[jboss-user] [JBoss Seam] - Lazy loading behaviour

[paul@xfact.nl]

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.

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