Re: Uregntly need help for thesis: Batch reading of collection with lazy OneToOne relation

by tware :: Rate this Message:

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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