@AssertTrue(message="Company ID already used. It must be unique")
public boolean isUniqueNifConstraint() {
IExternalCompanyDAO dao = Registry.getExternalCompanyDAO();
if (isNewObject()) {
return !dao.existsByNifInAnotherTransaction(nif);
} else {
try {
ExternalCompany company =
dao.findUniqueByNifInAnotherTransaction(nif);
return company.getId().equals(getId());