How to remove related documents after removing by TTL? - mongodb

Question

As part of my MongoDB, I have three different collections - A, B and AtoB.
A and B are different types of entities, where AtoB connects between them as follows-
A:
{
_id: ObjectId,
timestamp: Date,
keyA: string
}
B:
{
_id: ObjectId,
timestamp: Date,
keyB: number
}
AtoB:
{
_id: ObjectId,
aId: ObjectId, // Points to a document from A
bId: ObjectId // Points to a document from B
}
I created a TTL index on A documents - that will be deleted when the timestamp key is older than an hour.
Is it possible somehow to remove all the related AtoB documents, based on the removed _id property of the removed As?
In other words, is it possible to not only remove the A documents using the TTL, but also remove the related documents of the ones the were removed?
Thanks

Answer 1

In a word - no, not in this set up.
The options you have:
set up a changestream worker to delete links
set up a cron job to clean up links collection every minute
embed AtoB links into A documents
I would recommend the later, but it really depends on how feasible the change is for the rest of your application. Having a dedicated lookup collection is really a RDBS practice. It has very niche usecases in Mongo universe.
Your A documents will looks like this:
{
_id: ObjectId,
timestamp: Date,
keyA: string,
bIds: [
bId: ObjectId,
bId: ObjectId,
....
]
}
When the document's ttl expires the document is removed with all links at once.