java - 在 Hibernate 中，当对象已存在于数据库中时，为什么 saveOrUpdate 会抛出异常

Question

以前，当我使用 Hibernate 将一个实体添加到数据库时，我常常检查它是否已经被添加。但是为了提高性能，我忘记了这个检查，只是尝试在不检查的情况下添加，因为我正在使用 saveOrUpdate() 据我了解，如果 Hibernate 发现它已经被添加，它只会更新以及我的保存所做的更改。

但是它失败了

18/08/2018 21.58.34:BST:Errors:addError:SEVERE: Adding Error:Database Error:Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [com.jthink.songlayer.MusicBrainzReleaseWrapper#95f6f584-407f-4b26-9572-bb8c6e9c580a]
java.lang.Exception
    at com.jthink.songkong.analyse.general.Errors.addError(Errors.java:28)
    at com.jthink.songkong.exception.ExceptionHandling.handleHibernateException(ExceptionHandling.java:209)
    at com.jthink.songkong.db.ReleaseCache.addToDatabase(ReleaseCache.java:394)
    at com.jthink.songkong.db.ReleaseCache.add(ReleaseCache.java:65)




@Entity
    public class MusicBrainzReleaseWrapper
    {
        @Id
        private String guid;

        @Version
        private int version;

        @org.hibernate.annotations.Index(name = "IDX__MUSICBRAINZ_RELEASE_WRAPPER_NAME")
        @Column(length = 1000)
        private String name;

        @Lob
        @Column(length = 512000)
        private String xmldata;

        public String getGuid()
        {
            return guid;
        }

        public void setGuid(String guid)
        {
            this.guid = guid;
        }

        public String getName()
        {
            return name;
        }

        public void setName(String name)
        {
            this.name = name;
        }

        public String getXmldata()
        {
            return xmldata;
        }

        public void setXmldata(String xmldata)
        {
            this.xmldata = xmldata;
        }
    }

    private static boolean addToDatabase(Release release)
        {
            Session session = null;
            try
            {
                session = HibernateUtil.beginTransaction();
                //Marshall to String
                StringWriter sw = new StringWriter();
                Marshaller m = jc.createMarshaller();
                m.marshal(release, sw);
                sw.flush();

                MusicBrainzReleaseWrapper wrapper = new MusicBrainzReleaseWrapper();
                wrapper.setGuid(release.getId());
                wrapper.setName(release.getTitle().toLowerCase(Locale.UK));
                wrapper.setXmldata(sw.toString());
                session.saveOrUpdate(wrapper);
                session.getTransaction().commit();
                MainWindow.logger.info("Added to db release:" + release.getId() + ":" + release.getTitle());
                return true;
            }
            catch (ConstraintViolationException ce)
            {
                MainWindow.logger.warning("Release already exists in db:"+release.getId()+":"+release.getTitle());
                return true;
            }
            catch(GenericJDBCException jde)
            {
                MainWindow.logger.log(Level.SEVERE, "Failed:" +jde.getMessage());
                ExceptionHandling.handleDatabaseException(jde);
            }
            catch(HibernateException he)
            {
                MainWindow.logger.log(Level.SEVERE, "Failed:" +he.getMessage());
                ExceptionHandling.handleHibernateException(he);
            }
            catch(Exception e)
            {
                MainWindow.logger.log(Level.WARNING,"Failed AddReleaseToDatabase:"+release.getId()+ ':' +e.getMessage(),e);
                throw new RuntimeException(e);
            }
            finally
            {
                HibernateUtil.closeSession(session);
            }
            return false;
        }

用于在调用 addToDatabase 之前首先检查

        if(ReleaseCache.get(release.getId())==null)
        {
            addToDatabase(release)
        }        

Answer 1

Hiberante 对象对于一个实体有 3 种状态。他们是: - 短暂的或新的 - 分离(对象从数据库中获取并且 hibernate session 关闭) - 持久性(对象从数据库中获取并且 hibernate session 打开)在 saveOrUpdate 方法中，它要么保存临时对象，要么更新分离/持久对象。在您的代码中，您正在尝试创建 Transient/New 对象并在其中设置旧 ID。这就是您遇到上述错误的原因。正确的方法是先使用 id 获取对象，然后更新它。