Question

Just trying out Hibernate (with Annotations) and I’m having problems with my mappings. I have two entity classes, AudioCD and Artist.

@Entity
public class AudioCD implements CatalogItem {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    private String title;

    @ManyToOne(cascade = { CascadeType.ALL }, optional = false)
    private Artist artist;
    ....
}

@Entity
@Table(uniqueConstraints = { @UniqueConstraint(columnNames = { "name" }) })
public class Artist {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    @Column(nullable = false)
    private String name;
    .....
}

I get AudioCD objects from an external source. When I try to persist the AudioCD the Artist gets persisted as well, just like I want to happen. If I try persisting another different CD, but Artist already exists I get errors due to constraint violations.

I want Hibernate to recognise that the Artist already exists and shouldn’t be inserted again. Can this be done via annotations? Or do I have to manage the persistence of the AudioCD and Artist seperately?

Answer 1

No, AFAIK you can’t.

Since name is unique for every Artist instance, you should try to lookup an artist by name (via session.createCriteria(Artist.class).add(Restrictions.eq("name", artistName)).uniqueResult() or get yourself some service class with method Artist findByName(String artistName)) and then decide, whether to persist an artist or to use existing one.