Value not incrementing in mongoose when creating a new object - node.js

Question

Here is my code, I want to increment the total no of counts as soon as any user gives the rating. But the $inc command is not running and result is showing the default value which I set zero.
The given is my Schema.
const mongoose = require('mongoose');
const schema = mongoose.Schema;
let Rating = new schema({
user_id:{
type:mongoose.Types.ObjectId
},
stars:{
type:Number
},
ratingCount:{
type:Number,
default:0
}
})
const rating = mongoose.model('Rating', Rating);
module.exports = rating;
This is the function where I want to increment the value.
const express = require('express');
const Router = express.Router();
let Rating = require('../model/rating');
Router.route('/add/:userid').post((req,res)=>{
new Rating({
user_id: req.params.userid,
$inc: {ratingCount:1},
stars: req.body.stars
})
.save()
.then(rating=>res.send(rating))
.catch(err=>console.log(err));
});
module.exports = Router;
Result showing default value of ratingCount.

Answer 1

You need not to use .save() instead you can simply use .findOneAndUpdate() with option { new: true } to return updated document, if it doesn't find any matching document .findOneAndUpdate() will return null.
Code :
const express = require("express");
const Router = express.Router();
let Rating = require("../model/rating");
Router.route("/add/:userid").post((req, res) => {
Rating.findOneAndUpdate(
{ user_id: req.params.userid },
{ $inc: { ratingCount: 1 }, stars: req.body.stars },
{ new: true }
)
.then((rating) => res.send(rating))
.catch((err) => console.log(err));
});
module.exports = Router;
Usually .save() will track changes to document which is returned from find call. Otherwise if it's not the mongoose document returned from .find() call if it's the mongoose object which you're forming like what you're doing now then if it finds _id in object it will update the matching doc else if no matching doc exists with _id or no _id present in request it will insert the new document.