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jenslaufer
 Post subject: Bidirectional many-to-many on same entity
PostPosted: Thu Jan 28, 2010 9:12 am 
Newbie

Joined: Thu Jan 28, 2010 5:50 am
Posts: 5
Hello everybody,
I am struggling for a while now with a mapping problem: I want to realize a bidirectional many-to many relationship on the same entity.
I have a User that can have friends, which are of the type User as well. My mapping looks like that:
Code:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
   "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping default-cascade="all">
   <class name="com.objecttrax.tracking.domain.User" table="user">
      <id name="id" type="long">
         <generator class="native" />
      </id>
      <property name="username" unique-key="true" />
      <property name="password" />
      <array name="friends" table="tracking_user_friends" inverse="true">
         <key column="friend_id" />
         <index column="id" />
         <many-to-many column="user_id"
            class="com.objecttrax.tracking.domain.User" />
      </array>
      <array name="friendOf" table="tracking_user_friends" cascade="none">
         <key column="user_id" />
         <index column="id" />
         <many-to-many column="friend_id"
            class="com.objecttrax.tracking.domain.User" />
      </array>
   </class>
</hibernate-mapping>



On the first look that works. I am testing the following scenario:
I have 3 users, which are persisted:
user1
user2
user3

I am adding the following on the friendOf site of the relationship of the users and persist it:
user1.friendOf => [user2,user3]
user2.friendOf => [user3]

After persisting I test the friends site of the relationship and I get this:
user1.friends => [] (OK)
user2.friends => [user1] (OK)
user3.friends => [user2] (NOT OK) expected: [user1, user2]

It seems to me that index (<index column="id"/>) is causing the problem, but I don't know a better way for the mapping.
Does anybody has idea?

Thanks for your help.
Best regards,
Jens

---
Jens Laufer
http://www.objectworkz.org
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pb00067
 Post subject: Re: Bidirectional many-to-many on same entity
PostPosted: Thu Jan 28, 2010 9:35 am 
Expert
Expert

Joined: Tue Jun 16, 2009 3:36 am
Posts: 990
As I know, inverse="true" is for use with bidirectional OneToMany associations, not with ManyToMany associations.
Try to remove the inverse="true" definition.
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jenslaufer
 Post subject: Re: Bidirectional many-to-many on same entity
PostPosted: Thu Jan 28, 2010 9:47 am 
Newbie

Joined: Thu Jan 28, 2010 5:50 am
Posts: 5
Thanks for your quick answer, I removed the inverse, but I am still having the same problem.
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pb00067
 Post subject: Re: Bidirectional many-to-many on same entity
PostPosted: Thu Jan 28, 2010 10:22 am 
Expert
Expert

Joined: Tue Jun 16, 2009 3:36 am
Posts: 990
Sorry, I was wrong in my previous posting.
On Bidirectional many-to-many association it is mandatory to declare one side with inverse="true".

Did you remember to set both end of the association when establishing the association?
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jenslaufer
 Post subject: Re: Bidirectional many-to-many on same entity
PostPosted: Thu Jan 28, 2010 10:44 am 
Newbie

Joined: Thu Jan 28, 2010 5:50 am
Posts: 5
Do I have to set both ends. I thought I just have set the one end, where I have inverse="false"

Here the test code I use:
Code:
                User user1 = new User();
      user1.setUsername("friend1");
      dao.saveOrUpdate(user1);

      User user2 = new User();
      user2.setUsername("friend2");
      user2.setFriendOf(new User[] { user1 });
      dao.saveOrUpdate(user2);

      object = new User();
      object.setUsername("username");
      object.setFriendOf(new User[] { user1, user2 });
      dao.saveOrUpdate(object);

      User actual = dao.get(object.getId());
      User loadedUser1 = dao.get(user1.getId());

      assertEquals("friend1", actual.getFriendOf()[0].getUsername());
      assertEquals("friend2", actual.getFriendOf()[1].getUsername());
      assertEquals(2, loadedUser1.getFriends().length);
      assertEquals("username", loadedUser1.getFriends()[0]
            .getUsername());
      assertEquals("friend2",  loadedUser1.getFriends()[1]
            .getUsername());

      // Friends cannot be removed from "to" site
      loadedUser1.setFriends(new User[] {});
      dao.saveOrUpdate(loadedUser1);

      loadedUser1 = dao.get(user1.getId());
      actual = dao.get(object.getId());

      assertEquals("friend1",actual.getFriendOf()[0].getUsername());
      assertEquals("friend2", actual.getFriendOf()[1].getUsername());
      assertEquals(2, loadedUser1.getFriends().length);
      assertEquals("username", loadedUser1.getFriends()[0]
            .getUsername());
      assertEquals("friend2", loadedUser1.getFriends()[1]
            .getUsername());

      // Friends can be removed "from" site
           object.setFriendOf(new User[] {});
      dao.saveOrUpdate(object);

      loadedUser1 = dao.get(user1.getId());
      actual = dao.get(object.getId());

      assertEquals(1, loadedUser1.getFriends().length);
      assertEquals("friend2", loadedUser1.getFriends()[1]
            .getUsername());
      assertEquals(0, actual.getFriendOf().length);
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jenslaufer
 Post subject: Re: Bidirectional many-to-many on same entity
PostPosted: Thu Jan 28, 2010 10:48 am 
Newbie

Joined: Thu Jan 28, 2010 5:50 am
Posts: 5
...and the DAO, which is a standard HibernateDao supportetd by Spring:
Code:
jecttrax.tracking.domain.User;

public class UserDaoHibernateImpl extends HibernateDaoSupport implements
      UserDao {

   public void delete(User object) {
      getHibernateTemplate().delete(object);
   }

   public User get(long id) {
      return (User) getHibernateTemplate().get(User.class, id);
   }

   public User saveOrUpdate(User object) {
      User loadedLocation = get(object.getId());
      getHibernateTemplate().saveOrUpdate(object);
      return object;
   }
}
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pb00067
 Post subject: Re: Bidirectional many-to-many on same entity
PostPosted: Thu Jan 28, 2010 10:51 am 
Expert
Expert

Joined: Tue Jun 16, 2009 3:36 am
Posts: 990
>>Do I have to set both ends. I thought I just have set the one end, where I have inverse="false"

Hibernate documentation states that both ends must be set, even when working with inverse="false".

Anyway I guess that it wrong to refer to the same index column "id" twice (= from both sides)

Code:
<index column="id" />


Moreover the usage of <array> for associations is the last choice.
Hiberante documentation (and me too) suggests to use <set> of instead.
In this case you don't need the index column.
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jenslaufer
 Post subject: Re: Bidirectional many-to-many on same entity
PostPosted: Fri Jan 29, 2010 9:24 am 
Newbie

Joined: Thu Jan 28, 2010 5:50 am
Posts: 5
Thanks.
I am using a Set now, with the additional advantage, that lazy loading is supported.
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