MongoDB addToSet in nested array - mongodb

Question

I'm struggling to insert data inside a nested array in MongoDB.
My schema looks like this:
{
"_id" : ObjectId("5c0c55642440311ff0353846"),
"name" : "Test",
"email" : "test#gmail.com",
"username" : "test",
"password" : "$2a$10$RftzGtgM.DqIiaSvH4LqOO6RnLgQfLY3nk7UIAH4OAvvxo0ZMSaHu",
"created" : ISODate("2018-12-08T23:36:04.464Z"),
"classes" : [
{
"_id" : ObjectId("5c0c556e2440311ff0353847"),
"cName" : "1A",
"student" : [
{
"grades" : [ ],
"_id" : ObjectId("5c0c55812440311ff0353848"),
"name" : "StudentName",
"lname" : "StudenteLastName",
"gender" : "M"
}
insert }
],
"__v" : 0
}.
What I want to do is inserting a grade for the student inside "grades" array.
Expected result is:
{
"_id" : ObjectId("5c0c55642440311ff0353846"),
"name" : "Test",
"email" : "test#gmail.com",
"username" : "test",
"password" : "$2a$10$RftzGtgM.DqIiaSvH4LqOO6RnLgQfLY3nk7UIAH4OAvvxo0ZMSaHu",
"created" : ISODate("2018-12-08T23:36:04.464Z"),
"classes" : [
{
"_id" : ObjectId("5c0c556e2440311ff0353847"),
"cName" : "1A",
"student" : [
{
"grades" : [6],
"_id" : ObjectId("5c0c55812440311ff0353848"),
"name" : "StudentName",
"lname" : "StudenteLastName",
"gender" : "M"
}
]
}
],
"__v" : 0
}.
I tried some queries but none of them helped me, even searching a lot.
db.teachers.update({"_id": ObjectId("5c0c55642440311ff0353846"), "classes._id": ObjectId("5c0c556e2440311ff0353847"), "classes.student._id": ObjectId("5c0c55812440311ff0353848")},{$addToSet: {"classes.$.student.grades":6}})
Basically, I searched for the student with the first curly bracket (if I do "db.teachers.find(the three conditions) the result is correct) and then add to the grades array (of Integer) the value 6. But at this point I get errors, I think I'm making a mistake on the "adding" part.
I need also to do the same thing in Mongoose.
Any help is appreciated, thanks in advance!
Edit: I solved. I post my solution hoping it'll be useful to other:
For pushing inside a triple nested array do:
db.teachers.update({"_id":ObjectId("5c0c59985ae5981c58937e12"),"classes":{ $elemMatch : { _id : ObjectId("5c0c59a35ae5981c58937e13") }},"classes.student": { $elemMatch : { _id : ObjectId("5c0c59aa5ae5981c58937e14")} }},{$addToSet:{"classes.$.student.0.grades":3}})

Answer 1

https://docs.mongodb.com/manual/tutorial/query-array-of-documents/
Try using $elemMatch
"classes":{ $elemMatch : { _id : ObjectId("5c0c556e2440311ff0353847") }},
"classes.student": { $elemMatch : { _id : ObjectId("5c0c55812440311ff0353848")} }