Hibernate LazyInitializationException on find() with EAGER @ElementCollection

Question

I am getting org.hibernate.LazyInitializationException: illegal access to loading collection in my JPA code - all collections are EAGER fetch - when the collection entity also has a collection.

Could somebody please help me to fix this?

I have isolated a problem in my JPA code to the following @Entity definitions:

(note, I'm skipping the package and import statements to shorten the code. Some Lombok annotations are used, such as @Data to mean that the field has a getter/setter and @Cleanup to do the usual try/catch close() dance)

@Entity
@Data
public class MyEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

//    @ElementCollection(fetch = FetchType.EAGER)
//    private Set<String> tags = Sets.newTreeSet();
}

@Entity
@Data
public class MyOtherEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToMany(fetch = FetchType.EAGER)
    private Set<MyEntity> entities = Sets.newHashSet();
}

(I also get the same problem if I explicitly do a full @JoinTable, but Hibernate seems to generate everything fine without it - I'm happy leaving it out).

The problem is that if I uncomment the "tags" field in @MyEntity, then I always get the following PersistenceException

Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.LazyInitializationException: illegal access to loading collection
    at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1377)
    at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:828)
    at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:781)

The following is a short application which exemplifies the problem:

public class JpaQuestion {
    public static void main(String[] args) throws Exception {
        Properties properties = new Properties();
        properties.put("hibernate.connection.driver_class", "org.apache.derby.jdbc.EmbeddedDriver");
        properties.put("hibernate.connection.url", "jdbc:derby:playground;create=true");
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("PlaygroundPU", properties);

        populate(emf);

        @Cleanup("close") EntityManager em = emf.createEntityManager();
        MyOtherEntity other = em.find(MyOtherEntity.class, 1L);
        System.out.println(other != null ? other.toString() : "null");
    }

    public static void populate(EntityManagerFactory emf) {
        @Cleanup("close") EntityManager em = emf.createEntityManager();
        em.getTransaction().begin();
        MyEntity a = new MyEntity();
        em.persist(a);
        MyOtherEntity other = new MyOtherEntity();
        other.getEntities().add(a);
        em.persist(other);
        em.getTransaction().commit();
    }
}

UPDATE: I know about LazyInitializationException when field is eager but that seems to be because load() grabs a lazy version of the entity. I'm using "find" here. I've noticed that if I issue a JPA query (instead of find), then this problem goes away.

UPDATE: This really does work fine if instead of find(), I use a Query like "SELECT b FROM MyOtherEntity b WHERE b.id = :id". Maybe find() really does ignore EAGER loading! Hence this is likely a bug in Hibernate.

UPDATE: I've logged this as a bug report with Hibernate at https://hibernate.onjira.com/browse/HHH-7476

In which line of your code is the exception thrown? Just to be sure: without the `tags` field, this code works as expected? — Wolfram, Jul 22 '12 at 22:27
Yes, works without tags. Exception is on the find() method call. — fommil, Jul 23 '12 at 06:44

score 12 · Accepted Answer · answered Jul 30 '12 at 12:05

First of all it is useful to reference the full stack trace: http://pastie.org/4358203

The problem is being caused by your call to tags.hashCode() within the hashCode() implementation of MyEntity.

When you use Hibernate to load the MyOtherEntity instance, it's collection of MyEntity is initialised. When a MyEntity is added to the Set implementation within MyOtherEntity, it's hashCode() method is naturally called (sets cannot contain duplicates remember and hashCode() is part of how Java checks for object equality). The hashCode() method of MyEntity then attempts to invoke hashCode() on the tags collection. The tags collection is in the process of being initialised, which leads you to this error.

I think it is worth thinking about your hashCode() implementation for MyEntity. Does your use-case really require you to compare the value of the all elements within the tags collection to ensure object equality?

For more information on managing object equality in Hibernate, the following is a useful resource:

https://community.jboss.org/wiki/EqualsAndHashCode

Thanks! This one was making me want to tear out my hair. Using `id` only `equals`/`hashCode` doesn't make sense for my application and setting up a business key would be too much overhead. Instead, I can take the hit on hash collisions and simply remove the call to `tags.hashCode` from my `@MyEntity`'s `hashCode`. I've submitted an RFE for more advanced Lombok support on these sorts of matters at https://github.com/peichhorn/lombok-pg/issues/115 — fommil, Jul 30 '12 at 14:14

score 1 · Answer 2 · answered Jul 23 '12 at 14:09

LazyInitializationException – Indicates access to unfetched data outside of a session context. For example, when an uninitialized proxy or collection is accessed after the session was closed.

Some things you might want to try:

Removed @Cleanup - As a LazyInitializationException usually means that the Hibernate session was closed when a proxy tried to access a field, you should try it without those @Cleanup annotations. I never used them myself, but the docs say that the variable declaration gets cleaned up by calling .close() "the end of your scope".

Doublecheck configuration - Still odd, as you declare FetchType.EAGER for both associations. Have you checked that these options really get used? I know that the configuration might sometimes get a little tricky.

PersistenceContextType - You might want to try to set PersistenceContextType.EXTENDED for your EntityManager (I think TRANSACTION is the default, could be wrong but you might want to try to be sure).

In the case of a transaction-scoped persistence context, the entities become detached, that is, they are no longer managed. In the case of an extended persistence context, the entities remain managed.

I guess you already know the "LazyInitializationException overcome" wiki entry?

Thanks. Removing the `close()` call would be against the JPA guidelines so I'm not going to do that without good reason - in this case it would lead to a memory leak (lots of open `EntityManager`s). The `EAGER` is being used because if I remove them then other parts of my code are broken. I'm not keen on an `EXTENDED` configuration because `TRANSACTIONAL` works well for me - I want the instances to be detached. I've updated the question with some extra info. — fommil, Jul 26 '12 at 15:00

score 0 · Answer 3 · answered Jul 26 '12 at 15:50

0

The problem is that Hibernate ignores fetch = FetchType.EAGER for most queries. Try adding @Fetch(FetchMode.JOIN) to entities.

See: https://community.jboss.org/wiki/HibernateFAQ-AdvancedProblems#Hibernate_ignores_my_outerjointrue_or_fetchjoin_setting_and_fetches_an_association_lazily_using_n1_selects

answered Jul 26 '12 at 15:50

dex1304

164
2

Thanks, but that is to do with the Hibernate API, I want to stick to pure JPA annotations and it would appear that this is breaking the expectations of the annotations. Note that `Query` actually works, it is only `find()` that fails. – fommil Jul 26 '12 at 16:03

score 0 · Answer 4 · answered Nov 17 '13 at 07:31

This error Appears when hibernate try to initialize object and some error occur.

Error Can be

Hash Code And Equals Not properly implemented
the lazy object is expected to be encrypted but in db it is not properly encrypted
you are outside the hibernate session context.

Hibernate LazyInitializationException on find() with EAGER @ElementCollection

4 Answers4

Linked