Question

我在学校的项目中使用持久性，当我尝试删除和更新对象时，我遇到了问题，所有其他查询都有效。

例外是：

Illegal attempt to associate a collection with two open sessions

我关闭了我打开的每个会话。

HibernateUtils代码

public class Hibernate
{
 protected static final SessionFactory sessionFactory;

 private Session session;

 static 
 {
  try 
  {
   // Create the SessionFactory from hibernate.cfg.xml
   sessionFactory = new Configuration().configure().buildSessionFactory();
   session
  } 
  catch (Throwable ex) 
  {
   // Make sure you log the exception, as it might be swallowed
   System.err.println("Initial SessionFactory creation failed." + ex);
   throw new ExceptionInInitializerError(ex);
  }
 }

 public void create(Object obj)
 {
  this.session = sessionFactory.openSession();
  session.getTransaction().begin();
  session.save(obj);
  session.getTransaction().commit(); 
  session.close();
 }

 public void refresh(Object obj)
 {
  this.session = sessionFactory.openSession();
  session.getTransaction().begin();
  session.refresh(obj);
  session.getTransaction().commit();
  session.close();
 }

 public void update(Object obj)
 {
  this.session = sessionFactory.openSession();
  session.getTransaction().begin();  
  session.saveOrUpdate(obj);
  session.getTransaction().commit();
  session.close();

 }
 public void delete(Object obj)
 {
  this.session = sessionFactory.openSession();
  session.getTransaction().begin();
  session.delete(obj);
  session.flush();
  session.getTransaction().commit();  
  session.close();
 }
 protected String protectString(String toProtect)
 {
  return (toProtect.replace("'", "''"));
 }

}

DAOPerson：

public class DAOPerson extends Hibernate
{

 public void remove(Person p)
 {
  if (p instanceof Student)
  {
   Student s = (Student)p;
   Set<persistenceClass.Class> set = s.getClasses();
   Iterator<persistenceClass.Class> it = set.iterator();
   while (it.hasNext())
   {
    persistenceClass.Class r = it.next();
    r.getStudents().remove(s);
   }
   p.getBirthCountry();
   p.getCountry();
   this.delete(p);
  }
  else
   this.delete(p);
}

有关信息，我的学生映射文件是：

 <class name="persistenceClass.Person" table="T_PERSON">
  <id name="Id" column="PERSON_ID">
   <generator class="native" />
  </id>
  <property name="FirstName" column="PERSON_FIRST_NAME" not-null="true" />
  <property name="LastName" column="PERSON_LAST_NAME" not-null="true" />
  <property name="Type" column="PERSON_TYPE" not-null="true" />
  <property name="BirthDate" column="PERSON_BIRTH_DATE" />
  <property name="BirthCity" column="PERSON_BIRTH_CITY" />
  <property name="PhoneNumber" column="PERSON_PHONE_NUMBER" />
  <property name="MobileNumber" column="PERSON_MOBILE_NUMBER" />
  <property name="Mail" column="PERSON_MAIL" />
  <property name="Address" column="PERSON_ADDRESS_ADDRESS" />
  <property name="ZipCode" column="PERSON_ADDRESS_ZIPCODE" />
  <property name="City" column="PERSON_ADDRESS_CITY" />
  <property name="Image" column="PERSON_IMAGE" type="image" />
  <many-to-one name="Country" column="PERSON_ADDRESS_COUNTRY" class="persistenceClass.Country" />
  <many-to-one name="BirthCountry" column="PERSON_BIRTH_COUNTRY" class="persistenceClass.Country" />
  <many-to-one name="Civility" column="PERSON_CIVILITY" class="persistenceClass.Civility" />
  <many-to-one name="Sex" column="PERSON_SEX" class="persistenceClass.Sex" />
  <joined-subclass name="persistenceClass.Student" table="T_STUDENT">
   <key column="PERSON_ID" />
   <set name="Classes" table="T_CLASS_STUDENT" inverse="true" >
    <key column="PERSON_ID" />
    <many-to-many class="persistenceClass.Class" column="CLASS_ID" />  
   </set>
  </joined-subclass>
  <joined-subclass name="persistenceClass.Teacher" table="T_TEACHER">
   <key column="PERSON_ID" />
  </joined-subclass>
 </class>

主映射文件：

<hibernate-configuration>
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">org.gjt.mm.mysql.Driver</property>
<property name="connection.url">jdbc:mysql://localhost/projet</property>
<property name="connection.username">root</property>
<property name="connection.password"></property>
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">10</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.MySQLInnoDBDialect</property>
<!-- Drop and re-create the database schema on start-up, also try with “update” to keep the previous values -->
<property name="hbm2ddl.auto">update</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<mapping resource="persistenceConfigurations/Person.hbm.xml"/>
<mapping resource="persistenceConfigurations/Country.hbm.xml"/>
<mapping resource="persistenceConfigurations/Civility.hbm.xml"/>
<mapping resource="persistenceConfigurations/Sex.hbm.xml"/>
<mapping resource="persistenceConfigurations/Formation.hbm.xml"/>
<mapping resource="persistenceConfigurations/Year.hbm.xml"/>
<mapping resource="persistenceConfigurations/Class.hbm.xml"/>
<mapping resource="persistenceConfigurations/Subject.hbm.xml"/>
<mapping resource="persistenceConfigurations/Room.hbm.xml"/>
<mapping resource="persistenceConfigurations/Lesson.hbm.xml"/>
</session-factory>
</hibernate-configuration>

我尝试了很多配置，但我每次都有相同的例外，如果有人有想法，我想要它！

谢谢！

抱歉我的英文不好

Answer 1

该会话不适用于一个呼叫并已关闭。使用实用程序类作为POJO的基础不是一个好主意。

要删除的实体应使用从中检索的相同会话，或至少在删除之前刷新新会话。

同样，通过删除依赖的“Class”实体的迭代应该用级联REMOVE替换。

Answer 2

尝试使用getCurrentSession()代替openSession()并删除session.close();声明。

Answer 3

对于初学者我认为重构你给出的Class（path persistenceClass.Class）概念的名称是一个好主意。在java世界中，“Class”实际上是一个类。这可能会在未来造成一些破坏。

我在你的DAOPerson代码上意识到的一个问题是它看起来很奇怪。我知道你正试图将现有学生从课堂上删除，对吗？如果是这样，请在代码上尝试以下补丁：

 public void remove(Person p)
 {
  if (p instanceof Student)
  {
   Student s = (Student)p;
   Set<persistenceClass.Class> set = s.getClasses();
   Iterator<persistenceClass.Class> it = set.iterator();
   while (it.hasNext())
    {
     persistenceClass.Class r = it.next();
     r.getStudents().remove(s);

     //now effectively removing the student from the class. 
     //this will update the class and its persistent set of students.
     this.update(r); 
    }
   }
   this.delete(p); //now remove the student (or whatever comes as argument)
 }

现在另一个可能的问题：你的HibernateUtils没有正确处理事务。您应该重构您的代码，如下所示：

//Example
public void create(Object obj){
  this.session = sessionFactory.openSession();
  try{
    session.getTransaction().begin();
    session.save(obj);
    session.getTransaction().commit();     
  } catch (Exception e) {
    e.printStackTrace();
    session.getTransaction().rollback(); 
  } finally {
    session.flush();
    session.close();
    //keep in mind that too many flushes might cause db memory shortage.
    //So if you are treating list of objects and so on iterate and save them flushing
    //only when your batch size is reached.
  }
}

希望有所帮助！

Answer 4

我注意到你没有在你的人物映射文件中定义lazy=false，所以我假设你正在使用属性Set的延迟加载属性。您说在删除电话之前已经关闭了所有会话，那么为什么如何在s.getClasses() remove()方法中访问该媒体资源DAOPerson而不会抛出lazyInitializationException 。如果您忘记在映射文件中提及lazy=false，那么我的观察结果就不算数了。如果不是这种情况，那么你肯定会在Person p（传递给DAO remove方法）的某个地方打开一个会话。在此方法结束时，当您尝试使用另一个会话重新附加对象时，会出现异常。

Answer 5

问题是由于在其中一个映射中误用了级联更新。这是一个示例字段映射：

@ManyToOne(cascade = CascadeType.ALL)
@JoinColumn(name = “user_id”)
public User getAuthor() {
return author;
}

删除级联= CascadeType.ALL修复了问题。结论：小心使用级联更新，因为它可能会让您陷入困境。在业务逻辑需要时使用它。在下面的例子中没有必要，所以删除它既是业务，也是编程上的一个好决定。

来源：http://blog.tremend.ro/2007/03/05/illegal-attempt-to-associate-a-collection-with-two-open-sessions/

hibernate非法尝试将集合与两个打开的会话相关联

5 个答案: