Lazy loading behaviour

[pbakker]

I'm working on a demo-app and walked into some lazy-loading related issues.
I did find a solution, but I would like to find out why the other things I tried didn't work, so I can get a better understanding of things.

The situation is as follows:

There is a search page, that lists customers.
Every customer holds a list of messages, which should be lazily loaded.
The messages are not shown on the search page.
When clicked on a row, an edit screen is shown, which does show the customer's messages.

I use the SeamExtendedManagedPersistencePhaseListener and have a ManagedPersistenceContext configured.

The following code was my first trial, which gives a LazyInitializationException when opening the edit page.

FindCustomerBean

@Stateful
@Name("findCustomer")
@Scope(ScopeType.SESSION)
public class FindCustomersBean implements FindCustomer{
 @DataModel("customers")
 private List<Customer> customers;
 @DataModelSelection @Out(required=false)
 private Customer customer;
 @Logger
 private Log log;
 @In(create=true)
 private EntityManager seamEntityManager;

 public String edit() {
 log.debug("Editing customer '" + customer.getName() + "'");
 return "edit";
 }

 @Factory("customers")
 public void initializeCustomers() {
 customers = seamEntityManager.createQuery("select c FROM Customer c").getResultList();
 }

 @Destroy @Remove
 public void destoy() {

 }
}

EditCustomerBean

@Stateful
@Name("editCustomer")
@Scope(ScopeType.CONVERSATION)
public class EditCustomerBean implements EditCustomer {
 private FindCustomer findCustomer;
 @In private Customer customer;
 private String newMessage;
 @Logger private Log log;
 @In private EntityManager seamEntityManager;

 @Create @Begin
 public void create() {
 log.debug("Starting customer edit conversation");
 }

 public Customer getCustomer() {

 return customer;
 }

 @End
 public String save() {
 return "saved";
 }

 public void setCustomer(Customer customer) {
 this.customer = customer;
 }

 public String addMessage() {
 Message message = new Message();
 message.setMessage(newMessage);
 message.setDate(new Date());
 message.setFromTo("To");
 customer.getMessages().add(message);
 newMessage = new String();
 return "addedMessage";
 }

 public String getNewMessage() {
 return newMessage;
 }

 public void setNewMessage(String newMessage) {
 this.newMessage = newMessage;
 }

 @Remove @Destroy
 public void destroy() {
 log.debug("Destroying customer edit");
 }
}

In the editCustomer.xhtml Facelets page, the list of messsages is displayed in a datatable with value="#{editCustomer.customer.message}".

This doesn't work. From what I understand from the documentation, this is because I started a new conversation. Is this really the reason, or is something else happening?



The next thing I tried is to add the following line to the @Create method of EditCustomerBean:

customer = seamEntityManager.merge(customer);

This should re-attach the customer to the session.
The create method is executed without errors, but it didn't solve the problemm.


Now my final solution that did work. I do not understand why this is any different from the example above.

public Customer getCustomer() {
 customer = seamEntityManager.merge(customer);
 return customer;
}

I simply moved the same line of code to the getCustomer method.
The only difference I can think of, is that the getCustomer method is called at a later time.