How to create a nested arrays if not exist or add to nested

Working with Data
,
1

I have a schema of this shape

Parent:
{
childs:[ 
subchilds:[]]
}

How can I create the childs and subschilds if not exists
and
add to subchilds if it exists?
I tried running array filters from here but i don’t think it is the correct way to do it

2

How can I also remove both of them when the subchilds has one item to be deleted?

3

Please provide real sample input and resulting documents for all the cases you want.

While it is possible for us to create input documents from your schema, it is a very tedious process for us but should be easy for you since you most likely already have some data.

5

Imagine you want to save offers from different supermarkets
childs-> supermarket
subchilds->offers per supermarket

You save an offer you liked and want to see all saved offers from all supermarkets later.

What I am thinking of:
1-query to check shop existence then

in case shop doesn’t exist:
1-Create it
2-Create an offer inside it
total operations:3
in case shop does exist:
1-Check if offer exists in it
2- Update it
total operations:3

how to reduce the number of operations to do this? Or what is the best approach?