MongoDB aggregate nested grouping - mongodb

Question

I have Asset collection which has data like
{
"_id" : ObjectId("5bfb962ee2a301554915"),
"users" : [
"abc.abc#abc.com",
"abc.xyz#xyz.com"
],
"remote" : {
"source" : "dropbox",
"bytes" : 1234
}
{
"_id" : ObjectId("5bfb962ee2a301554915"),
"users" : [
"pqr.pqr#pqr.com",
],
"remote" : {
"source" : "google_drive",
"bytes" : 785
}
{
"_id" : ObjectId("5bfb962ee2a301554915"),
"users" : [
"abc.abc#abc.com",
"abc.xyz#xyz.com"
],
"remote" : {
"source" : "gmail",
"bytes" : 5647
}
What I am looking for is group by users and get the total of bytes according to its source like
{
"_id" : "abc.abc#abc.com",
"bytes" : {
"google_drive": 1458,
"dropbox" : 1254
}
}
I am not getting how to get the nested output using grouping.
I have tried with the query
db.asset.aggregate(
[
{$unwind : '$users'},
{$group:{
_id:
{'username': "$users",
'source': "$remote.source",
'total': {$sum: "$remote.bytes"}} }
}
]
)
This way I am getting the result with the repeated username.

Answer 1

With MongoDb 3.6 and newer, you can leverage the use of $arrayToObject operator within a $mergeObjects expression and a $replaceRoot pipeline to get the desired result.
You would need to run the following aggregate pipeline though:
db.asset.aggregate([
{ "$unwind": "$users" },
{ "$group": {
"_id": {
"users": "$users",
"source": "$remote.source"
},
"totalBytes": { "$sum": "$remote.bytes" }
} },
{ "$group": {
"_id": "$_id.users",
"counts": {
"$push": {
"k": "$_id.source",
"v": "$totalBytes"
}
}
} },
{ "$replaceRoot": {
"newRoot": {
"$mergeObjects": [
{ "bytes": { "$arrayToObject": "$counts" } },
"$$ROOT"
]
}
} },
{ "$project": { "counts": 0 } }
])
which yields
/* 1 */
{
"bytes" : {
"gmail" : 5647.0,
"dropbox" : 1234.0
},
"_id" : "abc.abc#abc.com"
}
/* 2 */
{
"bytes" : {
"google_drive" : 785.0
},
"_id" : "pqr.pqr#pqr.com"
}
/* 3 */
{
"bytes" : {
"gmail" : 5647.0,
"dropbox" : 1234.0
},
"_id" : "abc.xyz#xyz.com"
}
using the above sample documents.

Answer 2

You have to use $group couple of times here. First with the users and the source and count the total number of bytes using $sum.
And second with the users and $push the source and the bytes into an array
db.collection.aggregate([
{ "$unwind": "$users" },
{ "$group": {
"_id": {
"users": "$users",
"source": "$remote.source"
},
"bytes": { "$sum": "$remote.bytes" }
}},
{ "$group": {
"_id": "$_id.users",
"data": {
"$push": {
"source": "$_id.source",
"bytes": "$bytes"
}
}
}}
])
And even if you want to convert the source and the bytes into key value format then replace the last $group stage with the below two stages.
{ "$group": {
"_id": "$_id.users",
"data": {
"$push": {
"k": "$_id.source",
"v": "$bytes"
}
}
}},
{ "$project": {
"_id": 0,
"username": "$_id",
"bytes": { "$arrayToObject": "$data" }
}}