Question

I have a domain object which has a collection of primitive values, which represent the primary keys of another domain object (“Person”).

I have a Wicket component that takes IModel<List<Person>>, and allows you to view, remove, and add Persons to the list.

I would like to write a wrapper which implements IModel<List<Person>>, but which is backed by a PropertyModel<List<Long>> from the original domain object.

View-only is easy (Scala syntax for brevity):

class PersonModel(wrappedModel: IModel[List[Long]]) extends LoadableDetachableModel[List[Person]] {
   @SpringBean dao: PersonDao =_
   def load: List[Person] = {
       // Returns a collection of Persons for each id
       wrappedModel.getObject().map { id: Long =>
          dao.getPerson(id)
       }
   }
}

But how might I write this to allow for adding and removing from the original List of Longs?

Or is a Model not the best place to do this translation?

Thanks!

Answer 1

You can do something like this:

class PersonModel extends Model<List<Person>> {

    private transient List<Person> cache;
    private IModel<List<String>> idModel;

    public PersonModel( IModel<List<String>> idModel ) {
      this.idModel = idModel;
    }

    public List<Person> getObject() {
      if ( cache == null ) {
        cache = convertIdsToPersons( idModel.getObject() );
      return cache;
    }

    public void setObject( List<Person> ob ) {
      cache = null;
      idModel.setObject( convertPersonsToIds( ob ) );
    }

}

This isn’t very good code but it shows the general idea. One thing you need to consider is how this whole thing will be serialised between requests, you might be better off extending LoadableDetachableModel instead.

Another thing is the cache: it’s there to avoid having to convert the list every time getObject() is called within a request. You may or may not need it in practice (depends on a lot of factors, including the speed of the conversion), but if you use it, it means that if something else is modifying the underlying collection, the changes may not be picked up by this model.