Now when I select a specific country I need a related list of towns.
I suggest you to create simple entities for countries and towns. Their association will be “one-to-many”. Then just load towns using simple query like this: select t from app_Town t where t.country = :country.
Another question: is there the generator attribute implemented in Cuba 7?
I suggest you to use the Form component, because FieldGroup is legacy now. The Form component allows you to use pluggable component factories. Please read our documentation for further information