Ternary association & Query

Ternary association & Query

三个@Entity类Tc, Tracer, Track是三向关联的的表, @Embeddable类TcTracer则存储着三个表的ForeignKey

@Entity
@Table(name= "tc", catalog="first_hiber")
public class Tc {
      @org.hibernate.annotations.CollectionOfElements
      @JoinTable(name="tc_tracer", joinColumns=@JoinColumn(name="tc_id"))
      private Set<TcTracer> tcTracers = new HashSet<TcTracer>();

      @Id @GeneratedValue
      @Column(name="tc_id", nullable= false)
      private Long id;
}

  @Embeddable
  @Table(name="tc_tracer")
  public class TcTracer {
      @org.hibernate.annotations.Parent
      private Tc tc;
  
      @ManyToOne(cascade=CascadeType.ALL)
      @JoinColumn(name="tracer_id", nullable=false, updatable=false)
      private Tracer tracer;
  
      @ManyToOne(cascade=CascadeType.ALL)
      @JoinColumn(name="track_id", nullable=false, updatable=false)
      private Track track;
  }

如上，将TcTracer作为Tc的子元素，从而实现Tc的三相关联。

用HQL可以通过特定的Tc，Tracer得到对应的所有Track：

  select tctracers.track
  from Tc tc
      join tc.tcTracers tctracers
  where tc.name="tc name"
      and tctracers.tracer.name="tracer name"

 List<Track> tracks = session.createQuery(HQL).list();