create table t(
    file_id number primary key,
    file_name varchar2(30),
    parent_file_id references t,
    file_path varchar2(4000) GENERATED ALWAYS AS ('1') VIRTUAL VISIBLE
);
 
 
CREATE OR REPLACE FUNCTION get_path(vfile_id in int)
  return varchar2 deterministic is
  v_res varchar2(255);
begin
  select listagg(file_name, ' / ') within group(order by lvl desc) into v_res
    from (select file_name, level lvl
            from t
          connect by prior t.parent_file_id = t.file_id
           start with t.file_id = vfile_id);
  return v_res;
end;
/

alter table t modify file_path varchar2(4000) GENERATED ALWAYS AS (get_path(file_id)) VIRTUAL VISIBLE;