Question

I have a whole bunch of fields for each user in my redis database, and I want to be able to retrieve all their records and display them.
The way I do it, is store a set of all userids, When I want all their records, I recursively iterate the set grabbing their records using the userids in the set and adding them to a global array, then finally returning this global array. Anyway I don’t particularly like this method and would like to hear some suggestions of alternatives, I feel there must be better functionality in node.js or redis for this very problem. Maybe there is a way to do away with using the set entirely, but looking around I couldn’t see anything obvious.

This is an example of my psuedoish (pretty complete) node.js code, note the set size is not a problem as it will rarely be > 15.

Register Function:

var register = function(username, passwordhash, email){

    // Get new ID by incrementing idcounter
    redis.incr('db:users:idcounter', function(err, userid){

        // Setup user hash with user information, using new userid as key
        redis.hmset('db:user:'+userid, {
                'username':username,
                'passwordhash':passwordhash,
                'email':email
            },function(err, reply){

                 // Add userid to complete list of all users
                 redis.sadd('db:users:all', userid);

            }
        });
    });
}

Records retrieval function:
var getRecords = function(fcallback){

    // Grab a list of all the id's
    redis.smembers('db:users:all', function(err, allusersids){

        // Empty the returned (global) array
        completeArray = [];

        // Start the recursive function, on the allusersids Array.
        recursive_getNextUserHash(allusersids, fcallback);
    });  
}

Recursive function used to retrieve individual records:

// Global complete Array (so recursive function has access)
var completeArray = [];

// recursive method for filling up our completeArray
var recursive_getNextUserHash = function(userArray, callback){

    // If userArray==0 this means we have cycled entire list, 
    // call the callback, and pass it the completeArray which 
    // is now full of our usernames + emails

    if(userArray.length==0){
        callback.apply(this, [completeArray]);
        return;
    }

    // If still more items, start by popping the next user
    var userid = userArray.pop();

    // grab this users information
    redis.hvals('db:user:'+userid, function(err, fields){

        // Add users information to global array
        completeArray.push({username:fields[0],email:fields[2]});

        // Now move on to the next user
        recursive_getNextUserHash(userArray, callback);
    });

}

Use would be something like this:

register('bob', 'ASDADSFASDSA', '[e-mail]');
register('bill', 'DDDASDADSAD', '[e-mail]');
getRecords(function(records){
    for(var i=0;i<records.length;i++){
         console.log("u:"+records[i]['username']+',@:'+records[i]['email']);
    }
});

Summary: What is a good way to retrieve many fields of Hash’s using node.js and redis? After writing this question, I started to wonder if this is just the way you do it in redis, you make many roundtrips, regardless if this is the case, there must be a way to avoid the horrible recursion!

Answer 1

Assuming you are using https://github.com/mranney/node_redis – have a look at Multi and Exec. You can send all of your commands in a single request and wait for all the responses at once. No need for recursion.