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

> 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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