JPA /休眠 - 无法添加或更新子行：外键约束失败 - 但记录存在 [英] JPA/hibernate - Cannot add or update a child row: a foreign key constraint fails - BUT record exists

问题描述

我有一个奇怪的问题。我在数据库中有一些记录：

公司

• id = 1， Name = Microsoft


• id = 2，Name = Sun
  $ b

  现在我有另一个实体，有公司外键引用的事件：
  
  

    @Entity 
  公共类事件{
   
   @Id 
   @GeneratedValue（strategy = GenerationType.AUTO）
   private Long id; 
   
   @ManyToOne 
  私人公司公司; 
   
   
   
   $ b $ p 
   $ b在我的web服务层中，我使用一个公司ID一个URL参数：
   
   $ p $  @GET 
   @Path（addEvent）
   public String addEvent（@ QueryParam（cid）long companyId）{
   Company alreadyInDB = new Company（）; 
   alreadyInDB.setId（companyId）; 
   
  事件事件=新事件（）; 
   event.setCompany（alreadyInDB）; 
   eventService.addEvent（event）; 
  } 
    

  这比调用EventService。我原来是用这行代码注释掉的。但是，当外键约束失败失败时，我添加了代码以确保公司记录存在。当然，代码打印出正确的ID。但它仍然失败，违反外键约束。

    @Service（eventService）
   public class EventService { 
   
   @Autowired 
   EventDAO eventDAO; 
   
   @Autowired 
   CompanyDAO companyDAO; 
   
   @Transactional（propagation = Propagation.REQUIRED，rollbackFor = Exception.class）
   public void addEvent（Event event）throws Exception 
   {
   System.out.println （Company ID：+ event.getCompany（）。getId（））; 
   
  公司ensureRecordExists = companyDAO.findById（event.getCompany（）。getId（））; 
   System.out.println（ensureRecordExists：+ ensureRecordExists.getId（））; 
   event.setCompany（ensureRecordExists）; 
   //event.setCompany(companyDAO.getReferenceById(event.getCompany（）。getId（）））; 
   eventDAO.persist（event）; 
   
   
   
   
   $ p $这是stacktrace的相关部分：
   原因：com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException：无法添加或更新子行：外键约束失败``blah`.`event`，CONSTRAINT`FKE7E9BF09F9DCA789` FOREIGN KEY（`company_id`）REFERENCES`Company`（`id`））
   at sun.reflect.NativeConstructorAccessorImpl.newInstance0（Native Method）
   at sun.reflect.NativeConstructorAccessorImpl.newInstance（NativeConstructorAccessorImpl.java:39）
   at sun.reflect.DelegatingConstructorAccessorImpl.newInstance（DelegatingConstructorAccessorImpl.java:27）
    
  有什么想法发生了什么？我可以在物理上看到mysql workbench中存在的记录。我不知道为什么它失败。我认为这可能有冲突会议或一些交易问题...？但我看到记录... 
   
  解决方案
   
  我缩小了问题的范围，并在此发布了另一个问题：
   
   
    
   
   
   
  我在这里找到了解决方案： 
   
   
    http：/ /developmentality.wordpress.com/2011/05/23/hibernate-mysql-mac-foreign-key-nightmares-a-painless-solution-to-a-painful-problem/  
   
   
   
  由于mysql，hibernate和mac os x的组合，有一些问题需要在hibernate中使用小写的命名策略。 Hibernate默认使用骆驼命名策略。
   
  I'm having a strange problem.  I have some records in the database:
  
  Company
  
  
  id = 1, Name = Microsoft
  id = 2, Name = Sun
  
  
  Now I have another entity, Event which has a foreign key reference to Company:
  @Entity
  public class Event {
  
      @Id
      @GeneratedValue(strategy=GenerationType.AUTO)
      private Long id;
  
      @ManyToOne
      private Company company;
  }
  In my web service layer, I create an Event using a company ID passed as a URL param:
  @GET
  @Path("addEvent")
  public String addEvent(@QueryParam("cid") long companyId) {
      Company alreadyInDB = new Company();
      alreadyInDB.setId(companyId);
  
      Event event = new Event();
      event.setCompany(alreadyInDB);
      eventService.addEvent(event);
  }
  This than calls the EventService.  I originally was using the line of code commented out.  But when that failed with the foreign key constraint failure, I added the code to ensure the Company record exists.  Sure enough, the code prints out the proper ID.  But it still fails with a foreign key constraint violation.
  @Service("eventService")
  public class EventService {
  
      @Autowired
      EventDAO eventDAO;
  
      @Autowired
      CompanyDAO companyDAO;
  
      @Transactional(propagation=Propagation.REQUIRED, rollbackFor=Exception.class) 
      public void addEvent(Event event) throws Exception
      {
          System.out.println("Company ID: " + event.getCompany().getId());
  
          Company ensureRecordExists = companyDAO.findById(event.getCompany().getId());
          System.out.println("ensureRecordExists: " + ensureRecordExists.getId());
          event.setCompany(ensureRecordExists);
          //event.setCompany(companyDAO.getReferenceById(event.getCompany().getId()));
          eventDAO.persist(event);
      }
  }
  Here's the relevant part of the stacktrace:
  Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`blah`.`event`, CONSTRAINT `FKE7E9BF09F9DCA789` FOREIGN KEY (`company_id`) REFERENCES `Company` (`id`))
      at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
      at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
      at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
  Any idea what's going on?  I can physically see the record exists in mysql workbench.  I have no idea why it's failing.  I thought it might have something to do with flushing the session or some transactional issue...?  But I see the record...
  解决方案
  I narrowed the problem down and posted another question here:
  
  JPA/Hibernate - Entity name seems to be important. If I rename to "Bob" works fine
  
  I found the solution here:
  
  http://developmentality.wordpress.com/2011/05/23/hibernate-mysql-mac-foreign-key-nightmares-a-painless-solution-to-a-painful-problem/
  
  Due to the combination of mysql, hibernate, and mac os x, there's some issue where you have to use a lowercase naming strategy in hibernate.  Hibernate by default uses a camel case naming strategy.
  
                          
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