Using findOne in mongodb to get element with max id

You should use find, like you already are, and not aggregation which will be slower since it needs to scan all the values of _id fields to figure out the max.

As comments pointed out there is no difference between using find() and findOne() - functionally or elegance-wise. In fact, findOne in the shell (and in the drivers which implement it) is defined in terms of find (with limit -1 and with pretty print in the shell).

If you really want to do the equivalent of

db.collection.find().sort({_id:-1}).limit(1).pretty()

as findOne you can do it with this syntax:

db.collection.findOne({$query:{},$orderby:{_id:-1}})

You can get max _id using aggregation of mongodb. Find and sort may overkill's.

db.myCollection.aggregate({
    $group: {
        _id: '',
        last: {
            $max: "$_id"
        }
    }
});