GWT polymorphic lists with #ExtraTypes - gwt

Question

I have a little problem with a list that contains different types of elements and i would like to see if anyone of you have met the problem before. The issue should be solved with the use of #ExtraTypes, but it is not working for me, so i guess i am not using it correctly. So, the scenario is (bean names are changed for clarity):
GENERAL:
I am using GWT 2.5 with RequestFactory.
SERVER-SIDE:
I have a RootBean that contains, among other stuff, a List <ChildBean>.
This ChildBean contains some primitive attributes.
ChildBean is also extended by a MoreSpecificChildBean that inherits all the parent attributes and adds a few more.
The RootBean gets its list filled up with elements of type ChildBean and MoreSpecificChildBean depending on some logic.
CLIENT-SIDE:
IRootBeanProxy is a ValueProxy with these annotations:
#ProxyFor (value = RootBean.class)
#ExtraTypes ({IMoreSpecificChildBeanProxy.class})
and contains a list
List <IChildBeanProxy> getChildren ();
IChildBeanProxy is a ValueProxy:
#ProxyFor (value=ChildBean)
public interface IChildBeanProxy extends ValueProxy
IMoreSpecificChildBeanProxy is a ValueProxy:
#ProxyFor (value=MoreSpecificChildBean)
public interface IMoreSpecificChildBeanProxy extends IChildBeanProxy
the Request context has a method that returns Request and i added the #ExtraTypes annotation here too:
#Service (value = CompareService.class, locator = SpringServiceLocator.class)
#ExtraTypes ({IChildBeanProxy.class, IMoreSpecificChildBeanProxy.class})
public interface ICompareRequestContext extends RequestContext {
Request <IRootBeanProxy> compare (Integer id1, Integer id2);
Question
Supposedly with those annotations, RF should be aware of the existence of polymorphic inherited classes, but all i get in the client is an IRootBeanProxy with a list of IChildBeanProxy elements. This list includes the MoreSpecificChildBean, but in the shape of a IChildBeanProxy, so that i cannot tell it from the others.
So i am wondering what i am doing wrong, if i am setting the ExtraTypes annotation at the wrong place or something.
Anyone?
Thx for all the help!!

Answer 1

I do the exact same thing for quite a few classes but it will always return me the base type which I can iterate through and test for instanceof if needed. You will probably have to cast the object to the subclass. If you do not add the #ExtraTypes you will know because on the server side you will get a message stating that MoreSpecificChildBean cannot be sent to the client.
I only annotate the service and not the proxy, I ran into some quirks with 2.4 adding #ExtraTypes to the proxy.
/**
* Base proxy that all other metric proxies extend. It is used mainly for it's
* inheritence with the RequestFactory. It's concrete implementation is
* {#link MetricNumber}.
*
* #author chinshaw
*/
#ProxyFor(value = Metric.class, locator = IMetricEntityLocator.class)
public interface MetricProxy extends DatastoreObjectProxy {
/**
* Name of this object in the ui. This will commonly be extended by
* subclasses.
*/
public String NAME = "Generic Metric";
/**
* This is a list of types of outputs that the ui can support. This is
* typically used for listing types of supported Metrics in the operation
* output screen.
*
* #author chinshaw
*/
public enum MetricOutputType {
MetricNumber, MetricString, MetricCollection, MetricStaticChart, MetricDynamicChart
}
/**
* See {#link MetricNumber#setName(String)}
*
* #param name
*/
public void setName(String name);
/**
* See {#link MetricNumber#setContext(String)}
*
* #return name of the metric.
*/
public String getName();
/**
* Get the list of violations attached to this metric.
*
* #return
*/
public List<ViolationProxy> getViolations();
}
#ProxyFor(value = MetricNumber.class, locator = IMetricEntityLocator.class)
public interface MetricNumberProxy extends MetricProxy {
public List<NumberRangeProxy> getRanges();
public void setRanges(List<NumberRangeProxy> ranges);
}
...
#ProxyFor(value = MetricDouble.class, locator = IMetricEntityLocator.class)
public interface MetricDoubleProxy extends MetricNumberProxy {
/* Properties when fetching the object for with clause */
public static String[] PROPERTIES = {"ranges"};
public Double getValue();
}
...
#ProxyFor(value = MetricPlot.class, locator = IMetricEntityLocator.class)
public interface MetricPlotProxy extends MetricProxy {
/**
* UI Name of the object.
*/
public String NAME = "Static Plot";
public String getPlotUrl();
}
This is a made up method from because I usually always return composite classes that may contain a list of metrics. That being said this will return me the base type of metrics, and then I can cast them.
#ExtraTypes({ MetricProxy.class, MetricNumberProxy.class, MetricDoubleProxy.class, MetricIntegerProxy.class})
#Service(value = AnalyticsOperationDao.class, locator = DaoServiceLocator.class)
public interface AnalyticsOperationRequest extends DaoRequest<AnalyticsOperationProxy> {
Request<List<<MetricProxy>> getSomeMetrics();
}
Not an exact method I use but will work for getting a proxy of type.
context.getSomeMetrics().with(MetricNumber.PROPERTIES).fire(new Receiver<List<MetricProxy>>() {
public void onSuccess(List<MetricProxy> metrics) {
for (MetricProxy metric : metrics) {
if (metric instanceof MetricDoubleProxy) {
logger.info("Got a class of double " + metric.getValue());
}
}
}
}
You will know if you are missing an #ExtraTypes annotation when you get the error stated above.
Hope that helps