public void deleteByUserNameAndParticipantName(String userName, String participantName) {
		EntityManager em = PersistenceManager.createEntityManager();
		try {
			em.getTransaction().begin();
			
			List<Openchatroom> ochrs = em.createNamedQuery("Openchatroom.GetByUserAndParticipant", Openchatroom.class)
					.setParameter("u", userName)
					.setParameter("p", participantName)
					.getResultList();
			for (Openchatroom openchatroom : ochrs) {
				em.remove(openchatroom);
			}
			
			em.getTransaction().commit();
		} finally {
			if (em.getTransaction().isActive())
				em.getTransaction().rollback();
			em.close();
		}
	}