Grouping after Mongoose aggregation lookup - json

Question

Actually im new to mongoDB and mongoose, and im tryig to get nested join using three schemas and grouping them.
const company = Schema(
{
title: {type: String, required: true},
}
);
const plans = Schema(
{
companyId: {type: Schema.Types.ObjectId, ref: 'company', required: true},
title: {type: String, required: true},
}
);
const promotions = Schema(
{
planId: {type: Schema.Types.ObjectId, ref: 'plans', required: true},
title: {type: String, required: true},
}
);
I got the below result but separated, and I would like to group it, any help with this point would be appreciated?
[
{
_id: '621c2749ac447abf20a8a263',
title: 'test 1',
plans: {
_id: '621c290ad6bce1084f900b0b',
title: 'test 1',
promotions: {
_id: '621d1187b18de3c35fa3963b',
title: 'test 1',
},
},
},
{
_id: '621c2749ac447abf20a8a263',
title: 'test 2',
plans: {
_id: '621c290ad6bce1084f900b0b',
title: 'test 2',
promotions: {
_id: '621d1187b18de3c35fa3963d',
title: 'test 2',
},
},
},
];
The result that i want to achieve is:
[
{
title: 'company name',
plans: [
{
title:'plan name',
promotions: [
{
title:'promotion name'
}
]
},
...
]
},
...
]

Answer 1

A nested "$lookup" is one way to do it.
db.company.aggregate([
{
// lookup plans matching companies
"$lookup": {
"from": "plans",
"localField": "_id",
"foreignField": "companyId",
"pipeline": [
{
// lookup promotions matching plans
"$lookup": {
"from": "promotions",
"localField": "_id",
"foreignField": "planId",
"as": "promotions"
}
}
],
"as": "plans"
}
},
{
// drop unwanted fields
"$project": {
"_id": 0,
"plans._id": 0,
"plans.companyId": 0,
"plans.promotions._id": 0,
"plans.promotions.planId": 0
}
}
])
Try it on mongoplayground.net.