Caused by: javax.persistence.PersistenceException: org.hibernate.InstantiationException: Cannot instantiate abstract class or interface: de.thorsten.model.SportsEvent
   at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1361)
   at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl
...
   at org.jboss.weldx.persistence.EntityManager$-100333838$Proxy$_$$_Weld$Proxy$.merge(EntityManager$-100333838$Proxy$_$$_Weld$Proxy$.java)
   at de.thorsten.service.ParticipationService.update(ParticipationService.java:32)
...   

@Stateless
public class ParticipationService implements Serializable {
   
    @Inject
    private EntityManager em;

    public void update(Participation participation) throws Exception {
        em.merge(participation); // this statement fires the exception !
    }
}


The fragments below shows the related code snippets


// The abstract root class:
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@Table(uniqueConstraints = @UniqueConstraint(columnNames = "eventDate"))
public abstract class SportsEvent implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    protected long id;

    @NotNull
    protected Date eventDate;
   
   //...
}

// The concrete subclass
@Entity
public class Training extends SportsEvent implements Serializable {


    public Training() {
    }

    @OneToOne
    private TrainingDay trainingDay;
   
   //...
}

// The class which owns the relationship to the abstract base class
@Entity
public class Participation implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @OneToOne
    private SportsEvent trainingItem; // participating this relationship does not work !
   
   //...
}