Mongoose: find and aggregate together in db.collection() - node.js

Question

I have a collection in mongodb, called recipe, where I have a document, called comments, which is an array, and in each recipe is saving the comments. Inside the comments array I have a ratings, which type is Number. So I want to calculate the average the ratings, but don't know, how can I use the db.collection().aggregate code to work in the recipe collection, in the comments document with the ratings variable.
Here is the recipe collection in mongodb:
const { Double } = require('bson');
const { timeStamp } = require('console');
const mongoose = require('mongoose');
const recipeSchema = new mongoose.Schema({
name: {
type: String,
required: 'This field is required.'
},
description: {
type: String,
required: 'This field is required.'
},
quantity: {
type: Array,
required: 'This field is required.'
},
ingredients: {
type: Array,
required: 'This field is required.'
},
categoryByServing: {
type: String,
enum: ['Reggeli', 'Ebéd', 'Vacsora', 'Desszert', 'Levesek', 'Egyéb'],
required: 'This field is required.'
},
categoryByNationality: {
type: String,
enum: ['Thai', 'Kínai', 'Indiai', 'Olasz', 'Angol', 'Magyar', 'Egyéb'],
required: 'This field is required.'
},
image: {
type: Array,
required: 'This field is required.'
},
comments: [
{
username: String,
comment: String,
date: {
type: Date,
default: Date.now
},
rating: Number
},{
timestamps: true
}
],
count: {
type: Number
},
likes: {
type: Number
},
recipe_id: {
type: String
}
});
recipeSchema.index({ name: 'text', description: 'text' });
const Recipe = module.exports = mongoose.model('Recipe', recipeSchema);
Here is the code, where I implemented the rating avg calculation, which is inside the commenting post method:
/**
* POST /comment-recipe
* Comment Recipe
*/
module.exports.CommentRecipeOnPost = async(req, res) => {
let recipeId = req.params.id
const comment = new Comment({
username: req.body.username,
comment: req.body.comment,
date: req.body.date,
rating: req.body.rating
});
comment.save((err, result) => {
if (err){
console.log(err)
}else {
Recipe.findById(req.params.id, (err, post) =>{
if(err){
console.log(err);
}else{
post.comments.push(result);
post.save();
db.collection('recipes').aggregate([
{
$unwind: "$comments"
},
{
$group: {
_id: null,
avgrating: {
$avg: "$rating"
}
}
}
]).toArray()
.then(results => {
console.log({ rating: results[0].avgrating })
})
.catch(error => console.error(error))
console.log('====comments=====')
console.log(post.comments);
res.redirect('/recipe/' + recipeId);
}
})
}
})
}

Answer 1

UPDATE
There is a simpler way pointed out by chridam in the comments using only a $project which I didn't figure out at first demo
db.collection.aggregate([
{
$project: {
_id: 0,
name: 1,
avgRating: {
$avg: "$comments.rating"
}
}
}
])
..or using $addFields which will give the average of ratings as a new field avgRating for each record demo . you can use a project step after if need to get only certain fields
db.collection.aggregate([
{
$addFields: {
avgRating: {
$avg: "$comments.rating"
}
}
}
])
You have done the $unwind step correctly and now you will get a record for each comment.
{
"_id": "1",
"comments": {
"comment": "commment1-1",
"rating": 4
},
"name": "recipe 1"
},
{
"_id": "1",
"comments": {
"comment": "comment1-2",
"rating": 3
},
"name": "recipe 1"
},
...
In the $group stage group by something unique like the _id or the name and the $avg should be of $comments.rating instead of $rating.
In the end the pipeline should look something like this. demo
db.collection.aggregate([
{
$unwind: "$comments"
},
{
$group: {
_id: "$name", //group by something unique for that document containing comments
avgRating: {
$avg: "$comments.rating"
}
}
}
])