Re: best practice for persisting fields

[Lance Java]

Actually... on second thought you can't return null from add since tapestry
needs to render the empty record.

Try this instead:

eg:
<t:ajaxformloop t:id="foos" source="foos" value="foo"
encoder="nullNewEncoder">...</t:ajaxformloop>

public class NullNewValueEncoder<T> implements ValueEncoder<T> {
   private static final String CLIENT_NULL = "XXX";
   private ValueEncoder<T> encoder;
   private Class<T> type;
   public NullNewValueEncoder<T>(ValueEncoderSource source, Class<T> type) {
      this.encoder = source.getValueEncoder(type);
      this.type = type;
   }
   public String toClient(T value) {
      String client = encoder.toClient(value);
      if (client == null) {
         // eg hibernate entity id was null
         return CLIENT_NULL;
      }
   }
   public T toValue(String client) {
      if (CLIENT_NULL.equals(client)) {
         // this object will be used in the POST request (requires no-args
constructor)
         return type.newInstance();
      }
      return encoder.toValue(client);
   }
}

public class MyPage {
   @Property private List<Foo> foos;
   @Property private Foo foo;
   @Inject private ValueEncoderSource source;

   public ValueEncoder<Foo> getNullNewEncoder() {
      return new NullNewValueEncoder(source, Foo.class);
   }

   public Foo onAddRowFromFoos() {
      // this object will be used to render the empty row then discarded
      return new Foo();
   }
}