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Re: [eclipselink-users] Lazy loading does not work
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().
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