Deleting an element from redis list with Node.js

Question

I was trying to manage a list in redis with nodejs. I am able to store list with following code :

client.rpush(['room_'+room, data.customClient], function(err, reply) {

        client.lrange('room_'+room, 0, -1, function(err, reply) {
          console.log(reply);
      });
    });

The console output is

[ 'POanqn9llyTcuIurUPAN', 'm9vd57wecp6JvtHOrRSJ' ]

Now I want to delete one key POanqn9llyTcuIurUPAN from this list. How can I do this ?

Your Redis client should have an interface to the LREM command: redis.io/commands/lrem — Itamar Haber
– Itamar Haber, Commented Jun 15, 2016 at 16:21
Perhaps call client.lrem('room_'+room,reply,1); where you log the reply from lrange — Itamar Haber
– Itamar Haber, Commented Jun 15, 2016 at 16:54
Note, however, that lpop is probably what you're looking for. — Itamar Haber
– Itamar Haber, Commented Jun 15, 2016 at 16:56
@ItamarHaber can you please tell the syntax for lpop, I didn't find it in documentation. — Eshant Sahu
– Eshant Sahu, Commented Jun 15, 2016 at 17:09

Srijan · Accepted Answer · 2018-04-16 17:52:55Z

1

It can be done through lrem command. The usage to delete all the entries with that value will be:

client.lrem('room_'+room, data.customClient, 0, 'POanqn9llyTcuIurUPAN', function(err, data){
    console.log(data); // Tells how many entries got deleted from the list
});

Here 0 is a count telling delete all the entries with the value POanqn9llyTcuIurUPAN in the given list. From https://redis.io/commands/lrem the possible values of the count could be:

count > 0: Remove elements equal to value moving from head to tail.
count < 0: Remove elements equal to value moving from tail to head.
count = 0: Remove all elements equal to value.

answered Apr 16, 2018 at 17:52

Srijan

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2 Comments

JGCW Over a year ago

Why is data.customClient, passed into the lrem?

mjs Over a year ago

so wierd, you can access by index but not remove by index. why. not o(1). requires search for value. further you can not say to a list to remove a value starting from a certain index. its either head or tail meaning you can not be sure to be removing the same index.

JGCW · Accepted Answer · 2020-04-12 13:27:04Z

0

it can be done easily like this:

client.lrem('room_'+room, 0, 'POanqn9llyTcuIurUPAN', function(err, data){
    console.log(data); // Tells how many entries got deleted from the list
});

answered Apr 12, 2020 at 13:27

JGCW

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