saving multiple data with async nature of node.js with mongodb

Question

I have a array of ids:

var ids = ['53asd3','53asd2','53asd5'];

Each id has a corresponding document in the mongodb. I want to generate a object by populating data from each of them and save in some other document. Like this:

{
    person: {   /* data from some collection populated with first id */},
    company : { /* data from some collection populated with first id */},
    employee : {/* data from some collection populated with first id */}
}

WHAT I DID

var document = {}
models.persons.find({_id:'53asd3'},function(err,data){
    if(!err) {
        document['persons']=data;
        models.company.find({_id:'53asd2'},function(err,data){
            if(!err) {
                document['company']=data;
                models.employee.find({_id:'53asd2'},function(err,data){
                    if(!err) {
                        document['employee']=data;
                        document.save(function(err){ });
                    }
                });
            }
        });
    }
});

So I just use nested calls using callbacks and somewhat make it synchronous. Is there a chance where I can execute all these three find queries in parallel and then execute the save command? I actually want to leverage the async nature of node.js. Any suggestions?

Well i know the promises might work here but wanted to use something without any external library. So is there a way i can do it with node.js itself? My code is essentially synchronous now! However i really liked async.parallel! Amazing module :) — beNerd
– beNerd, Commented Jun 2, 2014 at 14:18
question aside...to reduce nesting, especial with a callback-centric platform like node.js, you should change if(!err) {...} to if(err) return;. Assuming of course you want to ignore any errors. Sorry, couldn't help myself :) — Eat at Joes
– Eat at Joes, Commented Jun 7, 2014 at 4:20

Tim · Accepted Answer · 2014-06-02 16:56:03Z

You could build something like async.parallel yourself if you don't want to include an external library. Here's what a simple parallel function might look like. It could be a nice exercise to implement the other functions in the async library.

var parallel = function () {
    var functs = arguments[0];
    var callback = arguments[1];

    // Since we're dealing with a sparse array when we insert the results,
    // we cannot trust the `length` property of the results.
    // Instead we count the results separately
    var numResults = 0;
    var results = [];
    var getCallback = function (i) {
        return function (err, res) {
            if (err) {
                callback(err)
            }
            else {
                results[i] = res;
                numResults += 1;

                if (numResults === functs.length) {
                    callback(null, results);
                }
            }
        }
    }

    functs.forEach(function (fn, i) {
        fn(getCallback(i));
    });
};


var getTest = function (timeout) {
    return function (callback) {
        setTimeout(function () {
            callback(null, timeout);
        }, timeout);
    }
};

parallel([getTest(99), getTest(1000), getTest(199)], console.log.bind(console));
>> null [99, 1000, 199]

Then in your case you can do something like

var findItem = function (collection, id) {
    return function (callback) {
        collection.find({
            _id: id
        }, callback);
    };
};

parallel([
    findItem(models.persons, '53asd3'),
    findItem(models.company, '53asd2'),
    findItem(models.employee, '53dsa2')
], function (err, results) {
    document.persons = results[0];
    document.company = results[1];
    document.employee = results[2];
    document.save(function (err) {
        // and so on
    });
});

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