Weird Error about Hibernate Proxy Class Cast Exception

[gunb0s]

I found some weird behavior of hibernate proxy, when casting.

when using findById of jpa repository,
some time hibernate proxy returns and sometime real entity returns.

i'm using

hibernate-core:6.4.1.Final
spring-data-jpa:3.2.2

My entity setting is like below

@Entity
@Table(name = "users")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "dtype")
@NoArgsConstructor(access = AccessLevel.PROTECTED)
@Getter
public abstract class User {
	@Id
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	@Column(name = "user_id")
	private Long id;

	private String name;

	@Column(updatable = false, insertable = false)
	private String dtype;

	public User(String name) {
		this.name = name;
	}
}

@Entity
@Getter
@DiscriminatorValue("S")
@NoArgsConstructor(access = AccessLevel.PROTECTED)
public class Student extends User {
	@Builder
	public Student(String name) {
		super(name);
	}
}

And i did find query

Post post = postRepository.findPostWithLecture(createCommentDto.getPostId()).orElseThrow();
Lecture lecture = post.getBoard().getLecture();
User user = userRepository.findById(createCommentDto.getUserId()).orElseThrow();

if (user.getDtype().equals("E")) {
	lectureRepository.findByIdAndEducator(lecture.getId(), (Educator) user).orElseThrow();
} else {
	enrollmentRepository.findByStudentAndLecture((Student) user, lecture).orElseThrow();
}

in above case userRepository.findById returns User$HibernateProxy$byHBV0qu
but when useRepository.findById is executed at the beginning of function, it returns just User.

postRepository.findPostWithLecture uses JPQL and i guess this is a root cause of weird return of findById
this function`s implementation is like below

@Query("select p from Post p join fetch p.board where p.id = :postId")
Optional<Post> findPostWithLecture(Long postId);

is this weird return a normal behavior? or bug??

[mp911de]

Please provide a minimal yet complete sample that reproduces the problem along with the exception stack trace.
You can share it with us by pushing it to a separate repository on GitHub or by zipping it up and attaching it to this issue.

[gunb0s]

Please provide a minimal yet complete sample that reproduces the problem along with the exception stack trace. You can share it with us by pushing it to a separate repository on GitHub or by zipping it up and attaching it to this issue.

i made a test in my repository to reproduce error

https://github.com/gunb0s/improved-eureka/blob/bug/hibernate-proxy/src/test/java/gunb0s/toy/ciazza/test/WeirdProxyBehaviorTest.java

[christophstrobl]

Thank you very much for providing the reproducer project. Unfortunately there's not much we can do from a spring data perspective as the issue stems from the underlying persistence provider and can be reproduced with plain JPA as outlined below (using the provided sample for reference).

Query query = em.createQuery("select p from Post p join fetch p.board where p.id = :postId", Post.class);
query.setParameter("postId", postId);
query.getSingleResult();

User user = em.find(User.class, studentId, Collections.emptyMap()); // <-- class ....user.entity.User$HibernateProxy$ouTchvQE

You may want to report the problem to the hibernate team. We'd appreciate it if you could leave a comment with a link to the new issue here.

[gunb0s]

Thank you very much for providing the reproducer project. Unfortunately there's not much we can do from a spring data perspective as the issue stems from the underlying persistence provider and can be reproduced with plain JPA as outlined below (using the provided sample for reference).

Query query = em.createQuery("select p from Post p join fetch p.board where p.id = :postId", Post.class);
query.setParameter("postId", postId);
query.getSingleResult();

User user = em.find(User.class, studentId, Collections.emptyMap()); // <-- class ....user.entity.User$HibernateProxy$ouTchvQE

You may want to report the problem to the hibernate team. We'd appreciate it if you could leave a comment with a link to the new issue here.

thank you for sugges pure jpa example, i made a question to zulip of hibernate orm ( hibernate orm github doesn't have issue tab)
#3362 (comment)