Add Hibernate 7 batches 2-6, batch 7, and batch 8: mapping styles, JPA annotations, natural IDs, @Immutable, stored procedures, in-memory test databases, JNDI mocking, proxies, associations, temporal mapping, named queries, HQL, Criteria API, EntityManager bootstrapping, Ehcache 3 L2 cache configuration, HikariCP connection pooling, Hibernate Validator CDI integration, aggregate functions, sorting, pagination, interceptors, and Hibernate Search 8 (Hibernate 7.4.5.Final + Spring Boot 4.1.1 + JDK 25)
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package com.ankurm.hibernatedemo.association;
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import static org.assertj.core.api.Assertions.assertThat;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import jakarta.persistence.EntityManager;
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import jakarta.persistence.EntityManagerFactory;
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import java.util.List;
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import org.hibernate.SessionFactory;
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import org.hibernate.stat.Statistics;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.Test;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.boot.test.context.SpringBootTest;
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/**
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* Backs ankurm.com post 4872, docs/12-association-mappings.md chapters "MultipleBagFetchException"
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* and "The cartesian-product trap".
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*/
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@SpringBootTest
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class BagFetchTest {
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private static final Logger DEMO = LoggerFactory.getLogger("DEMO");
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@Autowired
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private EntityManagerFactory emf;
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@BeforeEach
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void cleanTables() {
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EntityManager em = emf.createEntityManager();
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em.getTransaction().begin();
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em.createQuery("DELETE FROM BagBookL").executeUpdate();
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em.createQuery("DELETE FROM BagAwardL").executeUpdate();
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em.createQuery("DELETE FROM BagAuthorList").executeUpdate();
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em.createQuery("DELETE FROM BagBookS").executeUpdate();
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em.createQuery("DELETE FROM BagAwardS").executeUpdate();
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em.createQuery("DELETE FROM BagAuthorSet").executeUpdate();
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em.getTransaction().commit();
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em.close();
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}
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private Statistics stats() {
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return emf.unwrap(SessionFactory.class).getStatistics();
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}
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private Long seedListAuthor(int nBooks, int nAwards) {
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EntityManager em = emf.createEntityManager();
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em.getTransaction().begin();
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BagAuthorList author = new BagAuthorList("List Author");
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em.persist(author);
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for (int i = 0; i < nBooks; i++) {
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em.persist(new BagBookL("Book" + i, author));
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}
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for (int i = 0; i < nAwards; i++) {
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em.persist(new BagAwardL("Award" + i, author));
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}
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em.getTransaction().commit();
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Long id = author.getId();
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em.close();
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return id;
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}
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private Long seedSetAuthor(int nBooks, int nAwards) {
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EntityManager em = emf.createEntityManager();
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em.getTransaction().begin();
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BagAuthorSet author = new BagAuthorSet("Set Author");
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em.persist(author);
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for (int i = 0; i < nBooks; i++) {
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em.persist(new BagBookS("Book" + i, author));
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}
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for (int i = 0; i < nAwards; i++) {
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em.persist(new BagAwardS("Award" + i, author));
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}
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em.getTransaction().commit();
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Long id = author.getId();
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em.close();
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return id;
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}
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@Test
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void fetchJoiningTwoListsInOneQuery_throwsMultipleBagFetchException() {
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seedListAuthor(4, 3);
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EntityManager em = emf.createEntityManager();
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IllegalArgumentException ex = assertThrows(IllegalArgumentException.class, () ->
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em.createQuery(
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"SELECT a FROM BagAuthorList a JOIN FETCH a.books JOIN FETCH a.awards",
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BagAuthorList.class).getResultList());
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Throwable root = ex;
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while (root.getCause() != null && root.getCause() != root) {
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root = root.getCause();
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}
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DEMO.info("MultipleBagFetchException reproduction -- wrapper class: {}", ex.getClass().getName());
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DEMO.info("MultipleBagFetchException reproduction -- root cause class: {}", root.getClass().getName());
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DEMO.info("MultipleBagFetchException reproduction -- verbatim message: {}", root.getMessage());
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assertThat(ex.getClass().getName()).as("EntityManager.createQuery(...).getResultList() wraps it as IllegalArgumentException, NOT PersistenceException")
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.isEqualTo("java.lang.IllegalArgumentException");
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assertThat(root.getClass().getName()).isEqualTo("org.hibernate.loader.MultipleBagFetchException");
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em.close();
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}
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@Test
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void fix1_useSetsInsteadOfLists_noExceptionOneQuery() {
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seedSetAuthor(4, 3);
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EntityManager em = emf.createEntityManager();
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stats().clear();
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List<BagAuthorSet> authors = em.createQuery(
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"SELECT DISTINCT a FROM BagAuthorSet a JOIN FETCH a.books JOIN FETCH a.awards",
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BagAuthorSet.class)
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.getResultList();
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long queries = stats().getPrepareStatementCount();
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DEMO.info("Fix #1 (Set instead of List): {} distinct authors returned, {} queries fired", authors.size(), queries);
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assertThat(authors).hasSize(1);
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assertThat(authors.get(0).getBooks()).hasSize(4);
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assertThat(authors.get(0).getAwards()).hasSize(3);
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assertThat(queries).isEqualTo(1);
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em.close();
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}
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@Test
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void fix2_twoSeparateQueries_avoidsBagFetchExceptionEntirely() {
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Long id = seedListAuthor(4, 3);
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EntityManager em = emf.createEntityManager();
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stats().clear();
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BagAuthorList author = em.createQuery(
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"SELECT a FROM BagAuthorList a JOIN FETCH a.books WHERE a.id = :id", BagAuthorList.class)
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.setParameter("id", id)
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.getSingleResult();
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// second, separate query for the other bag -- no exception because only one JOIN FETCH per query
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author = em.createQuery(
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"SELECT a FROM BagAuthorList a JOIN FETCH a.awards WHERE a.id = :id", BagAuthorList.class)
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.setParameter("id", id)
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.getSingleResult();
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long queries = stats().getPrepareStatementCount();
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DEMO.info("Fix #2 (two queries): {} queries fired, books={}, awards={}",
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queries, author.getBooks().size(), author.getAwards().size());
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assertThat(author.getBooks()).hasSize(4);
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assertThat(author.getAwards()).hasSize(3);
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assertThat(queries).as("one JOIN FETCH per query, run twice").isEqualTo(2);
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em.close();
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}
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@Test
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void cartesianProduct_fetchJoiningTwoAllowedSetsExplodesRowCount() {
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seedSetAuthor(4, 3);
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EntityManager em = emf.createEntityManager();
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// Raw SQL join without DISTINCT to see the true row count the database returns.
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Object rawCount = em.createNativeQuery(
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"SELECT COUNT(*) FROM bag_author_set a " +
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"JOIN bag_book_s b ON b.author_id = a.id " +
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"JOIN bag_award_s w ON w.author_id = a.id")
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.getSingleResult();
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long rawRowCount = ((Number) rawCount).longValue();
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List<BagAuthorSet> entities = em.createQuery(
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"SELECT DISTINCT a FROM BagAuthorSet a JOIN FETCH a.books JOIN FETCH a.awards",
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BagAuthorSet.class)
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.getResultList();
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DEMO.info("Cartesian product: 4 books x 3 awards for 1 author -> raw SQL join rows = {}, distinct entities returned = {}",
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rawRowCount, entities.size());
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assertThat(rawRowCount).as("SQL returns one row per (book, award) pair: 4 x 3").isEqualTo(12);
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assertThat(entities).as("Hibernate's DISTINCT root-entity de-duplication collapses this back to 1 entity")
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.hasSize(1);
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assertThat(entities.get(0).getBooks()).hasSize(4);
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assertThat(entities.get(0).getAwards()).hasSize(3);
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em.close();
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}
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}
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