Mongodb multi level aggregation - mongodb

Question

Data in mongo
[{
"_id": "5d71d1432f7c8151c58c4481",
"payment": {
"transactions": [
{
"_id": "5d71d1ff2f7c8151c58c44cf",
"method": "paytm",
"amount": 100,
"paymentOn": "2019-09-06T03:26:44.959Z"
},
{
"_id": "5d71d1ff2f7c8151c58c44ce",
"method": "cash",
"amount": 650,
"paymentOn": "2019-09-06T03:26:55.531Z"
}
],
"status": "partial"
},
"customer": "5d66c434c24f2b1fb6772014",
"order": {
"orderNumber": "WP-ORD-06092019-001",
"total": 770,
"balance": 20
}
},
{
"_id": "5d71d1432f7c8151c58c4481",
"payment": {
"transactions": [
{
"_id": "5d71d1ff2f7c8151c58c44cf",
"method": "paytm",
"amount": 100,
"paymentOn": "2019-09-06T03:26:44.959Z"
}
],
"status": "partial"
},
"customer": "5d66c434c24f2b1fb6772014",
"order": {
"orderNumber": "WP-ORD-06092019-001",
"total": 200,
"balance": 100
}
}]
I want to aggregate payments by method.
So the result would look like below:
Output:
Paytm: 200
Cash : 650
Unpaid(Balance): 120
I have tried:
[
{
'$unwind': {
'path': '$payment.transactions',
'preserveNullAndEmptyArrays': true
}
}, {
'$project': {
'amount': '$payment.transactions.amount',
'method': '$payment.transactions.method'
}
}, {
'$group': {
'_id': '$method',
'amount': {
'$sum': '$amount'
}
}
}
]
But how to include balance calculation as well

Answer 1

Using the above dataset, use the aggregate pipeline for calculation using aggregate as:
db.collection.aggregate([
{
$facet: {
paidAmounts: [
{ '$unwind': { 'path': '$payment.transactions', 'preserveNullAndEmptyArrays': true } },
{
$group: {
_id: "$payment.transactions.method",
amount: {
$sum: "$payment.transactions.amount"
}
}
}
],
leftAmounts: [
{
$group: {
_id: null,
balance: {
$sum: "$order.balance"
}
}
}
]
}
}
])
giving output:
here leftAmounts has left balance and paidAmounts having grouped paid data on basis of payment type
[
{
"leftAmounts": [
{
"_id": null,
"balance": 120
}
],
"paidAmounts": [
{
"_id": "cash",
"amount": 650
},
{
"_id": "paytm",
"amount": 200
}
]
}
]

Answer 2

Working solution : https://mongoplayground.net/p/7IWELKKMsWe
db.collection.aggregate([
{
"$unwind": "$payment.transactions"
},
{
"$group": {
"_id": "$_id",
"balance": {
"$first": "$order.balance"
},
"paytm": {
"$sum": {
"$cond": [
{
"$eq": [
"$payment.transactions.method",
"paytm"
]
},
"$payment.transactions.amount",
0
]
}
},
"cash": {
"$sum": {
"$cond": [
{
"$eq": [
"$payment.transactions.method",
"cash"
]
},
"$payment.transactions.amount",
0
]
}
}
}
},
{
"$group": {
"_id": null,
"balance": {
"$sum": "$balance"
},
"cash": {
"$sum": "$cash"
},
"paytm": {
"$sum": "$paytm"
}
}
}
])