related to two x rows (abc and
+ # def) we look for one row with contradictory terms and join in another table
+ # (aliased 'x_2') which we never use
+ my $broken_rs = $rs->search({'x.name' => 'def'});
+
+ my $rs2 = $rs->as_subselect_rs;
+
+ # doesn't work - 'x' is no longer accessible in $rs2, having been sealed away
+ my $not_joined_rs = $rs2->search({'x.other' => 1});
+
+ # works as expected: finds a 'table' row related to two x rows (abc and def)
+ my $correctly_joined_rs = $rs2->search({'x.name' => 'def'});
+
+=cut
+
+sub as_subselect_rs {
+   my $self = shift;
+
+   return $self->result_source->resultset->search( undef, {
+      alias => 'me',
+      from => [{
+            me => $self->as_query,
+            -alias         => $self->current_source_alias,
+            -source_handle => $self->result_source->handle,
+         }]
+   });
+}
+
 # This code is called by search_related, and makes sure there
 # is clear separation between the joins before, during, and
 # after the relationship. This information is needed later

t/resultset/as_subselect_rs.t

@@ -0,0 +1,25 @@
+use strict;
+use warnings;
+
+use Test::More;
+use Test::Exception;
+
+use lib qw(t/lib);
+use DBICTest;
+use DBIC::SqlMakerTest;
+
+my $schema = DBICTest->init_schema();
+
+my $new_rs = $schema->resultset('Artist')->search({
+   'artwork_to_artist.artist_id' => 1
+}, {
+   join => 'artwork_to_artist'
+});
+lives_ok { $new_rs->count } 'regular search works';
+lives_ok { $new_rs->search({ 'artwork_to_artist.artwork_cd_id' => 1})->count }
+   '... and chaining off that using join works';
+lives_ok { $new_rs->search({ 'artwork_to_artist.artwork_cd_id' => 1})->as_subselect_rs->count }
+   '... and chaining off the virtual view works';
+dies_ok  { $new_rs->as_subselect_rs->search({'artwork_to_artist.artwork_cd_id'=> 1})->count }
+   q{... but chaining off of a virtual view using join doesn't work};
+done_testing;