Mongodb- group an array by key - mongodb

Question

I have an array field (contains objects) in multiple documents, I want to merge the arrays into one array and group the array by object key. I have manage to group the array but I dont know how to group the data. See the code I tried below
const test = await salesModel.aggregate([
{ $unwind: "$items" },
{
$group: {
_id: 0,
data: { $addToSet: '$items' }
},
}
])
Result of the query:
{
_id: 0,
data: [
{
_id: 61435b3c0f773abaf77a367e,
price: 3000,
type: 'service',
sellerId: 61307abca667678553be81cb,
},
{
_id: 613115808330be818abaa613,
price: 788,
type: 'product',
sellerId: 61307abca667678553be81cb,
},
{
_id: 61307c1ea667676078be81cc,
price: 1200,
type: 'product',
sellerId: 61307abca667678553be81cb,
}
]
}
Now I want to group the data array by object key data.sellerId and sum price
Desired Output:
{
data: [
{
sumPrice: 788,
sellerId: 613115808330be818abaa613,
},
{
sumPrice: 1200,
sellerId: 61307abca667678553be81cb,
}
]
}

Answer 1

Extend with the current query and result with:
$unwind: Deconstruct the array field to multiple documents.
$group: Group by data.sellerId to sum ($sum) for data.price.
$group: Group by 0 with $addToSet to combine multiple documents into one document with data.
MongoDB aggregation query
db.collection.aggregate([
{
$unwind: "$data"
},
{
$group: {
_id: {
sellerId: "$data.sellerId"
},
"sumPrice": {
$sum: "$data.price"
}
}
},
{
"$group": {
"_id": 0,
"data": {
$addToSet: {
"sellerId": "$_id.sellerId",
"sumPrice": "$sumPrice"
}
}
}
}
])
Sample Mongo Playground
Output
[
{
"_id": 0,
"data": [
{
"sellerId": ObjectId("61307abca667678553be81cb"),
"sumPrice": 4988
}
]
}
]
If you want to re-write the query, here are the query with sample input.
Input
[
{
items: [
{
_id: ObjectId("61435b3c0f773abaf77a367e"),
price: 3000,
type: "service",
sellerId: ObjectId("61307abca667678553be81cb"),
},
{
_id: ObjectId("613115808330be818abaa613"),
price: 788,
type: "product",
sellerId: ObjectId("61307abca667678553be81cb"),
},
{
_id: ObjectId("61307c1ea667676078be81cc"),
price: 1200,
type: "product",
sellerId: ObjectId("61307abca667678553be81cb"),
}
]
}
]
Mongo aggregation query
db.collection.aggregate([
{
$unwind: "$items"
},
{
$group: {
_id: {
sellerId: "$items.sellerId"
},
"sumPrice": {
$sum: "$items.price"
}
}
},
{
"$group": {
"_id": 0,
"data": {
$addToSet: {
"sellerId": "$_id.sellerId",
"sumPrice": "$sumPrice"
}
}
}
}
])
Sample 2 on Mongo Playground
Output
[
{
"_id": 0,
"data": [
{
"sellerId": ObjectId("61307abca667678553be81cb"),
"sumPrice": 4988
}
]
}
]