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;

@Entity
public 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
@GeneratedValue
public 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;

@Before
public 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
@Test
public 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
@Test
public 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);
}
}

@After
public void after(){
session.close();
factory.close();
}
}

数据库的建表语句：

Hibernate:
alter table Org
drop
foreign key FK_n4sv1hojgjugxnfjsourei39b
Hibernate:
drop table if exists Org
Hibernate:
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