Hibernate读书笔记-----a different object with the same

在web controller新增加了一个po状态的校验，即将系统中该记录的一个状态值先取出比较web上已经有的状态判断是否发生过变化。exception出现在update这个record的时候。系统报a different object with the same identifier value was already associated。

	@RequestMapping(params = "_p_action=save")
	public ModelAndView save(HttpServletRequest req, HttpServletResponse res,
			ItemCostNpriceChg itemCostNpriceChg) throws Exception {
		ModelAndView modelAndView = new ModelAndView("jsonView");
		Set<ItemCostNpriceDtl> itemCostNpriceDtls = new HashSet<ItemCostNpriceDtl>();
		HashMap<String, Object> ret = new HashMap<String, Object>();
		Credential user = userManager.getCredential();

		try {
			if (itemCostNpriceChg.getAppNo() == null) {
				itemCostNpriceChg = (ItemCostNpriceChg) CommUtils
						.copy(itemCostNpriceChg);
				itemCostNpriceChg.setBuyer(user.getUserID());

				itemCostNpriceChg = itemPriceAdjustService
						.add(itemCostNpriceChg);
				itemCostNpriceDtls = buildChangeDetail(req, itemCostNpriceChg,
						"add");

				itemPriceAdjustService
						.saveItemCostNpriceDtls(itemCostNpriceDtls);
				ret = buildWebReturn(itemCostNpriceChg);

			} else {
				if (!user.getUserID().equalsIgnoreCase(
						itemCostNpriceChg.getCreatedBy()))
					throw new BusinessException(
							"You have no right to update the application that other created!",
							"appNo");
				if (itemCostNpriceChg.getAppStatus() != 0
						&& itemCostNpriceChg.getAppStatus() != 4)
					throw new BusinessException(
							"You can not save the record that was completed!",
							"appNo");
				ItemCostNpriceChg check=new ItemCostNpriceChg();
				check=itemPriceAdjustService.getById(itemCostNpriceChg.getAppNo());
		
				if(check.getAppStatus().compareTo(itemCostNpriceChg.getAppStatus())!=0)
					throw new BusinessException(
							"The statuc of the application has been changed ! pls reload the application.",
							"btnNew");
				check = (ItemCostNpriceChg) CommUtils
				.copy(itemCostNpriceChg);
				itemCostNpriceChg=null; 
					
//				boolean check=itemPriceAdjustService.checkAppStatus(itemCostNpriceChg.getAppNo(),itemCostNpriceChg.getAppStatus());
//				if(!check)
//				{
//					throw new BusinessException(
//							"The statuc of the application has been changed ! pls reload the application.",
//							"btnNew");
//				}
				
		
//				itemCostNpriceChg.setBuyer(user.getUserID());
//				itemCostNpriceChg.setCreatedBy(user.getUserID());
//				itemCostNpriceChg.setCreatedTime(DateUtil.getServerDate());
//				itemPriceAdjustService.update(itemCostNpriceChg);
//				itemCostNpriceDtls = buildChangeDetail(req, itemCostNpriceChg,
//						"update");
//				itemPriceAdjustService
//						.saveItemCostNpriceDtls(itemCostNpriceDtls);
				
				
				check.setBuyer(user.getUserID());
				check.setCreatedBy(user.getUserID());
				check.setCreatedTime(DateUtil.getServerDate());
				
				
				itemPriceAdjustService.update(check);
				itemCostNpriceDtls = buildChangeDetail(req, check,
						"update");
				itemPriceAdjustService
						.saveItemCostNpriceDtls(itemCostNpriceDtls);
				ret = buildWebReturn(check);
			}
			

			modelAndView.addObject("data", ret);

			modelAndView.addObject("success", true);
			logger.debug(modelAndView.toString());
		} catch (BusinessException e) {
			e.printStackTrace();
			logger.error(e);
			modelAndView.addObject("success", false);
			modelAndView.addObject("message", e.getMessage());
			modelAndView.addObject("target", e.getTarget());
		} catch (Exception e) {
			e.printStackTrace();
			logger.error(e);
			modelAndView.addObject("success", false);
			modelAndView.addObject("message", e.getMessage());

		}
		return modelAndView;

	}

 注释部分就是出错代码。分析问题是session中的实体与系统又取出的实体都是在session中，但update时候就会报错。因此有二种解决方法：

1.将session中的

public ModelAndView save(HttpServletRequest req, HttpServletResponse res,
			ItemCostNpriceChg itemCostNpriceChg) 

itemCostNpriceChg去除，对数据库中po进行赋值操作。
代码会多很多，不采用


2.将使用merge方法,merge和update的区别是，hibernate会将用户要求的pocopy到session中的po中，因此不会引发冲突