Find balance from debit and credit entries mongodb - mongodb

Question

I have a Mongo collection like this:
{
"user_id" : "1",
"branch_id" : "1",
"trans_type":"DEBIT",
"total" : 500
},
{
"user_id" : "1",
"branch_id" : "1",
"trans_type":"CREDIT",
"total" : 200
},
{
"user_id" : "1",
"branch_id" : "3",
"trans_type":"DEBIT",
"total" : 1400
},
{
"user_id" : "2",
"branch_id" : "1",
"trans_type":"DEBIT",
"total" : 100
},
{
"user_id" : "2",
"branch_id" : "1",
"trans_type":"CREDIT",
"total" : 100
}
The expected output is this:
[
{
"user_id":"1",
"branch_id":"1",
"final_balance":"300"
},
{
"user_id":"1",
"branch_id":"3",
"final_balance":"1400"
},
{
"user_id":"2",
"branch_id":"1",
"final_balance":"0"
}
]
Note that in the output I am looking for the final balance after checking out debit and credit entries per user per branch.
Thank you.

Answer 1

That sounds like a simple $group with a $cond would do the job for you:
db.collection.aggregate({
$group: {
"_id": { // group by both fields, "user_id" and "branch_id"
"user_id": "$user_id",
"branch_id": "$branch_id"
},
"final_balance": {
$sum: { // calculate the sum of all "total" values
$cond: {
if: { $eq: [ "$trans_type", "DEBIT" ] }, // in case of "DEBIT", we want the stored value for "total"
then: "$total",
else: { $multiply: [ "$total", -1 ] } // otherwise we want the stored value for "total" times -1
}
}
}
}
}, {
$project: { // this is not really needed unless you specifically need the output format you mentioned in the question
"_id": 0,
"user_id": "$_id.user_id",
"branch_id": "$_id.branch_id",
"final_balance": "$final_balance",
}
})

Answer 2

let docData = await db.Transactions.aggregate(
[{
$match: where(any condition)
},
{
$addFields: {
runningBalance: { $subtract: ['$debit', '$credit'] }
}
},
stage2 = {
$setWindowFields: {
sortBy: { transaction_date: 1 },
output: {
runningTotal: {
$sum: "$runningBalance",
window: {
documents: ["unbounded", "current"]
}
}
}
}
},
{
$sort: sortByObj(any sorted by object)
},
]
);