I added this feature so that a Map of changed fields could be retrieved

after a model had been saved. This is useful in the after_save callback
when you need to know what fields changed. At present there is no way
to do this other than have code in the before_save callback that takes
a copy of the changes Map, which I thought was a bit messy.

Example.

  person = Person.find_by_name('bob')
  person.name = 'robert'
  person.changes # => {'name' => ['bob, 'robert']}
  person.save
  person.changes # => {}
  person.previous_changes # => {'name' => ['bob, 'robert']}
  person.reload
  person.previous_changes # => {}

Signed-off-by: Joshua Peek <josh@joshpeek.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/activemodel/lib/active_model/dirty.rb b/activemodel/lib/active_model/dirty.rb
index 624c3647ca..735c61df74 100644
--- a/activemodel/lib/active_model/dirty.rb
+++ b/activemodel/lib/active_model/dirty.rb
@@ -72,12 +72,26 @@ module ActiveModel
       changed.inject({}) { |h, attr| h[attr] = attribute_change(attr); h }
     end
 
+    # Map of attributes that were changed when the model was saved.
+    #   person.name # => 'bob'
+    #   person.name = 'robert'
+    #   person.save
+    #   person.previous_changes # => {'name' => ['bob, 'robert']}
+    def previous_changes
+      previously_changed_attributes
+    end
+
     private
       # Map of change <tt>attr => original value</tt>.
       def changed_attributes
         @changed_attributes ||= {}
       end
 
+      # Map of fields that were changed when the model was saved
+      def previously_changed_attributes
+        @previously_changed || {}
+      end
+
       # Handle <tt>*_changed?</tt> for +method_missing+.
       def attribute_changed?(attr)
         changed_attributes.include?(attr)