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Re: [eclipselink-users] Lazy loading does not work
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Hi,
not saying that this is feature is bad, it's just surprising initially.
Can you still clarify this a bit - since I have defined
EmployerService.findAll() with REQUIRES_NEW, the transaction that
fetched the Employer should be committed and closed at the point where
I am accessing the detached objects, correct? Does eclipseLink create
a new transaction for fetching the persons - one transaction for each
person, or what - how does it actually work?
On Tue, Sep 14, 2010 at 6:10 PM, Tom Ware <tom.ware@xxxxxxxxxx> wrote:
> 1. We choose to allow LAZY relationships to be traversed in detached objects
> where possible because we believe this provides a higher level of
> functionality. In other words... If we have everything we need to traverse
> the LAZY relationship, why would be disable the functionality that allows
> you to traverse it.
>
> 2. Yes. EclipseLink uses a 2nd level cache by default. There are a number
> of cache config settings. The following webpage shows a list of the caching
> options that are available through JPA config.
> http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29#Using_EclipseLink_JPA_Extensions_for_Entity_Caching
>
> -Tom
>
> janne postilista wrote:
>>
>> Well, yes, it sure seems like that is happening. Looking at the logs,
>> it seems that eclipselink first loads all Employers without the
>> persons (so lazy loading works)
>>
>>
>> [#|2010-09-14T17:44:32.494+0300|FINE|glassfish3.0.1|org.eclipse.persistence.session.file:/D:/projectszzz/glassfishv3-3/glassfish/domains/test-domai
>>
>> n/applications/services-ear/services-ejb_jar/zzz-pu.sql|_ThreadID=17;_ThreadName=Thread-1;ClassName=null;MethodName=null;|SELECT
>> ID, ZZZ, VERSION FROM EMPLOYER|#]
>>
>>
>> [#|2010-09-14T17:44:32.539+0300|FINER|glassfish3.0.1|org.eclipse.persistence.session.file:/D:/projects/zzz/sandbox/glassfishv3-3/glassfish/domains/test-doma
>>
>> in/applications/services-ear/services-ejb_jar/zzz-pu.transaction|_ThreadID=17;_ThreadName=Thread-1;ClassName=null;MethodName=null;|end
>> unit of work commit|
>> #]
>>
>> then after exiting findAll() I am mapping the entities to JAXB beans
>> and accessing the person references. Eclipselink loads the person from
>> db:
>>
>>
>> [#|2010-09-14T17:44:32.676+0300|FINE|glassfish3.0.1|org.eclipse.persistence.session.file:/D:/projects/zzz/sandbox/glassfishv3-3/glassfish/domains/test-domai
>>
>> n/applications/services-ear/services-ejb_jar/zzz-pu.sql|_ThreadID=17;_ThreadName=Thread-1;ClassName=null;MethodName=null;|SELECT
>> t1.ID, t1.LAST_NAME, t1.TI
>> TLE_SE, ZZZ FROM EMPLOYER_PERSON t0, PERSON t1 WHERE ((t0.E
>> MPLOYER_ID = ?) AND (t1.ID = t0.PERSON_ID))
>> bind => [20284]|#]
>>
>> 1. This seems counter-intuitive to me....how can Eclipselink fetch the
>> lazy relationships after a) the EJB transaction has already ended and
>> b) the entities have been explicitly detached? That's not at all what
>> I would be assuming
>> 2. If I redo the same method call, Eclipselink logs show that SQL
>> queries go to database to fetch the Employers, but there's no SQL for
>> the persons on the second go. Seems like the persons come from some
>> 2nd level cache or something? How does this work, I haven't configured
>> anything special related to caching? I have also noticed this in
>> practise, in that direct SQL updates to DB are not visible throught
>> the application. Does eclipseLink use 2nd level caching by default?
>>
>>
>> On Tue, Sep 14, 2010 at 4:47 PM, Tom Ware <tom.ware@xxxxxxxxxx> wrote:
>>>
>>> Hi Janne,
>>>
>>> Where in your code do you see the relationships traversed? You can turn
>>> on
>>> EclipseLink logging (persistence unit property:
>>> eclipselink.logging.level=FINEST) to see all of the logging. When do you
>>> see the SQL that traverses the relationship?
>>>
>>> EclipseLink has some functionality that allows LAZY relationships to be
>>> traversable after detachment if the connection is available. I am
>>> wondering
>>> if you are seeing that functionality in action.
>>>
>>> -Tom
>>>
>>> janne postilista wrote:
>>>>
>>>> Hi,
>>>>
>>>> I'm using Eclipselink to provide JPA. I'm using GlassFish 3.0.1.
>>>>
>>>> I have a some simple Employer and Person entities with many-to-many
>>>> (using join table) and one-to-many relationships. I want to have the
>>>> relationships lazy loaded, but it looks like they are always eagerly
>>>> loaded. I am aware that lazy/eager is just a hint to the JPA
>>>> implementation, but I'm thinking that lazy loading is probably
>>>> supposed to work with Eclipselink?
>>>>
>>>> Entities are along the lines of (likely irrelevant lines omitted):
>>>>
>>>>
>>>> @Entity
>>>> @NamedQueries({
>>>> @NamedQuery(name = "Employer.findAllLatest2", query = "select o
>>>> from Employer o"),
>>>> })
>>>> public class Employer implements Serializable {
>>>> @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.MERGE)
>>>> @JoinTable(name = "EMPLOYER_PERSON", joinColumns =
>>>> @JoinColumn(name = "EMPLOYER_ID"), inverseJoinColumns =
>>>> @JoinColumn(name = "PERSON_ID"))
>>>> private Set<Person> persons;
>>>>
>>>> @ManyToOne(fetch = FetchType.LAZY)
>>>> @JoinColumn(name = "BOSS_ID")
>>>> private Person boss;
>>>> }
>>>>
>>>> @Entity
>>>> @NamedQueries({
>>>> @NamedQuery(name = "EmployerPerson.findAll", query = "select o from
>>>> EmployerPerson o")
>>>> })
>>>> @Table(name = "EMPLOYER_PERSON")
>>>> @IdClass(EmployerPersonPK.class)
>>>> public class EmployerPerson implements Serializable {
>>>> @Id
>>>> @Column(name="EMPLOYER_ID", nullable = false, insertable = false,
>>>> updatable = false)
>>>> private Long employerId;
>>>> @Id
>>>> @Column(name="PERSON_ID", nullable = false, insertable = false,
>>>> updatable = false)
>>>> private Long personId;
>>>> @ManyToOne
>>>> @JoinColumn(name = "EMPLOYER_ID")
>>>> private Employer employer;
>>>> @ManyToOne
>>>> @JoinColumn(name = "PERSON_ID")
>>>> private Person person;
>>>> }
>>>>
>>>> @Entity
>>>> public class Person implements Serializable {
>>>> @ManyToMany(mappedBy="persons")
>>>> private Set<Employer> employers;
>>>>
>>>> @Stateless
>>>> @LocalBean
>>>> @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
>>>> public class EmployerService {
>>>>
>>>> @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
>>>> public List<Employer> findAll() {
>>>> String namedQuery = "Employer.findAllLatest2";
>>>> }
>>>> List<Employer> employers = em.createNamedQuery(namedQuery,
>>>> Employer.class).getResultList();
>>>> for (Employer e: employers) {
>>>> em.detach(e);
>>>> }
>>>> return employers;
>>>> }
>>>>
>>>> Now, when I use findAll(), I would expect that Employer objects do not
>>>> have the person references fecthed. But they are. Accessing persons
>>>> succeeds even though I did add (extraneous) detach() -calls to make
>>>> sure the entities are detached after returning from findAll().
>>>> _______________________________________________
>>>> eclipselink-users mailing list
>>>> eclipselink-users@xxxxxxxxxxx
>>>> https://dev.eclipse.org/mailman/listinfo/eclipselink-users
>>>
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