Update recursive document in MongoDB - mongodb

Question

I have a recursive structure in one of my MongoDB collections, like so:
{
"id": String,
"date": Date,
"text": String
"replies": [{
// Same structure as above
}]
}
I need to update a document in this hierarchy by adding in a reply to a nested document. The guarantees are as follows:
The object to reply to is guaranteed to exist.
The path to the object to which a reply is to be posted is known (i.e., we have a sequence of the _id attributes to navigate).
The recursion depth is not bounded.
Searching SO gives me the following relevant questions:
Querying, 2013 - The recommendation was to switch to a graph DB.
Updating, 2015 - The recommendation was to use the $[] operator.
Based on the latter, my attempt was:
await commCollection.update(
{ _id: topLevel['_id'] },
{
$push: {
'replies.$[].$[comment_arr].replies': {
id: commentId,
text: comment,
date,
replies: []
}
}
},
{ arrayFilters: [{ 'comment_arr.id': responseTo }]}
);
where topLevel is the root document, responseTo is the id attribute of the object to add the reply to. This however, does not seem to work. What am I doing wrong, and how do I achieve this?
Update: An example below. Here's an example of a document from MongoDB Atlas:
{
"_id": {
"$oid": "605fdb8d933c5f50b4d2225e"
},
"id": "mr9pwc",
"username": "recrimination-logistical",
"upvotes": {
"$numberInt": "0"
},
"downvotes": {
"$numberInt": "0"
},
"text": "Top-level comment",
"date": {
"$date": {
"$numberLong": "1616894861300"
}
},
"replies": [{
"id": "dflu1h",
"username": "patrolman-hurt",
"upvotes": {
"$numberInt": "0"
},
"downvotes": {
"$numberInt": "0"
},
"text": "Testing reply level 1!",
"date": {
"$date": {
"$numberLong": "1618387567042"
}
},
"replies": [] // ----> want to add a reply here
}]
}
I've indicated where we want a reply added. responseTo in this case would be dflu1h.

Answer 1

Just need to remove $[] positional
Field name in arrayFilters must be an alphanumeric string beginning with a lowercase letter, Change comment_arr to any alphabets only like commentArr, remove special characters
await commCollection.update(
{ _id: topLevel['_id'] },
{
$push: {
"replies.$[commentArr].replies": {
id: commentId,
text: comment,
date,
replies: []
}
}
},
{ arrayFilters: [{ "commentArr.id": responseTo }] }
)
Playground