Hello,

I have a relationship between two entities which is essentially a manytomany relation ship if not for the extra data the relationship can provide. Therefore I have created a connector class.

in Chemical.java

@OneToMany(mappedBy="chemical", cascade=CascadeType.ALL)
private List<ChemicalNoteConnector> notes;

in ChemicalNoteConnector.java

@ManyToOne
private Chemical chemical;

@ManyToOne
private ChemicalNote chemicalNote;

in ChemicalNote.java

@OneToMany(mappedBy="chemicalNote", cascade=CascadeType.ALL)
private List<ChemicalNoteConnector> chemicals;

A normal ManyToMany relation ship is quite easily solved using a selectManyCheckbox for the frontend. However it does not allow for the extra data. To solve this I added

    
@In(required=false)
@Out
private List<NoteSelectItem> notes;

which uses a class derived from SelectItem to contain the relationship. This uses a lot of plumbing code to make it work and just does not seam very efficient to me. Eg:

     @SuppressWarnings("unchecked")
     public void findNotes() {
          if (chemical == null)
               return;
          
          List<ChemicalNoteConnector> connectedNotes;
          if (entityManager.contains(chemical)) {
               connectedNotes = 
                    entityManager.createQuery("from ChemicalNoteConnector cnn where cnn.chemical = :chemical")
                    .setParameter("chemical", chemical)
                    .getResultList();
          } else {
               connectedNotes = new ArrayList<ChemicalNoteConnector>();
          }
          
          List<ChemicalNote> notesList = entityManager.createQuery("from ChemicalNote c order by c.number asc").getResultList();
          
          List<NoteSelectItem> items = new ArrayList<NoteSelectItem>();
          for (ChemicalNote n : notesList) {
               NoteSelectItem item = new NoteSelectItem();
               item.setLabel(Integer.toString(n.getNumber()));
               item.setValue(n);
               for (ChemicalNoteConnector cnn : connectedNotes) {
                    if (cnn.getChemicalNote().getNumber() == n.getNumber()) {
                         item.setSelected(true);
                         item.setExtra(cnn.getExtra());
                         break;
                    }     
               }
               items.add(item);
          }
          
          notes = items;
     }
     
     private void setNotes() {
          log.info("chemicalManager.setNotes called");
          
          if (entityManager.contains(chemical)) {
               for (ChemicalNoteConnector nc : chemical.getNotes()) {
                    nc.getChemicalNote().getChemicals().remove(nc);
                    entityManager.remove(nc);
               }
               chemical.setNotes(null);
               entityManager.flush();
          }
          
          List<ChemicalNoteConnector> connectors = new ArrayList<ChemicalNoteConnector>();
          for (NoteSelectItem item : notes) {
               if (!item.isSelected())
                    continue;
               log.info("Adding connector: " + item.getLabel() + " extra: " + item.getExtra());
               ChemicalNoteConnector connector = new ChemicalNoteConnector();
               connector.setChemical(chemical);
               connector.setChemicalNote((ChemicalNote) item.getValue());
               
               // Empty inputtexts are not null
               if (item.getExtra() != null || !item.getExtra().equals(""))
                    connector.setExtra(item.getExtra());
               
               connectors.add(connector);
          }
          chemical.setNotes(connectors);
     }

Well it works. But I was thinking there should be an easier way as I think the extra data part if a quite common requirement. Does someone have an idea and is willing to share it?

Thanks!