possible to apply filter on root object and on leaf ?

[Hashtagin]

Hi,
I need some helps to create query.
If we reuse the tutorial schema :

type Launch {
id: ID!
site: String
mission: Mission
rocket: Rocket
isBooked: Boolean!
}

type Rocket {
id: ID!
name: String
type: String
}

type Mission {
name: String
missionPatch(size: PatchSize): String
}

I would like to write a query that is able to filter on two fields, one in root, one in the leaf, for example :

type query{
launch( launchsite : String!, rocketType: String! ) : [Launch]
}
The aim is answering the question : " what are the launches on site "A" with rocket type "x" ?
How to write it, behind, if launch, rocket, and mission comes from differents RestDatasources ? I'm thinking of adding them in context but not sure that will work.

Thanks you for your help.