How to add two collections with single aggregation - mongodb

Question

I am new to MongoDb and would appreciate some help with this query. I wrote the following aggregation pipeline. I wrote the query from collection1 I got the output ("Conventional Energy" : 0.0036) and I wrote the query collection2 I got the output (LastMonthConsumption" : 2.08) but how to add two collection with single aggregation with(LastMonthConsumption" : 2.08 * Conventional Energy" : 0.0036/Conventional Energy" : 0.0036) this is my required output
I have this data in mongodb:
COLLECTION 1:DATA
{
"slcId" : "51",
"clientId" : "1",
"dcuId" : "1",
"type" : "L",
"officeId" : "200-24",
"lampStatus" : "OFF",
"cummulativeKWH" : 133.7,
"powerFactor" : 1.0,
"createDate" : ISODate("2018-09-06T00:01:34.816Z")
},
{
"slcId" : "52",
"clientId" : "1",
"dcuId" : "1",
"type" : "L",
"officeId" : "200-24",
"lampStatus" : "OFF",
"cummulativeKWH" : 133.7,
"powerFactor" : 1.0,
"createDate" : ISODate("2018-09-07T21:01:34.816Z")
}
COLLECTION2:DATA
{
"_class" : "MongoStreetLightMonthlyVo",
"timeId" : ISODate("2018-08-04T16:40:08.817Z"),
"vendor" : "CIMCON",
"slcId" : "123450",
"mongoStreetLightChildVo" : {
"totalConsumptionMtd" : 2.08,
"prevConsumptionMtd" : 3.45,
"perChargeKWH" : 9.85,
}
},
{
"_class" : "MongoStreetLightMonthlyVo",
"timeId" : ISODate("2018-09-04T16:40:08.817Z"),
"vendor" : "CIMCON",
"slcId" : "123450",
"mongoStreetLightChildVo" : {
"totalConsumptionMtd" : 2.08,
"prevConsumptionMtd" : 3.45,
"perChargeKWH" : 9.85,
}
}
Collection1:
db.collection1.aggregate([
{ $match:{"type" : "L"}},
{
$count: "TOTAL_Lights"
},
{ "$project": {
"Conventional Energy": {
"$divide": [
{ "$multiply": [
{ "$multiply": [ "$TOTAL_Lights" ,0.12 ] },
]},
1000
]
}
}},
])
output: {"Conventional Energy" : 0.0036}
Collection2:
db.collection2.aggregate(
[
// Stage 1
{
$group: {
_id:{year:{$year:"$timeId"},month:{$month:"$timeId"} },
LastMonthConsumption : {$sum:"$mongoStreetLightChildVo.totalConsumptionMtd"},
}
},
{
$redact: {
$cond: { if: { $and:[
{$eq: [ "$_id.year", {$year:new Date()} ]},
{$eq: [-1, {$subtract:[ "$_id.month", {$month:new Date()} ]}]}
]},
then: "$$KEEP",
else: "$$PRUNE"
}
}
},
{$project:{
_id:0,
LastMonthConsumption :1
}
}
]
);
output:{
"LastMonthConsumption" : 2.08
}
Expected output:
LastMonthConsumption - Conventional Energy/Conventional Energy*100

Answer 1

You can try below aggregation
db.collection2.aggregate([
{ "$group": {
"_id": { "year": { "$year": "$timeId" }, "month": { "$month": "$timeId" }},
"LastMonthConsumption": { "$sum": "$mongoStreetLightChildVo.totalConsumptionMtd" }
}},
{ "$redact": {
"$cond": {
"if": {
"$and": [
{ "$eq": ["$_id.year", { "$year": new Date() }] },
{ "$eq": [-1, { "$subtract": ["$_id.month", { "$month": new Date() }] }]
}
]
},
"then": "$$KEEP",
"else": "$$PRUNE"
}
}},
{ "$lookup": {
"from": "collection1",
"pipeline": [
{ "$match": { "type": "L" } },
{ "$count": "TOTAL_Lights" },
{ "$project": {
"ConventionalEnergy": {
"$divide": [{ "$multiply": [{ "$multiply": ["$TOTAL_Lights", 0.12] }] }, 1000]
}
}}
],
"as": "ConventionalEnergy"
}},
{ "$project": {
"_id": 0,
"totalConsumption": {
"$multiply": [
{
"$divide": [
{
"$subtract": [
"$LastMonthConsumption",
{ "$arrayElemAt": ["$ConventionalEnergy.ConventionalEnergy", 0] }
]
},
{ "$arrayElemAt": ["$ConventionalEnergy.ConventionalEnergy", 0] }
]
},
100
]
}
}}
])