1 files changed, 45 insertions, 9 deletions

diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb
index 74b44810d4..3c4c8f10ec 100644
--- a/activerecord/lib/active_record/attribute.rb
+++ b/activerecord/lib/active_record/attribute.rb
@@ -5,8 +5,8 @@ module ActiveRecord
         FromDatabase.new(name, value, type)
       end
 
-      def from_user(name, value, type)
-        FromUser.new(name, value, type)
+      def from_user(name, value, type, original_attribute = nil)
+        FromUser.new(name, value, type, original_attribute)
       end
 
       def with_cast_value(name, value, type)
@@ -26,10 +26,11 @@ module ActiveRecord
 
     # This method should not be called directly.
     # Use #from_database or #from_user
-    def initialize(name, value_before_type_cast, type)
+    def initialize(name, value_before_type_cast, type, original_attribute = nil)
       @name = name
       @value_before_type_cast = value_before_type_cast
       @type = type
+      @original_attribute = original_attribute
     end
 
     def value
@@ -38,21 +39,33 @@ module ActiveRecord
       @value
     end
 
+    def original_value
+      if assigned?
+        original_attribute.original_value
+      else
+        type_cast(value_before_type_cast)
+      end
+    end
+
     def value_for_database
       type.serialize(value)
     end
 
-    def changed_from?(old_value)
-      type.changed?(old_value, value, value_before_type_cast)
+    def changed?
+      changed_from_assignment? || changed_in_place?
+    end
+
+    def changed_in_place?
+      has_been_read? && type.changed_in_place?(original_value_for_database, value)
     end
 
-    def changed_in_place_from?(old_value)
-      has_been_read? && type.changed_in_place?(old_value, value)
+    def forgetting_assignment
+      with_value_from_database(value_for_database)
     end
 
     def with_value_from_user(value)
       type.assert_valid_value(value)
-      self.class.from_user(name, value, type)
+      self.class.from_user(name, value, type, self)
     end
 
     def with_value_from_database(value)
@@ -64,7 +77,7 @@ module ActiveRecord
     end
 
     def with_type(type)
-      self.class.new(name, value_before_type_cast, type)
+      self.class.new(name, value_before_type_cast, type, original_attribute)
     end
 
     def type_cast(*)
@@ -97,16 +110,39 @@ module ActiveRecord
 
     protected
 
+    attr_reader :original_attribute
+    alias_method :assigned?, :original_attribute
+
     def initialize_dup(other)
       if defined?(@value) && @value.duplicable?
         @value = @value.dup
       end
     end
 
+    def changed_from_assignment?
+      assigned? && type.changed?(original_value, value, value_before_type_cast)
+    end
+
+    def original_value_for_database
+      if assigned?
+        original_attribute.original_value_for_database
+      else
+        _original_value_for_database
+      end
+    end
+
+    def _original_value_for_database
+      value_for_database
+    end
+
     class FromDatabase < Attribute # :nodoc:
       def type_cast(value)
         type.deserialize(value)
       end
+
+      def _original_value_for_database
+        value_before_type_cast
+      end
     end
 
     class FromUser < Attribute # :nodoc: