Hibernate多对一自身关联

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：

+-----------+
| Part      |
+-----------+
| id        |<---------|<PK>
| name      |          |
| father_id |----------|<FK>
+-----------+

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。

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评论

1 楼 wpfwupengfeiwpf 2010-09-11  

你好,我想请问如何将父类father_id为null的记录在保存时保存为0