Mongodb - returns an _id array of all updated documents

Question

I need to update some documents in one collection and send an array of _idupdated documents to another collection.

Since it update()returns the number of updated elements, and not their identifiers, to get an array, I came up with the following:

var docsUpdated = [];
var cursor = myCollection.find(<myQuery>);
cursor.forEach(function(doc) {
  myCollection.update({_id : doc._id}, <myUpdate>, function(error, response){
    docsUpdated.push(doc._id);
  });
});

Or I could do:

var docsUpdated = myCollection.distinct("_id", <myQuery>);
myCollection.update(<myQuery>, <myUpdate>, {multi : true});

I assume the second version will be faster because it calls the database twice. But both seem annoyingly ineffective - is there any other way to do this without multiple database calls? Or am I embarrassing something?

Answer 1

I think you need the cursor operator ".aggregate ()"

db.orders.aggregate([
                 { $group: { _id: "$_id"} }
               ])

- , id