mongoose push to array

Student.findByIdAndUpdate(
            req.body._id, {
                $push: {
                    "comments": req.body.imagelink
                }
            },
            function (err, model) {
                if (err) {
                    console.log(err);
                    res.send(err);
                    next();
                } else {
                    res.json(model);
                    next();
                }

            });