Bulk Delete and Update - best practice?

public class TestDropTable3 {

@Test
public void testDrop() {
  EntityManagerFactory emf =
           Persistence.createEntityManagerFactory(
               "objectdb://localhost/testDrop.tmp;user=admin;password=admin");
 
  EntityManager em = emf.createEntityManager();
  em.getMetamodel().entity(CacheData.class);
  em.close();

  String payload = "somedata";
 
  em = emf.createEntityManager();
  CacheData data = new CacheData();
  data.setHash(payload.hashCode());
  data.setData(payload);
 
  em.getTransaction().begin();
  em.persist(data);
  em.getTransaction().commit();
  em.clear();
 
  TypedQuery<Long> q = em.createQuery("SELECT COUNT(d) from CacheData d", Long.class);
  long rows = q.getSingleResult();
  System.out.println(String.format("Found %s rows", rows));
 
  em.close();
 
  emf.close();
 
  emf = Persistence.createEntityManagerFactory(
               "objectdb://localhost/testDrop.tmp;drop;user=admin;password=admin");
 
  em = emf.createEntityManager();
  em.getMetamodel().entity(CacheData.class);
  em.close();
 
  em = emf.createEntityManager();
  q = em.createQuery("SELECT COUNT(d) from CacheData d", Long.class);
  rows = q.getSingleResult();
  System.out.println(String.format("Found %s rows", rows));
 
  em.close();
  emf.close();
}

@Entity
    public static class CacheData {
        @GeneratedValue @Id long id;
        @Index int hash;
        String data;
       
        public long getId() { return id; }
       
        public int getHash() { return hash; }
        public void setHash(int value) { hash = value; }
       
        public String getData() { return data; }
        public void setData(String value) { data = value; }
    }
}