member_id.lua

-- This script allow you to get an incremented unique integer id from a string
-- EVAL "SCRIPT" 1 key member1  -> return 1
-- EVAL "SCRIPT" 1 key member2  -> return 2
-- EVAL "SCRIPT" 1 key member1  -> return 1
-- EVAL "SCRIPT" 1 key member3  -> return 3

local nb_keys = redis.call('zcard', KEYS[1]);
local score = redis.call('zscore', KEYS[1], ARGV[1]);
if score then
  return tonumber(score);
else
  redis.call('zadd',KEYS[1], nb_keys + 1, ARGV[1]);
  return nb_keys + 1;
end