Nodejs for-loops and wait until loop finished

Question

I have the following code:

    //Marks all users which are reading the book with the bookId
 var markAsReading = function (bookId,cb) {
    User.find({}, function (err,users) {
        if(err)
            cb(err);
        //Go through all users with lodash each function
        _(users).each(function (user) {
            //Go through all books
            _(user.books).each(function (book) {

                if(book.matchId === bookId)
                {
                    user.isReading = true;
                    //cb();
                }
            });
        });
        //Need to callback here!!#1 cb(); -->Not working!
    });
       //Or better here! cb() --> Not working
};
exports.markAsReading = markAsReading;

I'am using nodejs with mongoose and mongodb. What i want to do:

Get all users from mongodb with mongoose
With the help of the lodash each-function go through all users
On each user go through the users books (also with lodash and each)
if the current bookId matches the bookId in the function parameter --> Set the book "isReading" property -> true

My problem is that i only need to callback when everything is finished on position #2 But then the whole User.find and its nested callbacks are not ready!

How can i solve this that i do the callback if all loops and the find methods are ready?

I have read something about promises and the async lib but how can i use it in this scenario?

Best Regards Michael

what line //cb(); mean ? Is it commented or you callback here ? You can use callback only once — Nikolay Lukyanchuk, May 29 '14 at 14:26
possible duplicate of [Asynchronous for cycle in JavaScript](http://stackoverflow.com/questions/4288759/asynchronous-for-cycle-in-javascript) — Andreas Hultgren, May 29 '14 at 14:29
Test `async` npm module, it has a bunch of handy utility functions for this. `each`, `eachSeries`, are two of them. — Diosney, May 29 '14 at 21:14

score 5 · Answer 1 · answered Jun 01 '14 at 16:44

I finaly soved this problem with the async library with this pattern:

async.forEach(list,function (item,callback) {
              //do something with the item
              callback();//Callback when 1 item is finished
           }, function () {
               //This function is called when the whole forEach loop is over
               cb() //--> This is the point where i call the callback because the iteration is over
           });

score 0 · Answer 2 · answered May 29 '14 at 14:36

You can use sync each loop from nimble http://caolan.github.io/nimble/

var nimble = require('nimble');

var markAsReading = function (bookId,cb) {
    User.find({}, function (err,users) {
        if(err)
            cb(err);

        nimble.each(users, function (user) {
             nimble.each(user.books, function (book) {
                if(book.matchId === bookId)
                {
                    user.isReading = true;
                }
            });
        });
        cb(null);
    });
};

I tried with nimble it not worked!! The callback is executed before the loops are finished! — rubiktubik, May 29 '14 at 17:40

Nodejs for-loops and wait until loop finished

2 Answers2

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