MongoDb : Find and filter values from nested map - mongodb

Question

I have some date in mongo db
[
{
"_id": ObjectId("5a934e000102030405000000"),
"orgId": "606abce197dc265ac41ae82c",
"registrations": {
"id1": {
"status": "status",
"topStage": {
"id": "stage1",
"name": "stage1"
}
},
"id2": {
"status": "status",
"topStage": {
"id": "stage1",
"name": "stage1"
}
},
"id3": {
"status": "status",
"topStage": {
"id": "stage2",
"name": "stage2"
}
}
}
}
]
I am expecting to pass a stage id (at path registrations-> topStage -> id) and return all matching key values.
i have written following query
db.collection.aggregate([
{
$project: {
teams: {
$objectToArray: "$registrations"
},
original: "$$ROOT"
}
},
{
"$project": {
"teams": {
"$filter": {
"input": "$teams",
"as": "team",
"cond": {
"$eq": [
"$$team.v.topStage.id",
"stage1"
]
}
}
}
}
},
{
"$project": {
"registrations": {
"$arrayToObject": "$teams"
}
}
}
])
It does return me right values
for stage1 as stage id
[
{
"_id": ObjectId("5a934e000102030405000000"),
"registrations": {
"id1": {
"status": "status",
"topStage": {
"id": "stage1",
"name": "stage1"
}
},
"id2": {
"status": "status",
"topStage": {
"id": "stage1",
"name": "stage1"
}
}
}
}
]
and for stage2 as stage id, it returns
[
{
"_id": ObjectId("5a934e000102030405000000"),
"registrations": {
"id3": {
"status": "status",
"topStage": {
"id": "stage2",
"name": "stage2"
}
}
}
}
]
Can someone let me know if this is the best way to write this query or this can be simplified ??

Answer 1

It's the correct way to do it but there will be performance impact in the following cases.
If you don't have any other match condition against the indices
if you have a match condition and it matches few docs where registrations has more objects
Other best option you could do is that altering the schema.
you can keep registrations.id1 as registrations : { id:1, status_id: 2}
or you could alter the way such that it will not need to use objectToArray on larger set
if your data is huge, I would recommend to add an index on nested status Id field.
And mongo documentation itself suggests to evaluate multiple schemas for any data to get the best out of it.