2 files changed, 39 insertions, 2 deletions
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index a439683185..24f0ccb239 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -51,12 +51,12 @@ module ActiveRecord
       end
 
       def changes_applied
-        super
+        @previous_mutation_tracker = @mutation_tracker
         store_original_attributes
       end
 
       def clear_changes_information
-        super
+        @previous_mutation_tracker = nil
         store_original_attributes
       end
 
@@ -89,6 +89,10 @@ module ActiveRecord
         end
       end
 
+      def previous_changes
+        previous_mutation_tracker.changes
+      end
+
       def attribute_changed_in_place?(attr_name)
         @mutation_tracker.changed_in_place?(attr_name)
       end
@@ -119,6 +123,10 @@ module ActiveRecord
         @mutation_tracker = @mutation_tracker.now_tracking(@attributes)
       end
 
+      def previous_mutation_tracker
+        @previous_mutation_tracker ||= NullMutationTracker.new
+      end
+
       def cache_changed_attributes
         @cached_changed_attributes = changed_attributes
         yield
diff --git a/activerecord/lib/active_record/attribute_mutation_tracker.rb b/activerecord/lib/active_record/attribute_mutation_tracker.rb
index e4be5c5524..168794fcb4 100644
--- a/activerecord/lib/active_record/attribute_mutation_tracker.rb
+++ b/activerecord/lib/active_record/attribute_mutation_tracker.rb
@@ -13,6 +13,14 @@ module ActiveRecord
       end
     end
 
+    def changes
+      attr_names.each_with_object({}.with_indifferent_access) do |attr_name, result|
+        if changed?(attr_name)
+          result[attr_name] = [original_attributes.fetch_value(attr_name), attributes.fetch_value(attr_name)]
+        end
+      end
+    end
+
     def changed?(attr_name)
       attr_name = attr_name.to_s
       modified?(attr_name) || changed_in_place?(attr_name)
@@ -52,4 +60,25 @@ module ActiveRecord
       end
     end
   end
+
+  class NullMutationTracker
+    def changed_values
+      {}
+    end
+
+    def changes
+      {}
+    end
+
+    def changed?(*)
+      false
+    end
+
+    def changed_in_place?(*)
+      false
+    end
+
+    def forget_change(*)
+    end
+  end
 end