yannbriancon

List<Message> getAllBy() {
  CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
  
  CriteriaQuery<Message> query = criteriaBuilder.createQuery(Message.class);
  Root<Message> message = query.from(Message.class);
  // Add fetching of the author field
  message.fetch(Message_.author, JoinType.LEFT);
  query.select(message);
  
  TypedQuery<Message> typedQuery = entityManager.createQuery(query);

yannbriancon

void logMessages() {
    // Get all the messages from the database
    // -> Triggers 1 query
    Set<Message> messages = messageDao.findAll();
    
    // Map through the N messages to create the DTO with the author display name
    // -> Triggers 1 query to fetch each author so N queries!
    messages.stream.map(
        message -> logger.info(
            message.getAuthor().getName() + ": " + message.getText()

yannbriancon

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
  @EntityGraph(attributePaths = {"messages"})
  List<User> findTop5By();

  // JPQL does not support LIMIT
  // We need to use Pageable to set the number of ids we want
  @Query("SELECT id " +
         "FROM User ")
  List<Long> findIds(Pageable pageable);

yannbriancon

@RunWith(SpringRunner.class)
@SpringBootTest("hibernate.query.interceptor.error-level=ERROR")
@Transactional
class NPlusOneQueriesLoggingTest {
    ...
}

yannbriancon

@RunWith(MockitoJUnitRunner.class)
@SpringBootTest
@Transactional
class NPlusOneQueriesLoggingTest {

    @Autowired
    private MessageRepository messageRepository;

    @Test
    void nPlusOneQueriesDetection_isLoggingWhenDetectingNPlusOneQueries() {

yannbriancon

<dependency>
    <groupId>com.yannbriancon</groupId>
    <artifactId>spring-hibernate-query-utils</artifactId>
    <version>1.0.3</version>
</dependency>