Mongoose update with limit - node.js

Question

I am looking to update X documents all at once. The short is I basically need to randomly select N documents and then update them as "selected". I'm trying to design an API that needs to randomly distribute questions. I can not find a way to do this in mongoose I have tried:
update ends up selecting everything
Question
.update({}, {
$inc: {
answerCount: 1,
lockedCount: 1
},
$push:{
devices: deviceID
}
}, {multi:true})
.limit(4)
--- I also tried
Question
.find()
.sort({
answerCount: 1,
lockedCount: 1
})
.limit(req.query.limit || 4)
.update({}, {
$inc: {
answerCount: 1,
lockedCount: 1
},
$push:{
devices: deviceID
}
}, { multi: true }, callback);
Both resulted in updating all docs. Is there a way to push this down to mongoose without having to use map ? The other thing I did not mention is .update() without multi resulted in 1 document being updated.

Answer 1

You could also pull an array of _ids that you'd like to update then run the update query using $in. This will require two calls to the mongo however the updates will still be atomic:
Question.find().select("_id").limit(4).exec(function(err, questions) {
var q = Question.update({_id: {$in: questions}}, {
$inc: {answerCount: 1, lockedCount:1},
$push: {devices: deviceid}
}, {multi:true});
q.exec(function(err) {
console.log("Done");
});
});

Answer 2

So I did an simple map implementation and will use it unless someone can find a more efficient way to do it.
Question
.find({
devices: { $ne: deviceID}
},
{ name: true, _id: true})
.sort({
answerCount: 1,
lockedCount: 1
})
.limit(req.query.limit || 4)
.exec(updateAllFound );
function updateAllFound(err, questions) {
if (err) {
return handleError(res, err);
}
var ids = questions.map(function(item){
return item._id;
});
return Question.update({ _id: { $in: ids} } ,
{
$inc: {
answerCount: 1,
lockedCount: 1
},
$push:{
devices: deviceID
}
}, { multi: true }, getByDeviceID);
function getByDeviceID(){
return res.json(200, questions);
}
}