bypass preloading for ids_reader

when fetching ids for a collection, bypass preloading
to avoid the unnecessary performance overhead

activerecord/lib/active_record/associations/collection_association.rb

@@ -49,10 +49,18 @@ def ids_reader
           end
         else
           column  = "#{reflection.quoted_table_name}.#{reflection.association_primary_key}"
+          relation = scoped
 
-          scoped.select(column).map! do |record|
-            record.send(reflection.association_primary_key)
+          including = (relation.eager_load_values + relation.includes_values).uniq
+
+          if including.any?
+            join_dependency = ActiveRecord::Associations::JoinDependency.new(reflection.klass, including, [])
+            relation = join_dependency.join_associations.inject(relation) do |r, association|
+              association.join_relation(r)
+            end
           end
+
+          relation.uniq.pluck(column)
         end
       end
 

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -528,6 +528,12 @@ def test_get_ids
     assert_equal [posts(:welcome).id, posts(:authorless).id].sort, people(:michael).post_ids.sort
   end
 
+  def test_get_ids_for_has_many_through_with_conditions_should_not_preload
+    Tagging.create!(:taggable_type => 'Post', :taggable_id => posts(:welcome).id, :tag => tags(:misc))
+    ActiveRecord::Associations::Preloader.expects(:new).never
+    posts(:welcome).misc_tag_ids
+  end
+
   def test_get_ids_for_loaded_associations
     person = people(:michael)
     person.posts(true)