Hibernate学习实例：关联表的树状结构设计

说明：

一、使用的Hibernate版本是hibernate-release-4.3.11.Final.

二、实例：一个公司有许多子公司

三、映射的时候，在同一个类中使用ManyToOne 和 OneToMany

四、本次只使用Annotation版本，其他版本可参考之前的博客

实体类：

Org.java：

package com.buaa.hibernate.homework;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.OneToMany;@Entitypublic class Org {private int id;private String name;private Set<Org> children = new HashSet<Org>();private Org parent;public Org(String name){this.name = name;}@Id@GeneratedValuepublic int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}@OneToMany(cascade={CascadeType.ALL},mappedBy="parent",fetch=FetchType.EAGER)public Set<Org> getChildren() {return children;}public void setChildren(Set<Org> children) {this.children = children;}@ManyToOne@JoinColumn(name="pid")public Org getParent() {return parent;}public void setParent(Org parent) {this.parent = parent;}}

hibernate配置文件 ：hibernate.cfg.xml:

<?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-configuration SYSTEM "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"><hibernate-configuration><session-factory><property name="connection.driver_class">com.mysql.jdbc.Driver</property><!-- Assume test is the database name --><property name="connection.url">jdbc:mysql://localhost/test</property><property name="connection.username">root</property><property name="connection.password">123456</property><property name="dialect">org.hibernate.dialect.MySQLDialect</property><property name="show_sql">true</property><property name="format_sql">true</property><property name="hbm2ddl.auto">create</property><mapping class="com.buaa.hibernate.homework.Org" /></session-factory></hibernate-configuration>

Junit测试类：

OrgTest.java:

package com.buaa.hibernate.homework;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import org.junit.After;import org.junit.Before;import org.junit.Test;public class OrgTest {private SessionFactory factory;private Session session;@Beforepublic void before(){Configuration configuration = new Configuration().configure();ServiceRegistry service = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties()).build(); factory = configuration.buildSessionFactory(service); session = factory.openSession();}//往数据库中存储数据@Testpublic void test(){Org o = new Org("company");Org o1 = new Org("company_1");Org o2 = new Org("company_2");Org o11 = new Org("company_1_1");Org o12 = new Org("company_1_2");o.getChildren().add(o1);o.getChildren().add(o2);o1.getChildren().add(o11);o1.getChildren().add(o12);o1.setParent(o);o2.setParent(o);o11.setParent(o1);o12.setParent(o1);session.beginTransaction();session.save(o);session.getTransaction().commit();}//从数据库中读取数据@Testpublic void loadTest(){test();session.beginTransaction();Org o = (Org)session.load(Org.class, 1);print(o,0);session.getTransaction().commit();}//用递归的方法，获取所有的子类，并且缩进显示private void print(Org o,int level) {String buffer = "";for(int i=0;i<level;i++){buffer += "----";}System.out.println(buffer + o.getName());for(Org child : o.getChildren()){print(child,level+1);}}@Afterpublic void after(){session.close();factory.close();}}

数据库的建表语句：

Hibernate:     alter table Org         drop         foreign key FK_n4sv1hojgjugxnfjsourei39bHibernate:     drop table if exists OrgHibernate:     create table Org (        id integer not null auto_increment,        name varchar(255),        pid integer,        primary key (id)    )Hibernate:     alter table Org         add constraint FK_n4sv1hojgjugxnfjsourei39b         foreign key (pid)         references Org (id)

最后是从数据库中读取到的数据：

company----company_2----company_1--------company_1_2--------company_1_1