MZs Notes - Pg 159

[Niranjan Deshpande]

I was reading the section

Identify correct and incorrect statements or examples about application-managed
persistence contexts. - [EJB_3.0_PERSISTENCE] 5.7; 5.7.1.1; 5.7.1.2; 5.7.1.3; 5.7.1.4 - PDF Page 159

After the text, there are three four sample codes.

I was trying to figure out what those samples explain, in context of the relevant text?
Can any one help me please.

[Devaka Cooray]

Howdy Niranjan,

I would like to kindly suggest you to feel kind to post the exact code here which makes you confused; so that we can help you quickly.

[Niranjan Deshpande]

Hi Devaka,

Here are those listings -

*********************************************************************************************************
                                                                                     Example 1
*********************************************************************************************************
/*
* Container-managed transaction demarcation is used.
* Session bean creates and closes an entity manager in
* each business method.
*/
@Stateless
public class ShoppingCartImpl implements ShoppingCart {
@PersistenceUnit
private EntityManagerFactory emf;
public Order getOrder(Long id) {
EntityManager em = emf.createEntityManager();
Order order = (Order)em.find(Order.class, id);
em.close();
return order;
}
public Product getProduct() {
EntityManager em = emf.createEntityManager();
Product product = (Product) em.createQuery("select p from Product p where p.name = :name")
.setParameter("name", name)
.getSingleResult();
em.close();
return product;
}
public LineItem createLineItem(Order order, Product product, int quantity) {
EntityManager em = emf.createEntityManager();
LineItem li = new LineItem(order, product, quantity);
order.getLineItems().add(li);
em.persist(li);
em.close();
return li; // remains managed until JTA transaction ends
}
}

/*
* Container-managed transaction demarcation is used.
* Session bean creates entity manager in PostConstruct
* method and clears persistence context at the end of each
* business method.
*/
@Stateless
public class ShoppingCartImpl implements ShoppingCart {
@PersistenceUnit
private EntityManagerFactory emf;
private EntityManager em;
@PostConstruct
public void init()
em = emf.createEntityManager();
}
public Order getOrder(Long id) {
Order order = (Order)em.find(Order.class, id);
em.clear(); // entities are detached
return order;
}
public Product getProduct() {
Product product = (Product) em.createQuery("select p from Product p where p.name = :name")
.setParameter("name", name)
.getSingleResult();
em.clear();
return product;
}
public LineItem createLineItem(Order order, Product product, int quantity) {
em.joinTransaction();
LineItem li = new LineItem(order, product, quantity);
order.getLineItems().add(li);
em.persist(li);
// persistence context is flushed to database;
// all updates will be committed to database on tx commit
em.flush();
// entities in persistence context are detached
em.clear();
return li;
}
@PreDestroy
public void destroy()
em.close();
}
}

*********************************************************************************************************
                                                                                     Example 3
*********************************************************************************************************
//Container-managed transaction demarcation is used
@Stateful
public class ShoppingCartImpl implements ShoppingCart {
@PersistenceUnit
private EntityManagerFactory emf;
private EntityManager em;
private Order order;
private Product product;
@PostConstruct
public void init() {
em = emf.createEntityManager();
}
public void initOrder(Long id) {
order = em.find(Order.class, id);
}
public void initProduct(String name) {
product = (Product) em.createQuery("select p from Product p where p.name = :name")
.setParameter("name", name)
.getSingleResult();
}
public LineItem createLineItem(int quantity) {
em.joinTransaction();
LineItem li = new LineItem(order, product, quantity);
order.getLineItems().add(li);
return li;
}
@Remove
public void destroy() {
em.close();
}
}

*********************************************************************************************************
                                                                                     Example 4
*********************************************************************************************************
Example of application-managed Persistence Context with Resource Transaction
// Usage in an ordinary Java class
public class ShoppingCart {
private EntityManager em;
private EntityManagerFactory emf;
public ShoppingCart() {
emf = Persistence.createEntityManagerFactory("orderMgt");
em = emf.createEntityManager();
}
private Order order;
private Product product;
public void initOrder(Long id) {
order = em.find(Order.class, id);
}
public void initProduct(String name) {
product = (Product) em.createQuery("select p from Product p where p.name = :name")
.setParameter("name", name)
.getSingleResult();
}
public LineItem createLineItem(int quantity) {
em.getTransaction().begin();
LineItem li = new LineItem(order, product, quantity);
order.getLineItems().add(li);
em.getTransaction().commit();
return li;
}
public void destroy() {
em.close();
emf.close();
}
}