Persisting a domain model with Hibernate 3 - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 242

6.6 Summary
Hibernate provides mostly transparent persistence for POJO classes. It provides a
rich ORM mechanism that makes it quite easy to persist a domain model such as the
one for the Place Order use case. Its features include embedded value objects, inher-
itance, and automatic deletion of orphaned children in a parent/child relationship.
Despite its power, Hibernate has several important limitations that can impact
the design of an application. One limitation is inefficient handling of unidirec-
tional one-to-many relationships that are mapped using a foreign key. Another
limitation is that lazily loaded objects do not support instanceof and downcast-
ing. In addition, recovering from an error when a HibernateException was
thrown can be difficult. Another challenge is dynamically configuring eager load-
ing on a per-request basis.
You can use a test-driven approach to develop a Hibernate persistence layer.
There are three different kinds of tests you can write for each persistent class.
First, you can write a test that uses the Hibernate metadata API s to verify that the
XML mapping document correctly implements the O/R mapping for the class.
Second, you can write persistence tests that verify that instances of the class can be
saved, updated, and deleted. Finally, you can write a test that that verifies that the
schema matches the O/R mapping. For each repository, you write mock object
tests that verify that the repository calls the Hibernate/Spring API s correctly. You
can also write database tests for the queries that are called by the repositories.
Now that we have looked at how to use Hibernate and JDO to persist a domain
model, the next step is to decide what kind of interface the business logic exposes
to the presentation. One option is to encapsulate the domain model with a POJO
façade that uses Spring for transaction management, as you'll see in the next chapter.