3 files changed, 23 insertions, 3 deletions
diff --git a/activemodel/lib/active_model/dirty.rb b/activemodel/lib/active_model/dirty.rb
index f57588b96d..dc6088a39a 100644
--- a/activemodel/lib/active_model/dirty.rb
+++ b/activemodel/lib/active_model/dirty.rb
@@ -17,6 +17,7 @@ module ActiveModel
   # * Call <tt>changes_applied</tt> after the changes are persisted.
   # * Call <tt>reset_changes</tt> when you want to reset the changes
   #   information.
+  # * Call <tt>undo_changes</tt> when you want to restore previous data.
   #
   # A minimal implementation could be:
   #
@@ -42,6 +43,10 @@ module ActiveModel
   #     def reload!
   #       reset_changes
   #     end
+  #
+  #     def rollback!
+  #       undo_changes
+  #     end
   #   end
   #
   # A newly instantiated object is unchanged:
@@ -72,6 +77,13 @@ module ActiveModel
   #   person.reload!
   #   person.previous_changes # => {}
   #
+  # Rollback the changes:
+  #
+  #   person.name = "Uncle Bob"
+  #   person.rollback!
+  #   person.name           # => "Bill"
+  #   person.name_changed?  # => false
+  #
   # Assigning the same value leaves the attribute unchanged:
   #
   #   person.name = 'Bill'
@@ -167,17 +179,22 @@ module ActiveModel
     private
 
       # Removes current changes and makes them accessible through +previous_changes+.
-      def changes_applied
+      def changes_applied # :doc:
         @previously_changed = changes
         @changed_attributes = ActiveSupport::HashWithIndifferentAccess.new
       end
 
-      # Removes all dirty data: current changes and previous changes
-      def reset_changes
+      # Removes all dirty data: current changes and previous changes.
+      def reset_changes # :doc:
         @previously_changed = ActiveSupport::HashWithIndifferentAccess.new
         @changed_attributes = ActiveSupport::HashWithIndifferentAccess.new
       end
 
+      # Restore all previous data.
+      def undo_changes # :doc:
+        changed_attributes.each_key { |attr| reset_attribute! attr }
+      end
+
       # Handle <tt>*_change</tt> for +method_missing+.
       def attribute_change(attr)
         [changed_attributes[attr], __send__(attr)] if attribute_changed?(attr)
diff --git a/activemodel/lib/active_model/naming.rb b/activemodel/lib/active_model/naming.rb
index 8cf1a191f4..86f5c96af9 100644
--- a/activemodel/lib/active_model/naming.rb
+++ b/activemodel/lib/active_model/naming.rb
@@ -216,6 +216,7 @@ module ActiveModel
   module Naming
     def self.extended(base) #:nodoc:
       base.class_eval do
+        remove_possible_method(:model_name)
         delegate :model_name, to: :class
       end
     end
diff --git a/activemodel/lib/active_model/secure_password.rb b/activemodel/lib/active_model/secure_password.rb
index fdfd8cb147..7e179cf4b7 100644
--- a/activemodel/lib/active_model/secure_password.rb
+++ b/activemodel/lib/active_model/secure_password.rb
@@ -64,6 +64,8 @@ module ActiveModel
         include InstanceMethodsOnActivation
 
         if options.fetch(:validations, true)
+          include ActiveModel::Validations
+
           # This ensures the model has a password by checking whether the password_digest
           # is present, so that this works with both new and existing records. However,
           # when there is an error, the message is added to the password attribute instead