Lazy relationships become loaded after EntityManager closes

[Braiam Yesid]

Hello guys

Using JPA 2.0, I do not want that lazy loaded relationships become loaded after closing EntityManager.

This is what I'm using
Netbeans 6.8
PostgreSQL 8.4
EclipseLink 2.0

I mean, If an Entity object has a (lazily loaded) collection of other Entities, I expect that after closing the EntityManager, those relationships are not loaded. I want null fields or a NullPointerException. But what I'm getting after closing the EntityManager is the full node tree.

Class A

/** CLASS A, has a collection of B's */
@Entity
public class A implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;


    @OneToMany(fetch=FetchType.LAZY)
    private List<B> bList;

	... getters/setters ...
	
}

Class B

/** CLASS B, has huge amounts of data in veryLargeField */
@Entity
public class B implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Lob
    @Basic(fetch=FetchType.LAZY)
    private byte[] veryLargeField;

	... getters/setters ...
}

Main Class

/** Main class */
public class Main {
    public static void main(String[] args) {
        Main o = new Main();
        o.go();
    }

	
    private void go() {
        A a = getA();
		
		//It is supposed that A->B Relationship has not been loaded, so 
		//calling to a.getbList() should return null (Believe it or not, I want a NullPointerException!)
        if(a.getbList() == null){
            System.out.println("Lazy loading did not load this relationship");
        }
        else{
            System.out.println("This relationship has been loaded");
        }


		//Printing graph tree 
        System.out.println(a.getId());
        List<B> bList = a.getbList();
        for(B b : bList){
            System.out.println("  >" + b.getId());
        }
    }

	// Metod to get A. This method uses and then discards an EntityManager
    private A getA() {
        EntityManager em = Persistence.createEntityManagerFactory("JPAPlaygroundPU").createEntityManager();
        A a = null;
        try {
            a = em.find(A.class, 1);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
			//It's here where lazily loaded relationships get loaded.
            em.close();
        }
        return a;
    }
}

Output

This relationship has been loaded
1
  >1
  >2
  >3
  >4

As you can see, B may be too big to keep in memory. For example, I want to list all the 500 instances of A. And each A has 100 B, so I have a total of 5000 B objects. I want ONLY the list of A, without their B's loaded. But I'm getting all the 500 A's and all the 5000 B's.

Am I missing some point?

Thank you guys

[James Sutherland]

It is odd that you would want a null-pointer exception when accessing your relationship instead of its value.

If you do not wish to have the value instantiated, then do not access it.

Otherwise, you could clone or serialize the object and leave the lazy relationship as null.