Redis Sorted Set: Check Exists (Detailed Guide w/ Code Examples)

Use Case(s)

Checking if a specific member exists in a Redis sorted set is a common operation when managing ordered data like leaderboards, task queues, and scheduling systems.

Code Examples

Python

import redis

r = redis.Redis(host='localhost', port=6379, db=0)

def check_member_exists(sorted_set_name, member):
    return r.zrank(sorted_set_name, member) is not None

# Example usage
exists = check_member_exists('my_sorted_set', 'member1')
print(exists)

Node.js

const redis = require('redis');
const client = redis.createClient();

function checkMemberExists(sortedSetName, member, callback) {
    client.zrank(sortedSetName, member, (err, rank) => {
        if (err) throw err;
        callback(rank !== null);
    });
}

// Example usage
checkMemberExists('my_sorted_set', 'member1', (exists) => {
    console.log(exists);
});

Golang

package main

import (
    "fmt"
    "github.com/go-redis/redis/v8"
    "context"
)

var ctx = context.Background()

func checkMemberExists(client *redis.Client, sortedSetName string, member string) (bool, error) {
    rank, err := client.ZRank(ctx, sortedSetName, member).Result()
    if err == redis.Nil {
        return false, nil
    }
    if err != nil {
        return false, err
    }
    return rank >= 0, nil
}

func main() {
    rdb := redis.NewClient(&redis.Options{
        Addr: "localhost:6379",
    })

    exists, err := checkMemberExists(rdb, "my_sorted_set", "member1")
    if err != nil {
        panic(err)
    }
    fmt.Println(exists)
}

Best Practices

• Always handle the potential for nil or errors when querying Redis to avoid runtime exceptions.
• Use connection pooling for efficiency when dealing with Redis in high-throughput applications.

Common Mistakes

• Forgetting to check for both nil and other possible errors.
• Not using context timeouts when working with Redis in Golang, which can lead to resource leakage.

FAQs

Q: Why use zrank to check for existence instead of another command?

A: zrank provides an efficient way to determine if a member exists by checking its rank. If the member does not exist, it returns nil.