Mongodb join multiple group of values - mongodb

Question

Hello I'm starting to learn mongoDB query
I have some understanding problems with aggregate
For example, I have these documents:
[
{
totalTaxInclusive: 15,
totalTaxExclusive: 12.5,
payments:[{
method: "CB",
amount: 10
},
{
method: "CASH",
amount: 5
}
],
},
{
totalTaxInclusive: 40,
totalTaxExclusive: 33.33,
payments:[{
method: "CB",
amount: 40
}
],
},
]
and so on.
How can I make a request, who I will have a:
$group: {
_id: "$payments.method",
amount: { $sum: "$payments.amount"},
}
and a
$group: {
_id: null,
totalCount: { $sum: 1 },
totalTaxInclusive: { $sum: "$totalTaxInclusive"},
totalTaxExclusive: { $sum:"$totalTaxExclusive" },
}
To have a result of something like:
{
totalCount: 2,
totalTaxInclusive: 55,
totalTaxExclusive: 45.83,
payments: [{
method: "CASH",
amount: 5,
},
{
method: "CB",
amount: 50,
}
]
}
Thanks a lot for your help.

Answer 1

$group by null and get the sum of required fields, construct the array of payments
$concatArrays to concat arrays
$reduce to concat nested array of payments to array
$unwind deconstruct payments array
$group by method and get the sum of amount and get required fields first value
$group by null and construct the array of payments and get count fields first value
db.collection.aggregate([
{
$group: {
_id: null,
totalTaxInclusive: { $sum: "$totalTaxInclusive" },
totalTaxExclusive: { $sum: "$totalTaxExclusive" },
totalCount: { $sum: 1 },
payments: { $push: "$payments" }
}
},
{
$addFields: {
payments: {
$reduce: {
input: "$payments",
initialValue: [],
in: { $concatArrays: ["$$this", "$$value"] }
}
}
}
},
{ $unwind: "$payments" },
{
$group: {
_id: "$payments.method",
amount: { $sum: "$payments.amount" },
totalTaxInclusive: { $first: "$totalTaxInclusive" },
totalTaxExclusive: { $first: "$totalTaxExclusive" },
totalCount: { $first: "$totalCount" }
}
},
{
$group: {
_id: null,
totalTaxInclusive: { $first: "$totalTaxInclusive" },
totalTaxExclusive: { $first: "$totalTaxExclusive" },
totalCount: { $first: "$totalCount" },
payments: {
$push: {
method: "$_id",
amount: "$amount"
}
}
}
}
])
Playground

Answer 2

First stage to group all documents and store their data in relevant arrays. Also count all documents in this stage.
Second stage to sum all items in totalTaxExclusive and totalTaxInclusive arrays
Third and forth stage to unwind payments because it is an array of arrays
Forth stage to group by payment_method and to get total sum by each payment_method
Fifth stage to output result in requested format
db.collection.aggregate([
{
"$group": {
"_id": null,
"totalTaxInclusive": {
"$addToSet": "$totalTaxInclusive"
},
"totalTaxExclusive": {
"$addToSet": "$totalTaxExclusive"
},
"payments": {
"$addToSet": "$payments"
},
"count": {
"$sum": 1
}
}
},
{
"$set": {
"totalTaxExclusive": {
"$sum": "$totalTaxExclusive"
},
"totalTaxInclusive": {
"$sum": "$totalTaxInclusive"
}
}
},
{
"$unwind": "$payments"
},
{
"$unwind": "$payments"
},
{
"$group": {
"_id": "$payments.method",
"amount": {
"$sum": "$payments.amount"
},
"totalTaxInclusive": {
"$first": "$totalTaxInclusive"
},
"totalTaxExclusive": {
"$first": "$totalTaxExclusive"
},
"count": {
"$first": "$count"
}
}
},
{
"$group": {
"_id": null,
"payments": {
"$addToSet": {
"method": "$_id",
"amount": "$amount"
}
},
"totalTaxInclusive": {
"$first": "$totalTaxInclusive"
},
"totalTaxExclusive": {
"$first": "$totalTaxExclusive"
},
"count": {
"$first": "$count"
}
}
}
])
Working example