[jira] Resolved: (WICKET-1968) PropertyModel not easily extendable

["Igor Vaynberg (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/WICKET-1968?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Igor Vaynberg resolved WICKET-1968.
-----------------------------------

    Resolution: Won't Fix
      Assignee: Igor Vaynberg

you can use composition to extend the propertymodel functionality instead of inheritance

> PropertyModel not easily extendable
> -----------------------------------
>
>                 Key: WICKET-1968
>                 URL: https://issues.apache.org/jira/browse/WICKET-1968
>             Project: Wicket
>          Issue Type: Bug
>          Components: wicket
>    Affects Versions: 1.4-RC1
>            Reporter: Mathieu Carbou
>            Assignee: Igor Vaynberg
>
> We wanted to create a LodableDetacheableProeprtyModel like this:
> public abstract class DetachablePropertyModel<T> extends PropertyModel<T> {
>     public DetachablePropertyModel(String expression) {
>         super(new LoadableDetachableModel<Object>() {
>             protected Object load() {
>                 return DetachablePropertyModel.this.load();
>             }
>         }, expression);
>     }
>     protected abstract Object load();
> }
> But this is not possible. Since we cannot access a method of a not yest instanciated class.
> So we wanted to chang to this:
> public abstract class DetachablePropertyModel<T> extends PropertyModel<T> {
>     public DetachablePropertyModel(String expression) {
>         super();
>         setChainedModel(new LoadableDetachableModel<Object>() {
>             protected Object load() {
>                 return DetachablePropertyModel.this.load();
>             }
>         });
>     }
>     protected abstract Object load();
> }
> But the constructor of AbstractPropertyModel requires a model and also (and here is the issue) check for null argument:
> public AbstractPropertyModel(final Object modelObject)
> 	{
> 		if (modelObject == null)
> 		{
> 			throw new IllegalArgumentException("Parameter modelObject cannot be null");
> 		}
> 		target = modelObject;
> 	}
> So the only way to bypass this was to call the super constructor like this:
> public abstract class DetachablePropertyModel<T> extends PropertyModel<T> {
>     public DetachablePropertyModel(String expression) {
>         super(expression, expression);
>         setChainedModel(new LoadableDetachableModel<Object>() {
>             protected Object load() {
>                 return DetachablePropertyModel.this.load();
>             }
>         });
>     }
>     protected abstract Object load();
> }
> By giving the expression to the super class, and giving the expression also as the object, it works. But it is not correct...
> I think a redesign of AbstractPropertyModel  would be necessary: to use the method setChainedModel on AbstractPropertyModel , we currently need to first have the object instanciated with a non null model.... Which is not what we may want...

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