multiple async mongo request generate messed up returns - json

Question

I'm trying to build a JSON out of multiple requests on my mongodb.
since I'm not using DBRef, I have to build the "table joints" by myself, and that's how I ended up in this mess.
This is the code that is giving me the headaches from a couple of days now.
(the mongo part is done with mongoskin)
var getUserFeed = function(thelimit, out) {
userfeed = db.collection("userfeed");
apparel = db.collection("apparel");
store = db.collection("stores");
if(thelimit)
args = {limit:thelimit, sort: [['date',-1]]};
userfeed.find({},args).toArray(function(e, feed) {
if (e) console.log("error: ", e);
// gather aparel infos
var i=0;
var ret_feeds = [];
feed.forEach(function(cur_feed) {
var outfits=[];
console.log("beginning with: " + cur_feed.url);
var resfeed = "";
resfeed = cur_feed;
resfeed.url = baseurl + snapurl + resfeed.url + "_small.jpg";
i=0;
cur_feed.apparel_ids.forEach(function(item) {
/*>>*/ apparel.find({"_id": item},{limit:1}).toArray(function(e, results) {
console.log(">>>>>>>>>>> APPAREL_FIND { i:" + i + "}");
if (e) console.log("error: ", e);
results = results[0];
if(results.apparel_cat == 1)
url_subcat = "pants/";
else if(results.apparel_cat == 2)
url_subcat = "shirts/";
else if(results.apparel_cat == 2)
url_subcat = "tshirts/";
results.thumb = baseurl + outfiturl + url_subcat + results.apparel_id + "/front.jpg";
results.size = "M"; ///// TOBE REAL VERY SOON
results.gallery = [
baseurl + outfiturl + url_subcat + results.apparel_id + "/model.jpg",
baseurl + outfiturl + url_subcat + results.apparel_id + "/front.jpg"
];
outfits.push(results); // quick and dirty, 2 b refined..
i++;
if(i>=cur_feed.apparel_ids.length)
{
// pack it up
// resfeed.url = resfeed.url;
resfeed.outfits = outfits;
resfeed.fav = false;
resfeed.bough = false;
// retrieve store infos
/*>>>*/ store.find({"_id":resfeed.store_id}, {limit: 1}).toArray(function(e, resstore) {
console.log("\t############# STORE_FIND { i:" + i + "}");
if (e) console.log("error: ", e);
resfeed.store = resstore[0];
resfeed.store.class = "hem";
ret_feeds.push(resfeed);
if(ret_feeds.length >= feed.length)
{
console.log("\t\t######################calling return [ ret_feeds.length = " + ret_feeds.length + " feed.length = " + feed.length);
out.send(ret_feeds);
}
});
}
});
});
});
});
}
This code fails, because returns the json before finishing its task, so the next time that it tries to return another json it crashes miserably due to the fact the the headers have already been sent.
Now as you can see, I have 3 collections: userfeed, apparel and stores.
the goal of this function is to retrieve all the items in the userfeed collection, extract the outfits (based on the outfit_id array that is part of the userfeed collection), and also extract the store infos related in the same way to each userfeed entry, like so:
I know that async.js or equivalent is the way to go: I've red like a gazillion of other posts here on SO, but I still can't get my head around it, probably because the whole mechanism behind the async.js or flow control in general it's still out of focus in my mind.
I'm still a noob at node :)
UPDATE
I think I found the right path for understanding here: http://www.sebastianseilund.com/nodejs-async-in-practice
this guy made a terrific job in describing use-case by use-case all the ways to apply async.js to your code.
I'll post the solution as soon as I get around it.
UPDATE 2
Thanks to the above dude I could work out a working solution, below is the answer.

Answer 1

After so much struggling I have finally managed to get a solution.
async.js was the answer as I was (obviously) suspecting.
FYI here's the working code.
If you like to point out improvements or anything else, you are more than welcome
var getUserFeed = function(thelimit, out) {
userfeed = db.collection("userfeed");
apparel = db.collection("apparel");
store = db.collection("stores");
var args;
if(thelimit)
args = {limit:thelimit, sort: [['date',-1]]};
var outfits=[];
var feeds = array();
async.series([
// userfeed find
function(callback) {
userfeed.find({},args).toArray(function(e, feed) {
if(e) callback(e);
feeds = array(feed);
console.log(feeds.length + " retrieved. stepping in");
callback(null, null);
});
},
// join
function(callback) {
async.forEach(feeds, function(thefeed, callback) {
var i = feeds.indexOf(thefeed);
async.parallel([
// load apparel infos
function(callback) {
console.log("\t >>> analyzing thefeed id " + thefeed._id);
async.forEach(thefeed.apparel_ids, function(apparel_id, callback) {
apparel.find({"_id": apparel_id},{limit:1}).toArray(function(e, results) {
if (e) console.log("error: ", e);
results = results[0];
if(results.apparel_cat == 1)
url_subcat = "pants/";
else if(results.apparel_cat == 2)
url_subcat = "shirts/";
else if(results.apparel_cat == 2)
url_subcat = "tshirts/";
results.thumb = baseurl + outfiturl + url_subcat + results.apparel_id + "/front.jpg";
results.size = "M"; ///// TOBE REAL VERY SOON
results.gallery = [
baseurl + outfiturl + url_subcat + results.apparel_id + "/model.jpg",
baseurl + outfiturl + url_subcat + results.apparel_id + "/front.jpg"
];
console.log("\t\t### pushing data into thefeed_index: " + i);
if(!util.isArray(feeds[i].oufits)) feeds[i].outfits = array();
feeds[i].outfits.push(results);
callback(null, null);
});
}, callback);
},
// load store infos
function(callback) {
store.find({"_id":thefeed.store_id}, {limit: 1}).toArray(function(e, resstore) {
console.log("\t### STORE_FIND");
if (e) console.log("error: ", e);
feeds[i].store = resstore[0];
feeds[i].store.class = "hem";
callback(null, null);
});
}
], callback);
}, callback);
}
// MAIN
], function(err, result) {
console.log("feed retrieval completed. stepping out");
if (err) return next(err);
out.send(feeds);
});
};