Array of Mongodb Document only show ObjectId - node.js

Question

So I want to update a document in Mongo.
I have a document and I want to modify it and send it back. But for some reason, when I do, it changes the value into ObjectId. And I figured out an alternative, but I don't like it...
async updateDogs() {
const cats = await this.catModel.find().exec();
const dog: DogDocument = await this.dogModel
.findOne({ _id: '62b57f65fa0e953b3e0494eb' })
.populate('cats')
.exec();
console.log('All cats:', cats);
console.log('Dingo Dog in find', dog);
dog.cats = cats;
console.log('Dingo dog in find but with Cat ObjectId()', dog.cats);
console.log(dog.cats[0].name);
dog.cats = [];
dog.cats.push(...cats);
console.log('Dingo dog in find and with cat', dog.cats);
console.log(dog.cats[0].name);
}
And this is the output:
All cats: [
{
_id: new ObjectId("62af2508025adb0b7e6e446f"),
name: 'Mikey',
age: 0,
breed: 'string',
__v: 0
},
{
_id: new ObjectId("62b57fd0fa0e953b3e0494f5"),
name: 'Mini',
age: 0,
breed: 'string',
__v: 0
}
]
Dingo Dog in find {
_id: new ObjectId("62b57f65fa0e953b3e0494eb"),
name: 'Dingo',
age: 0,
__v: 0,
cats: [
{
_id: new ObjectId("62af2508025adb0b7e6e446f"),
name: 'Mikey',
age: 0,
breed: 'string',
__v: 0
}
]
}
Dingo dog in find but with Cat ObjectId() [
new ObjectId("62af2508025adb0b7e6e446f"),
new ObjectId("62b57fd0fa0e953b3e0494f5")
]
First cat name is undefined
Dingo dog in find and with cat [
{
name: 'Mikey',
age: 0,
breed: 'string',
_id: new ObjectId("62af2508025adb0b7e6e446f"),
__v: 0
},
{
name: 'Mini',
age: 0,
breed: 'string',
_id: new ObjectId("62b57fd0fa0e953b3e0494f5"),
__v: 0
}
]
First cat name is Mikey
The way i add cats to dog.cats it change the result.
Do you have any idea why ? I Need to have CatDocument and not ObjectId.
And i can do another populate but i don't want to make another request because i already have it. And use push is ugly i think...