MongoDB - group by on facet result - mongodb

Question

Provided I have following collections
Customers
[
{
uuid: "first",
culture: "it-it"
},
{
uuid: "second",
culture: "de-de"
}
]
Vehicles
[
{
model: "mymodel",
users: [
{
uuid: "first",
isOwner: true,
createdOn: "2019-05-15T06: 00: 00"
}
]
},
{
model: "mymodel",
users: [
{
uuid: "first",
isOwner: false,
createdOn: "2019-05-15T06: 00: 00"
},
{
uuid: "second",
isOwner: true,
createdOn: "2019-05-15T06: 00: 00"
}
]
}
]
And following query:
db.customers.aggregate([
{
$lookup: {
from: "vehicles",
let: {
uuid: "$uuid"
},
pipeline: [
{
$match: {
$expr: {
$in: [
"$$uuid",
"$users.uuid"
]
}
}
},
{
$project: {
model: 1,
users: {
$filter: {
input: "$users",
as: "user",
cond: {
$eq: [
"$$user.uuid",
"$$uuid"
]
}
}
}
}
},
{
$unwind: "$users"
},
{
$replaceRoot: {
newRoot: {
isOwner: "$users.isOwner",
createdOn: "$users.createdOn"
}
}
}
],
as: "vehicles"
}
},
{
$facet: {
"createdOn": [
{
$match: {
"vehicles": {
$elemMatch: {
isOwner: true,
$and: [
{
"createdOn": {
$gte: "2019-05-15T00: 00: 00"
}
},
{
"createdOn": {
$lt: "2019-05-16T00: 00: 00"
}
}
]
}
}
}
},
{
$project: {
culture: 1,
count: {
$size: "$vehicles"
}
}
},
{
$group: {
_id: 0,
"total": {
$sum: "$count"
}
}
}
]
}
},
{
$project: {
"CreatedOn": {
$arrayElemAt: [
"$CreatedOn.total",
0
]
}
}
}
])
I get following result:
[
{
"createdOn": 2
}
]
What I would like to achieve is a result as follows:
[
{
culture: "it-it",
results: {
"createdOn": 1
}
},
{
culture: "de-de",
results: {
"createdOn": 1
}
}
]
But I cannot seem to figure out where I can group so that I can get that result.
Can someone show me the way to do this?
The query is more complex with more metrics so this is a trimmed down version of what I have.
I tried grouping everywhere but fail to get the desired result I want.

Answer 1

The following query can get us the expected output:
db.customers.aggregate([
{
$lookup: {
"from": "vehicles",
"let": {
"uuid": "$uuid"
},
"pipeline": [
{
$unwind: "$users"
},
{
$match: {
$expr: {
$and: [
{
$eq: ["$users.uuid", "$$uuid"]
},
{
$eq: ["$users.isOwner", true]
},
{
$gte: ["$users.createdOn", "2019-05-15T00: 00: 00"]
},
{
$lte: ["$users.createdOn", "2019-05-16T00: 00: 00"]
}
]
}
}
},
{
$count:"totalVehicles"
}
],
as: "vehiclesInfo"
}
},
{
$unwind: {
"path": "$vehiclesInfo",
"preserveNullAndEmptyArrays": true
}
},
{
$group: {
"_id": "$culture",
"culture": {
$first: "$culture"
},
"createdOn": {
$sum: "$vehiclesInfo.totalVehicles"
}
}
},
{
$project: {
"_id": 0,
"culture": 1,
"results.createdOn": "$createdOn"
}
}
]).pretty()
Output:
{ "culture" : "de-de", "results" : { "createdOn" : 1 } }
{ "culture" : "it-it", "results" : { "createdOn" : 1 } }