GWT ValueProxy and RequestFactory Domain Type error

Question

Im trying to create a Value Proxy (BrowserDetailItem ) that is formed of a query that only returns a String(name) and a Integer(id).

The SERVER code (each class in a different files)

public class BrowserDetailItem {

    private String name;
    private Integer id;

    public static EntityManager entityManager() {
        return (new UnitPersistence()).get();
    }

    BrowserDetailItem() {
    }

    BrowserDetailItem(String name, Integer id) {
        this.name = name;
        this.id = id;
    }

    public String getName() {

        if (name == null)
            return "";
        else
            return name;
    }

    public Integer getId() {

        if (id == null)
            return null;
        else
            return id;
    }

    public static List<BrowserDetailItem> getBrowserFilterList() {

        EntityManager entityManager = entityManager();
        try {

            List<BrowserDetailItem> tempList = new ArrayList<BrowserDetailItem>();

            Query query = entityManager
                    .createQuery("SELECT s.name,s.id FROM Song s, Playlist p, Composer c "
                            + "WHERE s.id_playlist = p.id AND c.id = p.id_composer ");

            tempList = query.getResultList();
            tempList.size();

            return tempList;

        } catch (Exception e) {
            return null;
        } finally {
            entityManager.close();
        }

    }
}
public class BrowserDetailItemDAO {

    public void save(BrowserDetailItem browserItem) {
    }

    public BrowserDetailItem findById(Integer id) {
        return null;
    }
}



public class BrowserDetailItemLocator extends
        Locator<BrowserDetailItem, Integer> {

    @Override
    public BrowserDetailItem create(Class<? extends BrowserDetailItem> clazz) {
        return new BrowserDetailItem();
    }

    @Override
    public BrowserDetailItem find(Class<? extends BrowserDetailItem> clazz,
            Integer id) {
        return getBrowserDetailItemDao().findById(id);
    }

    private BrowserDetailItemDAO getBrowserDetailItemDao() {
        return new BrowserDetailItemDAO();
    }

    @Override
    public Class<BrowserDetailItem> getDomainType() {
        return BrowserDetailItem.class;
    }

    @Override
    public Integer getId(BrowserDetailItem domainObject) {
        return domainObject.getId();
    }

    @Override
    public Class<Integer> getIdType() {
        return Integer.class;
    }

    @Override
    public Object getVersion(BrowserDetailItem domainObject) {
        // return domainObject.getVersion();
        return null;
    }

}

The SHARED code (each class in a different files)

@ProxyFor(value = BrowserDetailItem.class, locator = BrowserDetailItemLocator.class)
public interface BrowserDetailItemProxy extends ValueProxy {

    public String getName();

    public Integer getId();

}

@Service(BrowserDetailItem.class)
public interface BrowserDetailItemRequest extends RequestContext {

    Request<List<BrowserDetailItemProxy>> getBrowserFilterList();
}

I did all the wiring acording to the developer guide and http://cleancodematters.com/2011/06/04/tutorial-gwt-request-factory-part-i/

The code executes (returns the query and assigns the results to a list) up to the return of getBrowserFilterList() then I get the following error:

com.google.web.bindery.requestfactory.server.UnexpectedException: The domain type java.lang.Object[] cannot be sent to the client.

What am I doing wrong? please help

Answer 1

Solved it.

The problem was in: tempList = query.getResultList();

The result list returned from the query is a List<Object[][]> which couldn't be converted to List<BrowserDetailItem>.

This meant that the return method instead of returning a List<BrowserDetailItem> which is a ValueProxy, returned a List<Object[][]> which can't be sent to the server.

The solution was to iterate though the List and create a new BrowserDetailItem in each pass:

     Query query = entityManager 
            .createQuery("SELECT s.name,s.id FROM Song s,  Playlist p, Composer c WHERE s.id_playlist = p.id AND c.id = p.id_composer "); 

        List results = query.getResultList(); // Fetches list containing arrays of object

        Iterator it = results.iterator();

        while (it.hasNext()) {

            Object[] result = (Object[]) it.next(); // Iterating through the array object

            tempList.add(new BrowserDetailItem ((String) result[0], (Integer) result[1]));
        }

        tempList.size();

        return tempList;

I Also removed the locator was pointless because no persistence was required.

Hope it helps.

Thx Sam