Mongoose how to find object in array - node.js

Question

i have tried a few method but it doesn't work. How to find object from 2 array. My attempt:
Message.find({$and : [{_id : id}, {"users._id" : userID}]})
My Message Schema
const contentSchema = new Schema({
ismy : Boolean,
message : String
},{ timestamps: true });
const receiverSchema = new Schema({
_id : String,
messages : [contentSchema]
});
const messageSchema = new Schema({
_id : String,
users : [receiverSchema]
});
module.exports = mongoose.model('Message',messageSchema);
Returned All document but i want document that is with "_id": "5f38f3574644e92d0cbbc5be",
[
{
"_id": "20860f7806d19d7a29a8addc525f73b5",
"users": [
{
"messages": [
{
"_id": "5f38f3574644e92d0cbbc5be",
"ismy": true,
"message": "aaaa",
"createdAt": "2020-08-16T08:50:31.317Z",
"updatedAt": "2020-08-16T08:50:31.317Z"
},
{
"_id": "5f38f39d4a11553f38da0ec8",
"ismy": true,
"message": "aaaa",
"createdAt": "2020-08-16T08:51:41.093Z",
"updatedAt": "2020-08-16T08:51:41.093Z"
},
{
"_id": "5f38f3a84a11553f38da0eca",
"ismy": true,
"message": "aaaaDASDASDSA",
"createdAt": "2020-08-16T08:51:52.407Z",
"updatedAt": "2020-08-16T08:51:52.407Z"
},
{
"_id": "5f38f3f3cb7eec3ffc61c050",
"ismy": true,
"message": "aaaaDASDASDSA",
"createdAt": "2020-08-16T08:53:07.809Z",
"updatedAt": "2020-08-16T08:53:07.809Z"
},
{
"_id": "5f38f3ffcb7eec3ffc61c053",
"ismy": true,
"message": "hahaha",
"createdAt": "2020-08-16T08:53:19.781Z",
"updatedAt": "2020-08-16T08:53:19.781Z"
}
],
"_id": "9471e1b040fa962df160903066e75778"
},
{
"messages": [],
"_id": "11111111111"
}
],
"__v": 4
}
]

Answer 1

There might be easier ways to do this, but what should work is the following aggregation-pipeline:
const ObjectId = require('mongoose').Types.ObjectId;
const res = await Message.aggregate(Message.aggregate([
{
"$match": {
// set the document id here
_id: id
}
},
{
"$project": {
"filteredMessages": {
"$filter": {
"input": {
"$map": {
"input": "$users",
"as": "user",
"in": {
"messages": {
"$filter": {
"input": "$$user.messages",
"as": "msg",
"cond": {
// need to use ObjectId here, as the messages id's won't be plain string
"$eq": ["$$msg._id", ObjectId("5f38f3574644e92d0cbbc5be")]
}
}
}
}
},
},
"as": "filteredUser",
"cond": {
"$and": [
{"$gt": [{"$size": "$$filteredUser.messages"}, 0]}
]
}
}
}
}
}
]);
What I'm doing here is applying $filter and $map - $map is needed because the inner messages array can change as a result of the filtering, and the users array of course does not match the conditions when the messages-array was changed.