How to group MongoDB data by property? - mongodb

Question

Similar questions have been asked multiple times, but I couldn't find an answer for a problem like mine.
My data looks like this:
{ _id: 1, status: 'unpaid', subtotal: 5000, total: 4750, fees: 250 },
{ _id: 2, status: 'received', subtotal: 5000, total: 4750, fees: 250 },
{ _id: 3, status: 'paidout', subtotal: 5000, total: 4750, fees: 250 },
{ _id: <id>, status: 'paidout', subtotal: 5000, total: 4750, fees: 250 },
{ _id: <id>, status: 'unpaid', subtotal: 5000, total: 4750, fees: 250 }
What I am looking to achieve is, I want to get a sum of total for all records grouped by status and if the status is paidout then the sum will be of subtotal, and also the latest record with the status paidout.
This is my code right now:
const totals = await Payment.aggregate([
{
$match: {
_user: req.user._id,
}
},
{
$group: {
_id: '$status',
total: {
$sum: '$subtotal',
},
paidout: {
$sum: '$total'
},
lastPayout: {
$first: '$total'
}
}
}
])
This is the returned result:
[{ _id: 'paidout', total: 102000, paidout: 97962, lastPayout: 52825 },
{ _id: 'received', total: 60000, paidout: 57630, lastPayout: 57630 }]
Not quite the format I was looking for, so any help would be really appreciated!

Answer 1

Query :
db.collection.aggregate([
/** Checks a conditions and sum-up on either `subtotal` or `total` field */
/** Checks a conditions and adds last doc in iteration if `status is not paidout` then `latestDoc will be null` */
{
$group: {
_id: "$status",
totalAmount: { $sum: { $cond: [ { $eq: [ "$status", "paidout" ] }, "$subtotal", "$total" ] } },
latestDoc: { $last: { $cond: [ { $eq: [ "$status", "paidout" ] }, "$$ROOT", "$$REMOVE" ] } }
}
},
/** stage to remove `latestDoc` field where if it's `null` */
{ $addFields: { latestDoc: { $ifNull: [ "$latestDoc", "$$REMOVE" ] } } }
])
Test : mongoplayground
Note :
Getting the latest document latestDoc is working based on the order documents got inserted. But if your field status gets updated for existing documents then if you wanted to get latest document where status : 'paidout' maintain a timestamp field on which you need to sort prior to $group and then push last document to latestDoc field.