How to Populate and Aggregate - node.js

Question

i want to aggregate the ratings so i could get the total of feedbacks. But the thing is, it's referenced. Here's my schema
User
username: String,
fullname: String,
email: {
type: String,
lowercase: true,
unique: true
},
address: String,
password: String,
feedback: [{
type: mongoose.Schema.Types.ObjectId,
ref: 'Feedback'
}]
Feedback
var FeedbackSchema = new mongoose.Schema({
postname: String,
user: {
type: mongoose.Schema.Types.ObjectId,
ref: 'User'
},
message: String,
feedbacktype: String,
thumbsup: Boolean,
rating: {
communication: Number,
timeliness: Number,
delivery: Number
}
});
So what i want to achieve is, i will find the User by id then populate the feedbacks field, then i will aggregate the ratings on the feedback field so i would get a total of number of ratings for communication, for delivery and for timeliness. (The ratings are 1-5 stars)
Do you know how to aggregate and populate? thank you
**update
So i've run the aggregation to the user schema, now im getting 0 results from all ratings
User.aggregate([
{ "$match": { "_id": ObjectId('593150f6ac4d9b0410d2aac0') } },
{ "$lookup": {
"from": "feedbacks",
"localField": "feedback",
"foreignField": "_id",
"as": "feedback"
}},
{ "$project": {
"username": 1,
"fullname": 1,
"email": 1,
"password": 1,
"rating": {
"communication": { "$sum": "$feedback.rating.communication" },
"timeliness": { "$sum": "$feedback.rating.timeliness" },
"delivery": { "$sum": "$feedback.rating.delivery" }
}
}}
]).exec(function(err, a){
console.log(a)
})
result rating: { communication: 0, timeliness: 0, delivery: 0 } } ]
also tried it with other users, all of them 0 result rating

Answer 1

Simple Listing to Follow
var async = require('async'),
mongoose = require('mongoose'),
Schema = mongoose.Schema;
mongoose.connect('mongodb://localhost/rating');
var userSchema = new Schema({
username: String,
feedback: [{ type: Schema.Types.ObjectId, ref: 'Feedback' }]
});
var feedbackSchema = new Schema({
rating: {
communication: Number,
timeliness: Number,
delivery: Number
}
});
var User = mongoose.model('User', userSchema);
var Feedback = mongoose.model('Feedback', feedbackSchema);
async.series(
[
(callback) => {
async.each([User,Feedback],(model,callback) => {
model.remove({},callback);
},callback);
},
(callback) => {
async.waterfall(
[
(callback) => {
async.map(
[
{ "rating": {
"communication": 1, "timeliness": 2, "delivery": 3
}},
{ "rating": {
"communication": 2, "timeliness": 3, "delivery": 4
}}
],
(item,callback) => {
Feedback.create(item,callback)
},
callback
);
},
(feedback, callback) => {
User.create({ "username": "Bill", "feedback": feedback },callback);
},
(user, callback) => {
User.aggregate([
{ "$match": { "_id": user._id } },
{ "$lookup": {
"from": "feedbacks",
"localField": "feedback",
"foreignField": "_id",
"as": "feedback"
}},
{ "$project": {
"username": 1,
"rating": {
"communication": { "$sum": "$feedback.rating.communication" },
"timeliness": { "$sum": "$feedback.rating.timeliness" },
"delivery": { "$sum": "$feedback.rating.delivery" }
}
}}
],(err,results) => {
console.log(JSON.stringify(results, undefined, 2));
callback(err);
});
}
],
callback
)
}
],
(err) => {
if (err) throw err;
mongoose.disconnect();
}
);
This will create two collections as User
{
"_id" : ObjectId("593548455198ab3c09cf736b"),
"username" : "Bill",
"feedback" : [
ObjectId("593548455198ab3c09cf7369"),
ObjectId("593548455198ab3c09cf736a")
],
"__v" : 0
}
And feedbacks:
{
"_id" : ObjectId("593548455198ab3c09cf7369"),
"rating" : {
"communication" : 1,
"timeliness" : 2,
"delivery" : 3
},
"__v" : 0
}
{
"_id" : ObjectId("593548455198ab3c09cf736a"),
"rating" : {
"communication" : 2,
"timeliness" : 3,
"delivery" : 4
},
"__v" : 0
}
Program Output Shows the aggregation:
[
{
"_id": "5935494a159c633c1b34807b",
"username": "Bill",
"rating": {
"communication": 3,
"timeliness": 5,
"delivery": 7
}
}
]
Also package.json if the two dependencies are not clear enough:
{
"name": "ratings",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"keywords": [],
"author": "",
"license": "ISC",
"dependencies": {
"async": "^2.4.1",
"mongoose": "^4.10.4"
}
}
Original Answer
Personally I would work this from the "Feedback" since you have the user already recorded there, and it is actually the way this scales better.
Instead of using population, we can instead use $lookup with a MongoDB server version of at least 3.2:
Feedback.aggregate([
{ "$match": { "user": userId } },
{ "$group": {
"_id": "$user",
"communication": { "$sum": "$rating.communication" },
"timeliness": { "$sum": "$rating.timeliness" },
"delivery": { "$sum": "$rating.delivery" }
}},
{ "$lookup": {
"from": "users",
"localField": "_id",
"foreignField": "_id",
"as": "user"
}},
{ "$unwind": "$user" }
])
If you do not have a server version that supports $lookupthen you can still "manually join" the User details with something like this:
Feedback.aggregate([
{ "$match": { "user": userId } },
{ "$group": {
"_id": "$user",
"communication": { "$sum": "$rating.communication" },
"timeliness": { "$sum": "$rating.timeliness" },
"delivery": { "$sum": "$rating.delivery" }
}}
],function(err, results) {
result = results[0];
User.findById(userId).lean().exec(function(err, user) {
result.user = user; // swap the _id for the Object
// Then output result
});
})
Which is basically what .populate() does, but we are doing it manually and efficiently for the result returned.
You can work the other way around from the User model, but it's likely more efficient to simply work this way around.
User.aggregate([
{ "$match": { "_id": userid } },
{ "$lookup": {
"from": "feedbacks",
"localField": "feedback",
"foreignField": "_id",
"as": "feedback"
}},
{ "$project": {
"username": 1,
"fullname": 1,
"email": 1,
"password": 1,
"rating": {
"communication": { "$sum": "$feedback.rating.communication" },
"timeliness": { "$sum": "$feedback.rating.timeliness" },
"delivery": { "$sum": "$feedback.rating.delivery" }
}
}}
])