Framework magic (Hibernate)

@Entity
@Table(name = "orders", schema = "com"})
public class Order implements Serializable {

    @Id
    @GeneratedValue(strategy = SEQUENCE, generator = "order_seq")
    @Column(name = "ID", unique = true, nullable = false)
    private Integer id;

    @Column(name = "NUMBER", nullable = false, length = 8)
    private String number;

    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinTable(name = "order_items", catalog = "com",
        joinColumns = {@JoinColumn(name = "ORDER_ID",
                       updatable = false, nullable = false)}, 
        inverseJoinColumns = {@JoinColumn(name = "ITEM_ID",
                              updatable = false, nullable = false)})
    private Set<Item> items = new HashSet<Item>();

}