Move around AR::Dirty and fix _attribute method

We already have a _read_attribute method that can get the value we need
from the model.  Lets define that method in AM::Dirty and use the
existing one from AR::Dirty rather than introducing a new method.

2 files changed, 22 insertions, 4 deletions

diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index 63978cfb3e..bd5003d63a 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -328,10 +328,6 @@ module ActiveRecord
         def clear_changed_attributes_cache
           remove_instance_variable(:@cached_changed_attributes) if defined?(@cached_changed_attributes)
         end
-
-        def _attributes(attr)
-          _read_attribute(attr)
-        end
     end
   end
 end
diff --git a/activerecord/test/cases/dirty_test.rb b/activerecord/test/cases/dirty_test.rb
index 15d7a32e21..721861975a 100644
--- a/activerecord/test/cases/dirty_test.rb
+++ b/activerecord/test/cases/dirty_test.rb
@@ -671,6 +671,28 @@ class DirtyTest < ActiveRecord::TestCase
     assert binary.changed?
   end
 
+  test "changes is correct for subclass" do
+    foo = Class.new(Pirate) do
+      def catchphrase
+        super.upcase
+      end
+    end
+
+    pirate = foo.create!(catchphrase: "arrrr")
+
+    new_catchphrase = "arrrr matey!"
+
+    pirate.catchphrase = new_catchphrase
+    assert pirate.catchphrase_changed?
+
+    expected_changes = {
+      "catchphrase" => ["arrrr", new_catchphrase]
+    }
+
+    assert_equal new_catchphrase.upcase, pirate.catchphrase
+    assert_equal expected_changes, pirate.changes
+  end
+
   test "changes is correct if override attribute reader" do
     pirate = Pirate.create!(catchphrase: "arrrr")
     def pirate.catchphrase