Unable to convert client value 'null' back into a server-side object

Question

This question is about Tapestry components issue.

I'm looking for a solution of exactly this issue, not any workaround or alternative ways, how to implement this interface.

1. Consider ajaxformloop element on the Tapestry form:

   <tr t:type="ajaxformloop" t:id="items" source="getItems()" value="item">

   ...

   </tr>

2. getItems() method inside class returns synthetic combination (List interface) of persisted objects and not-yet-persisted newly added items (with null id inside them).

3. When submitting the form I receive this error:

   Unable to convert client value 'null' back into a server-side object

This error occurs before onSuccessFromSave() method (save is id of submit link).

I wonder, how can I manage such not-persisted objects with ajaxformloop to prevent such error. Actually, I want to save (in DB) these items inside my onSucceccFrom...() method.

What have I missed here?

Answer 1

Actually I've missed custom ValueEncoder for my ajaxformloop container. The mentioned error produced by default encoder of this component.

Custom encoder should be set in such way:

<tr t:type="ajaxformloop" t:id="items" source="getItems()" value="item" encoder="itemEncoder">

where itemEncoder is @Property annotated field in java class:

@Property
private ValueEncoder<MyItem> itemEncoder = new ValueEncoder<MyItem>() {
    @Override
    public String toClient(MyItem value) {
        return value.id != null ? value.id.toString() : "";
    }

    @Override
    public MyItem toValue(String clientValue) {
        if (clientValue != null && !clientValue.isEmpty()) {
            Long id = Long.parseLong(clientValue);
            return (MyItem) session.get(MyItem.class, id);
        }
        return new MyItem();
    }
};