MongoDB aggregate with foreign model inside array - arrays

Question

I am trying to aggregate data with a foreign model.
The structure I am trying to supercharge is the following:
{
"_id" : ObjectId("62b489664cbb9bc8c947f19f"),
"user_id" : ObjectId("61a775da4cbb9bc8c947edd9"),
"product_types" : [
{
"type" : NumberLong(1),
"product_id" : ObjectId("62b4890f4cbb9bc8c947e5ef"),
},
{
"type" : NumberLong(1),
"product_id" : ObjectId("62b4890f4cbb9bc8c947e5ed"),
}
]
}
I am trying to add product data from product_id, and I think I am pretty close to it, but I am adding 2 identical products in an array instead of the correct one:
Query:
db.getCollection('interests').aggregate([
{
$lookup:{
from: "products",
localField: "product_types.product_id",
foreignField: "_id",
as: "productInterestData"
}
},
{
$set: {
"product_types.product": {
$map: {
input: "$product_types",
in: {
$mergeObjects: [
"$this",
{
$arrayElemAt: [
"$productInterestData",
{$indexOfArray: ["$productInterestData.id", "$this.id"]}
]
}
]
}
}
}
}
},
{$unset: "productInterestData"}
])
Result (with an array of 2 identical products, instead of the correct one):
{
"_id" : ObjectId("62b489664cbb9bc8c947f19f"),
"user_id" : ObjectId("61a775da4cbb9bc8c947edd9"),
"product_types" : [
{
"type" : NumberLong(0),
"product_id" : ObjectId("62b4890f4cbb9bc8c947e5ef"),
"product" : [
{
"_id" : ObjectId("62b4890f4cbb9bc8c947e5ef"),
"name" : "olive",
},
{
"_id" : ObjectId("62b4890f4cbb9bc8c947e5ef"),
"name" : "olive",
}
]
},
{
"type" : NumberLong(1),
"product_id" : ObjectId("62b4890f4cbb9bc8c947e5ed"),
"product" : [
{
"_id" : ObjectId("62b4890f4cbb9bc8c947e5ef"),
"name" : "olive",
},
{
"_id" : ObjectId("62b4890f4cbb9bc8c947e5ef"),
"name" : "olive",
}
]
}
]
}
Any idea on how to fix the query to have only one product instead of an array of identical ones?

Answer 1

Few small adjustments on the $set phase:
product_types, not product_types.product, in order to avoid duplication of the array. In order to nest it anther product add the key product in the $mergeObjects operation.
$productInterestData._id instead of $productInterestData.id
$$this instead of $this (we need two $ here)
$$this.product_id instead of $this.id
db.interests.aggregate([
{
$lookup: {
from: "products",
localField: "product_types.product_id",
foreignField: "_id",
as: "productInterestData"
}
},
{
$set: {
product_types: {
$map: {
input: "$product_types",
in: {
$mergeObjects: [
"$$this",
{product:{
$arrayElemAt: [
"$productInterestData",
{$indexOfArray: ["$productInterestData._id", "$$this.product_id"]}
]
}}
]
}
}
}
}
},
{$unset: "productInterestData"}
])
See how it works on the playground example