删除一个分类（作为外键），有这分类的产品要设相对字段为null

public ModelAndView del(HttpServletRequest request,
			HttpServletResponse response) throws Exception {
		long id = Long.parseLong(request.getParameter("id"));
		
		//新加的编历person,修改person
		HrJob hrjob = hrJobService.getHrJob(id);
		Set hrjobSet = hrjob.getHrPersons();
		Iterator iterator = hrjobSet.iterator();
		iterator.hasNext();
		while(iterator.hasNext())
		{
			HrPerson hrPerson = (HrPerson)iterator.next();
			hrPerson.setHrJob(null);
			hrPersonService.edit(hrPerson);
		}
		//新加的编历person,修改person
		
		hrJobService.delById(id);
		Map model = new HashMap();
        model.put("msg","删除职位成功！");
        model.put("url","manage/hr/job/list.htm");
		return new ModelAndView("/WEB-INF/jsp/messagejs.jsp","model", model);
	}