node.js redis and how to use promise when using a module

Question

I have an Express route like this in an node server (file is required):

var redis = require('../modules/redis');

module.exports = function (app) {

var redisClient = redis.init();


app.post('/auth/ticket', cors(), function (req, res) {


    var hashes = ['hash1','hash2', 'hash3'];

    var candidates = [];  // An array to collect valid hashes
    var key;  
    // to check each hash against a RedisDB I use a For Loop
    for (key in hashes) {
        var hash = hashes[key];
        console.log("Hash " + hash + "  will be proofed now:");
       //now I try to collect the valid hashes in the candidates array
       if (redisClient.exists(hash) === 1) candidates.push(hash);
    }
    console.log(JSON.stringify(candidates));
});
};

Now here is the code of my module which shall manage all the redis requests:

exports.init = function () {
Redis = exports.Redis = function () {
    var promiseFactory = require("q").Promise,
        redis = require('promise-redis')(promiseFactory);

    this.client = redis.createClient();
    this.client.on('error', function (err) {
        console.log('redis error – ' + client.host + ':' + client.port + ' – ' + err);
    });

Redis.prototype.exists = function (key) {
    this.client.exists(key, function (err, data) {
       return data === 1 ? true : false;
    });
};

return new Redis();
};

So what I experience is that the module is able to console.log the results properly. If a hash is valid, it returns true and otherwise false. This works as expected. Problem is, that the for-loop continuous the execution without fetching getting the results. I think this is caused by race-conditions.

As you can see, I have started to workout something there with the use of Q and promise-redis in the top of my code:

 var promiseFactory = require("q").Promise,
    redis = require('promise-redis')(promiseFactory);

this.client = redis.createClient();

I like to know, how I make my for-loop (in the Express route) waiting for the results of redisClient.exists(hash) or in other words, to get all valid hashes into my candidates array.

Please help

Answer 1

like @brad said, you could use Q.all, it would take an array of promises as input and then return an array of results when all the promises are finished:

there is a mistake in your answer:

Redis.prototype.exists = function (key) {

return this.client.exists(key)      // CHANGED, you still need to return a promise.
    .then(function (reply) {
        console.log("reply " + reply);
        return (reply);
    })
    .catch(console.log);

};

If I understand correctly, what you want is something like

exports.init = function () {
Redis = exports.Redis = function () {
    var Q = require("q"),
        promiseFactory = Q.Promise,
        redis = require('promise-redis')(promiseFactory);

    this.client = redis.createClient();
    this.client.on('error', function (err) {
        console.log('redis error – ' + client.host + ':' + client.port + ' – ' + err);
    });

Redis.prototype.exists = function (key) {
    return this.client.exists(key).then(function (data) {
       return data === 1 ? true : false;
    });
};

Redis.prototype.getActive = function (arry) {
    var self = this;
    return  Q.all(arry.map(self.exists.bind(self))
            ).then(function(res){
                return arry.filter(function(val, idx){ return res[idx];});
            });
};



return new Redis();
};

Answer 2

@ mido22: But did you also recognize that I outsourced all the reds functions to the module file (1st Codeblock) which requires the promise-redid and builds a factory for Q. I changed the code inside the module file to:

    Redis.prototype.exists = function (key) {

    this.client.exists(key)
        .then(function (reply) {
            console.log("reply " + reply);
            return (reply);
        })
        .catch(console.log);

    };

and this results correctly like the console.log evidently shows. Your codechange of the for-loop works very well but I think it don't fulfills my needs perfectly. If I could, I would like to have it completely outsourced in to the module file, so that I can use the prototyped method in similar cases from everywhere. Is that possible anyhow? I see, that it would result in having two promise supported functionalities, if I would create an Instance of Redis Client with promise-redid and Q inside the auth/ticket/ router, too. like this:

var Q = require('q'),
promiseFactory = Q.Promise,
redis = require("promise-redis")(promiseFactory),
client;

an then the express route (there are a lot of more routes each in a single file) like in your code.

Do you understand what I mean? Of course your solution will be fine for my needs at all, but a module resolving the job completely could have more elegance if possible so far.