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Get complete Map from Redis if a key contains a String

I am able to add and get a particular user object from Redis I am adding object like this:

 private static final String USER_PREFIX = ":USER:";
 public void addUserToRedis(String serverName,User user) {
    redisTemplate.opsForHash().put(serverName + USER_PREFIX + user.getId(),  
   Integer.toString(user.getId()),user);    
    }

If a userId is 100 I am able to get by key: SERVER1:USER:100
Now I want to retrieve all Users as Map<String,List<User>> ,
For example, get all users by this key SERVER1:USER:
Is it possible ? Or I need to modify my addUserToRedis method? Please suggest me.

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3

Answers


  1. Chosen as BEST ANSWER
    0

    Finally I came up with this solution with wildcard search and avoiding KEYS, and here is my complete method:

      public Map<String, User> getUserMapFromRedis(String serverName){
    Map<String, User> users=new HashMap<>();
     RedisConnection redisConnection = null;
     try {
            redisConnection = redisTemplate.getConnectionFactory().getConnection();
           ScanOptions options = ScanOptions.scanOptions().match(serverName + USER_PREFIX+"*").build();
           Cursor<byte[]> scan = redisConnection.scan(options);
           while (scan.hasNext()) {
           byte[] next = scan.next();
           String key = new String(next, StandardCharsets.UTF_8);
           String[] keyArray=key.split(":");
           String userId=keyArray[2];
           User user=//get User by userId From Redis
           users.put(userId, user);
           }
           try {
           scan.close();
      } catch (IOException e) {
          
      }
       }finally {
       redisConnection.close(); //Ensure closing this connection.
       }
     return users;
    }

  2. 0

    I would recommend not using the "KEYS" command in production as this can severely impact REDIS latencies (can even bring down the cluster if you have a large number of keys stored)

    Instead, you would want to use a different command than plain GET/SET.

    It would be better if you use a Sets or Hashes

    127.0.0.1:6379> sadd server1 user1 user2
(integer) 2
127.0.0.1:6379> smembers server1
1) "user2"
2) "user1"
127.0.0.1:6379>

    Using sets you can simply add your users to server keys and get the entire list of users on a server.

    If you really need a map of < server, list < users > > you can use hashes with stringified user data and then convert it to actual User POJO at application layer

    127.0.0.1:6379> hset server2 user11 name
(integer) 1
127.0.0.1:6379> hset server2 user13 name
(integer) 1
127.0.0.1:6379> hgetall server2
1) "user11"
2) "name"
3) "user13"
4) "name"
127.0.0.1:6379>

    Also do note that keeping this much big data into a single key is not an ideal thing to do.

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  3. 0

    i dont use java but here’s how to use SCAN

    const Redis = require('ioredis')
const redis = new Redis()

async function main() {
    const stream = redis.scanStream({
        match: "*:user:*",
        count: 100,
    })

    stream.on("data", (resultKeys) => {
        for (let i = 0; i < resultKeys.length; i++) {
            // console.log(resultKeys[i])
            // do your things here
        }
    });
    stream.on("end", () => {
        console.log("all keys have been visited");
    });
}

main()
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