Mongodb aggregation lookup join two collection array of object fields sum of matched object index field - mongodb

Question

I have a two collections "datasets" and "users". I tried to lookup for array of object both collections.
I want to join the "datasets.stateHistory.date" field and "users.prices.date" field. get the result of the datasets collection i want sum of "users.prices.price" sum values
Datasets json Data:
"datasets": [
{
"colorDescription": "braun, rose gold",
"stateHistory": [
{
"state": "scanning",
"date": "2022-02-22T13:06:13.493+00:00"
},
{
"state": "scanned",
"date": "2022-02-18T13:06:13.493+00:00"
},
{
"state": "reconstructing",
"date": "2022-02-16T13:06:13.493+00:00"
}
]
},
{
"colorDescription": "beige, silber",
"stateHistory": [
{
"state": "scanning",
"date": "2022-03-22T13:06:13.493+00:00"
},
{
"state": "scanned",
"date": "2022-03-18T13:06:13.493+00:00"
},
{
"state": "reconstructing",
"date": "2022-03-16T13:06:13.493+00:00"
}
]
}
]
Users json Data:
"users": [
{
"name": "Aravinth",
"prices": [
{
"date": "2022-02-16T13:06:13.493+00:00",
"price": 45
},
{
"date": "2022-03-22T13:06:13.493+00:00",
"price": 55
}
]
},
{
"name": "Raja",
"prices": [
{
"date": "2022-02-24T13:06:13.493+00:00",
"price": 75
},
{
"date": "2022-03-23T13:06:13.493+00:00",
"price": 85
}
]
}
]
Expected result json Data:
[
{
"colorDescription": "braun, rose gold",
"cgPrices: 45,
"stateHistory": [
{
"state": "scanning",
"date": "2022-02-22T13:06:13.493+00:00"
},
{
"state": "scanned",
"date": "2022-02-18T13:06:13.493+00:00"
},
{
"state": "reconstructing",
"date": "2022-02-16T13:06:13.493+00:00"
}
]
},
{
"colorDescription": "beige, silber",
"cgPrices: 0,
"stateHistory": [
{
"state": "scanning",
"date": "2022-03-22T13:06:13.493+00:00"
},
{
"state": "scanned",
"date": "2022-03-18T13:06:13.493+00:00"
},
{
"state": "reconstructing",
"date": "2022-03-16T13:06:13.493+00:00"
}
]
}
]
"cgPrice" field i need to sum of matched prices with date of two collection added.
my code:
db.datasets.aggregate([
{
"$lookup": {
"from": "users",
"as": "details",
"localField": "stateHistory.date",
"foreignField": "prices.date"
}
},
{
"$project": {
color: "$details.colorDescription",
prices: "$details"
}
}
])
How to join the lookup and get prices for matched field add the additional field "cgPrice" count sum.
mongo playground link: https://mongoplayground.net/p/vv8R3DlEDYo

Answer 1

You just need to do quite a lot of restructure, here is an example using the $map, $filter and $reduce operators:
db.datasets.aggregate([
{
"$lookup": {
"from": "users",
"as": "details",
"localField": "stateHistory.date",
"foreignField": "prices.date"
}
},
{
"$project": {
colorDescription: 1,
stateHistory: 1,
prices: {
$sum: {
$map: {
input: {
$filter: {
input: {
$reduce: {
input: {
$map: {
input: "$details",
in: "$$this.prices"
}
},
initialValue: [],
in: {
"$concatArrays": [
"$$this",
"$$value"
]
}
}
},
cond: {
$in: [
"$$this.date",
"$stateHistory.date"
]
}
}
},
in: "$$this.price"
}
}
}
}
}
])
Mongo Playground