Unidirectional @ManyToOne and Cascades

puccio · **Posted:** Wed Mar 08, 2006 6:48 am

Hi,
I am using hibernate-3.1.2 and hibernate-annotations-3.1beta8 with hsqldb-1.8.0.

In my OO I want to have (let's say) class X, class Y, and class Association, which explicitly represents the many-to-many relational association between entities X and Y.

I want the navigability to be unidirectional from Association to X (and Y), so there is not reference from X (Y) to Association

So I have something like:

Code:

@Entity
public class X { 
    private Long id;

   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   public Long getId() {
   
   public void setId(Long id) {
   this.id = id;
   }   

    // NO references to Association
}

Code:

@Entity
public class Y { 
    private Long id;

   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   public Long getId() {
   
   public void setId(Long id) {
   this.id = id;
   }   
   
   // NO references to Association
}

Code:

@Entity
public class Association { 
    private Long id;
    private X x;    // reference to one X
    private Y y;    // reference to one Y

   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   public Long getId() {
   
   public void setId(Long id) {
   this.id = id;
   }   

    @ManyToOne(cascade={CascadeType.PERSIST,CascadeType.REFRESH,   CascadeType.MERGE},fetch= FetchType.EAGER)
    @JoinColumn(name="x_id")
    @Column(nullable=false)
    public X getX(){
        return x;
    }

    public void setX(X x){
          this.x=x;
    }

    @ManyToOne(cascade={CascadeType.PERSIST,CascadeType.REFRESH,   CascadeType.MERGE},fetch= FetchType.EAGER)
    @JoinColumn(name="y_id")
    @Column(nullable=false)
    public Y getY(){
        return x;
    }

    public void setY(Y y){
          this.y=y;
    }
}

The issues are:

When I delete an already saved instance of X, it does not delete automatically all the persistent instances of Association that reference that X that has been deleted, and so I have a database that is invalid indeed (because the foreign key x_id value points to something that does not exist anymore in the db)
If a save a newly crated instance of Association which is composed on a newly created instance of (let's say) X, X is not persisted as well. If instead I change the @ManyToOne Annotation from:
Code:
@ManyToOne(cascade={CascadeType.PERSIST,CascadeType.REFRESH, CascadeType.MERGE}

to:
Code:
@ManyToOne(cascade={CascadeType.ALL}

it performs that but has the drawback that if I delete the Association, it deletes as well the X instance, which is not what I want of course! (because it does not reflect the semantic of the model)

The DAO codes for X, Y and Association is based on the GenericDAO pattern (integrated with Spring, throught HibernateDAOSupport), which simply does:

Code:

public void saveOrUpdate(T entity) throws DataAccessException{   
    getHibernateTemplate().saveOrUpdate(entity);
}
       
public void remove(ID id) throws DataAccessException {
    T o = (T) getHibernateTemplate().load(persistentClass, id);
    if (o != null)
        getHibernateTemplate().delete(o);
    else
   throw new ObjectRetrievalFailureException(persistentClass, id);
}

Which didn't give any other problem in the model.

Help would be appreciated, thanks a lot in advance.