Merge d54fed5 into 661b3d3

lib/DBIx/Class/Helper/ResultSet/Shortcut.pm

@@ -159,10 +159,28 @@ calling C<< $rs->count >>.
 
  my $results_exist = $schema->resultset('Bar')->search({...})->results_exist;
 
+ # there is no easily expressable equivalent, so this is not exactly a
+ # shortcut. Nevertheless kept in this class for historical reasons
+
 Uses C<EXISTS> SQL function to check if the query would return anything.
-Possibly lighter weight than the much more common C<< foo() if $rs->count >>
+Usually much less resource intensive the more common C<< foo() if $rs->count >>
 idiom.
 
+=method results_exist_as_query
+
+ ...->search(
+    {},
+    { '+columns' => {
+       subquery_has_members => $some_correlated_rs->results_exist_as_query
+    }},
+ );
+
+ # there is no easily expressable equivalent, so this is not exactly a
+ # shortcut. Nevertheless kept in this class for historical reasons
+
+The query generator behind L</results_exist>. Can be used standalone in
+complex queries returning a boolean result within a larger query context.
+
 =method null(@columns || \@columns)
 
  $rs->null('status');

lib/DBIx/Class/Helper/ResultSet/Shortcut/ResultsExist.pm

@@ -5,14 +5,36 @@ use warnings;
 
 use parent 'DBIx::Class::ResultSet';
 
+sub results_exist_as_query {
+   my $self = shift;
+
+
+   my $reified = $self->search_rs( {}, {
+      columns => { _results_existence_check => \ '42' }
+   } )->as_query;
+
+
+   $$reified->[0] = "( SELECT EXISTS $$reified->[0] )";
+
+
+   $reified;
+}
+
+
 sub results_exist {
-   my $self   = shift;
+   my $self = shift;
+
+   my( undef, $sth ) = $self->result_source
+                             ->schema
+                              ->storage
+                               ->_select(
+                                  $self->results_exist_as_query,
+                                  \'*',
+                                  {},
+                                  {},
+                               );
 
-   $self
-      ->result_source
-      ->resultset
-      ->search({ -exists => $self->as_query })
-      ->first
+   $sth->fetchall_arrayref->[0][0] ? 1 : 0;
 }
 
 1;

t/ResultSet/Shortcut/ResultsExist.t

@@ -16,4 +16,32 @@ my $rs2 = $schema->resultset( 'Foo' )->search({ id => { '<' => 0 } });
 ok( $rs->results_exist, 'check rs has some results' );
 ok(!$rs2->results_exist, 'and check that rs has no results' );
 
+is_deeply(
+   [
+      $rs->search({}, { order_by => 'id', columns => {
+
+         id => "id",
+
+         has_lesser => $rs->search(
+            { 'correlation.id' => { '<' => { -ident => "me.id" } } },
+            { alias => 'correlation' }
+         )->results_exist_as_query,
+
+         has_greater => $rs->search(
+            { 'correlation.id' => { '>' => { -ident => "me.id" } } },
+            { alias => 'correlation' }
+         )->results_exist_as_query,
+
+      }})->hri->all
+   ],
+   [
+      { id => 1, has_lesser => 0, has_greater => 1 },
+      { id => 2, has_lesser => 1, has_greater => 1 },
+      { id => 3, has_lesser => 1, has_greater => 1 },
+      { id => 4, has_lesser => 1, has_greater => 1 },
+      { id => 5, has_lesser => 1, has_greater => 0 },
+   ],
+   "Correlated-existence works",
+);
+
 done_testing;