1.2. Part 2 - Mapping associations
So far we have mapped a single persistent entity class to a table in isolation. Let's expand on that a bit and add some class associations. We will add people to the application and store a list of events in which they participate.
1.2.1. Mapping the Person class
The first cut of the
Person class looks like this:
package org.hibernate.tutorial.domain;
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'
}
Save this to a file named
src/main/java/org/hibernate/tutorial/domain/Person.java
Next, create the new mapping file as
src/main/resources/org/hibernate/tutorial/domain/Person.hbm.xml
<hibernate-mapping package="org.hibernate.tutorial.domain">
<class name="Person" table="PERSON">
<id name="id" column="PERSON_ID">
<generator class="native"/>
</id>
<property name="age"/>
<property name="firstname"/>
<property name="lastname"/>
</class>
</hibernate-mapping>
Finally, add the new mapping to Hibernate's configuration immediately after the existing mapping for
Event.hbm.xml:
<mapping resource="events/Event.hbm.xml"/> <mapping resource="events/Person.hbm.xml"/>
Create an association between these two entities. Persons can participate in events, and events have participants. The design questions you have to deal with are: directionality, multiplicity, and collection behavior.
