Re: [eclipselink-users] Uregntly need help for thesis: Batch reading of

[Tom Ware <tom.ware@xxxxxxxxxx>]

First of all, I'd like to reiterate that this is a fairly uncommon thing to do 
and that I am surprised that your performance-measuring app is doing something 
that uncommon.

I am not sure how the code below works in the case where "role" is not and 
Employee.  You'll get a ClassCastException from java regardless of the 
persistence provider.  Are all your roles Employees?

>>>   for (Partner partner : l) {
>>>     for (Role role : partner.getRoles()) {
>>>       // results in l.size() SELECTs
>>>       BankAccount ba = ((Employee) role).getBankAccount();
>>>     }
>>>   }

In EclipseLink, there is the option of setting the mapping itself to batch read, 
so one way you could make it work for this scenario is by using a 
DescriptorCustomizer to make the Employee.roles mapping always use batch 
reading.  It would be a matter of getting the query for that mapping and 
enabling batch reading on it.

-Tom

Mario Sandro Schwarz wrote:
> Hello Tom,
>
> unfortunately the problem is that not the role has the "bankaccount". 
> Just the specific role "employee" does.
> I remember you replying to my last post telling me that there is a an 
> open enhancement request for this kind of thing (Downcasting in 
> queries). Thanks a lot for the try to help though.
>
> Anyone got any other suggestions that might help?
>
> Mario
>
>
> Tom Ware schrieb:
> > EclipseLink allows multi-level fetch joins and batch reading.  Have 
> > you tried any of these?
> >
> > http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#Join_Fetch 
> >
> >
> > (something like @QueryHint(name = QueryHints.LEFT_FETCH, value = 
> > "p.roles.bankAccount")
> >
> > http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#Batch
> >  (something like @QueryHint(name=QueryHints.BATCH, 
> > value="p.roles.bankAccount");
> >
> > Mario Schwarz wrote:
> > > Hi everybody.
> > >
> > > I have to do a run time comparison on Eclipselink and Hibernate for 
> > > my Bachelor Thesis. I really have an urgent problem, I don't get 
> > > BatchReading to work correctly.
> > >
> > > I implemented use-case based test cases that call specific methods of 
> > > a  SessionBean called "PartnerService". PartnerService acts as a 
> > > Facade and manages the transactions 
> > > (@TransactionAttributeType.REQUIRED). It calls methods on a DAO 
> > > called "PartnerDAO". PartnerDAO requires an open transaction 
> > > (@TransactionAttributeType.MANDATORY)
> > >
> > > I have the following NamedQuery which retrieves me all partners with 
> > > their addresses and their roles:
> > >
> > > @NamedQuery(name = "getAllPartnersWithAdressesAndRoles", query = 
> > > "SELECT p FROM Partner as p ", hints = {
> > > @QueryHint(name = QueryHints.LEFT_FETCH, value = "p.roles"),
> > > @QueryHint(name = QueryHints.LEFT_FETCH, value = "p.addresses"),
> > > @QueryHint(name = QueryHints.JDBC_FETCH_SIZE, value = "1000") })
> > >
> > > Now I also want to retrieve the bank account of the specific role 
> > > "employee"  which is a unidirectional onetoone-relation. In the 
> > > PartnerDAO-method I do the following:
> > >
> > > public List<Partner> findAllPartners() {
> > >   Query q = em.createNamedQuery("getAllPartnersWithAdressesAndRoles");
> > >   // results in just 1 SELECTs
> > >   List<Partner> l = q.getResultList();
> > >   for (Partner partner : l) {
> > >     for (Role role : partner.getRoles()) {
> > >       // results in l.size() SELECTs
> > >       BankAccount ba = ((Employee) role).getBankAccount();
> > >     }
> > >   }
> > > }
> > >
> > > My goal is to iterate over all roles and retrieve all BankAccounts in 
> > > a single SELECT. I guess the problem is, that BankAccount has no 
> > > ForeignKey of its Employee. With Hibernate it works though. Oh, by 
> > > the way, I am not able to change the mapping to bidirectional anymore!
> > >
> > > Any help is more than appeciated!
> > > Thanks
> > > Mario
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