{
ObjectDatastore ds = new AnnotationObjectDatastore();
A a;
B b;
ds.store(a = new A());
ds.store(b = new B());
ds.store(new AB(a, b));
final AB ab = ds.find().type(AB.class).addFilter("a", Query.FilterOperator.EQUAL,
ds.associatedKey(a)).returnResultsNow().next();