Mongodb aggregation pipeline, combine result from two facet pipeline - mongodb

Question

I'm having a claim type:
type TClaim: {
insuredId: number,
treatmentInfo: { amount: number }[]
}
and a list of claims:
[
{
insuredId: 1,
treatmentInfo: [{amount: 1}, {amount: 2}]
},
{
insuredId: 1,
treatmentInfo: [{amount: 3}, {amount: 4}]
},
{
insuredId: 2,
treatmentInfo: [{amount: 1}, {amount: 2}]
}
]
I want to get the result like:
[{insuredId: 1, numberOfClaims: 2, amount: 10},{insuredId: 2, numberOfClaims: 1, amount: 3}]
I'm using the $facet operator in mongodb aggregation, one for counting numberOfClaims and one for calculating the amount of each insurer. But I can't combine it to get the result that I want.
$facet: {
totalClaims: [ { $group: { _id: '$insuredId', totalClaims: { $count: {} } } } ],
amount: [ { $unwind: { path: '$treatmentInfo'}},
{ $group:
{ _id: '$insuredId',
amount: { $sum: '$treatmentInfo.amount',
},
},
},
]

Answer 1

Is there a reason why you want to use $facet? - I am just curious
You just need to add a new fields that sums up all the amount in the array first and then do a group stage by insuredId. The query is pretty much self-explanatory.
db.collection.aggregate([
{
"$addFields": {
"totalAmount": {
"$sum": "$treatmentInfo.amount"
}
}
},
{
"$group": {
"_id": "$insuredId",
"numberOfClaims": {
"$sum": 1
},
"amount": {
"$sum": "$totalAmount"
}
}
}
])
Result:
[
{
"_id": 1,
"amount": 10,
"numberOfClaims": 2
},
{
"_id": 2,
"amount": 3,
"numberOfClaims": 1
}
]
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