Make an asynchronous call inside forEach

Question

I am trying to iterate over an array of objects and add some things inside these objects using the async function in Node.js.

So far, my code looks like this:

var channel = channels.related('channels');
channel.forEach(function (entry) {

    knex('albums')
        .select(knex.raw('count(id) as album_count'))
        .where('channel_id', entry.id)
        .then(function (terms) {
            var count = terms[0].album_count;
            entry.attributes["totalAlbums"] = count;
        });

});
//console.log("I want this to be printed once the foreach is finished");
//res.json({error: false, status: 200, data: channel});

How can I achieve such a thing in JavaScript?

Answer 1

Use async.each

async.each(channel, function(entry, next) {
    knex('albums')
         .select(knex.raw('count(id) as album_count'))
         .where('channel_id', entry.id)
         .then(function (terms) {
            var count = terms[0].album_count;
            entry.attributes["totalAlbums"] = count;
            next();
         });
}, function(err) {
    console.log("I want this to be printed once the foreach is finished");
    res.json({error: false, status: 200, data: channel});
});

The last call will be called when all records are processed.

Answer 2

Since you are already using promises, it’s best not to mix this metaphor with async. Instead, just wait until all the promises are over:

Promise.all(channel.map(getData))
    .then(function() { console.log("Done"); });

where getData:

function getData(entry) {
    return knex('albums')
        .select(knex.raw('count(id) as album_count'))
        .where('channel_id', entry.id)
        .then(function (terms) {
            var count = terms[0].album_count;
            entry.attributes["totalAlbums"] = count;
        })
    ;
}