Select all values by pattern from redis server using node js

Question

I had a multiple chanel like this

client.HMSET('live:user:1', {
    "a": "1",
    "b": "1"
});
client.HMSET('live:user:2', {
    "a": "2",
    "b": "2"
});
client.HMSET('live:user:3', {
    "a": "3",
    "b": "3"
});

client.HMSET('otherchanel:user:4', {
    "a": "4",
    "b": "4"
});
client.HMSET('otherchanel:user:5', {
    "a": "5",
    "b": "5"
});
client.HMSET('otherchanel:user:6', {
    "a": "6",
    "b": "6"
});

How can i select all values by key pattern "live:*"? I need it to retern JSON object to my client app like this:

[{user:1, a:1, b:1}, {user:2, a:2, b:2}, {user:3, a:3, b:3}]

Answer 1

To get all keys with a pattern use

client.keys('live:*', function (err, keys) {
    if (err) return console.log(err);

    for(var i = 0, len = keys.length; i < len; i++) {
        console.log(keys[i]);
    }
});

Answer 2

It's simple, but you have to also fetch all the keys and combine them. I suggest using async to make the calls asynchronous:

function getAllUsersInChannel_suboptimal(channelName, functionCallback) {
client.keys(channelName + ":user:*", function(err, userKeys) {
    if (!err) {
        async.map(userKeys, 
            function(userKey, callback) {
                client.hgetall(userKey, function(err, user) {
                    if (!err) {
                        callback(null, user);
                    }
                    else {
                        callback(err);
                    }
                });
            }, 
            function(err, userList) {
                if (!err) {
                    functionCallback(null, userList);
                }
                else {
                    functionCallback(err);
                }
            });
    }
    else {
        functionCallback(err);
    }
});
}

Using a pattern match can drastically reduce performance even on medium sized databases. I suggest you also index the id's of the users using a set.

Create the counter key if it does not exist and set its value to 0:

SETNX <channel_name>:user:counter 0

When you add a new user, first increment the counter key, which also fetches its value:

INCR <channel_name>:user:counter => <new_id>

This will yield the new id for the user. Now you have to save a new member in the "user:index" set like so:

SADD <channel_name>:user:index <new_id>

You can now add the new user key like so:

HMSET <channel_name>:user:<new_id> <list of values>

To fetch data for all users you would first get a the list of existing users like so:

SMEMBERS <channel_name>:user:index => <list of all user ids>

For each id you would have to fetch the hash values:

asynchronous each <list of all user ids> as <user_id>
HGETALL channel_name>:user:<user_id> => all values of key
end asynchronous each

In Node.js, considering that you've already used the techniques above to index users, you retrieve all users in a channel using something like this:

function getAllUsersInChannel_optimal(channelName, functionCallback) {
client.smembers(channelName + ":user:index", function(err, userIds) {
    if (!err) {
        async.map(userIds, 
            function(userId, callback) {
                client.hgetall(channelName + ":user:" + userId, function(err, user) {
                    if (!err) {
                        callback(null, user);
                    }
                    else {
                        callback(err);
                    }
                });
            }, 
            function(err, userList) {
                if (!err) {
                    functionCallback(null, userList);
                }
                else {
                    functionCallback(err);
                }
            });
    }
    else {
        functionCallback(err);
    }
});
}