Updating Sorted Set with Redis

Question

Currently I am trying to update a sorted set member. Looking at the docs, using ZADD appears that it should update a member if its score already exists. However, upon using this code to try to update a member,

db.zadd("users", parseInt(key, 10) + 1, JSON.stringify(newData));

....a new entry is added even if a score already exists! How to I update a sorted set member with redis?

Answer 1

ZADD will replace an old member's score so long as the key and member match between entries:

redis localhost:6379> ZADD test-key 40 blah
(integer) 1
redis localhost:6379> ZRANGE test-key 0 -1 WITHSCORES
1) "blah"
2) "40"
redis localhost:6379> ZADD test-key 45 blah
(integer) 0
redis localhost:6379> ZRANGE test-key 0 -1 WITHSCORES
1) "blah"
2) "45"

Perhaps you're using different keys or members between ZADD commands?

Answer 2

@Eli already explained how to update element score and now zadd added new options which is explained by @ZettaCircl and I'm explaining how to update element with examples using score and element.

1. NX = add new element
2. XX = update element

Add three countries into sorted set

 127.0.0.1:6379> zadd country nx 1 'pakistan' // nx = add new element
(integer) 1
127.0.0.1:6379> zadd country nx 2 'turkey'
(integer) 1
127.0.0.1:6379> zadd country nx 3 'UK'
(integer) 1

Get country with scores

127.0.0.1:6379> zrange country 0 10 withscores
1) "pakistan"
2) "1"
3) "turkey"
4) "2"
5) "UK"
6) "3"

Update country

Update country Pakistan (element) to new name using score

127.0.0.1:6379> zadd country xx ch 1 'islamic republic of pakistan'
(integer) 0 // 0 means not updated

Update country score of Pakistan using element name ('pakistan')

127.0.0.1:6379> zadd country xx ch 4 'pakistan'
(integer) 1 // updated successfully 

Get country with scores

We can see here we updated the score only.

127.0.0.1:6379> zrange country 0 10 withscores
1) "turkey"
2) "2"
3) "UK"
4) "3"
5) "pakistan"
6) "4" // score updated

Conclusion

We can update only score in sorted sets using element name.

---

How we can update elements

First we need to remove country paksitan.

127.0.0.1:6379> zrem country pakistan
(integer) 1 // removed successfully

Get countries with scores

127.0.0.1:6379> zrange country 0 10 withscores
1) "turkey"
2) "2"
3) "UK"
4) "3"

Add Pakistan with new name

Add new element into country sorted set with new name and previous score

127.0.0.1:6379> zadd country nx 1 'islamic republic of pakistan'
(integer) 1

Get countries with scores

127.0.0.1:6379> zrange country 0 10 withscores
1) "islamic republic of pakistan"
2) "1"
3) "turkey"
4) "2"
5) "UK"
6) "3"

Conclusion

First we need to delete element then add new element into sorted set.