MongoDB: Aggregate with nested $group - node.js

Question

I have the following query:
db.test.aggregate([
{
$match: {
'type': 'energy'
}
},
{
$limit: 10000
},
{
$addFields: {
day: {
$dateToString: {
date: "$when.date",
format: "%d/%m/%Y"
}
},
sensor: "$id"
},
},
{
$project: {
_id: 1,
sensor: 1,
when: 1,
value: 1,
day: 1
}
},
{
$group: {
_id: "$day",
data: {
$push: "$$ROOT"
},
}
},
{
$sort: {
'data': 1
}
}
])
Which returns this data format:
{
"_id" : "05/04/2018",
"data" : [
{
"_id" : ObjectId("5ac66be9b02d5c18fd4106c7"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-05T13:53:22.703-03:00"),
"unix" : 1522947202,
"milli" : 1522947202703
},
"day" : "05/04/2018",
"sensor" : "sen3"
},
{
"_id" : ObjectId("5ac66be9b02d5c18fd4106c8"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-05T13:53:22.705-03:00"),
"unix" : 1522947202,
"milli" : 1522947202705
},
"day" : "05/04/2018",
"sensor" : "sen4"
}
]
},
{
"_id" : "06/04/2018",
"data" : [
{
"_id" : ObjectId("5ac7e5d2efe88a4e76c008d2"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-06T18:25:38.885-03:00"),
"unix" : 1523049938,
"milli" : 1523049938885
},
"day" : "06/04/2018",
"sensor" : "sen3"
},
{
"_id" : ObjectId("5ac7e5e4efe88a4e76c008d5"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-06T18:25:56.105-03:00"),
"unix" : 1523049956,
"milli" : 1523049956105
},
"day" : "06/04/2018",
"sensor" : "sen3"
}
]
},
...
Note that we have in each "data" document, different types of sensors (sen3, sen4, ... ,senN).
I'm trying to aggregate this result once more, agrouping the data by sensor, to get the output something like this:
{
"_id" : "05/04/2018",
"sen3" : [
{
"_id" : ObjectId("5ac66be9b02d5c18fd4106c7"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-05T13:53:22.703-03:00"),
"unix" : 1522947202,
"milli" : 1522947202703
},
"day" : "05/04/2018",
"sensor" : "sen3"
},
{
"_id" : ObjectId("5ac66be9b02d5c18fd4106c7"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-05T13:53:22.703-03:00"),
"unix" : 1522947202,
"milli" : 1522947202703
},
"day" : "05/04/2018",
"sensor" : "sen3"
}
],
"sen4" : [
{
"_id" : ObjectId("5ac66be9b02d5c18fd4106c8"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-05T13:53:22.705-03:00"),
"unix" : 1522947202,
"milli" : 1522947202705
},
"day" : "05/04/2018",
"sensor" : "sen4"
},
{
"_id" : ObjectId("5ac66be9b02d5c18fd4106c8"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-05T13:53:22.705-03:00"),
"unix" : 1522947202,
"milli" : 1522947202705
},
"day" : "05/04/2018",
"sensor" : "sen4"
}
]
},
{
"_id" : "06/04/2018",
"sen3" : [
{
"_id" : ObjectId("5ac7e5d2efe88a4e76c008d2"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-06T18:25:38.885-03:00"),
"unix" : 1523049938,
"milli" : 1523049938885
},
"day" : "06/04/2018",
"sensor" : "sen3"
},
{
"_id" : ObjectId("5ac7e5e4efe88a4e76c008d5"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-06T18:25:56.105-03:00"),
"unix" : 1523049956,
"milli" : 1523049956105
},
"day" : "06/04/2018",
"sensor" : "sen3"
}
],
"sen4": [
{
"_id" : ObjectId("5ac7e7a7efe88a4e76c008de"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-06T18:33:27.365-03:00"),
"unix" : 1523050407,
"milli" : 1523050407365
},
"day" : "06/04/2018",
"sensor" : "sen4"
},
{
"_id" : ObjectId("5ac7e7a7efe88a4e76c008de"),
"value" : 0,
"when" : {
"date" : ISODate("2018-04-06T18:33:27.365-03:00"),
"unix" : 1523050407,
"milli" : 1523050407365
},
"day" : "06/04/2018",
"sensor" : "sen4"
}
]
}
In short: I want to group the data in days, sensors and inside each sensor the results that belongs with that day and sensor.
I'm trying to create a nested $group but in all tentatives it goes wrong.
Is this possible to do and case yes, how?

Answer 1

You can try below aggregation in mongodb 3.6 and above
db.collection.aggregate([
{ "$match": { "type": "energy" }},
{ "$limit": 10000 },
{ "$addFields": {
"day": { "$dateToString": { "date": "$when.date", "format": "%d/%m/%Y" }},
"sensor": "$id"
}},
{ "$project": { "_id": 1, "sensor": 1, "when": 1, "value": 1, "day": 1 }},
{ "$group": {
"_id": { "day": "$day", "sensor": "$sensor" },
"data": { "$push": "$$ROOT" }
}},
{ "$group": {
"_id": { "day": "$_id.day" },
"data": { "$push": { "k": "$_id.sensor", "v": "$data" }}
}},
{ "$addFields": { "data": { "$arrayToObject": "$data" }}},
{ "$replaceRoot": { "newRoot": { "$mergeObjects": [ "$_id", "$data" ] }}}
])