Mongodb - Updating nested object array without loosing attributes - mongodb

Question

How do I update or if not existent create a nested object array with one query? The update should only touch existing properties.
So I have a documents structure like this:
[
{
_id: ObjectId("61c296c1fe6de82e5eafd9e1"),
id: 1235,
name: 'Package',
type: 'product',
exampleOuter: 'test1',
size: [
{
length: '10cm',
height: '13cm',
exampleInner: 'test2',
},
{
length: '23cm',
height: '15cm',
exampleInner: 'test3',
}
]
},
...
]
I try to update this given object by the id. Lets assume I have a second object for ease lets call it: "updateObject" and I just want to update those fields from the original object that are existing in the updateObject. If the id is not found in the document than a new object from the updateObject should be created.
[
{
id: 1235,
name: 'Package2',
size: [
{
length: '20cm',
height: '23cm'
},
{
length: '33cm',
height: '25cm'
}
]
}
]
The normal behavior of MongoDB is that the attributes type, exampleOuter are gone in the original object after performing this query since they are not existing in the updateObject. I prevent that from happening by using $setwhich looks like this: {$set: updateObject}. But this doesn't work for the object array in the size attribute. They are all loosing the exampleInner because it is not existing in the updateObject.
I first tried to wrap every object in the size array with a $set to achieve the desired behavior but obv that didn't work.
After reasearch i got the tip using the dot notation and an index. So my updateObject looks like this:
[
{
id: 1235,
name: 'Package2',
size.0.length: '20cm',
size.0.height: '23cm',
size.1.length: '33cm',
size.1.height: '25cm',
}
]
Which works fantastic for the update part but if the id of this new updateObject is not in the document than this will create a new object - which is correct but instead of an array of objects it will create an object with the index 0, 1, ... as the key size.
So the new created document looks like this:
size: {
0: {
length: '10cm',
},
1: {
length: '23cm',
}
}
Am I on the right track with this or is there a complete other way to go? If it's the right approach how do I make sure that the if not existend objects the size attribute is created as an array and not as an object with the key as index?