How to map these classes with Hibernate?

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.

From stackoverflow

• 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

  gotch4 : thanks but I was looking for xml based mapping...

  gotch4 : moreover are you sure that it is safe to use one-to-one isn't it one to many for A?

  smeg4brains : well that depends on the data model, if you have one and only one reference from one AClass to one BClass it works, even if there are 2 fields holding BClasses in AClass. they just shouldnt be referencing the same instance

• 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,