Greetings,

We are designing a new system and considering using EJB3 for it. One of the issues we are trying to resolve is how to pass search criteria from presentation layer to EJB layer. On the previous project we used OJB and Criteria class from OJB. It worked like a charm: presentation layer would populate Criteria object based on user's selection on a wep page and pass it to EJB where it was used as it was without any modifications. It was very convenient and uniformed. Now what does EJB3 have to offer? Presentation layer constructing EJB QL? This doesn't seem right. Presentation layer passing a Map of fields/values to be used in querying database to EJB and the EJB using it to construct EJB QL? I remember doing the same with Maps and JDBC/SQL 4 years ago and it was quite messy and not elegant at all.

I also tried to marry EJB3 and Hibernate approaches so that I could use Hibernate's Criteria class but didn't get anywhere. I got "duplicate class mapping" exception as I had both @Entity annotation and Hibernate mapping file for a specific class.

Any thoughts?

Regards,
Yuriy

Why would you need duplicate mapping information? Just cast your EntityManager and move on: ((HibernateEntityManager)myEntityManager).getSession().createCriteria()....

And, if the presentation layer can query for anything it wants, why have layering at all?

I know that having domain objects for business layer and presentation/search/criteria object for presentation layer is a text book approach. For example, I could have domain class Customer and then another class CustomerSerachCriteria that presentation layer would pass to business layer whenever a search needs to be performed. The problem is that I would have to have some kind of mapping between two classes which is an extra coding I don't want to do.

Let's say I don't care about a clean separation between domain and presentation objects. Let my presentation layer also operate with domain objects. So whenever a user would perform a customer search, the presentation layer would do something like this:

Criteria crit = new Criteria(Customer.class);
crit.add(Expression.eq("name", "bob"));
// pass crit to an EJB

The EJB would just then run the criteria against a Hibernate session. The problem is that Criteria can only be obtained from Session itself. In OJB, for example, Criteria could be instantiated on its own which is very slick.

Basically, I don't want to do extra coding if I don't see a need for it. I cannot see a clear way to pass search criteria between presentation layer and Hibernate/EJB3 in a business layer. Any advices or best practices?

Regards,
Yuriy

Thanks! That was a prompt reply.

I will take a look at DeattachedCriteria and may fire up some additional questions if I have.

Regards,
Yuriy