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Working around HHH-9663: Orphan removal does not work for OneToOne relations

HHH-9663 means that orphan removal doesn’t work for OneToOne relationships. For example, given File and FileContent as below (taken from the bug report):

  1. package pl.comit.orm.model;
  2.  
  3. import javax.persistence.Entity;
  4. import javax.persistence.FetchType;
  5. import javax.persistence.Id;
  6. import javax.persistence.OneToOne;
  7.  
  8. @Entity
  9. public class File {
  10.  
  11. 	private int id;
  12.  
  13. 	private FileContent content;
  14.  
  15. 	@Id
  16. 	public int getId() {
  17. 		return id;
  18. 	}
  19.  
  20. 	public void setId(int id) {
  21. 		this.id = id;
  22. 	}
  23.  
  24. 	@OneToOne(fetch = FetchType.LAZY, orphanRemoval = true)
  25. 	public FileContent getContent() {
  26. 		return content;
  27. 	}
  28.  
  29. 	public void setContent(FileContent content) {
  30. 		this.content = content;
  31. 	}
  32. }
  1. package pl.comit.orm.model;
  2.  
  3. import javax.persistence.Entity;
  4. import javax.persistence.Id;
  5.  
  6. @Entity
  7. public class FileContent {
  8.  
  9. 	private int id;
  10.  
  11. 	@Id
  12. 	public int getId() {
  13. 		return id;
  14. 	}
  15.  
  16. 	public void setId(int id) {
  17. 		this.id = id;
  18. 	}
  19. }
  1. package pl.comit.orm.dao;
  2.  
  3. import javax.persistence.EntityManager;
  4. import javax.persistence.PersistenceContext;
  5.  
  6. import org.springframework.stereotype.Repository;
  7. import org.springframework.transaction.annotation.Transactional;
  8.  
  9. import pl.comit.orm.model.File;
  10. import pl.comit.orm.model.FileContent;
  11.  
  12. @Repository
  13. public class Dao {
  14.  
  15. 	@PersistenceContext
  16. 	private EntityManager entityManager;
  17.  
  18. 	@Transactional
  19. 	public void assureCreatedTaskAndNote(int fileId, int contentId) {
  20. 		FileContent content = entityManager.find(FileContent.class, contentId);
  21. 		if (content == null) {
  22. 			content = new FileContent();
  23. 			content.setId(contentId);
  24. 			entityManager.persist(content);
  25. 		}
  26.  
  27. 		File file = entityManager.find(File.class, fileId);
  28. 		if (file == null) {
  29. 			file = new File();
  30. 			file.setId(fileId);
  31. 			entityManager.persist(file);
  32. 		}
  33. 		file.setContent(content);
  34. 	}
  35.  
  36. 	@Transactional
  37. 	public void removeContent(int fileId) {
  38. 		File file = entityManager.find(File.class, fileId);
  39. 		file.setContent(null);
  40. 	}
  41.  
  42. 	public FileContent find(int contentId) {
  43. 		return entityManager.find(FileContent.class, contentId);
  44. 	}
  45. }

Running this as the main class will result in an exception:

  1. package pl.comit.orm;
  2.  
  3. import org.springframework.context.support.ClassPathXmlApplicationContext;
  4.  
  5. import pl.comit.orm.dao.Dao;
  6. import pl.comit.orm.model.FileContent;
  7.  
  8. public final class Application {
  9.  
  10. 	private static final String CFG_FILE = "applicationContext.xml";
  11.  
  12. 	public static void main(String[] args) {
  13. 		test(new ClassPathXmlApplicationContext(CFG_FILE).getBean(Dao.class));
  14. 	}
  15.  
  16. 	public static void test(Dao dao) {
  17. 		dao.assureCreatedTaskAndNote(1, 2);
  18. 		dao.removeContent(1);
  19. 		FileContent content = dao.find(2);
  20. 		if (content != null) {
  21. 			System.err.println("Content found: " + content);
  22. 		}
  23. 	}
  24. }

A workaround is to manually remove and detach the old referent, and then persist the new referent. Here’s an updated File.java:

  1. package pl.comit.orm.model;
  2.  
  3. import org.springframework.stereotype.Component;
  4.  
  5. import javax.annotation.PostConstruct;
  6. import javax.annotation.PreDestroy;
  7. import javax.persistence.Entity;
  8. import javax.persistence.FetchType;
  9. import javax.persistence.Id;
  10. import javax.persistence.OneToOne;
  11. import javax.persistence.PersistenceContext;
  12.  
  13. @Entity
  14. public class File {
  15.  
  16. 	private int id;
  17.  
  18. 	private FileContent content;
  19.  
  20. 	@Id
  21. 	public int getId() {
  22. 		return id;
  23. 	}
  24.  
  25. 	public void setId(int id) {
  26. 		this.id = id;
  27. 	}
  28.  
  29. 	@OneToOne(fetch = FetchType.LAZY, orphanRemoval = true)
  30. 	public FileContent getContent() {
  31. 		return content;
  32. 	}
  33.  
  34. 	public void setContent(FileContent content) {
  35. 		if(this.content != content){
  36. 			final oldContent = this.content;
  37. 			this.content = content;
  38. 			if(oldContent!=null){
  39. 				// Hibernate won't remove the oldContent for us, so do it manually; workaround HHH-9663
  40. 				WorkaroundHHH9663.entityManager.remove(oldContent);
  41. 				WorkaroundHHH9663.entityManager.detach(oldContent);
  42. 			}
  43. 		}
  44. 	}
  45.  
  46. 	// WORKAROUND https://hibernate.atlassian.net/browse/HHH-9663 "Orphan removal does not work for OneToOne relations"
  47. 	@Component
  48. 	public static class WorkaroundHHH9663 {
  49. 		@PersistenceContext
  50. 		private EntityManager injectedEntityManager;
  51.  
  52. 		private static EntityManager entityManager;
  53.  
  54. 		@PostConstruct
  55. 		public void postConstruct(){
  56. 			entityManager = injectedEntityManager;
  57. 		}
  58.  
  59. 		@PreDestroy
  60. 		public void preDestroy(){
  61. 			this.entityManager = null; // NOPMD
  62. 		}
  63. 	}
  64. 	// END WORKAROUND
  65. }

Note that no Dao changes were made, so if, for example, Spring Data was used instead of such a Dao, you wouldn’t have to modify anything else. And you can just remove this workaround code easily when a version of Hibernate because available with HHH-9963 fixed.
Finally, yes, this approach does exhibit a bit of code smell (the use of the static variable in this way and the entity having a container managed component aren’t exactly best practices), but, it’s a workaround – hopefully just a temporary one.

CC BY-SA 4.0 Working around HHH-9663: Orphan removal does not work for OneToOne relations by Craig Andrews is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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