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amazon-web-servicesredis

Redis HINCRBY hash field -1 counter for decrementing only till 0 or non negative value

Counts in negative: redis.hincrby(User:${targetUser.id}, "followerCount", -1)

I want it to stop at 0

Solution

  • HINCRBY operation returns the new value after the increment operation.

    redis> HSET myhash field 5
(integer) 1
redis> HINCRBY myhash field 1
(integer) 6
redis> HINCRBY myhash field -1
(integer) 5

    If your HINCRBY operation returns -1, that means the followerCount for this user was 0, and hence should not be decreased. So, you can fire a HSET to 0 to set it to zero. A better approach would be to have an redis transaction which will:

    • first check the value using HGET,
    • if it is more than zero, then do a HINCRBY with -1 increment
    • if it is zero, do nothing.