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：