How to map these classes with Hibernate?

Question

Suppose I've these 2 classes:

class A{

    B ref1 = null; //Can both be null
    B ref2 = null;

}

class B{

    ..
}

I'm omitted the getters and setters for ref1 and ref2. Of course I want to add ids... Anyway what I want is to have hibernate handle automatic persistence of these two references... and to have automatic deletion of B objects. I thought of using one-to-one between each property ref* of A and B. But I got lost :) Can you give suggestions? I want to use SchemaExport.

Thank you.

Answer 1

you can achieve this behaviour by using the Cascade property of the OneToOne-Annotation. so with Hibernate Annotations / JPA Annotations youd have something like:

@Entity
public class AClass{
    @Id
    @GeneratedValue
    private long id;
    @OneToOne(cascade={Cascade.ALL, Cascade.DELETE_ORPHANS})
    private BClass b_1;
    @OneToOne(cascade={Cascade.ALL, Cascade.DELETE_ORPHANS})
    private BClass b_2;
}

@Entity
public class BClass{
    private String someField;
}

in an XML-mapping the association should look something like this:

<hibernate-mapping>
    <class name="AClass">
        <one-to-one cascade="all,delete-orphans" name="b_1" class="BClass" />
        <one-to-one cascade="all,delete-orphans" name="b_2" class="BClass" />
    </class>
</hibernate-mapping>

This should give you the wanted behaviour in cascading persistence operations onto the BClasses and delete any nonreferenced BClass Objects from the persistence layer.

Have Fun!

Frank

Answer 2

Hi,

You have a @OneToMany relationship. But you have to adapt ORM to your model because of There is no @OneToTwo relationship available.

 <hibernate-mapping>
     <class name="ClassAa">
         <list name="classBbList">
             <key column="CLASS_AA_ID" not-null="true"/>
             <list-index column="CLASS_BB_INDEX"/>
             <one-to-many class="ClassBb"/>
         </list>
     </class>
 <hibernate-mapping>

Now your ClassAa looks like

public class ClassAa {

    private ClassBb classBb1;
    private ClassBb classBb2;

    private List<ClassBb> classBbList = new ArrayList<ClassBb>();

    public void setClassBb1(ClassBb classBb1) {
        // You can use index 0 to store your classBb1
        if(getClassBbList().size == 0)
            getClassBbList().add(classBb1);
        else
            getClassBbList().set(0, classBb1);
    }

    public ClassBb getClassBb1() {
        if(getClassBbList().size() == 0)
            return null;

        return getClassBbList().get(0);
    }

    public void setClassBb2(ClassBb classBb2) {
        // You can use index 1 to store your classBb2
        switch(getClassBbList().size()) {
            case 0:
                getClassBbList().add(null);

                getClassBbList().add(classBb2);
            break;
            case 1:
                getClassBbList().add(classBb2);
            break;
            case 2:
                getClassBbList().set(1, classBb2);
            break;
        }
    }

    public ClassBb getClassBb2() {
        if(getClassBbList().size() < 2)
            return null;

        return getClassBbList().get(1);
    }

    public List<ClassBb> getClassBbList() {
        return this.classBbList;
    }

    public void setClasBbList(List<ClassBb> classBbList) {
        this.classBbList = classBbList;
    }

}

regards,