Unexpected JPA SELECT statements logged when JSF page submitted

Question

I'm using Glassfish Server 4.1 with bundled JSF. I've enabled JPA FINE logging in "persistence.xml".

I have this Facelets page:

<p:dataTable var="customer" value="#{customerService.customers}">
</p:dataTable>
<h:form>
    <h:commandButton value="Test"/>
</h:form>

(Note that that's really all there is: I haven't associated an action with the button, or added columns to the table, and if I do, the behaviour I'm about to describe doesn't change. Also recall that default render behaviour is @none.)

And this Stateless EJB (with @Named so that the page can refer to it directly):

@Stateless
@Named
public class CustomerService {

    @PersistenceContext
    private EntityManager em;

    public List<Customer> getCustomers() {
        return em.createNamedQuery("Customer.findAll", Customer.class).getResultList();
    }
    ...

When I load the page, the following message appears in the log:

Fine:   SELECT ID, CUSTOMERNAME, EMAIL, PAID, QUANTITY, TYPE FROM CUSTOMER

So far so good. When I click the button though, this appears in the logs:

Fine:   SELECT ID, CUSTOMERNAME, EMAIL, PAID, QUANTITY, TYPE FROM CUSTOMER
Fine:   SELECT ID, CUSTOMERNAME, EMAIL, PAID, QUANTITY, TYPE FROM CUSTOMER
... Same message appears five more times ...

The Customers table is empty.

Can anyone reproduce or explain this behaviour? One SELECT for page load makes sense, but seven SELECTS for form submit is confusing.

UPDATE

The behaviour is unchanged if I move the EJB into a ViewScoped JSF backing-bean and update the Facelets page to use it:

@ManagedBean // javax.faces.bean.
@ViewScoped
public class BackingBean {
    @EJB
    private CustomerService cs;
    public List<Customer> getCustomers() {
        return cs.getCustomers();
    } 
}

Answer 1

I think the problem is in the scope you are using in the bean, let me quote this from other question:

If it's CDI via @Named, then it defaults to @Dependent, as mentioned in Weld documentation: Finally, CDI features the so-called dependent pseudo-scope. This is the default scope for a bean which does not explicitly declare a scope type.The effect is that the bean instance is newly created on every single EL expression. So, imagine a login form with two input fields referring a bean property and a command button referring a bean action, thus with in total three EL expressions, then effectively three instances will be created.

Now, how do we solve it? May be you should try another scope for your bean depending on your requirements, Check out this documentation about Scopes and context in JSF.

Answer 2

As Tiny explained in a comment on my question, the extra logging is occurring because I placed business logic inside the getter method used by the Facelets page. It is usually frowned upon to put business logic in the accessors (getter and setter) methods used by Facelets pages, as these methods are used by the JSF framework and you have little control over when and how often they are called.

In this case the issue can be "fixed" by initializing customers in the @PostConstruct method of a JSF view-scoped backing-bean:

@PostConstruct
public void init() {
    customers = customerService.getCustomers();
}
public List<Customer> getCustomers() {
    return customers;
}

This is a more conventional set-up, but I was trying to get by without a JSF backing-bean.

If someone can explain why the JSF framework is calling the method seven times, which seems arbitrary, I would definitely mark that answer correct, but in the meantime I am satisfied with this.

UPDATE

The explanation for the exact number of calls, seven, is probably similar to this answer, Why is the getter called so many times by the rendered attribute?:

The getter calls are all done by rendered="#{selector.profilePage == 'some'}" during the render response phase. When it evaluates false the first time, in UIComponent#encodeAll(), then no more calls will be done. When it evaluates true, then it will be re-evaluated six more times in the following sequence...