public class Category  implements java.io.Serializable {  
       
    @Id   
    @GeneratedValue(strategy=IDENTITY)  
    @Column(name="CAT_ID", unique=true, nullable=false)  
     private Integer id;  
      
    @ManyToOne(fetch=FetchType.LAZY)  
    @JoinColumn(name="CAT_PARENT_ID")  
     private Category parent;  
      
    @Column(name="CAT_NAME", nullable=false, length=50)  
     private String name;  
      
    @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.LAZY, mappedBy="parent")
     private Set<Category> children = new HashSet<Category>(0);  
      
    //省略getter/setter  
  

}