How to use aggregate to group mongodb - node.js

Question

I'm trying to populate my user document with his talents and talent media. But I'm getting repeated objects. I want to get talent as an object and the medias against that talent inside an array.
my user model:
{
_id: '5f1acd6e6985114f2c1567ea',
name: 'test user',
email: 'test#email.com'
}
talent model
{
_id: '5f1acd6e6985114f2c1567fa',
categoryId: '5f1acd6e6985114f2c1567ga',
userId: '5f1acd6e6985114f2c1567ea'
level: '5',
}
talent-media model
{
_id: 5f1acd6e6985114f2c156710',
talentId: '5f1acd6e6985114f2c1567fa',
media: 'file.jpg',
fileType: 'image'
}
I have another model for storing the category
{
_id: '5f1acd6e6985114f2c1567ga',
title: 'java'
}
I want the result as follows
user: {
_id: '',
name: 'test user',
email: 'test#email.com',
talents: [
{
_id: '',
level: '5',
categoryId: {
_id: '',
title: 'java'
},
medias: [
{
_id: '',
file: 'file1.jpg',
fileType: 'image'
},
{
_id: '',
file: 'file2.jpg',
fileType: 'image'
},
]
}
]
}
And I also tried adding talent-medias embedded in talent documents. But in MongoDB document found is not mostly recommended.
Is it better to have talent model like this,
{
_id: '5f1acd6e6985114f2c1567fa',
categoryId: '5f1acd6e6985114f2c1567ga',
userId: '5f1acd6e6985114f2c1567ea'
level: '5',
medias: [
{
_id: '',
file: 'file1.jpg',
fileType: 'image'
},
{
_id: '',
file: 'file2.jpg',
fileType: 'image'
},
]
}

Answer 1

You can achieve this by using $lookup multiple times:
db.users.aggregate([
{
$lookup: {
from: "talents",
let: {
userId: "$_id"
},
pipeline: [
{
$match: {
$expr: {
$eq: [
"$$userId",
"$userId"
]
}
}
},
{
$lookup: {
from: "categories",
let: {
categoryId: "$categoryId"
},
pipeline: [
{
$match: {
$expr: {
$eq: [
"$$categoryId",
"$_id"
]
}
}
},
{
$project: {
_id: "",
title: 1
}
}
],
as: "categoryId"
}
},
{
$lookup: {
from: "talent_media",
let: {
talentId: "$_id"
},
pipeline: [
{
$match: {
$expr: {
$eq: [
"$$talentId",
"$talentId"
]
}
}
},
{
$project: {
_id: "",
file: "$media",
fileType: "$fileType"
}
}
],
as: "medias"
}
},
{
$unwind: {
path: "$categoryId",
preserveNullAndEmptyArrays: true
}
},
{
$project: {
_id: "",
categoryId: 1,
level: 1,
medias: 1
}
}
],
as: "talents"
}
},
{
$project: {
_id: "",
email: 1,
name: 1,
talents: 1
}
}
])
*You'll probably have to adapt the collection names.
MongoPlayground

Answer 2

You have to use nested $lookup,
lookup with Talent Collection and match userId
$match for specific user _id document, commented here
db.User.aggregate([
/** add here
Optional for single user
{
$match: {
_id: "XXXXXXXXXXXX"
}
},
*/
{
$lookup: {
from: "Talent",
as: "talents",
let: {
userId: "$_id"
},
pipeline: [
{
$match: {
$expr: {
$eq: [
"$$userId",
"$userId"
]
}
}
},
we are now inside Talent Document and lookup with Category Collection and match with categoryId
$unwind category because it will return array and we need object
{
$lookup: {
from: "Category",
as: "categoryId",
localField: "categoryId",
foreignField: "_id"
}
},
{
$unwind: {
path: "$categoryId",
preserveNullAndEmptyArrays: true
}
},
again we are inside Talent Document and lookup with Talent Media Collection and match with talentId
$project for add/remove not needed fields, here removed talentID from TalentMedia nad removed userId from Talent
{
$lookup: {
from: "TalentMedia",
as: "medias",
let: {
talentId: "$_id"
},
pipeline: [
{
$match: {
$expr: {
$eq: [
"$$talentId",
"$talentId"
]
}
}
},
{
$project: {
talentId: 0
}
}
]
}
},
{
$project: {
userId: 0
}
}
]
}
}
])
Separated query in parts for explanation, You can combine as they are in sequence.
Working Playground: https://mongoplayground.net/p/poIbvFUMvT4