3 files changed, 22 insertions, 4 deletions
diff --git a/activerecord/lib/active_record/type/mutable.rb b/activerecord/lib/active_record/type/mutable.rb
new file mode 100644
index 0000000000..64cf4b9b93
--- /dev/null
+++ b/activerecord/lib/active_record/type/mutable.rb
@@ -0,0 +1,16 @@
+module ActiveRecord
+  module Type
+    module Mutable
+      def type_cast_from_user(value)
+        type_cast_from_database(type_cast_for_database(value))
+      end
+
+      # +raw_old_value+ will be the `_before_type_cast` version of the
+      # value (likely a string). +new_value+ will be the current, type
+      # cast value.
+      def changed_in_place?(raw_old_value, new_value) # :nodoc:
+        raw_old_value != type_cast_for_database(new_value)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/type/serialized.rb b/activerecord/lib/active_record/type/serialized.rb
index e6d84eadc0..ebde14634c 100644
--- a/activerecord/lib/active_record/type/serialized.rb
+++ b/activerecord/lib/active_record/type/serialized.rb
@@ -1,6 +1,8 @@
 module ActiveRecord
   module Type
     class Serialized < SimpleDelegator # :nodoc:
+      include Mutable
+
       attr_reader :subtype, :coder
 
       def initialize(subtype, coder)
@@ -17,10 +19,6 @@ module ActiveRecord
         end
       end
 
-      def type_cast_from_user(value)
-        type_cast_from_database(type_cast_for_database(value))
-      end
-
       def type_cast_for_database(value)
         return if value.nil?
         unless is_default_value?(value)
diff --git a/activerecord/lib/active_record/type/value.rb b/activerecord/lib/active_record/type/value.rb
index efcdab1c0e..b34d1697cd 100644
--- a/activerecord/lib/active_record/type/value.rb
+++ b/activerecord/lib/active_record/type/value.rb
@@ -60,6 +60,10 @@ module ActiveRecord
         old_value != new_value
       end
 
+      def changed_in_place?(*) # :nodoc:
+        false
+      end
+
       private
       # Takes an input from the database, or from attribute setters,
       # and casts it to a type appropriate for this object. This method