public class Parent {
   Set<Child> children ;
   ...
   
   @OneToMany(mappedBy="parent")
   @JoinColumn(name="PARENT_ID")
   @Cascade( {CascadeType.SAVE_UPDATE, CascadeType.REFRESH})
   public Set<Child> getChildren() {
      return children ;
   }
   public void setChildren( Set<Child> _set ){
      children = _set ;
   }
}
public class Child {
   Parent      parent ;
   Set<GrandChild> grandChildren ;
   
   Language language ;
   
   @OneToMany(mappedBy="child")
   @JoinColumn(name="CHILD_ID")
   @Cascade( {CascadeType.SAVE_UPDATE, CascadeType.REFRESH})
   public Set<Child> getGrandChildren() {
      return grandChildren ;
   }
   public void setGrandChildren( Set<GrandChild> _set ){
      grandChildren = _set ;
   }
   
   @ManyToOne
   @JoinColumn(name="LANGUAGE_ID")
   public Language getLanguage() {
      return language ;
   }
   public void setLanguage( Language lang ) {
      language = lang ;
   }
   
   
   @ManyToOne
   @JoinColumn(name="PARENT_ID")
   public Parent getParent() {
      return parent ;
   }
   public void setParent( Parent _parent) {
      parent = _parent ;
   }
   
}

public class GrandChild {
   Language language ;
   Child   child ;

   @ManyToOne
   @JoinColumn(name="LANGUAGE_ID")
   public Language getLanguage () {
      return language ;
   }
   public void setLLanguage ( Language lang ) {
      language = lang ;
   }
   
   @ManyToOne
   @JoinColumn(name="CHILD_ID")
   public Parent getChild() {
      return child;
   }
   public void setChild( Child _parent) {
      child = _parent ;
   }
}

AND
public class Language {
   Child   child ;
   GrandChild   grandChild;
   String   description ;
   
   @ManyToOne
   @JoinColumn(name="LANGUAGE_ID")
   public Parent getChild() {
      return child;
   }
   public void setChild( Child _parent) {
      child = _parent ;
   }
   
   @ManyToOne
   @JoinColumn(name="LANGUAGE_ID")
   public Parent getGrandChild() {
      return grandChild;
   }
   public void setGrandChild( GrandChild _parent) {
      grandChild = _parent ;
   }
   

}

   
        session.flush( parent ) ;
   session.persist( parent );      /// Inserts gc to the DB.
   session.refresh( parent );
   
   ...
   // Following generates null pointer exception
   for ( GrandChild gc : child.getGrandChildren() ) {
      System.out.println( gc.getLanguage().getDescription ) ;    
      // -- the getLanguage on the gc recently added is null 
   }