query.graphql

query {
  user(id: "12345") {
    id
  }
  viewer {
    user {
      id
    }
  }
}

schema.ex

defmodule Schema do
  object :user do
    field :id, non_null(:id)
  end
  
  object :viewer do
    field :user, :user
  end
  
  query do
    field :viewer, :viewer do
      resolve(&Resolvers.Viewer.resolve/3)
    end
    
    field :user, :user do
      arg(:id, non_null(:string))
      resolve(&Resolvers.User.resolve/3)
    end
  end
end