Flush ve SQL Sırası — save() Satırında Neden Hiçbir Şey Olmuyor?

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// A customer's saved payees: unique (customer_id, iban).
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@Service
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class PayeeService {
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    private final PayeeRepository payees;
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    PayeeService(PayeeRepository payees) {
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        this.payees = payees;
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    }
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    // Preferred: one UPDATE, no ordering question at all.
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    @Transactional
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    public void rename(long payeeId, String nickname) {
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        payees.findById(payeeId).orElseThrow().rename(nickname);
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    }
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    // When a delete-then-insert is truly needed (the payee changed hands and must
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    // lose its history, e.g. an account closed and reopened under a new owner):
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    @Transactional
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    public long replace(long oldId, long customerId, String iban, String name) {
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        payees.deleteById(oldId);
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        payees.flush();                  // DELETE goes now; flush order would put INSERT first
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        return payees.save(new Payee(customerId, iban, name)).getId();
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    }
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}

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@Service
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class LoanContracts {
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    private final LoanContractRepository contracts;
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    LoanContracts(LoanContractRepository contracts) {
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        this.contracts = contracts;
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    }
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    @Transactional
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    public LoanContract open(String contractNo, long customerId, BigDecimal principal) {
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        try {
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            // Flush here so a duplicate contract number fails on THIS line, not at commit.
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            return contracts.saveAndFlush(LoanContract.open(contractNo, customerId, principal));
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        } catch (DataIntegrityViolationException ex) {
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            // The transaction is now rollback-only; do not keep using it.
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            // Translate and rethrow: the caller sees a domain error, the TX rolls back.
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            throw new DuplicateContractNumberException(contractNo, ex);
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        }
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    }
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}

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interface LoanContractRepository extends JpaRepository<LoanContract, Long> {
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    // Called inside the loop that restructures a customer's loans, which modifies
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    // other entities. With AUTO, every call would flush and dirty-check the whole
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    // persistence context first. This query does not depend on those pending
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    // changes, so it may skip the flush.
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    @QueryHints(@QueryHint(name = "org.hibernate.flushMode", value = "COMMIT"))
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    @Query("select count(c) from LoanContract c where c.customerId = :customerId and c.status = 'ACTIVE'")
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    long countActiveFor(long customerId);
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}

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@RestControllerAdvice
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class LoanErrors {
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    @ExceptionHandler(DuplicateContractNumberException.class)
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    ProblemDetail duplicate(DuplicateContractNumberException ex) {
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        ProblemDetail problem = ProblemDetail.forStatusAndDetail(HttpStatus.CONFLICT,
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                "Bu sözleşme numarası zaten kullanılıyor: " + ex.contractNo());
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        problem.setTitle("Sözleşme numarası çakışması");
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        return problem;
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    }
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}

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logging:
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  level:
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    org.hibernate.SQL: DEBUG              # every statement, in the order it is sent
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    org.hibernate.orm.jdbc.bind: TRACE    # with its parameter values: never in production,
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                                          # it would write IBANs and amounts into the logs

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@DataJpaTest
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@Import(PayeeService.class)
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class PayeeReplaceTest {
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    private static final String IBAN = "TR330006100519786457841326";
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    @Autowired PayeeService service;
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    @Autowired PayeeRepository payees;
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    @Autowired TestEntityManager em;
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    @Test
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    void deleteThenInsertWithoutFlushHitsTheUniqueConstraint() {
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        long id = em.persistAndGetId(new Payee(7L, IBAN, "Ev sahibi"), Long.class);
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        em.flush();
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        payees.deleteById(id);
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        payees.save(new Payee(7L, IBAN, "Yeni ev sahibi"));
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        // Flush order: INSERT before DELETE -> the old row still holds (7, IBAN).
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        assertThatThrownBy(() -> em.flush())
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                .isInstanceOf(org.hibernate.exception.ConstraintViolationException.class);
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    }
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    @Test
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    void replaceFlushesInBetween() {
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        long id = em.persistAndGetId(new Payee(8L, IBAN, "Ev sahibi"), Long.class);
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        em.flush();
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        assertThatCode(() -> {
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            service.replace(id, 8L, IBAN, "Yeni ev sahibi");
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            em.flush();
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        }).doesNotThrowAnyException();
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    }
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}