JPA树形结构实体关系映射

　　有时候我们需要设计树形结构实体，比如常见的部门组织就是典型的树形结构。

　　1、组织架构实体代码：

package cn.luxh.jpa.entity;



import java.util.HashSet;

import java.util.Set;



import javax.persistence.CascadeType;

import javax.persistence.Column;

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;

import javax.persistence.Table;







/**

 * 组织架构

 * @author Luxh

 */

@Entity

@Table(name="t_organization")

public class Organization {

    

    @Id

    @GeneratedValue

    private Long id;

    

    /**组织名称*/

    @Column(length=64)

    private String name;

    

    /**组织编码*/

    @Column(length=64)

    private String code;

    

    /**父组织*/

    @ManyToOne

    @JoinColumn(name="parent_id")

    private Organization parent;

    

    /**子组织*/

    @OneToMany(cascade=CascadeType.ALL,fetch=FetchType.LAZY)

    @JoinColumn(name="parent_id")

    private Set<Organization> children = new HashSet<Organization>();

    

    //省略get/set方法

    //...

    

}

　　JPA生成的对应表结构为：

                                  

　　2、单元测试代码：

package cn.luxh.jpa.test;



import java.util.HashSet;

import java.util.Iterator;

import java.util.Set;



import javax.persistence.EntityManager;

import javax.persistence.EntityManagerFactory;

import javax.persistence.Persistence;



import org.junit.After;

import org.junit.Before;

import org.junit.Test;



import cn.luxh.jpa.entity.Organization;







public class JPATest {

    

    EntityManagerFactory emf = null;

    

    @Before

    public void before() {

        //根据在persistence.xml中配置的persistence-unit name 创建EntityManagerFactory

        emf = Persistence.createEntityManagerFactory("myJPA");

    }

    

    /**

     * 保存父组织,级联保存子组织

     */

    @Test

    public void testAddParentOrg() {

        

        //父组织

        Organization chinaOrg = new Organization();

        chinaOrg.setName("中国");

        chinaOrg.setCode("CHINA");

        

        //子组织

        Organization gdOrg = new Organization();

        gdOrg.setName("广东");

        gdOrg.setCode("GD");

        

        //子组织

        Organization gxOrg = new Organization();

        gxOrg.setName("广西");

        gxOrg.setCode("GX");

        

        Set<Organization> children = new HashSet<Organization>();

        children.add(gdOrg);

        children.add(gxOrg);

        

        //添加子组织

        chinaOrg.setChildren(children);

        

        EntityManager em = emf.createEntityManager();

        em.getTransaction().begin();

        em.persist(chinaOrg);

        em.getTransaction().commit();

        em.close();

    }

    

    /**

     * 保存子组织

     */

    @Test

    public void testAddChildOrg() {

        

        

        Organization gzOrg = new Organization();

        gzOrg.setName("广州");

        gzOrg.setCode("GZ");

        

        

        EntityManager em = emf.createEntityManager();

        //找出广州所属的父组织广东

        Organization parent = em.find(Organization.class, 3L);

        //设置广州的父组织

        gzOrg.setParent(parent);

                

        em.getTransaction().begin();

        //保存广州

        em.persist(gzOrg);

        em.getTransaction().commit();

        em.close();

    }

    

    /**

     * 根据子组织查询父组织

     */

    @Test

    public void testQueryParentByChild() {

        EntityManager em = emf.createEntityManager();

        //找出广州

        Organization gzOrg = em.find(Organization.class, 4L);

        //找出父组织

        Organization parent = gzOrg.getParent();

        System.out.println("父组织名称："+parent.getName());

        em.close();

    }

    

    /**

     * 根据父组织查询子组织

     */

    @Test

    public void testQueryChildrenByParent() {

        EntityManager em = emf.createEntityManager();

        //找出广东

        Organization gdOrg = em.find(Organization.class, 3L);

        //找出子组织

        Set<Organization> children = gdOrg.getChildren();

        Iterator<Organization> it = children.iterator();

        while(it.hasNext()) {

            Organization  child = it.next();

            System.out.println("子组织名称："+child.getName());

        }

        em.close();

    }

    

        

    /**

     * 关闭EntityManagerFactory

     */

    @After

    public void after() {

        if(null != emf) {

            emf.close();

        }

    }



}

　　1）执行完testAddParentOrg()方法，表中的数据为：

                                                                   

　　2）执行完testAddChildOrg()方法，表中的数据为：