@Test
 public void testDeleteById() {
   Event event = genEvent();
   dataRepository.save(event);
   dataRepository.delete(event.getId());
   Assert.assertFalse(dataRepository.exists(event.getId()));
 }
 @Test
 public void testDeleteByIdBatch() {
   List<Event> events = new LinkedList<Event>();
   for (int i = 0; i < 10; i++) {
     events.add(genEvent());
   }
   dataRepository.save(events);
   List<Object[]> ids = new LinkedList<Object[]>();
   for (Event e : events) {
     Assert.assertTrue(dataRepository.exists(e.getId()));
     ids.add(e.getId());
   }
   dataRepository.delete(ids);
   for (Event e : events) {
     Assert.assertFalse(dataRepository.exists(e.getId()));
     ids.add(e.getId());
   }
 }