Detect in-place changes on mutable AR attributes

We have several mutable types on Active Record now. (Serialized, JSON,
HStore). We need to be able to detect if these have been modified in
place.

1 files changed, 16 insertions, 0 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