값 타입 컬렉션 중복저장

강의에서 값 타입 컬렉션은 모든 컬럼이 기본키가 되기 때문에 중복저장이 되지 않는다고 하셨는데 중복 저장이 가능하여 문의 드립니다.

public static void main(String[] args) {
  EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
  EntityManager em = emf.createEntityManager();

  EntityTransaction tx = em.getTransaction();
  tx.begin();

  try {
    Address address = new Address("city", "street", "1");

    Member member = new Member();
    member.setUsername("member1");
    member.setWorkAddress(address);

    member.getFavoriteFoods().add("치킨");
    member.getFavoriteFoods().add("피자");

    member.getAddressHistory().add(address);
    member.getAddressHistory().add(address);
    em.persist(member);

    em.flush();
    em.clear();

    System.out.println("=====================");
    Member findMember = em.find(Member.class, member.getId());

    List<Address> addressHistory = findMember.getAddressHistory();
    addressHistory.forEach(Address::getCity);

    Set<String> favoriteFoods = findMember.getFavoriteFoods();
    favoriteFoods.forEach(System.out::println);

    findMember.setHomeAddress(new Address("newCity", address.getStreet(), address.getZipcode()));

    // 치킨 -> 한식
    findMember.getFavoriteFoods().remove("치킨");
    findMember.getFavoriteFoods().add("한식");

    // 주소 변경
    findMember.getAddressHistory().remove(new Address("city", "street", "1"));
    findMember.getAddressHistory().add(new Address("newcity", "new", "100"));

    tx.commit();
  } catch (Exception e) {
    e.printStackTrace();
    tx.rollback();
  } finally {
    em.close();
  }

  emf.close();
}