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?

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?

• javascript
• node.js
• nosql
• redis

3 Answers 3

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?

@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.

It seems the documentation changed since your 2013 answer.

ZADD options (Redis 3.0.2 or greater)
ZADD supports a list of options, specified after the name of the key and before the first score argument. Options are:

XX: Only update elements that already exist. Never add elements.
NX: Don't update already existing elements. Always add new elements.
CH: Modify the return value from the number of new elements added, to the total number of elements changed (CH is an abbreviation of changed). Changed elements are new elements added and elements already existing for which the score was updated. So elements specified in the command line having the same score as they had in the past are not counted. Note: normally the return value of ZADD only counts the number of new elements added.
INCR: When this option is specified ZADD acts like ZINCRBY. Only one score-element pair can be specified in this mode.

From https://redis.io/commands/zadd

So now, you can tell what behavior you are expected from ZADD. Given your answer, the option XX would do the work. So something like :

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