Hibernate ManyToOne with FetchType.LAZY not fetching lazy

Question

I am using Hibernate with spring.

I have a model-class like this.


@Entity
@Table(name = "forumtopic")
public final class Forumtopic extends AbstractUserTracking implements
    java.io.Serializable {

/**SNIP **/

    private Forumcategory forumcategory;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "FkForumcategoryId", nullable = false)
    public Forumcategory getForumcategory() {
        return this.forumcategory;
    }

    public void setForumcategory(final Forumcategory forumcategory) {
        this.forumcategory = forumcategory;
    }
}

It works in general, but the Category is not loaded lazy, but eagerly after the ForumEntry has been loaded.

Hibernate: 
    select
        forumtopic0_.PkId as PkId19_0_,
        forumtopic0_.CreateDate as CreateDate19_0_,
        forumtopic0_.FkCreateUserId as FkCreate3_19_0_,
        forumtopic0_.FkLastUserId as FkLastUs4_19_0_,
        forumtopic0_.LastChange as LastChange19_0_,
        forumtopic0_.FkForumcategoryId as FkForum10_19_0_,
        forumtopic0_.PublishCategory as PublishC6_19_0_,
        forumtopic0_.State as State19_0_,
        forumtopic0_.Text as Text19_0_,
        forumtopic0_.Topic as Topic19_0_,
        forumtopic0_.FkTpUserId as FkTpUserId19_0_ 
    from
        forumtopic forumtopic0_ 
    where
        forumtopic0_.PkId=?
Hibernate: 
    select
        forumcateg0_.PkId as PkId17_0_,
        forumcateg0_.CreateDate as CreateDate17_0_,
        forumcateg0_.Name as Name17_0_,
        forumcateg0_.FkRequestId as FkReques4_17_0_,
        forumcateg0_.FkTpUserId as FkTpUserId17_0_ 
    from
        forumcategory forumcateg0_ 
    where
        forumcateg0_.PkId=?

Altough the getter was not called the ForumCategory is loaded right after ForumTopic.

This problems appears in all my @ManyToOne-associations. However @OneToMany associating are loaded lazily.

I am using maven2 for the build. These are my dependencies.




  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring</artifactId>
    <version>2.5.6</version>
  </dependency>


  <dependency>
    <groupId>org.hibernate</groupId> 
    <artifactId>hibernate-core</artifactId> 
    <version>3.3.1.GA</version> 
  </dependency>
  <dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>ejb3-persistence</artifactId>
    <version>1.0.2.GA</version>
  </dependency>
  <dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-annotations</artifactId>
    <type>jar</type>
    <version>3.4.0.GA</version>
  </dependency>
  <dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-entitymanager</artifactId>
    <type>jar</type>
    <version>3.4.0.GA</version>
  </dependency>
  <dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-search</artifactId>
    <version>3.1.0.GA</version>
</dependency>

Can someone please help me understand what is happening?

axtavt · Accepted Answer · 2011-04-08 12:12:25Z

18

I guess it's caused by the fact that your classes are declared as final, therefore Hibernate cannot generate lazy proxies for them. Try to remove final from class declarations.

answered Apr 8, 2011 at 12:12

axtavt

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Comments

kalyan · Accepted Answer · 2011-04-08 12:00:03Z

Looks like the transaction/session is closed after returning ForumTopic. Hence it becomes detached entity. When you try to do a getForumCategory there is no session to do the operation. You can prefetch the ForumCategory in the same session like,

In your getForumTopic, before returning a list (assuming you have a getAllForumTopic)

public List<ForumTopic> getAllForumTopic() {
  <snip> 
  List<ForumTopic> topics = <SNIP: get the list of ForumTopic>

  for(ForumTopic topic: topics)
      topic.getForumCategory()

  return topics;
}

This will fetch the ForumCategory in the same session. Otherwise you have to create a transaction in the calling function of getAllForumTopic and use the same transaction where ever you need to call getForumCategory.

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