How to query for sub-document in an array with Mongoose - node.js

Question

I have a Schema of Project that looks like this:
const ProjectSchema = new mongoose.Schema({
name: {
type: String,
Required: true,
trim: true
},
description: {
type: String,
},
devices: [{
name: {type: String, Required: true},
number: {type: String, trim: true},
deck: {type: String},
room: {type: String},
frame: {type: String}
}],
cables: {
type: Array
},
user: {
type: mongoose.Schema.Types.ObjectId,
ref: 'User'
},
adminsID: {
type: Array
},
createdAt: {
type: Date,
default: Date.now
}
I want to query an object from array of "devices".
I was able to add, delete and display all sub-documents from this array but I found it really difficult to get single object that matches _id criteria in the array.
The closest I got is this (I'm requesting: '/:id/:deviceID/edit' where ":id" is Project ObjectId.
let device = await Project.find("devices._id": req.params.deviceID).lean()
console.log(device)
which provides me with below info:
[
{
_id: 6009cfb3728ec23034187d3b,
cables: [],
adminsID: [],
name: 'Test project',
description: 'Test project description',
user: 5fff69af08fc5e47a0ce7944,
devices: [ [Object], [Object] ],
createdAt: 2021-01-21T19:02:11.352Z,
__v: 0
}
]
I know this might be really trivial problem, but I have tested for different solutions and nothing seemed to work with me. Thanks for understanding

Answer 1

This is how you can filter only single object from the devices array:
Project.find({"devices._id":req.params.deviceID },{ name:1, devices: { $elemMatch:{ _id:req.params.deviceID } }})

Answer 2

You can use $elemMatch into projection or query stage into find, whatever you want it works:
db.collection.find({
"id": 1,
"devices": { "$elemMatch": { "id": 1 } }
},{
"devices.$": 1
})
or
db.collection.find({
"id": 1
},
{
"devices": { "$elemMatch": { "id": 1 } }
})
Examples here and here
Using mongoose is the same query.
yourModel.findOne({
"id": req.params.id
},
{
"devices": { "$elemMatch": { "id": req.params.deviceID } }
}).then(result => {
console.log("result = ",result.name)
}).catch(e => {
// error
})

Answer 3

You'll need to use aggregate if you wish to get the device alone. This will return an array
Project.aggregate([
{ "$unwind": "$devices" },
{ "$match": { "devices._id": req.params.deviceID } },
{
"$project": {
name: "$devices.name",
// Other fields
}
}
])
You either await this or use .then() at the end.
Or you could use findOne() which will give you the Project + devices with only a single element
Or find, which will give you an array of object with the _id of the project and a single element in devices
Project.findOne({"devices._id": req.params.deviceID}, 'devices.$'})
.then(project => {
console.log(project.devices[0])
})

Answer 4

For now I worked it around with:
let project = await Project.findById(req.params.id).lean()
let device = project.devices.find( _id => req.params.deviceID)
It provides me with what I wanted but I as you can see I request whole project. Hopefuly it won't give me any long lasting troubles in the future.