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Question

Mapping same class relation - continuation

Answer 1

+1 A:

Just Facebook and MyFriends

Facebook Notice add convenience method and MutableLong (later, i tell you why to use MutableLong)

public class Facebook {

    private MutableLong id = new MutableLong();
    public Long getId() { return id.longValue(); }
    public void setId(Long id) { this.id.setValue(id); }

    public MutableLong getIdAsMutableLong() {
        return id;
    }

    private Collection<MyFriends> myFriends = new ArrayList<MyFriends>();
    public Collection<MyFriends> getMyFriends() { return myFriends; }
    public void setMyFriends(Collection<MyFriends> myFriends) { this.myFriends = myFriends; }

    /**
     * add convenience method
     */
    public void addFriend(Facebook myFriendFacebook) {
        myFriends.add(new MyFriends(this, myFriendFacebook));
    }

}

MyFriends

public class MyFriends {

    private MyFriendsId myFriendId;
    public MyFriendsId getmyFriendId(){ return this.myFriendId; }
    public void setmyFriendId(MyFriendsId myFriendId){ this.myFriendId = myFriendId; }

    private Facebook me;
    public Facebook getme() { return this.me; }
    public void setme(Facebook me){ this.me = me; }

    private Facebook myFriend;
    public Facebook getmyFriend() { return this.myFriend; }
    public void setmyFriend(Facebook friend) { this.myFriend = friend; }

    public MyFriends() {}
    public MyFriends(Facebook meFacebook, Facebook myFriendFacebook){
        this.me = meFacebook ;
        this.myFriend = myFriendFacebook;

        this.myFriendId = new MyFriendsId(meFacebook.getIdAsMutableLong(), myFriendFacebook.getIdAsMutableLong());
    }

    public static class MyFriendsId implements Serializable {

        private MutableLong meId = new MutableLong();
        public Long getMeId() { return this.meId.longValue(); }
        public void setMeId(Long id) { this.meId.setValue(id); }

        private MutableLong myFriendId = new MutableLong();
        public Long getMyFriendId(){ return this.myFriendId.longValue(); }
        public void setMyFriendId(Long id) { this.myFriendId.setValue(id); }

        public MyFriendsId() {}
        public MyFriendsId(MutableLong meId, MutableLong myFriendId) {
            this.meId = meId;
            this.myFriendId = myFriendId;
        }

        @Override
        public boolean equals(Object o) {
            if (!(o instanceof MyFriendsId))
                return false;

            MyFriendsId other = (MyFriendsId) o;
            return new EqualsBuilder()
                       .append(getMeId(), other.getMeId())
                       .append(getMyFriendId(), getMyFriendId())
                       .isEquals();
        }

        @Override
        public int hashCode() {
            return new HashCodeBuilder()
                       .append(getMeId())
                       .append(getMyFriendId())
                       .hashCode();
        }

    }
}

Mapping

<hibernate-mapping package="br.com._3845772.model.domain">
    <class name="User">
        <id name="id">
            <generator class="native"/>
        </id>
        <many-to-one cascade="all" class="Facebook" name="facebook"/>
    </class>
    <class name="Facebook">
        <id name="id">
            <generator class="native"/>
        </id>
        <bag cascade="all" name="myFriends">
            <key column="ME_FACEBOOK_ID" update="false"/>
            <one-to-many class="MyFriends"/>
        </bag>
    </class>
    <class name="MyFriends">
        <composite-id class="MyFriends$MyFriendsId" name="myFriendId">
            <key-property column="ME_FACEBOOK_ID" name="meId"/>
            <key-property column="MY_FRIEND_FACEBOOK_ID" name="myFriendId"/>
        </composite-id>
        <many-to-one class="Facebook" column="ME_FACEBOOK_ID" insert="false" name="me" update="false"/>
        <many-to-one class="Facebook" column="MY_FRIEND_FACEBOOK_ID" insert="false" name="myFriend" update="false"/>
    </class>
</hibernate-mapping>

And this sample

Facebook meFacebook = new Facebook();
Facebook myFriendFacebook = new Facebook();

meFacebook.addFriend(myFriendFacebook);

Session session = sessionFactory.openSession();
session.beginTransaction();

session.save(myFriendFacebook);
session.save(meFacebook);

session.getTransaction().commit();
session.close();

Which gives me

Hibernate: insert into Facebook values ( )
Hibernate: insert into Facebook values ( )
Hibernate: select myfriends_.ME_FACEBOOK_ID, myfriends_.MY_FRIEND_FACEBOOK_ID from MyFriends myfriends_ where myfriends_.ME_FACEBOOK_ID=? and myfriends_.MY_FRIEND_FACEBOOK_ID=?
Hibernate: insert into MyFriends (ME_FACEBOOK_ID, MY_FRIEND_FACEBOOK_ID) values (?, ?)

A couple of notes

Hibernate does not support automatic generation of composite primary key. You must set up its value before saving
Your database must support the target generator strategy (If you does not know which generator strategy your database support, prefer to use a native strategy)
Each entity must supply a no-arg constructor

Now why MutableLong (encapsulated by a Long property) instead of Long ?

Number and its subclasses (Long is a Number) are immutable. So if you want Facebook.id (configured by database) and its counterpart MyFriend$MyFriendId.meId share the same value, you must use MutableLong. When the database set up Facebook.id, MyFriend$MyFriendId.meId automatically get its newest value. But it just occurs if you use a MutableLong.

Arthur Ronald F D Garcia 2010-10-02 14:50:51

It works :) Thank you so much. I learned a lot from your examples. It was big pleasure for me.

danny.lesnik 2010-10-03 00:21:34

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Mapping same class relation - continuation

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