Cascaded join using mongoose node js - node.js

Question

I am trying to fetch data from MongoDB using Node Js. I have three schemas: Projects, Users, and Teams.
I need to retrieve the project details based on it's type with the worker users.
I got stuck in making join for these schemas:
Projects:
const Project = new Schema({
projectName: { type: String, required: true, trim: true },
type: { type: String, required: true, trim: true },
teamID: { type: Schema.Types.ObjectId, required: true },
});
Teams
const Team = new Schema({
teamId: { type: Schema.Types.ObjectId, required: true, trim: true },
users: { type: [Schema.Types.ObjectId], required: true, trim: true },
teamName: { type: String, required: true },
});
Users:
const User = new Schema({
userId: { type: Schema.Types.ObjectId, required: true, trim: true },
name: { type: String, required: true, trim: true },
profilePicture: { type: String, required: true, trim: true },
});
I am trying to find a way to get
[
{
projectName: "s",
type: "w",
users: ["Jon", "Ali", "Mark"]
},
{
projectName: "a",
type: "w",
users: ["Jon", "Mark"]
}, {
projectName: "s",
type: "w",
users: ["Jon", "Ali", "Mark"]
},
]
I tried to use $lookup, but I can not use it because the relation is complex many to many relations.
Is there a way more efficient than retrieving all users, all teams, and all projects?

Answer 1

I think there is no other efficient way except aggregation and without lookup we can't join collections, You can use nested lookup,
$match condition for type
$lookup to join Team collection using teamID
$match teamID
$lookup to join User collection using users array
$project to convert user's name array using $map
$addFields to get users array in users using $arrayElemAt
db.Project.aggregate([
{ $match: { type: "w" } },
{
$lookup: {
from: "Team",
let: { teamID: "$teamID" },
as: "users",
pipeline: [
{ $match: { $expr: { $eq: ["$$teamID", "$teamId"] } } },
{
$lookup: {
from: "User",
localField: "users",
foreignField: "userId",
as: "users"
}
},
{
$project: {
users: {
$map: {
input: "$users",
in: "$$this.name"
}
}
}
}
]
}
},
{ $addFields: { users: { $arrayElemAt: ["$users.users", 0] } } }
])
Playground
Second possible way, you can combine $project and $addFields stages in single stage,
{
$addFields: {
users: {
$arrayElemAt: [
{
$map: {
input: "$users.users",
in: "$$this.name"
}
},
0
]
}
}
}
Playground