How to add type extensions in fusion gateway?

[liyanjie2048]

I'm new to learning Hotchocolate Fusion. I want to know how stitch multiple schemas from different service and extend types in this situation:

type User // from A service
{
    Id
    ...
}
type Order // from B service
{
    UserId
    ...
}

I wonder how to add "Orders" to "User" type and "User" to "Order" type and query data.
Is there any way like "AddTypeExtensions" in Stitching Gateway or docs to learn?

[PascalSenn]

@liyanjie2048
In fusion your Order service would have a field called user of type User.
service A

type User
{
    id: ID!
    name: String
}

serivce b

type Order
{
    id: ID!
    user: User
}
type User
{
    id: ID!
    name: String
}