// TODO EntityBuilder ???
private Operation buildOperation(User user, String description, Double amount) {
Operation operation = new Operation();
operation.setUser(user);
Set<Account> accounts = user.getAccounts();
Account account = null;
Iterator<Account> iterator = accounts.iterator();
while (iterator.hasNext()) {
account = iterator.next();
}
operation.setAccount(account);
operation.setAmount(amount);
operation.setDescription(description);
operation.setDate(Calendar.getInstance());
return operation;
}