hibernate —— 树状存储

package com.pt.treeStrut;

import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;

@Entity
public class ArticleTree {
    int id;
    String title;
    String content;
    ArticleTree p_article;
    
    Set<ArticleTree> sons;
    
    @OneToMany(mappedBy="p_article",cascade=CascadeType.ALL)
    public Set<ArticleTree> getSons() {
        return sons;
    }
    
    
    public void setSons(Set<ArticleTree> sons) {
        this.sons = sons;
    }
    public ArticleTree(){
        
    }
    public ArticleTree(int id, String title, String content){
        setId(id);
        setTitle(title);
        setContent(content);
    }
    @Id
    //@GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public String getContent() {
        return content;
    }
    public void setContent(String content) {
        this.content = content;
    }
    
    @ManyToOne(cascade=CascadeType.ALL)
    @JoinColumn(name="parent_id")
    public ArticleTree getP_article() {
        return p_article;
    }
    public void setP_article(ArticleTree p_article) {
        this.p_article = p_article;
    }


    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return title + "  " + content;
    }
    
    
}

import java.sql.Connection;
import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.pt.hibernate.Student;
import com.pt.hibernate.Teacher;
import com.pt.treeStrut.ArticleTree;


public class Test {
    public static void main(String[] arges){
        Configuration cfg = new Configuration();
        SessionFactory factory = cfg.configure().buildSessionFactory();
        //Session ss=factory.openSession();
        Session ss= factory.getCurrentSession();
//        Teacher hong = new Teacher();
//        hong.setName("gaolihong");
//        hong.setCourese("english");
//        
//        Set<Student> students=new HashSet<Student>();
//        Student student = new Student();
//        student.setId(2);
//        student.setSchoolName("DuYangGang2");
//        students.add(student);
//        hong.setMyStudents(students);
        ss.beginTransaction();
//        ss.save(hong);
//        ss.getTransaction().commit();
        ArticleTree a_p = new ArticleTree(1000,"第一章","导论");
        ArticleTree a_s1 = new ArticleTree(1001,"第一节","导论——1");
        ArticleTree a_s2 = new ArticleTree(1002,"第二节","导论——2");
        
        ArticleTree a_p1 = new ArticleTree(2000,"第二章","光学");
        ArticleTree a_s11 = new ArticleTree(2001,"第一节","光学——1");
        ArticleTree a_s12 = new ArticleTree(2002,"第二节","光学——2");
        
        a_s11.setP_article(a_p1);
        a_s12.setP_article(a_p1);
        a_p1.setSons(new HashSet<ArticleTree>());    //否则会报空指针异常
        a_p1.getSons().add(a_s11);
        a_p1.getSons().add(a_s12);
        
        
        a_s1.setP_article(a_p);
        a_s2.setP_article(a_p);
        a_p.setSons(new HashSet<ArticleTree>());
        a_p.getSons().add(a_s1);
        a_p.getSons().add(a_s2);
        
        ArticleTree all = new ArticleTree(1,"物理","物理");
        a_p1.setP_article(all);
        a_p.setP_article(all);
        all.setSons(new HashSet<ArticleTree>());    //否则会报空指针异常
        all.getSons().add(a_p);
        all.getSons().add(a_p1);
        
        //ss.save(all);    //由于设置了cascade，存储一个，整个树都会存储进去
        
        //ss.save(a_s1);
        ss.save(a_s1);    //由于设置了cascade，存储一个，整个树都会存储进去
        ss.getTransaction().commit();
        //ss.close();        //getsession  不用close
        
        /****取出树来，并打印*******/
        Session ss2= factory.getCurrentSession();
        ss2.beginTransaction();
        ArticleTree getAll = ss2.load(ArticleTree.class, 1);  //取出父节点
        printTree(getAll,0);
        ss2.getTransaction().commit();
        factory.close();
    }
    
    public static void printTree(ArticleTree parent,int level){
        for(int i = 0; i< level; i++){
            System.out.print("--");
        }
        System.out.println(parent);
        for(ArticleTree article : parent.getSons()){
            printTree(article, level + 1);
        }
    }
}

PS:开发过程中写的bug:

　　1、commit的时候提示没有session   原因：session没有beginTransion

　　2、提示set<sons>  字段找不到匹配的数据库字段类型，  原因：@oneTomany 写在了get上