How to group documents in mongodb and project _id as different name? - node.js

Question

db.getCollection("analytics").aggregate(
[
{
"$match" : {
"uID" : {
"$in" : [
"202003008",
"20200306"
]
},
"midNightTimeStamp" : {
"$gte" : ISODate("2022-03-26T18:30:00.000+0000")
}
}
},
{
"$group" : {
"_id" : "$midNightTimeStamp",
"energyConsumed" : {
"$sum" : "$energyConsumed"
},
}
},
{
"$project" : {
"midNightTimeStamp" : 1.0, // I also want to project with a different name.
"energyConsumed" : 1.0
}
}
],
{
"allowDiskUse" : false
}
);
As shown in the above query I want to project a field as midNightTimeStamp which is same as _id (accumulator object) so that when I receive the documents, I get it something as
{
midNightTimeStamp: ISODate("2022-03-26T18:30:00.000+0000"),
energyConsumed: 100
}

Answer 1

If I've understood correctly you only need to do this:
{
"$project" : {
"_id": 0, // Not output the "real" _id
"midNightTimeStamp" : "$_id", // output _id value with name "midNightTimeStamp"
"energyConsumed" : 1.0
}
}
Example here

Answer 2

It can be achieved by adding a field in project stage as
"$project" : {
"_id" : 0.0,
"midNightTimeStamp" : "$_id", // This will be added.
"energyConsumed" : 1.0
}
Which will result to the following query:
db.getCollection("analytics").aggregate(
[
{
"$match" : {
"uID" : {
"$in" : [
"202003008",
"20200306"
]
},
"midNightTimeStamp" : {
"$gte" : ISODate("2022-03-26T18:30:00.000+0000")
}
}
},
{
"$group" : {
"_id" : "$midNightTimeStamp",
"energyConsumed" : {
"$sum" : "$energyConsumed"
}
}
},
{
"$project" : {
"_id" : 0.0,
"midNightTimeStamp" : "$_id",
"energyConsumed" : 1.0
}
}
],
{
"allowDiskUse" : false
}
);