Accessing nested documents within nested documents - mongodb

Question

I'm having a problem that is really bugging me. I don't even want to use this solution I don't think but I want to know if there is one.
I was creating a comment section with mongodb and mongoose and keeping the comments attached to the resource like this:
const MovieSchema = new mongoose.Schema({
movieTitle: {type: String, text: true},
year: Number,
imdb: String,
comments: [{
date: Date,
body: String
}]
})
When editing the comments body I understood I could access a nested document like this:
const query = {
imdb: req.body.movie.imdb,
"comments._id": new ObjectId(req.body.editedComment._id)
}
const update = {
$set: {
"comments.$.body": req.body.newComment
}
}
Movie.findOneAndUpdate(query, update, function(err, movie) {
//do stuff
})
I then wanted to roll out a first level reply to comments, where every reply to a comment or to another reply just appeared as an array of replies for the top level comment (sort of like Facebook, not like reddit). At first I wanted to keep the replies attached to the comments just as I had kept the comments attachted to the resource. So the schema would look something like this:
const MovieSchema = new mongoose.Schema({
movieTitle: {type: String, text: true},
year: Number,
imdb: String,
comments: [{
date: Date,
body: String,
replies: [{
date: Date,
body: String
}]
}]
})
My question is how would you go about accessing a nested nested document. For instance if I wanted to edit a reply it doesn't seem I can use two $ symbols. So how would I do this in mongodb, and is this even possible?
I'm pretty sure I'm going to make Comments have its own model to simplify things but I still want to know if this is possible because it seems like a pretty big drawback of mongodb if not. On the other hand I'd feel pretty stupid using mongodb if I didn't figure out how to edit a nested nested document...

Answer 1

according to this issue: https://jira.mongodb.org/browse/SERVER-27089
updating nested-nested elements can be done this way:
parent.update({},
{$set: {“children.$[i].children.$[j].d”: nuValue}},
{ arrayFilters: [{ “i._id”: childId}, { “j._id”: grandchildId }] });
this is included in MongoDB 3.5.12 development version, in the MongoDB 3.6 production version.
according to https://github.com/Automattic/mongoose/issues/5986#issuecomment-358065800 it's supposed to be supported in mongoose 5+
if you're using an older mongodb or mongoose versions, there are 2 options:
find parent, edit result's grandchild, save parent.
const result = await parent.findById(parentId);
const grandchild = result.children.find(child => child._id.equals(childId))
.children.find(grandchild => grandchild._id.equals(grandchildId));
grandchild.field = value;
parent.save();
know granchild's index "somehow", findByIdAndUpdate parent with:
parent.findByIdAndUpdate(id,
{ $set: { [`children.$.children.${index}.field`]: value }});