Updating the result returned by find() method alone in Node.js using Mongoose

I am a newbie to Node.js. My Node.js application has a model called Selfie.

# model/selfie.js
var mongoose = require('mongoose'),
    Schema = mongoose.Schema,
    selfieSchema = new Schema({
        path: { type: String },
        caption: { type: String },
        sent_mod: { type: Number, default: -1 }, // -1 not sent, 0 sent, 1 accepted
        display_count: { type: Number, default: -1 }, // -1 not sent, 0 sent, 1 displayed
        time_stamp: { type: Date, default: new Date() }
    }),
    Selfie = mongoose.model('selfie', selfieSchema);

module.exports = Selfie;

Am breaking down the problem as follows:

1. Retrieve 20 selfies whose mod_sent is -1.


2. Update the mod_count of those 20 selfies to 0.

To retrieve 20 selfies am using find(), limit() and then exec() method. Once I have those selfies I can use forEach() and update() to iterate and update each of their sent_mod to 0. But this approach performs update operation 20 times. I think there might be a better way to do it. I read about findAndUpdate() from MongoDB documentation and found out that Mongoose has various methods like findOne(), findOneAndUpdate(). But am unable to find a better way to solve my problem using those methods also.

# routes/selfie.js
var express = require('express'),
    router = express.Router(),

    Selfie = require('../models/selfie'),

    mongoose = require('mongoose');

router.get('/moderate', function(req, res) {

        Selfie.find({ sent_mod: -1 }).limit(2).exec(function(err, selfies) {
            if(err) {
                console.log(err);
                return;
            }
            console.log(selfies);

        });
});


module.exports = router;