EntityManager injected by Spring but null on first use - spring

Question

I am just working on a basic webapp that implements spring + hibernate entitymanager
I set up my dao and context exactly as described by this post:
http://blog.springsource.com/2006/08/07/using-jpa-in-spring-without-referencing-spring/
And created a test for it as shown here:
http://lstierneyltd.com/blog/development/examples/unit-testing-spring-apps-with-runwithspringjunit4classrunner-class/
For some reason when I try to access the entitymanager for creating a query, its null.
However from setting a breakpoint inside the setter method for the entitymanager I can see that Spring is injecting it correctly, and the field is being initialized.
Any clue as to why the entitymanager might be getting nullified after the setter has returned ?
Edit:
The dao code where I am setting the breakpoint:
public class ProductDaoImpl implements ProductDao {
private EntityManager entityManager;
#PersistenceContext
public void setEntityManager(EntityManager entityManager) {
this. entityManager = entityManager;
}
public Collection loadProductsByCategory(String category) {
return entityManager.createQuery("from Product p where p.category = :category")
.setParameter("category", category).getResultList();
}
}

Answer 1

The <tx:annotation-driven/> that I presume you do have, tells Spring to put transactional advice on any class or method that has an #Transactional annotation on it.
Transactions should be defined on the Service/Business layer, hence your ProductDaoImpl is usually called from within a service, which will have #Transactional. e.g.
pubic class ProductService {
#Resource(...) // inject it the way you like e.g. #Autowired / Setter / Constructor injection, etc..
ProductDao yourProductDao;
#Transactional
public List<Product> findCarProducts {
yourProductDao.loadProductsByCategory( "car" );
}
}
(alternatively, you can use an XML based transaction configuration)
Now the actual call to your DAO will be within a transaction => which is very important for entityManager / Hibernate Session. Otherwise you'll see all the usual errors: e.g. entityManager is null, entityManager is closed, etc..
In case you'd like to test a DAO in solo, you have to make sure that your test case is wrapped within a transaction via #TransactionConfiguration. For example, if your transaction manager bean is defined as:
<bean id="txManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactory" />
</bean>
Your DAO test would include this bean name:
#ContextConfiguration
#TransactionConfiguration(transactionManager="txManager", defaultRollback=false)
public class ProductDaoTransactionalTests {
// your use cases here..
}
You can read more about transactional tests in Spring Documentation