AngularJS - Deferred recursive promises

Question

I have a function that calls an asynchronous function (in a loop) that will provide me a parameter for the next call of the function. I think writing the code will make more sense so here is what I tried (with no success). I know many questions have been asked about this subject but I really tried everything I saw.

    removeMultipleAttachments: function(docid, rev, attachmentIDs) {
        var requests = [];
        var deferred = $q.defer();
        var p = $q.when();
        console.log(attachmentIDs);
        angular.forEach(attachmentIDs, function(file, index) {
            p = p.then(function (formerRes) {

                return pouch.removeAttachment(docid, attachmentIDs[index].name, rev, function (err, res) {
                    $rootScope.$apply(function () {
                        if (err) {
                            deferred.reject(err);
                        } else {
                            rev = res.rev;
                            console.log(rev);
                            deferred.resolve(res);
                        }
                    })
                });
            });
            requests.push(p);
        })
        $q.all(requests).then(function(){
            console.log('DONE');
        });

        return deferred.promise;
    }

First thing I see is var p = $q.when(); should be var p = $q.defer(); — DrDyne, Jun 06 '14 at 15:42
Do you need to remove attachment one by one in order, or you don't care about the order? — Ye Liu, Jun 06 '14 at 15:55
but every call need a new `rev` from previous call, is that right? — Ye Liu, Jun 06 '14 at 15:58
exactly, each time I call pouch.removeAttachment(), I need to use the rev from the previous call — Nate, Jun 06 '14 at 15:59
Where in your code are you using `formerRes`? Why don't you run them in parallel? — Bergi, Jun 09 '14 at 15:09

Ye Liu · Answer 1 · 2014-06-09T13:18:38.740

Since you need a new rev for each removeAttachment(), you can't use $q.all(), you need to ensure the async call ordering by using then(), like this:

removeMultipleAttachments: function(docid, rev, attachmentIDs) {
    console.log(attachmentIDs);
    var p = $q.when();
    angular.forEach(attachmentIDs, function(file, index) {
        p = p.then(function (formerRes) {
            var deferred = $q.defer();

            pouch.removeAttachment(docid, attachmentIDs[index].name, rev, function (err, res) {
                if (err) {
                    deferred.reject(err);
                } else {
                    rev = res.rev;
                    console.log(rev);
                    deferred.resolve(res);
                }
                $rootScope.$apply();
            });

            return deferred.promise;
        });

    return p.then(function(res) {
        console.log('DONE');
        return res;
    });
}

Thanks Ye, it solves most of my problems but where can add a function or console.log('DONE') when all the promises have been done? — Nate, Jun 07 '14 at 18:43
Oh and I also need to catch the last response... what should I do to be able to call this function as follow: removeMultipleAttachments(docid, rev, attachmentIDs).then(function(response){ ... catch response here ...}) — Nate, Jun 08 '14 at 12:41

AngularJS - Deferred recursive promises

1 Answers1