Adding a new child to an entity removes the persisted one

rheydenr · **Joined:** Tue Aug 15, 2006 8:51 am **Posts:** 1

Hi all,
I have a simple parent-child relationship:

The parent class:

Code:

@Entity
public class Parent implements Serializable {
   @Id
   @GeneratedValue
   @Column(name = "PARENT_ID")
   public long getId() {
      return id;
   }

// some other fields

   @OneToMany(cascade = CascadeType.ALL, fetch=FetchType.EAGER)
   @JoinTable(name = "PARENT_CHILD", 
           joinColumns = { @JoinColumn(name = "PARENT_ID") }, 
           inverseJoinColumns = { @JoinColumn(name = "CHILD_ID") })
   public Set<Child> getRelatedChildren() {
      return relatedChildren;
   }
}

...and the child class:

Code:

@Entity
public class Child implements Serializable {

   private static final long serialVersionUID = -46484016106062423L;
   private long id;
   
   /**
    * @return the id
    */
   @Id
   @GeneratedValue
   @Column(name = "CHILD_ID")
   public long getId() {
      return id;
   }

// some other fields
}

Now I get a Parent object from the DB, give it to the real world and get it back with some added children. Then I give this to my DAO for updating the existing one:

Code:

   public void update(Parent parent) {
      Parent parentFromDB = getParentById(parent.getId());
      Set<Child> relatedChildrenFromDB = parentFromDB.getRelatedChildren();
      
      // merge the new picture from incoming parent into the entity
      relatedChildrenFromDB.addAll(parent.getRelatedChildren());
      parentFromDB = (Parent)getCurrentSession.merge(parentFromDB);
   }

Now, the new child is persisted, but all previous entries for this relation are thrown away. What is the trick to get it all together???

TIA,
Ralf

Sukirtha · **Posted:** Thu Nov 19, 2009 7:48 am

Try saving the parent object directly without manipulating the one from the db

Something like this:

Code:

public void update(Parent parent) {
       // merge the new picture from incoming parent into the entity
           getCurrentSession.merge(parent);
}

I feel this should work since the parent object that you get as parameter is just a detached instance of the object you loaded before passing it on to the real world. It is enough if you attach it back to the session.