[FIXED] How to use FetchType.LAZY with ManyToMany?

Issue

I have two entities with many-to-many relationship.

in class Role:

@ManyToMany(mappedBy = "roles")
private Set<User> users = new HashSet<>();

and in class User:

@ManyToMany
@JoinTable(name = "role_user", joinColumns = @JoinColumn(name = "user_id"),
        inverseJoinColumns = @JoinColumn(name = "role_id"))
private Set<Role> roles = new HashSet<>();

And I get the exception:

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: User.roles, could not initialize proxy - no Session

When I add fetch = FetchType.EAGER, I get another exception:

java.lang.StackOverflowError: null

and cycle between Role and User.

How can I resolve this problem? I saw similar questions on Stackoverflow, but I didn't find real worked solution for me.

UPD: Where the exception gets thrown:

@Service
public class UserAuthenticationProvider implements AuthenticationProvider {
    ...

    @Override
    @Transactional
    public Authentication authenticate(final Authentication authentication) {
        final String login = authentication.getName();
        final String password = authentication.getCredentials().toString();

        final User user = userRepository.findByLogin(login);
        if (user != null && passwordEncoder.matches(password, user.getPassword())) {
            return new UsernamePasswordAuthenticationToken(login, password,
                    user.getRoles()); // problem here
        } else {
            return null;
        }
    }

    ...

Solution

It looks like @Transactional doesn't work for an overridden method of AuthenticationProvider. I should have created a separate service to handle this issue.

A similar answer here: https://stackoverflow.com/a/23652569/8253837

Answered By - Daria Pydorenko
Answer Checked By - Dawn Plyler (JavaFixing Volunteer)