hibernate illegal attempt to associate a collection with two open sessions

Question

I'm using persistence in a project for school, and I have a problem when I'm try to deleting and updating object, all others queries works.

The exception is :

Illegal attempt to associate a collection with two open sessions

I close every session I have opened.

HibernateUtils code

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);
}

For information my mapping file of students is :

 <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>

And the main mapping file :

<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>

I try a lot of configuration but I've everytime the same exception, if somebody have an idea, I want it !

Thanks !

Sorry for my bad english

Answer 1

The session is not meant to be used for one call and closed. Using the utility class as a base for your POJO is not a good idea.

The entity that is being deleted should use the same session that it was retrieved from or at least be refreshed on the new session before being removed.

Also the iterating through the removal of the dependent 'Class' entities should be replaced with a cascade REMOVE.

Answer 2

Try using getCurrentSession() instead of openSession() and remove the session.close(); statement.