Hibernate @CreationTimestamp filed is null on findById()

Question

Here is a quick scenario.

Environment

• Java 8
• Spring boot 2.7.5
• Hibernate 5.6.12.Final (comes with spring data JPA)

My Entity

@Entity
@Getter
@Setter
@Table(name = "test_entity")
public class TestEntity {

  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  @Column(insertable = false, updatable = false)
  private UUID id;

  @CreationTimestamp
  @Column(name = "created_at", insertable = false, updatable = false, nullable = false)
  private LocalDateTime createdAt;

}

My Repository

public interface TestEntityRepository extends JpaRepository<TestEntity, UUID> {

}

My Test

@DataJpaTest
@EnableAutoConfiguration
@AutoConfigureTestDatabase(replace = Replace.NONE)
@ContextConfiguration(classes = {TestEntityRepository.class})
@EnableJpaRepositories(basePackages = "...")
@EntityScan(basePackages = "...")
public class TestEntityRepositoryTest {

  @Autowired
  private TestEntityRepository repository;


  @Test
  public void primaryChangeApplied() {

    //given
    TestEntity entity = new TestEntity();
    TestEntity savedEntity = repository.save(entity);

    //when
    Optional<TestEntity> entityOptional = repository.findById(savedEntity.getId());
    //repository.findAll(); -> The trick is here if I uncomment this test is green

    //then
    assertTrue(entityOptional.isPresent());
    TestEntity result = entityOptional.get();
    assertNotNull(result);
    assertNotNull(result.getId());
    assertNotNull(result.getCreatedAt());

  }
}

The problem is that if I uncomment the repository.findAll() test starts to fail with created_at being null.

• I checked that actual data in DB has created_at set correctly

Interestingly if I write any custom method in Repository like TestEntity findByCreatedAt(LocalDateTime createdAt); it mapping createdAt and the test passes.

So its has something to do with finding by id.

---

UPDATE:

I changed save() to saveFlush(), and the test started to pass. Still not clear why.