Question

我是Hibernate + Derby的新手......我在谷歌中看到过这个问题，但是没有看到合适的分辨率。

以下代码适用于mysql，但是当我在derby上尝试这个时，我得到例外：

（每个标签有两组文件，反之亦然 - 很多文件）

Tags.java

@Entity
@Table(name="TAGS")
public class Tags implements Serializable 
{

   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   public long getId()
   {
      return id;
   }

   @ManyToMany(targetEntity=Files.class
   )
   @ForeignKey(name="USER_TAGS_FILES",inverseName="USER_FILES_TAGS")
   @JoinTable(name="USERTAGS_FILES",
         joinColumns=@JoinColumn(name="TAGS_ID"),
         inverseJoinColumns=@JoinColumn(name="FILES_ID"))
         public Set<data.Files> getUserFiles()
         {
      return userFiles;
         }

   @ManyToMany(mappedBy="autoTags",
         targetEntity=data.Files.class)
         public Set<data.Files> getAutoFiles()
         {
      return autoFiles;
         }

Files.java


@Entity
@Table(name="FILES")
public class Files implements Serializable
{
   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   public long getId()
   {
      return id;
   }
      @ManyToMany(mappedBy="userFiles",
         targetEntity=data.Tags.class)
   public Set getUserTags()
   {
      return userTags;
   }
   @ManyToMany(targetEntity=Tags.class
         )
         @ForeignKey(name="AUTO_FILES_TAGS",inverseName="AUTO_TAGS_FILES")
   @JoinTable(name="AUTOTAGS_FILES",
         joinColumns=@JoinColumn(name="FILES_ID"),
         inverseJoinColumns=@JoinColumn(name="TAGS_ID"))
   public Set getAutoTags()
   {
      return autoTags;
   }

我向数据库添加了一些数据，但是当在Derby上运行时，这些异常会出现（不使用mysql）

例外


SEVERE: DELETE on table 'FILES' caused a violation of foreign key constraint 'USER_FILES_TAGS' for key (3).  The statement has been rolled back.
Jun 10, 2010 9:49:52 AM org.hibernate.event.def.AbstractFlushingEventListener performExecutions
SEVERE: Could not synchronize database state with session
org.hibernate.exception.ConstraintViolationException: could not delete: [data.Files#3]
   at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96)
   at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
   at org.hibernate.persister.entity.AbstractEntityPersister.delete(AbstractEntityPersister.java:2712)
   at org.hibernate.persister.entity.AbstractEntityPersister.delete(AbstractEntityPersister.java:2895)
   at org.hibernate.action.EntityDeleteAction.execute(EntityDeleteAction.java:97)
   at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:268)
   at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:260)
   at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:184)
   at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
   at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
   at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1206)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.lang.reflect.Method.invoke(Method.java:613)
   at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:344)
   at $Proxy13.flush(Unknown Source)
   at data.HibernateORM.removeFile(HibernateORM.java:285)
   at data.DataImp.removeFile(DataImp.java:195)
   at booting.DemoBootForTestUntilTestClassesExist.main(DemoBootForTestUntilTestClassesExist.java:62)

我以前从来没有使用过德比，所以也许有一些我错过的残酷事物 1）我做错了什么？
2）当我在两个类之间有2对多关系时，有没有正确级联的方法？

谢谢！

Answer 1

以下代码适用于MySQL，但是当我在derby上尝试这个时，我得到例外：

我的猜测是你没有使用MySQL的引用完整性（即不是InnoDB引擎），因此约束违规没有被“触发”。但错误就在那里。

实际上，问题在于您应该将mappedBy置于双向关联的同一侧，例如Tags上的ManyToMany（并将其从Files）：

@Entity
public class Tags implements Serializable {

    @ManyToMany(mappedBy = "userTags")
    @ForeignKey(name = "USER_TAGS_FILES", inverseName = "USER_FILES_TAGS")
    @JoinTable(name = "USERTAGS_FILES", joinColumns = @JoinColumn(name = "TAGS_ID"), inverseJoinColumns = @JoinColumn(name = "FILES_ID"))
    public Set<Files> getUserFiles() {
        return userFiles;
    }

    @ManyToMany(mappedBy = "autoTags")
    public Set<Files> getAutoFiles() {
        return autoFiles;
    }

    //...
}

Files成为：

@Entity
public class Files implements Serializable {

    @ManyToMany
    public Set<Tags> getUserTags() {
        return userTags;
    }

    @ManyToMany
    @ForeignKey(name = "AUTO_FILES_TAGS", inverseName = "AUTO_TAGS_FILES")
    @JoinTable(name = "AUTOTAGS_FILES", joinColumns = @JoinColumn(name = "FILES_ID"), inverseJoinColumns = @JoinColumn(name = "TAGS_ID"))
    public Set<Tags> getAutoTags() {
        return autoTags;
    }

    // ...
}

通过这些更改，以下测试通过（在测试方法之外创建session）：

@Test
public void removeFiles() {
    Files files = (Files) session.get(Files.class, 1L);

    session.delete(files);
    session.flush();

    Query q = session.createQuery("from Files f where f.id = :id");
    q.setParameter("id", 1l);
    Files result = (Files) q.uniqueResult();
    assertNull(result);
}

并生成以下查询：

Hibernate: select files0_.id as id100_0_ from Files files0_ where files0_.id=?
Hibernate: delete from AUTOTAGS_FILES where FILES_ID=?
Hibernate: delete from Files_TAGS where userFiles_id=?
Hibernate: delete from Files where id=?
Hibernate: select files0_.id as id100_ from Files files0_ where files0_.id=?

使用Derby进行测试。

使用manytomany关系的derby + hibernate ConstraintViolationException

1 个答案: