Problem in Mongoose $lookup for nested array of objects - node.js

Question

Suppose that I have the following three collections:
product: [
{
_id: ObjectId('p1'),
name: 'Box1'
}
]
// ----------
order: [
{
_id: ObjectId('o1'),
productId: ObjectId('p1'),
quantity: 10
},
{
_id: ObjectId('o2'),
productId: ObjectId('p1'),
quantity: 20
}
]
// ----------
status: [
{
_id: ObjectId('s1'),
orderId: ObjectId('o1'),
title: 'in-progress'
},
{
_id: ObjectId('s2'),
orderId: ObjectId('o2'),
title: 'succeeded'
}
]
I need to join these three to get following result:
{
_id: ObjectId('p1'),
name: 'Box1',
order: [
{
_id: ObjectId('o1'),
quantity: 10,
status: {
_id: ObjectId('s1'),
title: 'in-progress'
}
},
{
_id: ObjectId('o2'),
quantity: 20
status: {
_id: ObjectId('s2'),
title: 'succeeded'
}
}
]
}
Actually the problem is inside the order array which has 2 objects in it to correlate with the relevant status collection.
Here what I did something like:
db.getCollection('product').aggregate([
{
$lookup: {
from: 'order',
localField: 'productId',
foreignField: '_id',
as: 'product.order'
},
},
{
$lookup: {
??? // Make status inside each element of order array
},
},
]);
Does anyboady have idea?

Answer 1

You will need to $unwind the result of the first lookup so that you can consider each separately, do a $lookup from the status collection on orderId, and then $group by the product _id and $push the orders back into an array.

Answer 2

The answer:
db.getCollection('product').aggregate([{
$lookup: {
from: 'order',
localField: '_id',
foreignField: 'productId',
as: 'orders'
}
},
{
$unwind: '$orders'
},
{
$lookup: {
from: 'status',
localField: 'orders._id',
foreignField: 'orderId',
as: 'orders.status'
}
},
{
$unwind: '$orders.status'
},
{
$group: {
_id: '$_id',
name: {
$first: '$name'
},
order: {
$push: '$orders'
}
}
}
]);
Then result would be something like this:
[{
_id: ObjectId('p1'),
name: 'Box1',
order: [{
_id: ObjectId('o1'),
productId: ObjectId('p1'),
quantity: 10,
status: {
_id: ObjectId('s1'),
orderId: ObjectId('o1'),
title: 'in-progress'
}
},
{
_id: ObjectId('o2'),
productId: ObjectId('p1'),
quantity: 20,
status: {
_id: ObjectId('s2'),
orderId: ObjectId('o2'),
title: 'succeeded'
}
}
]
}]