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Re: [eclipselink-users] Uregntly need help for thesis: Batch reading of collection with lazy OneToOne relation
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Hi Tom,
I think I explained it the wrong way last time. The
performance-measuring is just a small part in which
provider-specifically performance-optimized use-cases (goal: at least
SQLs as possible) are measured and compared. The main focus of the
thesis lies on evaluating the persistence providers performance
optimization capabilities by means of typical use-cases. My bad!
You´re right. So far, a partner just might have the role "employee".
Sorry I missed that fact out.
I did already try it with a customizer based on the workaround from Doug
Clarke "Accessing un-mapped attributes using QueryKey "
(http://wiki.eclipse.org/EclipseLink/Development/JPA/QueryDownCast). The
role entity class was annotated with this Customizer:
package customizer;
import org.eclipse.persistence.config.DescriptorCustomizer;
import org.eclipse.persistence.descriptors.ClassDescriptor;
// The customizer adds the direct query keys
public class RoleCustomizer implements DescriptorCustomizer {
public void customize(ClassDescriptor descriptor) throws Exception {
descriptor.addDirectQueryKey("bankaccount", "BANKACCOUNT");
}
}
But how am I supposed to use my NamedQuery with the ExpressionBuilder
like in the example then?
Like the following code snippet or would I have to modify the NamedQuery
and do something like .addBatchReadAttribute(batchReadRoles) and also
.addBatchReadAttribute(batchReadBankAccount)?
Query q = em.createNamedQuery("getAllPartnersWithAdressesAndRoles");
ExpressionBuilder eb = q.getExpressionBuilder();
Expression batchReadBankAccount = eb.get("bankaccount");
readAllQuery.addBatchReadAttribute(batchReadBankAccount);
q.setSelectionCriteria(eb.get("bankaccount").like("bankaccount"));
// Wrap in JPA Query
Query query = JpaHelper.createQuery(q, em);
// Execute Query
List<A> results = query.getResultList();
Thanks for your help!!!
Mario
Tom Ware schrieb:
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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