How to get result from passing array in mongodb?

Question

I have an array, using this I want to search some products. The array shown below.

 "productIds": [
   {
     "productId": ObjectId("574592dfc07f13943255c19d") 
   },
   {
     "productId": ObjectId("5745934cc07f13943255c19f") 
   },
   {
     "productId": ObjectId("57459397c07f13943255c1a1") 
   } 
 ]

using this productId I want to search particular products. I have written some query but it takes only first productId and it's not taking remaining.

router.post('/getItemOfWishList', function(req,res){
    var wId = ObjectId(req.body.wID);
    var findwishlists = function(db, callback) {
        var cursor =db.collection('wishlists').find({_id: wId}).toArray(function(err, docs){
            if(err){  
                callback(new Error("Some problem"));
            }else{
                callback(null,docs);
            } 
        });
    };

    MongoClient.connect(config.database, function(err, db) {
        assert.equal(null, err);
        findwishlists(db, function(err,docs) {
            db.close();

            //console.log(docs[0].productIds);//It contains that array.


            for(var key in docs){
                console.log(docs[key].productIds[key].productId);
                var pID = ObjectId(docs[key].productIds[key].productId);

                var findproducts = function(db, callback) {
                    var cursor =db.collection('proInfo').find({_id: pID}).toArray(function(err, docs){
                        if(err){  
                            callback(new Error("Some problem"));
                        }else{
                            callback(null,docs);
                        } 
                    });
                };

                MongoClient.connect(config.database, function(err, db) {
                    assert.equal(null, err);
                    findproducts(db, function(err,docs) {
                        db.close();
                        if(err) return res.json({result:null})
                        else
                        return res.json({result: docs});
                    });
                });                 
            }
        });
    });
});

return res.json({result: docs}); line is stopping the loop I think. Why you are doing return? — Shrabanee
– Shrabanee, Commented Jun 27, 2016 at 13:32
return for to get result from node.js to angular controller. — Kevin
– Kevin, Commented Jun 27, 2016 at 13:34

Vasil Dininski · Accepted Answer · 2016-06-27 13:42:43Z

There are a couple of issues here:

The asynchronous flow of the program is incorrect - the for statement starts a bunch of asynchronous tasks and you are not waiting for all of them to complete.
You are sending the response back as soon as you receive the first result - you are writing to the response as soon as the findProducts is called the first time.

You can address all these issues by utilizing the $in MongoDb operator:

MongoClient.connect(config.database, function(err, db) {
    db.collection('wishlists').find({_id: wId}).toArray(function(err, wishlist) {
      var productIds = wishlist.productIds.map(function(product) {
         return product.productId;
        });
      
      db.collection('products').find({_id: {$in: productIds}}).toArray(function (err, products) {
        return res.json(products);
      });
    });
});

You should, of course, handle all the unexpected errors and rework the snippet in order for it to fit your case more precisely.

I'd also recommend reading up a bit more on how node.js handles asynchronous work and on flow control as you are assuming that all the code will be done synchronously - one after the other. A good place to start would be: https://blog.risingstack.com/node-hero-async-programming-in-node-js/

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