@MappedSuperclass and @OneToMany

Question

I need association @OneToMany from Country to superclass Place (@MappedSuperclass). It could be bidirectional. I would need something like @OneToAny.

@MappedSuperclass
public class Place {

    private String name;
    private Country country;

    @Column
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @ManyToOne
    @JoinColumn(name="country_id")
    public Country getCountry() {
        return country;
    }

    public void setCountry(Country country) {
        this.country = country;
    }
}

Country:

@Entity
   public class Country {
   private long id;
   private String name;
   private List<Place> places;

   @Any(metaColumn = @Column(name = "place_type"), fetch = FetchType.EAGER)
   @AnyMetaDef(idType = "integer", metaType = "string", metaValues = {
         @MetaValue(value = "C", targetEntity = City.class),
         @MetaValue(value = "R", targetEntity = Region.class) })
   @Cascade({ org.hibernate.annotations.CascadeType.ALL })
   //@JoinColumn(name="unnecessary") 
   //@OneToMany(mappedBy="country")  // if this, NullPointerException...
   public List<Place> getPlaces() {
      return places;
   }
//and rest of class

Without @JoinColunm there is an exception:

Caused by: org.hibernate.AnnotationException: @Any requires an explicit @JoinColumn(s): tour.spring.bc.model.vo.Country.places

In table City and Region is foreign key to table Country (Region.country_id, City.country_id) which is ok. But I do NOT need foreign key in table Country to tables Region and City so I don't need @JoinColum.

What can I do?

Caprine

Answer 1

@Any doesn't make sense here since foreign key is at the Places side and therefore it doesn't need additional meta column.

I'm not sure if it's possible to create a polymorphic relationship to @MappedSuperclass. However, you can try to declare Place as @Entity @Inheritance(InheritanceType.TABLE_PER_CLASS), it should produce the same database schema and allow polymorpic relationship.

Brunet

There is a subtle but important difference in the database schema though. With @MappedSuperclass, each of the concrete subclasses of Place can have its own ID generator, whereas with @Inheritance(InheritanceType.TABLE_PER_CLASS), they all have to have the same. For example, instances of two different subtypes of Place can in the former case have the same ID number, but in the latter case they can't. – Sandlin