Add elements in nested document then retrieve the _id - node.js

Question

I have the following collection definition:
// Includes
import mongoose from 'mongoose';
const Schema = mongoose.Schema;
// Create required sub schemas
const subSchema0 = new Schema({
value: String,
});
const subSchema = new Schema({
idWordsLibraryName: {
type: Schema.Types.ObjectId,
ref: 'WordsLibrary1_0',
},
type: String,
values: [
subSchema0,
],
});
const schema = new Schema({
version_: String,
idWordsLibraryName: {
type: Schema.Types.ObjectId,
ref: 'WordsLibrary1_0',
},
idsDads: [{
type: Schema.Types.ObjectId,
ref: 'LocationStructure1_0',
}],
params: [
subSchema,
],
});
Summary -> One document with nested parameters with nested values.
I have the following request that add some values into a particular parameter
this.findOneAndUpdate({
_id: data.idLocationStructure,
'params._id': data.idLocationStructureParameter,
}, {
$push: {
'params.$.values': {
$each: dataToPush,
},
},
}, {
new: true,
});
It works as expected.
What I want now is to get the _id of pushed elements, but without loading all values of the parameter.
I have tried to use the select option of findOneAndUpdate but it don't work using the projection:
this.findOneAndUpdate({
_id: data.idLocationStructure,
'params._id': data.idLocationStructureParameter,
}, {
$push: {
'params.$.values': {
$each: dataToPush,
},
},
}, {
new: true,
select: {
'params.$.values': 1,
},
});
It gets me:
{
"_id": "57273904135f829c3b0739dd",
"params": [
{},
{},
{},
{},
],
},
I have tried to perform a second request to get the _ids as well, but it don't work either:
this.find({
_id: data.idLocationStructure,
'params._id': data.idLocationStructureParameter,
}, {
_id: 1,
'params.$.values': {
$slice: -nbAdded,
},
});
If you have any idea of how retrieving the _id of the pushed values without loading all values of the parameter, you are very welcome :)

Answer 1

Well after tons of researches all over the web and stack overflow <3 I have found a solution, which is:
this.aggregate([{
$match: {
_id: new mongoose.Types.ObjectId(data.idLocationStructure),
},
},
{
$unwind: '$params',
}, {
$match: {
'params._id': new mongoose.Types.ObjectId(data.idLocationStructureParameter),
},
},
{
$unwind: '$params.values',
},
{
$sort: {
'params.values._id': -1
},
},
{
$limit: nbAdded,
},
{
$project: {
_id: '$params.values._id',
},
},
]);
If you experience the same problem, here is the explaination:
$match makes me taking the good high level document
$unwind makes me to go into the params array in the document we $match
$match makes me taking the good parameter
$unwind makes me to go into the values array
I $sort all values by _id DESC
I $limit to the number of values I added previsoulsy
I change the name of the _id (like an alias)
So I got as result an array that contains the last added values _ids