final String name = "should_update_existing_entity_with_simplemapper";
Simple simple = new Simple(name);
simple.setEnabled(Boolean.TRUE);
entityManager.persist(simple);
SimpleDto dto = new SimpleDto();
dto.setName(name + "_updated");
dto.setEnabled(Boolean.TRUE);
dto.setId(new SimpleId(simple.getId()));
// when
dtoRepository.save(dto);
Simple lookup = entityManager.find(Simple.class, simple.getId());