Hibernate多对一自身关联

最新推荐文章于 2021-03-02 14:47:02 发布

原创最新推荐文章于 2021-03-02 14:47:02 发布 · 90 阅读

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本文通过实例演示了如何利用MyEclipse实现部门与子部门之间的树形关系持久化，包括数据库配置、实体生成及测试过程。

http://jinnaxu-tju-edu-cn.iteye.com/blog/606308

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  
     
    
+-----------+  
| 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]">

<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>