How to retrieve value from table value Redis Lua script

Question

I am trying to extract a value from a json encoded string that returned from a sorted set in Redis.

127.0.0.1:6379> eval 'local r= redis.call("ZRANGEBYSCORE", "iprange:locations", 34625535, "+inf", "LIMIT", 0, 1); return type(r);' 0
"table"
127.0.0.1:6379> eval 'local r= redis.call("ZRANGEBYSCORE", "iprange:locations", 34625535, "+inf", "LIMIT", 0, 1); return r;' 0
1) "{\"countryCode\": \"IT\", \"countryName\": \"Italy\"}"

I just want to extract countryValue from the result.

Tried return r.countryCode;, return r["countryCode"]; but all of them returned (nil)

By the way, I alread handle this json encoded string in my app by decoding this json into data. Just trying to delegate this simple task to Redis Lua script engine.

Kevin Christopher Henry Kevin Christopher Henry · Accepted Answer · 2019-04-06T10:28:43

Use the built-in JSON library:

eval 'local  r = redis.call("ZRANGEBYSCORE", "iprange:locations", 34625535, "+inf", "LIMIT", 0, 1);
      return cjson.decode(r[1])["countryCode"];'

Note that ZRANGEBYSCORE returns an array of results, represented in Lua by a table. Presumably you'll want to loop over the results and extract countryCode for each.

How to retrieve value from table value Redis Lua script

1 Answers