final SimpleFooEventHandler<SimpleBarProxy> handler =
new SimpleFooEventHandler<SimpleBarProxy>();
EntityProxyChange.registerForProxyType(req.getEventBus(), SimpleBarProxy.class, handler);
Request<SimpleFooProxy> request = context.persistCascadingAndReturnSelf().using(foo);
SimpleFooProxy editFoo = context.edit(foo);
editFoo.setOneToManyField(bars);
editFoo.setSimpleBarKeyMap(barAsKeyMap);
editFoo.setSimpleBarValueMap(barAsValueMap);
request.fire(new Receiver<SimpleFooProxy>() {