Return q resolve when all operations complete

Question

I have a function that I only want to resolve when the foreach has completed.. im using q, and mongoose which is what the capitalised things refer to, and basically i want to create a set of items first, then run a function after the foreach is complete.

function createItems() {

  var deferred = Q.defer();

  var itemsArray = [{ 'name' : 'spade' }, { 'name' : 'bucket' } , { 'name' : 'sand'}];

  itemsArray.forEach(function(itemObj) {
    var item = new Item(itemObj); // forces it to use a schema (dont worry)
    Item.findOneAndUpdate({
      url: item.short_name
    }, item, {
      upsert: true
    }, function(err) {
      if (!err) {
        console.log(item.name + ' created.');
        deferred.resolve();
      } else {
        deferred.reject(new Error(err));
      }
    });
  });


  return deferred.promise;
}

createItems()
    .then(function() {
      console.log('All items done.');
    });

So i would expect to see on the console something like;

spade item created bucket item created sand item created All items done.

Answer 1

Quick aside: your array has a syntax issue, it contains one object with multiple attempts to write name. I assumed you intended to have an array of objects, each with a name.

Basically, your approach fails because you are resolving your promise on the very first instance. You want a promise that represents multiple async calls completing. The standard way to do that is to pass an array of promises into a library function like Q.all / Bluebird.all / Promise.all. The all function takes an array of promises and returns a promise for an array of results. It resolves when all the promises resolve, or it rejects when any one of the promises reject.

function createItems() {

  var promisesForUpdatedDocs = [];

  var itemsArray = [
    { name: 'spade'},
    { name: 'bucket'},
    { name: 'sand'}
  ];

  itemsArray.forEach(function(itemObj) {
    var item = new Item(itemObj);
    var updatedDocPromise = Item.findOneAndUpdate({
      url: item.short_name
    }, item, {
      upsert: true
    }).exec(); // returns an mPromise
    promisesForUpdatedDocs.push(Q(updatedDocPromise)); // using Q to turn the mPromise to a Q promise, and adding it to an array
  });

  return Q.all(promisesForUpdatedDocs); // creates a promise for array of results (from array of promises)
}

createItems()
  .then(function(items) {
    console.log('All items done:', items);
  }).catch(console.log); // never forget to handle errors! Always `return` or `catch` a promise chain.