def djb_hash(str, len)
      hash = 5381
      for i in (0..len) 
        hash = ((hash << 5) + hash) + str[i].to_i
      end
      return hash
    end
def djb_hash(str, len)
      hash = 5381
      for i in (0..len) 
        hash = ((hash << 5) + hash) + str[i].to_i
      end
      return hash
    end
use djb hash function to generate temp object id