Return mongojs query result from function

Question

Return mongojs query result from function

I made the function below for getting usernames from ids. It is not working well. I can write console.log(result.first_name); within the query function, and the usernames shows up in my terminal, but not the browser. I tried adding “return 'something';” at the end of the function, to see if that showed up in the browser – It did. How can I write the function so that the query result is returned?

function (global function in app.js)

function usernameFromId(id, callback){
    db.users.findOne({ _id: ObjectId(id.toString()) }, function(err, result) {
        var first_name = result.first_name;
        console.log(first_name); // names show up in the console…
        callback(first_name);
    });
};

page handler (in app.js)

app.get('/books', function(req, res){
    function timeSince(dato){
        moment.lang('nb');
        return moment(dato).fromNow();
    };
    db.books.find().sort({ added:-1 }, function(err, docs) {
        var books = docs;
        db.activity.find().limit(9).sort({ time:-1 }, function(err, docs) {
            var activity = docs;
            res.render('books', {
                books: books,
                activity: activity,
                timeSince: timeSince,
                usernameFromId: usernameFromId
            })
        });
    });
});

template (books.jade)

- each a in activity
    p=usernameFromId(a.user_id, function(name){return name;})

node.js
mongodb
express
jade

Answer 1

No because of the asynchronous nature of JavaScript. I have added some comments to your code to indicate the actual order of execution. This is why you are getting the error.

function usernameFromId(id){
    var id = id.toString(); // 1
    db.users.findOne({ _id: ObjectId(id) }, function(err, result) {
        var first_name = result.first_name; // 3
    });
    return first_name; // 2
};

Edit: you probably want something like the following

function usernameFromId(id, callback){
    var id = id.toString();
    db.users.findOne({ _id: ObjectId(id) }, function(err, result) {
        var first_name = result.first_name; 
        callback(first_name);
    });
};

Answer 2

Okay, I found a solution. Not sure whether it’s any good, but it works. No need for a function.

page handler (in app.js):

app.get('/books', function(req, res){
    db.activity.find().limit(9).sort({ time:-1 }, function(err, docs) {
        var activity = docs;
        db.users.find(function(err, docs) {
            var users = docs;
            res.render('books', {
                page_title:'books',
                activity: activity,
                users: users
            })
        });
    });
});

template (books.jade):

- each a in activity
    - for u in users
        - if (a.user_id == u._id.toString())
            | #{u.first_name}