public class MusicOrderedLayoutPolicy extends OrderedLayoutEditPolicy {
@Override
protected Command createAddCommand(EditPart child, EditPart after) {
if (!(child instanceof BasicElement))
throw new MusicNotImplementedException();
BasicElement part = (BasicElement) child.getModel();
AddCommand add = new AddCommand();
add.setParent((MusicContainerForm) getHost().getModel());
add.setChild(part);
return add;