1.3. Part 2 - Mapping associations

We mapped a persistent entity class to a table. Let's build on this and add some class associations. First we'll add people to our application, and store a list of events they participate in.

1.3.1. Mapping the Person class

The first cut of the Person class is simple:
package events;

public class Person {

    private Long id;
    private int age;
    private String firstname;
    private String lastname;

    public Person() {}

    // Accessor methods for all properties, private setter for 'id'

Create a new mapping file called Person.hbm.xml (don't forget the DTD reference at the top):

    <class name="events.Person" table="PERSON">
        <id name="id" column="PERSON_ID">
            <generator class="native"/>
        <property name="age"/>
        <property name="firstname"/>
        <property name="lastname"/>

Finally, add the new mapping to Hibernate's configuration:
<mapping resource="events/Event.hbm.xml"/>
<mapping resource="events/Person.hbm.xml"/>
We'll now create an association between these two entities. Obviously, persons can participate in events, and events have participants. The design questions we have to deal with are: directionality, multiplicity, and collection behavior.