Finding nested array objects with mongoose - mongodb

Question

I have a user collection like this
{
"_id": {
"$oid": "62fe22f5d37c317701922d66"
},
"name": "Fahim Faisal",
"email": "fahim.faisal.abir#gmail.cc",
"password": "$2a$12$bkjeD.GesX4f7BNVF7C0CuKkkTyQA19kv6SAWuhObmPlAB11Tz9dy",
"notes": [],
"folders": [
{
"_id": {
"$oid": "62fe22f5d37c317701922d67"
},
"name": "My Notes",
"notes": []
},
{
"_id": {
"$oid": "62fe22f5d37c317701922d68"
},
"name": "Todos",
"notes": []
},
],
"__v": 0
}
I want to check if an exact item in folders exists or not.
What I have tried so far
User.findOne(
{ _id: req.userId },
{
folders: {
$elemMatch: {
_id,
},
},
},
(err, system) => {
if (err) {
console.log(err);
} else {
console.log(system);
}
}
);
It doesn't return the exact item. It returns this
{
_id: new ObjectId("62faf0c424411076eb9b80e6"),
folders: [
{
_id: new ObjectId("6302110a230f9123c1110273"),
name: 'My Notes',
notes: []
},
{
_id: new ObjectId("6302110a230f9123c1110274"),
name: 'Todos',
notes: []
},
{
_id: new ObjectId("6302110a230f9123c1110275"),
name: 'Projects',
notes: []
},
{
_id: new ObjectId("6302110a230f9123c1110276"),
name: 'Journals',
notes: []
},
{
_id: new ObjectId("6302110a230f9123c1110277"),
name: 'Reading list',
notes: []
}
]
}
What should I do to get the exact item in the folders array exists or not?

Answer 1

Add the $elemMatch filter for folders in the first object parameter, and with $ (projection) to limit and return the first (matched) item of folders array.
Assume that i_d is ObjectId type.
User.findOne(
{
_id: req.userId,
folders: {
$elemMatch: {
_id: _id
}
}
},
{
"folders.$": 1
},
(err, system) => {
if (err) {
console.log(err);
} else {
console.log(system);
}
}
);
Demo # MongoPlayground

Answer 2

You should specify an Id in the elemMatch. For example something like this
User.findOne(
{ _id: req.userId },
{
folders: {
$elemMatch: {
_id:ObjectId('String Id'),
},
},
},
(err, system) => {
if (err) {
console.log(err);
} else {
console.log(system);
}
}
);