Extract attribute serialization code into a separate module

activerecord/lib/active_record.rb

@@ -92,6 +92,7 @@ module AttributeMethods
       autoload :Read
       autoload :TimeZoneConversion
       autoload :Write
+      autoload :Serialization
     end
   end
 

activerecord/lib/active_record/attribute_methods/read.rb

@@ -34,22 +34,12 @@ def cache_attribute?(attr_name)
 
         protected
           def define_method_attribute(attr_name)
-            if serialized_attributes.include?(attr_name)
-              define_read_method_for_serialized_attribute(attr_name)
-            else
-              define_read_method(attr_name, attr_name, columns_hash[attr_name])
-            end
+            define_read_method(attr_name, attr_name, columns_hash[attr_name])
           end
 
         private
           def cacheable_column?(column)
-            serialized_attributes.include?(column.name) || attribute_types_cached_by_default.include?(column.type)
-          end
-
-          # Define read method for serialized attribute.
-          def define_read_method_for_serialized_attribute(attr_name)
-            access_code = "@attributes_cache['#{attr_name}'] ||= @attributes['#{attr_name}']"
-            generated_attribute_methods.module_eval("def _#{attr_name}; #{access_code}; end; alias #{attr_name} _#{attr_name}", __FILE__, __LINE__)
+            attribute_types_cached_by_default.include?(column.type)
           end
 
           # Define an attribute reader method. Cope with nil column.
@@ -107,28 +97,15 @@ def _read_attribute(attr_name)
         value = @attributes[attr_name]
         unless value.nil?
           if column = column_for_attribute(attr_name)
-            if unserializable_attribute?(attr_name, column)
-              unserialize_attribute(attr_name)
-            else
-              column.type_cast(value)
-            end
+            type_cast_attribute(column, value)
           else
             value
           end
         end
       end
 
-      # Returns true if the attribute is of a text column and marked for serialization.
-      def unserializable_attribute?(attr_name, column)
-        column.text? && self.class.serialized_attributes.include?(attr_name)
-      end
-
-      # Returns the unserialized object of the attribute.
-      def unserialize_attribute(attr_name)
-        coder = self.class.serialized_attributes[attr_name]
-        unserialized_object = coder.load(@attributes[attr_name])
-
-        @attributes.frozen? ? unserialized_object : @attributes[attr_name] = unserialized_object
+      def type_cast_attribute(column, value) #:nodoc:
+        column.type_cast(value)
       end
 
       private

activerecord/lib/active_record/attribute_methods/serialization.rb

+module ActiveRecord
+  module AttributeMethods
+    module Serialization
+      extend ActiveSupport::Concern
+
+      module ClassMethods
+        def define_method_attribute(attr_name)
+          if serialized_attributes.include?(attr_name)
+            generated_attribute_methods.module_eval(<<-CODE, __FILE__, __LINE__)
+              def _#{attr_name}
+                @attributes_cache['#{attr_name}'] ||= @attributes['#{attr_name}']
+              end
+              alias #{attr_name} _#{attr_name}
+            CODE
+          else
+            super
+          end
+        end
+
+        def cacheable_column?(column)
+          serialized_attributes.include?(column.name) || super
+        end
+      end
+
+      def type_cast_attribute(column, value)
+        coder = self.class.serialized_attributes[column.name]
+
+        if column.text? && coder
+          unserialized_object = coder.load(@attributes[column.name])
+
+          if @attributes.frozen?
+            unserialized_object
+          else
+            @attributes[column.name] = unserialized_object
+          end
+        else
+          super
+        end
+      end
+    end
+  end
+end

activerecord/lib/active_record/base.rb

@@ -2219,6 +2219,7 @@ def populate_with_current_scope_attributes
     include AttributeMethods::PrimaryKey
     include AttributeMethods::TimeZoneConversion
     include AttributeMethods::Dirty
+    include AttributeMethods::Serialization
     include ActiveModel::MassAssignmentSecurity
     include Callbacks, ActiveModel::Observing, Timestamp
     include Associations, NamedScope