Implement `_was` and `changes` for in-place mutations of AR attributes

1 files changed, 16 insertions, 3 deletions

diff --git a/activemodel/lib/active_model/dirty.rb b/activemodel/lib/active_model/dirty.rb
index d11243c4c0..ed00d8cf12 100644
--- a/activemodel/lib/active_model/dirty.rb
+++ b/activemodel/lib/active_model/dirty.rb
@@ -114,7 +114,7 @@ module ActiveModel
     include ActiveModel::AttributeMethods
 
     included do
-      attribute_method_suffix '_changed?', '_change', '_will_change!', '_was'
+      attribute_method_suffix '_changed?', '_change', '_will_change!', '_was', '_was='
       attribute_method_affix prefix: 'reset_', suffix: '!'
       attribute_method_affix prefix: 'restore_', suffix: '!'
     end
@@ -180,13 +180,26 @@ module ActiveModel
       attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
     end
 
+    # Handle <tt>*_was=</tt> for +method_missing+
+    def attribute_was=(attr, old_value)
+      attributes_changed_by_setter[attr] = old_value
+    end
+    alias_method :set_attribute_was, :attribute_was=
+
     # Restore all previous data of the provided attributes.
     def restore_attributes(attributes = changed)
       attributes.each { |attr| restore_attribute! attr }
     end
 
+    # Remove changes information for the provided attributes.
+    def clear_attribute_changes(attributes)
+      attributes_changed_by_setter.except!(*attributes)
+    end
+
     private
 
+      alias_method :attributes_changed_by_setter, :changed_attributes # :nodoc:
+
       # Removes current changes and makes them accessible through +previous_changes+.
       def changes_applied # :doc:
         @previously_changed = changes
@@ -219,7 +232,7 @@ module ActiveModel
         rescue TypeError, NoMethodError
         end
 
-        changed_attributes[attr] = value
+        set_attribute_was(attr, value)
       end
 
       # Handle <tt>reset_*!</tt> for +method_missing+.
@@ -233,7 +246,7 @@ module ActiveModel
       def restore_attribute!(attr)
         if attribute_changed?(attr)
           __send__("#{attr}=", changed_attributes[attr])
-          changed_attributes.delete(attr)
+          clear_attribute_changes([attr])
         end
       end
   end