JPA Derived Column value based on Identity column

Question

JPA 2.0 (Hibernate 4.2.4.Final/Spring 3.2.8.Release) / Mysql 5.6

For a managed entity E w/ auto-generated primary key e.g.

...
@Id
@GeneratedValue
pr         


        

Answer 1

You can create an interceptor for this requirement, see below example:

Let's say you have an entity called Student with properties id (acts as an identifier) and foo.

@Entity
@Table(name = "test_student")
public class Student {
    @Id
    @GeneratedValue
    private int id;
    private String foo;
    // Setters & Getters
}

Now you can create an interceptor that extends Empty Interceptor of hibernate and overrides the onSave method that sets the foo property with value as :{id} like this:

import java.io.Serializable;
import org.hibernate.CallbackException;
import org.hibernate.EmptyInterceptor;
import org.hibernate.type.Type;

public class MyInterceptor extends EmptyInterceptor {

    public boolean onSave(Object entity, Serializable id, Object[] state,
            String[] propertyNames, Type[] types) throws CallbackException {
        System.out.println("Entered onSave : class - " + entity.getClass());
        if (entity instanceof Student) {
            Student s = (Student) entity;
            System.out.println("class:" + entity.getClass() + " , id: "+s.getId());
            s.setFoo(":"+id);
        }
        return false;

    }
}

Now you need to tell hibernate to use this interceptor like this:

Configuration configuration = new Configuration().setInterceptor( new LogInterceptor() );
configuration.configure();