Nested validation for related children

How would you do nested validation for related children?

I want to validate field options under field 1 against field options in field 2.

Show validation message in field option 1 if field option 1 attribute value is not in field option 4/5/6.

• Field 1

  • Field Option 1 - hello
    • error: value hello is not in field option 4/5/6
  • Field Option 2 - foo
  • Field Option 3 - bar

• Field 2

  • Field Option 4 - foo
  • Field Option 5 - bar
  • Field Option 6 - baz

defmodule Helpdesk.FieldOption do
  use Ash.Resource, otp_app: :helpdesk

  actions do
    defaults [:read, create: [:name]]

    update :update do
      primary? true
      accept [:name]

      require_atomic? false
    end

  end

  attributes do
    uuid_primary_key :id

    attribute :name, :string do
      allow_nil? false
      public? true
    end

    timestamps()
  end

  relationships do
    belongs_to :form_field, Helpdesk.FormField
  end

  validations do
    validate fn changeset, context ->
      # ???
      :ok
    end
  end
end