if association is already loaded and if a find operation is performed on the already loaded association list with an empty hash then do not perform another sql

[#5972 state:resolved]

activerecord/lib/active_record/associations/association_collection.rb

@@ -75,6 +75,7 @@ def first(*args)
           find(:first, *args)
         else
           load_target unless loaded?
+          args = args[1..-1] if args.first.kind_of?(Hash) && args.first.empty?
           @target.first(*args)
         end
       end
@@ -544,7 +545,7 @@ def ensure_owner_is_not_new
         end
 
         def fetch_first_or_last_using_find?(args)
-          args.first.kind_of?(Hash) || !(loaded? || !@owner.persisted? || @reflection.options[:finder_sql] ||
+          (args.first.kind_of?(Hash) && !args.first.empty?) || !(loaded? || !@owner.persisted? || @reflection.options[:finder_sql] ||
                                          !@target.all? { |record| record.persisted? } || args.first.kind_of?(Integer))
         end
 

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -66,6 +66,17 @@ def test_create_from_association_should_respect_default_scope
     assert_equal 'exotic', bulb.name
   end
 
+  def test_no_sql_should_be_fired_if_association_already_loaded
+    car = Car.create(:name => 'honda')
+    bulb = car.bulbs.create
+    bulbs = Car.first.bulbs
+    bulbs.inspect # to load all instances of bulbs
+    assert_no_queries do
+      bulbs.first()
+      bulbs.first({})
+    end
+  end
+
   def test_create_resets_cached_counters
     person = Person.create!(:first_name => 'tenderlove')
     post   = Post.first