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

Solution 1

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

Solution 2

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?