Use indifferent access attributes instead of stringifying them

activerecord/lib/active_record/nested_attributes.rb

@@ -283,7 +283,7 @@ def _delete #:nodoc:
     # <tt>:_destroy</tt> key set to a truthy value, then the existing record
     # will be marked for destruction.
     def assign_nested_attributes_for_one_to_one_association(association_name, attributes, allow_destroy)
-      attributes = attributes.stringify_keys
+      attributes = attributes.with_indifferent_access
 
       if attributes['id'].blank?
         unless reject_new_record?(association_name, attributes)
@@ -336,7 +336,7 @@ def assign_nested_attributes_for_collection_association(association_name, attrib
       end
 
       attributes_collection.each do |attributes|
-        attributes = attributes.stringify_keys
+        attributes = attributes.with_indifferent_access
 
         if attributes['id'].blank?
           unless reject_new_record?(association_name, attributes)

activerecord/test/cases/nested_attributes_test.rb

@@ -104,6 +104,14 @@ def test_reject_if_method_with_arguments
     pirate.ship_attributes = { :name => 'Red Pearl', :_reject_me_if_new => true }
     assert_difference('Ship.count') { pirate.save! }
   end
+
+  def test_reject_if_with_indifferent_keys
+    Pirate.accepts_nested_attributes_for :ship, :reject_if => proc {|attributes| attributes[:name].blank? }
+
+    pirate = Pirate.new(:catchphrase => "Stop wastin' me time")
+    pirate.ship_attributes = { :name => 'Hello Pearl' }
+    assert_difference('Ship.count') { pirate.save! }
+  end
 end
 
 class TestNestedAttributesOnAHasOneAssociation < ActiveRecord::TestCase