[
Date Prev][
Date Next][
Thread Prev][
Thread Next][
Date Index][
Thread Index]
[
List Home]
|
Re: [eclipselink-users] Lazy loading performance problem
|
Hello Warren,
Can you describe the relationships you have from ChoiceQuestions? Is
there a reason why you are using a query with pagination to read in the
questions instead of just accessing the relationship on the particular
Exam?
Some options: If you do not need to use the relationships from the
ChoiceQuestion, you can mark them as lazy so they are only queried when
needed. A second option is to not map the relationships from the
ChoiceQuestion side and instead query for them when needed (as you are
doing with the Exam->Questions already).
A third option is to break up the ChoiceQuestion query into chunks, or
to read in all the ChoiceQuestion pks and then read in the full objects
a bunch at a time. Ie,
"select questions from ExamPaper p join p.questions questions where
p.id=:paperId and mod(questions.id, 2) = :split"
Or
"select questions.id from ExamPaper p join p.questions questions where
p.id=:paperId" then
"select questions from ChoiceQuestions questions where questions.id
in(:listOfIds)"
This would allow you to use joining or batching on any relationships in
ChoiceQuestion.
Best Regards,
Chris
On 07/11/2011 10:41 AM, Warren Tang wrote:
But fetch join on OneToMany/ManyToMany relationship has problems with
pagination.
The problem seems to be called N+1 select problem. I searched hard but
could found a solution.
It's a problem everyone faces, right? How do you solve it?
Regards,
Warren Tang <http://blog.tangcs.com>
On Friday, November 04, 2011 5:43:32 PM, Leon Derks wrote:
Hello.
I think you can do this with a fetch join like:
SELECT pub FROM Publisher pub JOIN pub.magazines mag
Leon
On Nov 4, 2011, at 10:36 AM, Warren Tang wrote:
Hi, everybody
I have an ExamPaper entity which has many ChoiceQuestions. The
questions are lazy loaded by default (fetch=LAZY).
Now I want to get all the quesitions that belong to a specific
ExamPaper, so I use the following JPQL:
"select p.questions from ExamPaper p where p.id=:paperId";
The problem is that questions are "lazy" loaded, so there is one
"SELECT" executed for *every single* question. But I want to select
them all in one go for performance reasons. What should I do?
------------------ Code listing -----------------------------------
@Entity
public class ExamPaper {
public static final String SELECT_QUESTION_BY_PAPER = "select
p.questions from ExamPaper p where p.id=:paperId";
@Id @GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
@OneToMany(fetch = FetchType.LAZY, orphanRemoval = true, cascade =
{CascadeType.ALL})
List<ChoiceQuestion> questions;
... ...
}
query = em.createQuery(ExamPaper.SELECT_QUESTION_BY_PAPER,
ChoiceQuestion.class);
query.setParameter("paperId", examPaperId);
query.setFirstResult(startPosition);
query.setMaxResults(maxResult);
list = query.getResultList();
--
Regards,
Warren Tang <http://blog.tangcs.com/>
_______________________________________________
eclipselink-users mailing list
eclipselink-users@xxxxxxxxxxx <mailto:eclipselink-users@xxxxxxxxxxx>
https://dev.eclipse.org/mailman/listinfo/eclipselink-users
_______________________________________________
eclipselink-users mailing list
eclipselink-users@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/eclipselink-users
_______________________________________________
eclipselink-users mailing list
eclipselink-users@xxxxxxxxxxx
https://dev.eclipse.org/mailman/listinfo/eclipselink-users
