Make AM::Dirty less dirty to plugin into AR or other library

activemodel/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Added new API methods `reset_changes` and `changed_applied` to AM::Dirty
+    that control changes state. Previsously you needed to update internal
+    instance variables, but now API methods are available.
+
+    *Bogdan Gusiev*
+
 *   Fix regression in has_secure_password. When a password is set, but a
     confirmation is an empty string, it would incorrectly save.
 

activemodel/lib/active_model/dirty.rb

@@ -14,13 +14,7 @@ module ActiveModel
   #   track.
   # * Call <tt>attr_name_will_change!</tt> before each change to the tracked
   #   attribute.
-  #
-  # If you wish to also track previous changes on save or update, you need to
-  # add:
-  #
-  #   @previously_changed = changes
-  #
-  # inside of your save or update method.
+  # * Call <tt>changes_applied</tt> after the changes are persisted.
   #
   # A minimal implementation could be:
   #
@@ -39,8 +33,8 @@ module ActiveModel
   #     end
   #
   #     def save
-  #       @previously_changed = changes
-  #       @changed_attributes.clear
+  #       # do persistence work
+  #       changes_applied
   #     end
   #   end
   #
@@ -129,7 +123,7 @@ def changes
     #   person.save
     #   person.previous_changes # => {"name" => ["bob", "robert"]}
     def previous_changes
-      @previously_changed
+      @previously_changed ||= {}
     end
 
     # Returns a hash of the attributes with unsaved changes indicating their original
@@ -144,6 +138,18 @@ def changed_attributes
 
     private
 
+      # Removes current changes and makes them accessible through +previous_changes+.
+      def changes_applied
+        @previously_changed = changes
+        @changed_attributes = {}
+      end
+
+      # Removes all dirty data: current changes and previous changes
+      def reset_changes
+        @previously_changed = {}
+        @changed_attributes = {} 
+      end
+
       # Handle <tt>*_changed?</tt> for +method_missing+.
       def attribute_changed?(attr)
         changed_attributes.include?(attr)

activemodel/test/cases/dirty_test.rb

@@ -29,8 +29,7 @@ def color=(val)
     end
 
     def save
-      @previously_changed = changes
-      @changed_attributes.clear
+      changes_applied
     end
   end
 

activerecord/lib/active_record/attribute_methods/dirty.rb

@@ -30,25 +30,22 @@ def self.partial_updates; partial_writes; end
       # Attempts to +save+ the record and clears changed attributes if successful.
       def save(*)
         if status = super
-          @previously_changed = changes
-          @changed_attributes.clear
+          changes_applied
         end
         status
       end
 
       # Attempts to <tt>save!</tt> the record and clears changed attributes if successful.
       def save!(*)
         super.tap do
-          @previously_changed = changes
-          @changed_attributes.clear
+          changes_applied
         end
       end
 
       # <tt>reload</tt> the record and clears changed attributes.
       def reload(*)
         super.tap do
-          @previously_changed.clear
-          @changed_attributes.clear
+          reset_changes
         end
       end
 
@@ -59,11 +56,11 @@ def write_attribute(attr, value)
 
         # The attribute already has an unsaved change.
         if attribute_changed?(attr)
-          old = @changed_attributes[attr]
-          @changed_attributes.delete(attr) unless _field_changed?(attr, old, value)
+          old = changed_attributes[attr]
+          changed_attributes.delete(attr) unless _field_changed?(attr, old, value)
         else
           old = clone_attribute_value(:read_attribute, attr)
-          @changed_attributes[attr] = old if _field_changed?(attr, old, value)
+          changed_attributes[attr] = old if _field_changed?(attr, old, value)
         end
 
         # Carry on.

activerecord/lib/active_record/core.rb

@@ -438,8 +438,6 @@ def init_internals
       @aggregation_cache        = {}
       @association_cache        = {}
       @attributes_cache         = {}
-      @previously_changed       = {}
-      @changed_attributes       = {}
       @readonly                 = false
       @destroyed                = false
       @marked_for_destruction   = false
@@ -456,7 +454,7 @@ def init_changed_attributes
       # optimistic locking) won't get written unless they get marked as changed
       self.class.columns.each do |c|
         attr, orig_value = c.name, c.default
-        @changed_attributes[attr] = orig_value if _field_changed?(attr, orig_value, @attributes[attr])
+        changed_attributes[attr] = orig_value if _field_changed?(attr, orig_value, @attributes[attr])
       end
     end
   end

activerecord/lib/active_record/persistence.rb

@@ -433,7 +433,7 @@ def touch(name = nil)
 
         changes[self.class.locking_column] = increment_lock if locking_enabled?
 
-        @changed_attributes.except!(*changes.keys)
+        changed_attributes.except!(*changes.keys)
         primary_key = self.class.primary_key
         self.class.unscoped.where(primary_key => self[primary_key]).update_all(changes) == 1
       end

guides/source/active_model_basics.md

@@ -120,8 +120,8 @@ class Person
   end
 
   def save
-    @previously_changed = changes
     # do save work...
+    changes_applied
   end
 end
 ```