Problems with retrieving a SET

tmk · **Joined:** Thu Mar 29, 2007 11:57 am **Posts:** 27

Hi,

I expanded the mapping tutorial (http://www.hibernate.org/hib_docs/v3/re ... sociations)and run in some problems. Perhaps you can help me.

I have three database tables like described in the tutorial:
- person
- event
- person_event

I want to list all events of a person.

Here is my mapping file Person.hbm.xml:

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
  
<hibernate-mapping>

    <class name="events.Person" table="person">
        <id name="id" column="person_id">
            <generator class="native"/>
        </id>
        <property name="age"/>
        <property name="firstname"/>
        <property name="lastname"/>
        
        <set name="events" table="person_event">
           <key column="person_id"/>
           <many-to-many column="event_id" class="events.Event" lazy="false"/>
       </set>
    </class>

</hibernate-mapping>

This is the method where I want to list all events of all Persons. The problem is that I get an error when I want to get a Set of events belonging to the person.
Perhaps you can help me (I am a hibernate newbie :) )

Here is my method code:

Code:

private List listPersons() {
       Session session = HibernateUtil.getSessionFactory().getCurrentSession();
       
       session.beginTransaction();
       
       List result = session.createQuery("from Person").list();
       
       
       
       for (int i = 0; i < result.size(); i++) {
           Person aPerson = (Person) result.get(i);
           System.out.println("Person: " + aPerson.getFirstname() + " " + aPerson.getLastname() + " participates in the following events:");
           HashSet pSet =  (HashSet) aPerson.getEvents();
           
              System.out.println("Event count: " + aPerson.getEvents().toArray().length);
          
        }
       session.getTransaction().commit();
       
       return result;
    }

Furthermore here are the two classes of event and person:

Class person:

Code:

public class Person {

    private Long id;
    private int age;
    private String firstname;
    private String lastname;
    private Set events = new HashSet();

    //getter and setter methods

Class Event:

Code:

    private Long id;
    private String title;
    private Date date;

    //getter and setter methods

Regards,
TMK

scesbron · **Joined:** Thu Sep 04, 2003 8:23 am **Posts:** 368

Which error do you have ?

I think it is a ClassCastException. Here is the problem :

Code:

HashSet pSet = (HashSet) aPerson.getEvents();

HahSet is an implementation, Set is the interface an you have to program by interface. Internally hibernate does not use HashSet but it's own implementation PersistentSet which deal with persistent features like lazy loading.
Here is the code you must have :

Code:

Set pSet = aPerson.getEvents();

chucky · **Joined:** Mon Jun 12, 2006 5:33 am **Posts:** 63

Hi tmk,

what is exactly your problem. You forgot to post your stack trace

chucky