How to aggregate nested lookup array in mongoose? - mongodb

Question

I have a problem with how to lookup nested array, for example i have 4 collections.
User Collection
"user": [
{
"_id": "1234",
"name": "Tony",
"language": [
{
"_id": "111",
"language_id": "919",
"level": "Expert"
},
{
"_id": "111",
"language_id": "920",
"level": "Basic"
}
]
}
]
Language Collection
"language": [
{
"_id": "919",
"name": "English"
},
{
"_id": "920",
"name": "Chinese"
}
]
Job
"job": [
{
"_id": "10",
"title": "Programmer",
"location": "New York"
}
],
CvSubmit Collection
"cvsubmit": [
{
"_id": "11",
"id_user": "1234",
"id_job": "11"
}
]
And my query aggregation is:
db.cvsubmit.aggregate([
{
$lookup: {
from: "user",
localField: "id_user",
foreignField: "_id",
as: "id_user"
}
},
{
$lookup: {
from: "language",
localField: "id_user.language.language_id",
foreignField: "_id",
as: "id_user.language.language_id"
}
},
])
But the result is:
[
{
"_id": "11",
"id_job": "11",
"id_user": {
"language": {
"language_id": [
{
"_id": "919",
"name": "English"
},
{
"_id": "920",
"name": "Chinese"
}
]
}
}
}
]
I want the result like this, also showing all user data detail like name:
[
{
"_id": "11",
"id_job": "11",
"id_user": {
"_id": "1234",
"name": "Tony"
"language": [
{
"_id": "919",
"name": "English",
"Level": "Expert"
},
{
"_id": "920",
"name": "Chinese",
"level": "Basic"
}
]
}
}
]
Mongo Playground link https://mongoplayground.net/p/i0yCucjruey
Thanks before.

Answer 1

$lookup with user collection
$unwind deconstruct id_user array
$lookup with language collection and return in languages field
$map to iterate look of id_user.language array
$reduce to iterate loop of languages array returned from collection, check condition if language_id match then return name
db.cvsubmit.aggregate([
{
$lookup: {
from: "user",
localField: "id_user",
foreignField: "_id",
as: "id_user"
}
},
{ $unwind: "$id_user" },
{
$lookup: {
from: "language",
localField: "id_user.language.language_id",
foreignField: "_id",
as: "languages"
}
},
{
$addFields: {
languages: "$$REMOVE",
"id_user.language": {
$map: {
input: "$id_user.language",
as: "l",
in: {
_id: "$$l._id",
level: "$$l.level",
name: {
$reduce: {
input: "$languages",
initialValue: "",
in: {
$cond: [
{ $eq: ["$$this._id", "$$l.language_id"] },
"$$this.name",
"$$value"
]
}
}
}
}
}
}
}
}
])
Playground
You database structure is not accurate as per NoSQL, there should be max 2 collections, loot of join using $lookup and $unwind will cause performance issues.