1 files changed, 42 insertions, 9 deletions

diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb
index 8604ccb90d..13c8bc3676 100644
--- a/activerecord/lib/active_record/attribute.rb
+++ b/activerecord/lib/active_record/attribute.rb
@@ -8,6 +8,10 @@ module ActiveRecord
       def from_user(value, type)
         FromUser.new(value, type)
       end
+
+      def uninitialized(type)
+        Uninitialized.new(type)
+      end
     end
 
     attr_reader :value_before_type_cast, :type
@@ -37,10 +41,22 @@ module ActiveRecord
       type.changed_in_place?(old_value, value)
     end
 
+    def with_value_from_user(value)
+      self.class.from_user(value, type)
+    end
+
+    def with_value_from_database(value)
+      self.class.from_database(value, type)
+    end
+
     def type_cast
       raise NotImplementedError
     end
 
+    def initialized?
+      true
+    end
+
     protected
 
     def initialize_dup(other)
@@ -49,27 +65,44 @@ module ActiveRecord
       end
     end
 
-    class FromDatabase < Attribute
+    class FromDatabase < Attribute # :nodoc:
       def type_cast(value)
         type.type_cast_from_database(value)
       end
     end
 
-    class FromUser < Attribute
+    class FromUser < Attribute # :nodoc:
       def type_cast(value)
         type.type_cast_from_user(value)
       end
     end
 
-    class Null
-      class << self
-        attr_reader :value, :value_before_type_cast, :value_for_database
+    class NullAttribute < Attribute # :nodoc:
+      def initialize
+        super(nil, Type::Value.new)
+      end
 
-        def changed_from?(*)
-          false
-        end
-        alias changed_in_place_from? changed_from?
+      def value
+        nil
       end
     end
+
+    class Uninitialized < Attribute # :nodoc:
+      def initialize(type)
+        super(nil, type)
+      end
+
+      def value
+        nil
+      end
+      alias value_for_database value
+
+      def initialized?
+        false
+      end
+    end
+    private_constant :FromDatabase, :FromUser, :NullAttribute, :Uninitialized
+
+    Null = NullAttribute.new # :nodoc:
   end
 end