CAS index if no key?

[lud4ik]

I perform get, use meta.LastIndex for ModifyIndex in CAS

             &api.KVPair{
                Key:         q.cacheKey,
                Value:       body,
                ModifyIndex: lastIndex,
            },

But if no key exists, it returns some random number for response meta.LastIndex and always fails on CAS operation (false for first param in api).
Consul 0.5.0

2016/03/22 13:15:35 [DEBUG] http: Request /v1/kv/service/go-asterisk/flush/originate?consistent=&dc=dc1 (109.407µs)
2016/03/22 13:15:35 [DEBUG] http: Request /v1/kv/service/go-asterisk/flush/originate?cas=531&dc=dc1 (227.414µs)

If key is present everything works ok.

[slackpad]

Hi @lud4ik if you query and don't get a key back the index is set to the last index that modified the KV store, since there's no key present that you are querying (you could use this to do a blocking query to wait for that key to get created, for example). If the key doesn't exist you can use ?cas=0 which means "create the key only if it isn't already there". Hope that helps!

?cas= : This flag is used to turn the PUT into a Check-And-Set operation. This is very useful as a building block for more complex synchronization primitives. If the index is 0, Consul will only put the key if it does not already exist. If the index is non-zero, the key is only set if the index matches the ModifyIndex of that key.