MongoDB Nested GroupBy - mongodb

Question

I have a sample data like below:
(Every floor has multiple sensor data)
{"Floor_Id": "Galileo_001",
"name": "Forklifts",
"Sensor_data": [{
"Floor_Id": "Galileo_001",
"Floor_name": "Forklifts",
"Name": "forkLift_002",
"Asset_Id": 123,
"Load": 1.7096133,
"Timestamp": 1537878750996
},
{
"Floor_Id": "Galileo_001",
"Floor_name": "Forklifts",
"Name": "forkLift_003",
"Asset_Id": 456,
"Load": 1.7096133,
"Timestamp": 1537878750996,
},
{
"Floor_Id": "Galileo_001",
"Floor_name": "Forklifts",
"Name": "forkLift_005 ",
"Asset_Id": 127,
"Load": 1.7096133,
"Timestamp": 1537878750996
},
{
"Floor_Id": "Galileo_001",
"Floor_name": "Forklifts",
"Name": "forkLift_001",
"Asset_Id": 157,
"Load": 1.7096133,
"Timestamp": 1537878750996,
}
]}
For the response, I need total load calculated for every floor and individual load for every day. The desired response is like below:
{
"TotalLoad": 3214,
"Floor_Id": "Galileo_001",
"LoadUnit": "Kgs",
"AssetStatus": [{
"TotalLoad": 200,
"LoadUnit": "Kgs",
"Date": "1539588994"
}, {
"TotalLoad": 400,
"LoadUnit": "Kgs",
"Date": "1539475200"
}, {
"TotalLoad": 100,
"LoadUnit": "Kgs",
"Date": "1539388800"
}]
}
I am writing the below Mongo aggregation:
db.sensordata.aggregate([{"$unwind" : "$Sensor_data" },
{"$group": {
"_id": {"Floor_Id": "$Floor_Id",
"DailyDate":{"$dateFromParts":{
"year":{"$year":{"$add": [new Date("1970-01-01"), "$Sensor_data.Timestamp"]}},
"month":{"$month":{"$add": [new Date("1970-01-01"), "$Sensor_data.Timestamp"]}},
"day":{"$dayOfMonth":{"$add": [new Date("1970-01-01"), "$Sensor_data.Timestamp"]}}
}
}
},
"AssetLoad": {"$sum": "$Sensor_data.Load" }
}
},
{
"$group" : {
"_id": {"Floor_Id": "$_id.Floor_Id"},
"TotalLoad": { "$sum": "$Sensor_data.Load" },
"AssetStatus":{
"$push":{
"TotalLoad": "$AssetLoad",
"LoadUnit": "Kgs",
"Date": "$_id.DailyDate"
}
}
}
}
])
Problem:
For the total load calculated for every floor, I am getting 0.
{
"_id" : {
"Floor_Id" : "Galileo_001"
},
"TotalLoad" : 0,
"AssetStatus" : [
{
"TotalLoad" : 8.5480665,
"LoadUnit" : "Kgs",
"Date" : ISODate("2018-09-25T00:00:00.000Z")
}
]
}
What am I doing wrong here?
How can I get the desired output?

Answer 1

You're getting zero because the second $group pipeline does not recognise the field Sensor_data.Load so it defaults to 0.
Replace the expression
"TotalLoad": { "$sum": "$Sensor_data.Load" },
with the pipeline-changed field AssetLoad
"TotalLoad": { "$sum": "$AssetLoad" },
To calculate the number of sensors each floor has in total, your first pipeline needs to calculate the size of the
sensor data using $size, store that in a new field using $addFields then retain the field in the preceding pipeline stages pipelines by using the $first operators.audit
Amend your pipeline to the following:
db.sensordata.aggregate([
{ "$addFields": {
"TotalSensors": { "$size": "Sensor_data" }
} },
{"$unwind" : "$Sensor_data" },
{ "$group": {
"_id": {
"Floor_Id": "$Floor_Id",
"DailyDate": {
"$dateFromParts": {
"year": { "$year": {
"$add": [new Date("1970-01-01"), "$Sensor_data.Timestamp"]
} },
"month": { "$month": {
"$add": [new Date("1970-01-01"), "$Sensor_data.Timestamp"]
} },
"day": { "$dayOfMonth": {
"$add": [new Date("1970-01-01"), "$Sensor_data.Timestamp"]
} }
}
}
},
"AssetLoad": {"$sum": "$Sensor_data.Load" },
"TotalSensors": { "$first": "$TotalSensors" }
} },
{ "$group" : {
"_id": {"Floor_Id": "$_id.Floor_Id"},
"TotalLoad": { "$sum": "$Sensor_data.Load" },
"AssetStatus":{
"$push": {
"TotalLoad": "$AssetLoad",
"LoadUnit": "Kgs",
"Date": "$_id.DailyDate"
}
},
"TotalSensors": { "$first": "$TotalSensors" }
} }
])