Hibernate / JPA自动更新我的实体主 - 详细信息

Question

我与Car的关系@OneToMany - ＆gt;工具。工具在汽车中使用后，先前已在系统中注册。我有以下代码：

public void addToolToCar(ActionEvent event){
 if (car == null)
 car = new Car();

 Tool tool = findToolByNumer('1234');
 tool.setSituation('PUTTED');
 car.addTool(tool);

 /*
  After adding the first Tool object to Car, everything is fine, but when i try
  to find the Tool '667', the Hibernate UPDATE in PostgreSQL the Tool '1234'. 
    The  BIG problem is that user can choose don't click in "save button" and the Car                  will not inserted (this is complete normally and often, as a CANCEL action) but the Tool
  situation was changed, this is a problem for my bussiness rule because when Tool 
   is in "PUTTED" situation, this Tool cannot be used for another Car.

  And have a wrost situation, the Tool can be removed from the Car list, like: 
  'car.removeTool('1234'), but as Tool was changed in Database i will have a serius
  problem of consistence.
 */

  tool = findToolByNumer('667');
 tool.setSituation('PUTTED');
 car.addTool(tool);
 }

 public void save(ActionEvent event){
   dao.persist(car);
 }

EDIT1：Car类中的addTool方法非常简单，没有任何错误

 public Car(){
   tools = new ArrayList<Tool>();
 } 

 private List<Tool> tools;
 ...
 public void addTool(Tool tool){
   tools.add(tool);
 }