public String tryInviteNewMember(String account, int cid) {	// needs dao's isMember & isInviting
		int user = this.userDao.findUidByAccount(account);
		// if that guy already existed in the club's member list
		for (int existedMember : this.userDao.clubMembersUid(cid)) {
			if (user == existedMember)
				return "member";
		}
		// if that guy already existed in the club's inviting list
		for (Object obj : this.userDao.clubInvitingList(cid)) {
			Map<?, ?> map = (Map<?, ?>) obj;
			if (user == Integer.parseInt(map.get("guest_uid").toString()))
				return "inviting";
		}
		
		return "OK";
	}