Lazy loading collections with JPA / EclipseLink

Question

Is there any way that each child of a collection will be loaded individually by EclipseLink?

I have got the two Entities:

@Entity
public class A {

    private List<Item> collection = new LinkedList<Item>();

    @OneToMany(fetch = FetchType.LAZY)
    public List<Item> getCollection() {
        return this.collection;
    }

    public void setCollection (List<Item> collection) {
        this.collection = collection;
    }
}

@Entity
public class Item {

    private byte[] data;

    @Lob
    public byte[] getData() {
        return data;
    }

    public void setData(byte[] data) {
        this.data = data;
    }
}

My collection contains a large number of items, hence I don’t want EclipseLink to load all children when I access e.g. only the first item. But calling a.getCollection().get(0).getData() results in loading all items of the collection in memory. Is there a way to avoid this? (And only loading the first item in memory)

Answer 1

Add (actually mappedBy should rather be on the OneToMany side, but for the sake of simplicity):

@ManyToOne(mapped="collection")
private A a;

to the Item class and fetch each item by foreign key individually:

SELECT i
FROM Item i
WHERE i.a = :a

Where :a parameter is an instance of A.

Answer 2

If you never want to read in the collection, then do not map it. Instead just query for it.