def load_or_create idx
      return from_redis(idx) if exists?(idx)
      obj = from_index idx
      obj.save
      obj
    end
def load_or_create idx
      return from_redis(idx) if exists?(idx)
      obj = from_index idx
      obj.save
      obj
    end
Returns an instance based on +idx+ otherwise it
 creates and saves a new instance base on +idx+.
 See from_index