Unable to push into empty Array JS

Question

The findOne query is returning a user from the DB. When i console.log(user) it does print out user data. But for some reason isn't pushing into user_contacts. Its just returning as an empty array.

get_contacts: function (req, res){
                var user_contacts = [];
                for(var i=0;i<req.body.contacts.length;i++){
                    User.findOne({_id: req.body.contacts[i]._User}, function (err, user) {
                        if(user){
                            console.log(user);
                            user_contacts.push(user);
                        }else{
                            console.log("Error");
                        }
                    })  
                }
            console.log(user_contacts);
            res.json(user_contacts);
            }

This should be so simple, but just cannot see what I am doing wrong. Appreciate the help.

The DB call is async - when you call res.json your DB calls haven't executed yet - hence the empty response. — tymeJV
– tymeJV, Commented Feb 23, 2016 at 1:57
but the console.log(user) is still printing out the user data, if the DB calls haven't executed how can I have user data to print? — simba777
– simba777, Commented Feb 23, 2016 at 2:10

tymeJV · Accepted Answer · 2016-02-23 02:02:30Z

1

Since the call is async - your logs and response are executed before everything is finished. You'll probably also run into some issues with looping that async call - your best bet is to use $in and then return:

get_contacts: function (req, res){
    var ids = req.body.contacts.map(function(contact) { return contact._User });
    User.find({_id: {$in: ids}}, function(err, users) {
        res.json(users)
    });
}

answered Feb 23, 2016 at 2:02

tymeJV

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4 Comments

simba777 Over a year ago

will this not return only one single user data? .. I am trying to retrieve multiple users data together. Thus created the empty array and tried pushing.

tymeJV Over a year ago

This will query all the ids of the users passed back and return an array @Ani777

simba777 Over a year ago

tried it, it works. Thanks a lot. so basically whats happening is ids is returning all the _User fields in req.body.contacts and the the Query is searching for users with the ids that have been returned. Am i right? will be reading about $in as well.

tymeJV Over a year ago

@Ani777 -- Yep - that's exactly what's happening

TuanNguyen · Accepted Answer · 2016-02-23 02:00:10Z

0

User.findOne({}) is async, which mean the callback function where you push data into user_contacts array is executed with delay. Therefore, the moment you console.log, user_contacts is still empty.

answered Feb 23, 2016 at 2:00

TuanNguyen

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1 Comment

simba777 Over a year ago

Thanks for the link to async, reading it right now, hope can make some sense out of it.

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