CODEWITHSUNDEEP
redis
Bernie Reiter
Bernie Reiter

Reputation: 116

How to use counters in a redis key?

Is there a way to do this in redis ?

SET counter 0
INCR counter
SET KEY:{counter} "Content of line 1"
INCR counter
SET KEY:{counter} "Different content of line 2"

My example code should be substituted (i.e., transformed at runtime by the redis-cli) into: 

SET counter 0
INCR counter
SET KEY:1 "Content of line 1"
INCR counter
SET KEY:2 "Different content of line 2"
etc.

My problem is NOT how to auto-increment the counter.
My problem is syntax: How to include a generic {wildcard} into something like: 

SET keyname:{currentcounter} "value" ...

Any help is appreciated. Thanks a lot !

bernie

Upvotes: 3

Views: 5317

Answers (2)

sberry
sberry

Reputation: 131978

If you are using redis 2.6+ then you can use lua scripting along with EVAL command like the following:

eval "local c = redis.call('incr', KEYS[1]); 
      return redis.call('set', KEYS[2] .. ':' .. c, ARGV[1])"
      2 counter KEY "Content of line 1"

I broke it up onto multiple lines to make it easier to read.

EDIT
Sorry, I was away on business for a few days. Here is a sample showing that it works.

redis 127.0.0.1:6379> flushdb
OK
redis 127.0.0.1:6379> eval "local c = redis.call('incr', KEYS[1]); return redis.call('set', KEYS[2] .. ':' .. c, ARGV[1])" 2 counter KEY "Content of line 1"
OK
redis 127.0.0.1:6379> keys *
1) "KEY:1"
2) "counter"
redis 127.0.0.1:6379> get counter
"1"
redis 127.0.0.1:6379> get KEY:1
"Content of line 1"
redis 127.0.0.1:6379> eval "local c = redis.call('incr', KEYS[1]); return redis.call('set', KEYS[2] .. ':' .. c, ARGV[1])" 2 counter KEY "Content of the next thing"
OK
redis 127.0.0.1:6379> keys *
1) "KEY:1"
2) "KEY:2"
3) "counter"
redis 127.0.0.1:6379> get counter
"2"
redis 127.0.0.1:6379> get KEY:2
"Content of the next thing"

Upvotes: 1

Tommaso Barbugli
Tommaso Barbugli

Reputation: 12031

Nope, SET/GET commands don't support this.

You can do similar things using LUA scripts in redis, or even simpler; you can issue the commands as redis expect them using trivial programming/scripting

Upvotes: 0

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