use Object#class instead of Object#type

activerecord/lib/active_record/association_preload.rb

@@ -333,7 +333,7 @@ def preload_belongs_to_association(records, reflection, preload_options={})
 
           table_name = klass.quoted_table_name
           primary_key = reflection.options[:primary_key] || klass.primary_key
-          column_type = klass.columns.detect{|c| c.name == primary_key}.type
+          column_type = klass.columns.detect{|c| c.name == primary_key}.class
           ids = id_map.keys.map do |id|
             if column_type == :integer
               id.to_i