[hibernate-issues] [JIRA] (HHH-13740) Problem with duplicates when fetching multiple many-to-many relations with Hibernate FetchMode.JOIN

Evgeniy Khyst ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=557058%... ) *updated* an issue Hibernate ORM ( https://hibernate.atlassian.net/browse/HHH?atlOrigin=eyJpIjoiNDg0MmQzNWRi... ) / Bug ( https://hibernate.atlassian.net/browse/HHH-13740?atlOrigin=eyJpIjoiNDg0Mm... ) HHH-13740 ( https://hibernate.atlassian.net/browse/HHH-13740?atlOrigin=eyJpIjoiNDg0Mm... ) Problem with duplicates when fetching multiple many-to-many relations with Hibernate FetchMode.JOIN ( https://hibernate.atlassian.net/browse/HHH-13740?atlOrigin=eyJpIjoiNDg0Mm... ) Change By: Evgeniy Khyst ( https://hibernate.atlassian.net/secure/ViewProfile.jspa?accountId=557058%... ) When there are multiple many-to-many relations with {{FetchMode.JOIN}}, {{session.find}} returns a result with a child relation of type {{List}} containing duplicates. To avoid {{MultipleBagFetchException: cannot simultaneously fetch multiple bags}} when multiple {{@ManyToMany}} collections have {{(a)Fetch(FetchMode.JOIN)}}, only one collection has type {{List}} and others have type {{Set}}. {code:java}@Entity @Data @EqualsAndHashCode(onlyExplicitlyIncluded = true) public class Book implements Serializable { @Id @GeneratedValue private Long id; @NaturalId @EqualsAndHashCode.Include private String isbn; private String title; private LocalDate publicationDate; @ManyToMany @Fetch(FetchMode.JOIN) private List<Author> authors = new ArrayList<>(); @ManyToMany @Fetch(FetchMode.JOIN) private Set<Category> categories = new LinkedHashSet<>(); }{code} With the following test data {code:java}softwareDevelopment = new Category("Software development"); session.save(softwareDevelopment); systemDesign = new Category("System design"); session.save(systemDesign); martinFowler = new Author("Martin Fowler"); session.save(martinFowler); gregorHohpe = new Author("Gregor Hohpe"); session.save(gregorHohpe); gregorHohpe = new Author(); gregorHohpe.setFullName("Gregor Hohpe"); session.save(gregorHohpe); bobbyWoolf = new Author(); bobbyWoolf.setFullName("Bobby Woolf"); session.save(bobbyWoolf); poeaa = new Book(); poeaa.setIsbn("007-6092019909"); poeaa.setTitle("Patterns of Enterprise Application Architecture"); poeaa.setPublicationDate(LocalDate.parse("2002-11-15")); poeaa.getAuthors().addAll(List.of(martinFowler)); poeaa.getCategories().addAll(List.of(softwareDevelopment, systemDesign)); session.save(poeaa); eip = new Book(); eip.setIsbn("978-0321200686"); eip.setTitle("Enterprise Integration Patterns"); eip.setPublicationDate(LocalDate.parse("2003-10-20")); eip.getAuthors().addAll(List.of(gregorHohpe, bobbyWoolf)); eip.getCategories().addAll(List.of(softwareDevelopment, systemDesign)); session.save(eip);{code} a Book entity found by ID contains duplicates in {{List<Author> authors}} because {{Set<Category> categories}} has size 2: {{["Software development", "System design"]}}. {code:java}@Test void testFindByIdNoTrans findByIdOneAuthor () { try (Session session = HibernateUtil.getSessionFactory().openSession()) { Book poeaa Transaction transaction = session. find beginTransaction ( Book.class, this.poeaa.getId( ) ) ; Book eip poeaa = session.find(Book.class, this. eip poeaa.getId()); assertThat(poeaa.getTitle()).isEqualTo(this.poeaa.getTitle()); //    The following line results in exception //    because the actual poeaa.authors contains duplicates: ["Martin Fowler", "Martin Fowler"] assertThatHasAuthors(poeaa, martinFowler.getFullName()); transaction.commit(); } }{code} {code:java}List<Author> authors = ["Martin Fowler", "Martin Fowler"]{code} {code:java}@Test void findByIdTwoAuthors() { try (Session session = HibernateUtil.getSessionFactory().openSession()) { Transaction transaction = session.beginTransaction(); Book eip = session.find(Book.class, this.eip.getId()); assertThat(eip.getTitle()).isEqualTo(this.eip.getTitle()); //    The following line results in exception //    because the actual eip.authors contains duplicates: ["Gregor Hohpe", "Gregor Hohpe", "Bobby Woolf", "Bobby Woolf"] assertThatHasAuthors(eip, gregorHohpe.getFullName(), bobbyWoolf.getFullName()); transaction.commit(); } }{code} {code:java}List<Author> authors = [" Martin Fowler Gregor Hohpe ", " Martin Fowler Gregor Hohpe " ]{code} Probably , because {{categories}} has size 2: {code:java}Set<Category> categories = [ " Software development Bobby Woolf ", " System design Bobby Woolf "]{code} When there There are 2 authors and 2 categories there are no duplicates in child relations. Beginning transaction with {{ session.beginTransaction() List<Author> authors }} doesn't have any effect on the duplicates when {{Set<Category> categories}} has size 1. See the test [https://github.com/evgeniy-khist/hibernate-fetch-mode-join/blob/master/sr...] . Using The same problem is present when using Spring Data JPA and making the test transactional with {{(a)org.springframework.transaction.annotation.Transactional}} solves the problem with duplicates. ( Spring Boot version - 2.2. 1 6.RELEASE, Spring Data JPA version - 2.2. 1 6.RELEASE, Hibernate version - 5.4. 8 12.Final. See the test [https://github.com/evgeniy-khist/spring-data-jpa-fetch-mode-join/blob/mas...] . ( https://hibernate.atlassian.net/browse/HHH-13740#add-comment?atlOrigin=ey... ) Add Comment ( https://hibernate.atlassian.net/browse/HHH-13740#add-comment?atlOrigin=ey... ) Get Jira notifications on your phone! 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