Question

When I load an entity which contains lazy-loading fields and I want to send this entity through an object message with ActiveMQ, will I receive :

1. The full entity (with lazy-loading fields loaded)
   OR
2. The entity as sent (without lazy-loading fields loaded) ?

In any case do I need to put the Serializable marker in my entity ?

In case of answer 1 what do I need to do to get the entity as described in answer 2 ?

Answer 1

Lets assume you have an entity with some lazy loading fields like this:

@Entity
public class Foo
{
    @Id
    private Long id;
    @OneToMany
    private List<Bar> bars;
}

When you receive this entity from your database only the id field will be loaded as the bars field is lazy loaded (OneToMany is lazy by default). Now when you pass this entity through JMS for example the bars field is not initialized because the getBars() method isn’t called. When the remote end calls the getter it will get a LazyInitializationException as the entity is detached and the collection isn’t initialized.

If you however want the remote end to be able to call the getBars() method you need to initialize the collection in some way. You can make the fetching of the collection eager using @OneToMany(fetch = FetchType.EAGER). An alternative is to use a separate query for eager loading the entity (which is my personal preference).

Example:

select f from Foo f join fetch l.bars

If you really want to go wild and want the collection to be initialized lazily on the remote end you can take a look at Hibernate remote lazy loading using RMI. I’m not going to explain this because it seems out of the scope of the question. 😉