Hibernate problem - "Use of @OneToMany or @ManyToMany targeting an unmapped class"

Your annotations look fine. Here are the things to check:

• make sure the annotation is javax.persistence.Entity, and not org.hibernate.annotations.Entity. The former makes the entity detectable. The latter is just an addition.

• if you are manually listing your entities (in persistence.xml, in hibernate.cfg.xml, or when configuring your session factory), then make sure you have also listed the ScopeTopic entity

• make sure you don't have multiple ScopeTopic classes in different packages, and you've imported the wrong one.

Mine was not having @Entity on the many side entity

@Entity // this was commented
@Table(name = "some_table")
public class ChildEntity {
    @JoinColumn(name = "parent", referencedColumnName = "id")
    @ManyToOne
    private ParentEntity parentEntity;
}

Your entity may not listed in hibernate configuration file.