gistfile1.rb

  class Version
    named_scope :as_of, lambda { |a_certain_time|
      effkay = original_class.versioned_foreign_key
      { :conditions => [
          "#{table_name}.version = (
            SELECT  MAX(vtn.version) 
              FROM  #{table_name} AS vtn
              WHERE vtn.#{effkay} = #{table_name}.#{effkay}
                AND vtn.updated_at <= ?
           )", a_certain_time.to_s(:db) ] }
    }
  end