Multithreading throws org.hibernate.LazyInitializationException: could not initialize proxy - no Session

Question

I keep getting this error when I try to use multithreading (no problem if I run the program sequentially) in this service:

@Service
@RequiredArgsConstructor
public class Service {

    private final Repository repository;

    public List<A> getAs(String[] ids) {
        List<A> as = Collections.synchronizedList(new ArrayList<>());

        List<CompletableFuture<Boolean>> futures = new ArrayList<>();
        for (String id : ids) {
            futures.add(CompletableFuture.supplyAsync(() -> repository.findById(id).orElse(null)).thenApply(as::add));
        }

        futures.forEach(CompletableFuture::join);

        return as;
    }

}

Repository is a standard JpaRepository<A, String> and A:

public class A {

    @Id
    @Column(name = "id")
    private String id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "b")
    private B b;

}

The error is thrown when executing A#getB on any element of the returned list

Add @Transactional annotation above into your getAs method

iwritecomeinmymind
– iwritecomeinmymind

2022-11-28 11:52:08 +00:00
Commented Nov 28, 2022 at 11:52 — iwritecomeinmymind
– iwritecomeinmymind, Commented Nov 28, 2022 at 11:52
@AnarMəmmədov already tried and it did not work

thmasker
– thmasker

2022-11-28 11:55:24 +00:00
Commented Nov 28, 2022 at 11:55 — thmasker
– thmasker, Commented Nov 28, 2022 at 11:55

thmasker · Accepted Answer · 2022-11-29 04:56:18Z

1

Because B is Lazy loaded.

You can make this part in transaction and add init query:

repository.findById(id).map(v -> {v.getB(); return v;}).orElse(null))

Or you can use create not lazy query:

public interface ARepository extends JpaRepository<A, String> { 
    @Query(value = "SELECT c FROM A c LEFT JOIN FETCH c.b where c.id = :id")   
    A findById(@Param("id") String id);
}

edited Nov 29, 2022 at 4:56

thmasker

6602 gold badges14 silver badges34 bronze badges

answered Nov 28, 2022 at 11:44

Shakirov Ramil

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