Hibernate Cannot instantiate abstract class or interface

Question

I have following project:

@Entity
@Table(name = "A")
public class A{
    @Id
    private Long id = null;

    @OneToMany(mappedBy = "a_1", cascade = CascadeType.ALL,
               fetch = FetchType.EAGER)
    private List<B> bs;
}

@Entity
@Table(name = "B")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "BTYPE",
                     discriminatorType = DiscriminatorType.STRING)
public abstract class B{
    @Id
    private Long id = null;

    @Embedded
    private C c;

    @ManyToOne(cascade=CascadeType.REFRESH)
    @JoinColumn(name="a_id")
    @XmlTransient
    private A a_1;
}

@Embeddable
public class C {
@OneToMany(mappedBy = "b_1", cascade = CascadeType.ALL,
           fetch = FetchType.EAGER))
    private Set<D> ds;
}

@Entity
@Table(name = "D")
public class D {
@ManyToOne(cascade=CascadeType.REFRESH)
    @JoinColumn(name="b_id")
    private B b_1;
}

@Entity
@DiscriminatorValue(value = "X_D")
public class X extends B {

}

@Entity
@DiscriminatorValue(value = "Y_D")
public class Y extends B {

}

All these classes implement Serializable except X and Y

At the moment when I call entityManager.merge(A) I get:

Caused by: org.hibernate.InstantiationException: Cannot instantiate abstract class or interface: B

Can anybody helpe me please?

Thnaks in advance

Answer 1

I saw similar issues where people had to make concrete classes (X and Y here) to implement Serializable in order to make it work