Is it possible to pass EntityManager as a parameter through multiple beans? - jpa

Question

I know i can do the following :
public class MyDao{
private EntityManager em;
public void setEm(EntityManager em){
this.em = em;
}
...
and then, using #PostConstuct to pass the EntityManager
public class MyBean{
private EntityManager em;
#Inject
private MyDao myDao;
#PostConstruct
private void init(){
myDao.setEm(em);
}
...
But due to my application's architecture restriction i cannot directly inject MyDao into MyBean, i should pass by MyBusinessDao Class, so i tried the following but i'm getting a nullPointerExeception on the value of EntityManager in MyDao :
public class MyBean{
private EntityManager em;
public MyBean(){
em = createEntityManager();
}
private EntityManager createEntityManager(){
//dynamically create the EntityManager
}
#Inject
private MyBusinessDao myBusinessDao;
#PostConstruct
private void init(){
myBusinessDao.setEm(em);
}
...
and in MyBusinessDao i inject MyDao:
public class MyBusinessDao {
private EntityManager em;
#Inject
private MyDao myDao;
#PostConstruct
private void init(){
myDao.setEm(em);
}
...
I should mention that i'm not using a J2EE container

Answer 1

You can implement an CDI Producer Method for providing the EntityManager via CDI injection.
#ApplicationScoped
class EntityManagerProducer {
#PersistenceContext(...)
private EntityManager em;
#Produces
#RequestScoped
public EntityManager produceEm() {
return em;
}
}
You can also inject the EntityManagerFactory and call emf.createEntityManager() in the producer method and implement an CDI-Disposer method, which closes the EntityManager before the scope is finished.
public void dispose(#Disposes EntityManager em) { ... }
If you have multiple persistence contexts, then implement a producer method for each persistence context and qualify them with a CDI-Qualifier.

Answer 2

I resolved it this way :
public class MyBusinessDao {
private EntityManager em;
#Inject
private MyDao myDao;
private void setEm(EntityManager em){
this.em = em;
//and here i call the setEm method of myDao also
myDao.setEm(em);
}
...