说明：一个部门有若干个子部门，子部门还可以有子部门，本文通过这个演示myeclipse如何实现这种树形关系的持久化。
开发工具：myeclipse 7.0 GA
数 据 库：mysql-5.0.41
操作系统：windows xp professional 中文版
步骤：
1、建立mysql5数据库testdb，脚本下面已经给出。
2、配置myeclipse的数据库服务器，并建立名称为mysql的数据库链接。
3、建议myeclipse的web工程，名称为hibernateRel，并加入hibernate支持。
4、在myeclipse的数据库视图中链接数据库并通过表生成实体POJO和配置文件，中间不生成DAO。
5、检查配置文件的正确性，然后测试类进行测试。
一、建立数据库的脚本:
drop table if exists part;
-- alter table part drop foreign key fk_part;
create table part(
id bigint not null primary key,
name varchar(20),
father_id bigint
);
alter table part add index fk_part (father_id),
add constraint fk_part foreign key (father_id) references part(id);
表关系的逻辑图：
Java代码
1. +-----------+
2. | Part |
3. +-----------+
4. | id |<---------|<PK>
5. | name | |
6. | father_id |----------|<FK>
7. +-----------+
特别注意：因为有外键约束，需要事务支持，在安装数据库的时候，需要配置mysql数据库服务器的参数。数据库的引擎应该用InnoDB，关闭了自动提交模式，也就是SET AUTOCOMMIT=0。
二、通过myeclipse生成实体和配置文件：
Part.java
public class Part implements java.io.Serializable {
// Fields
private Long id;
private String name;
private Part part; //父Part
private Set parts = new HashSet(0); //子Part
// Constructors
/** default constructor */
public Part() {
}
/** minimal constructor */
public Part(Long id) {
this.id = id;
}
public Part(String name) {
this.name = name;
}
/** full constructor */
public Part(Long id, Part part, String name, Set parts) {
this.id = id;
this.part = part;
this.name = name;
this.parts = parts;
}
// Property accessors
public Long getId() {
return this.id;
}
public void setId(Long id) {
this.id = id;
}
public Part getPart() {
return this.part;
}
public void setPart(Part part) {
this.part = part;
}
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
public Set getParts() {
return this.parts;
}
public void setParts(Set parts) {
this.parts = parts;
}
}
Part.hbm.xml
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"[url]http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd[/url]">
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
<class name="org.lavasoft.Part" table="part">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="increment" />
</id>
<property name="name" type="java.lang.String">
<column name="name" length="20" />
</property>
<many-to-one name="part" class="org.lavasoft.Part" fetch="select">
<column name="father_id" />
</many-to-one>
<set name="parts" cascade="save-update" inverse="true">
<key>
<column name="father_id" />
</key>
<one-to-many class="org.lavasoft.Part" />
</set>
</class>
</hibernate-mapping> 三、写测试类进行测试：
Test.java
package org.lavasoft;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
public class Test {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Part p1=new Part("p1");
Part p11=new Part("p11");
Part p12=new Part("p12");
p1.getParts().add(p11);
p1.getParts().add(p12);
p11.setPart(p1);
p12.setPart(p1);
Configuration config = new Configuration().configure();
SessionFactory factory = config.buildSessionFactory();
Session session = factory.openSession();
Transaction tx = session.beginTransaction();
try{
session.save(p1);
tx.commit();
}catch(HibernateException e){
e.printStackTrace();
tx.rollback();
}finally{
session.close();
}
}
} 四、运行测试类Test，控制台打印信息：
------------------------------------------
Hibernate: select max(id) from part
Hibernate: insert into part (name, father_id, id) values (?, ?, ?)
Hibernate: insert into part (name, father_id, id) values (?, ?, ?)
Hibernate: insert into part (name, father_id, id) values (?, ?, ?)
查看数据库：
D:\mysql-5.0.41-win32\bin>mysql -uroot -123456
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 13
Server version: 5.0.41-community MySQL Community Edition (GPL)
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.
mysql> use testdb;
Database changed
mysql> describe part;
+-----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| id | bigint(20) | NO | PRI | | |
| name | varchar(20) | YES | | NULL | |
| father_id | bigint(20) | YES | MUL | NULL | |
+-----------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> select * from part;
+----+------+-----------+
| id | name | father_id |
+----+------+-----------+
| 1 | p1 | NULL |
| 2 | p12 | 1 |
| 3 | p11 | 1 |
+----+------+-----------+
3 rows in set (0.00 sec)
mysql> 测试结果表明，保存父机关的时候，可以级联保存父机关下的子机关。
总结：这个表建立好后，由myeclipse生成的POJO不需要做任何改动，生成的mapping也需要添加一个cascade="save-update"。然后就直接写测试类进行测试。
