MongoDB nested aggregation based on time values - mongodb

Question

I have a structure like this coming from IOT sensor device
[{
"_id" : ObjectId("5e8e1af3f1563046e084cf65"),
"value" : 462.2382850719,
"start" : 1586293200001,
"year" : 2020,
"month" : "04",
"day" : "07",
"hour" : "21",
"channelId" : 3462
},
{
"_id" : ObjectId("5e8e1af3f1563046e084cf64"),
"value" : 1636.8770905333,
"start" : 1586289600001,
"year" : 2020,
"month" : "04",
"day" : "07",
"hour" : "19",
"channelId" : 3462
},
{
"_id" : ObjectId("5e8e1af3f1563046e084cf63"),
"value" : 1665.4116577475,
"start" : 1586286000001,
"year" : 2020,
"month" : "04",
"day" : "07",
"hour" : "20",
"channelId" : 3462
}]
I want to group this structure first by channelId, then by year,month,day and hour. I want to develop this sort of nested structure
{"channel_id":XXX,"aggregates":[2020:[04:[01:[00:AVG_VALUE,01:AVG_VALUE...],...],...]}
Similar like this
output = [
{
channelId: 3462,
"value": '',
aggregates: [
{
year: 2020,
months: [
{
month: 4,
value: '',
days: [
{
day: 7,
value: '',
hours: [
{ hour: 19, value: '' },
{ hour: 20, value: '' },
{ hour: 21, value: '' }
]
}
]
}
]
}
]
}
]
I can do one level $group by and then push the $$ROOT in it, but don't know how to go nested with groups. Do I have to use reduce logic or any.
Need help

Answer 1

Check if the solution meets your requirements:
db.collection.aggregate([
{
$group: {
_id: {
"channelId": "$channelId",
"year": "$year",
"month": "$month",
"day": "$day",
"hour": "$hour"
},
value: {
$avg: "$value"
}
}
},
{
$group: {
_id: {
"channelId": "$_id.channelId",
"year": "$_id.year",
"month": "$_id.month",
"day": "$_id.day"
},
value: {
$avg: "$value"
},
hours: {
$push: {
hour: "$_id.hour",
value: "$value"
}
}
}
},
{
$group: {
_id: {
"channelId": "$_id.channelId",
"year": "$_id.year",
"month": "$_id.month"
},
value: {
$avg: "$value"
},
days: {
$push: {
day: "$_id.day",
value: "$value",
hours: "$hours"
}
}
}
},
{
$group: {
_id: {
"channelId": "$_id.channelId",
"year": "$_id.year"
},
value: {
$avg: "$value"
},
months: {
$push: {
month: "$_id.month",
value: "$value",
days: "$days"
}
}
}
},
{
$group: {
_id: {
"channelId": "$_id.channelId"
},
channelId: {
$first: "$_id.channelId"
},
value: {
$avg: "$value"
},
aggregates: {
$push: {
year: "$_id.year",
value: "$value",
months: "$months"
}
}
}
},
{
$project: {
_id: 0
}
}
])
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