callback in loop node.js

Question

callback in loop node.js

I don't understant how to set a callback in a loop:

models.chat_user.find( {user_id: app.locals.session.user._id}, function(err, result){
    if(result.length < 1){
        chat.user = new models.chat_user({
        user_id: app.locals.session.user._id
        })
        chat.user.save();
    }
    models.chat_user.find(function(err, result){
        for(value in result){
        models.user.findOne({_id: result[value].user_id}, function(err, user){
                chat.users[value] = {};
                chat.users[value].username = user.username
                chat.users[value].mail = app.locals.user.getAvatar(user.mail, 50);
            });
        }
    })
});

I'd like to set a callback when I find all datas in my loop but I don't know how mayme with a condition on the result.lenth but that's not very clean

Thanks

node.js
callback

Answer 1

Use async.forEach like so:

models.chat_user.find(function(err, result){
    async.forEach(result, function(value, callback) {
        models.user.findOne({_id: result[value].user_id}, function(err, user){
            chat.users[value] = {};
            chat.users[value].username = user.username
            chat.users[value].mail = app.locals.user.getAvatar(user.mail, 50);
            callback(err);
        });
    }, topLevelCallback);
});

topLevelCallback is called when all forEach iterations have called their callback, passing along any error if there was one.