JPA樹形結構實體關聯映射

　　有時候我們需要設計樹形結構實體，比如常見的部門組織就是典型的樹形結構。

　　1、組織架構實體代碼：

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;/** * 組織架構 * @author Luxh */@Entity@Table(name="t_organization")public class Organization {        @Id    @GeneratedValue    private Long id;        /**組織名稱*/    @Column(length=64)    private String name;        /**組織編碼*/    @Column(length=64)    private String code;        /**父組織*/    @ManyToOne    @JoinColumn(name="parent_id")    private Organization parent;        /**子組織*/    @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產生的對應表結構為：

                                  

　　2、單元測試代碼：

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() {        //根據在persistence.xml中配置的persistence-unit name 建立EntityManagerFactory        emf = Persistence.createEntityManagerFactory("myJPA");    }        /**     * 儲存父組織,級聯儲存子組織     */    @Test    public void testAddParentOrg() {                //父組織        Organization chinaOrg = new Organization();        chinaOrg.setName("中國");        chinaOrg.setCode("CHINA");                //子組織        Organization gdOrg = new Organization();        gdOrg.setName("廣東");        gdOrg.setCode("GD");                //子組織        Organization gxOrg = new Organization();        gxOrg.setName("廣西");        gxOrg.setCode("GX");                Set<Organization> children = new HashSet<Organization>();        children.add(gdOrg);        children.add(gxOrg);                //添加子組織        chinaOrg.setChildren(children);                EntityManager em = emf.createEntityManager();        em.getTransaction().begin();        em.persist(chinaOrg);        em.getTransaction().commit();        em.close();    }        /**     * 儲存子組織     */    @Test    public void testAddChildOrg() {                        Organization gzOrg = new Organization();        gzOrg.setName("廣州");        gzOrg.setCode("GZ");                        EntityManager em = emf.createEntityManager();        //找出廣州所屬的父組織廣東        Organization parent = em.find(Organization.class, 3L);        //設定廣州的父組織        gzOrg.setParent(parent);                        em.getTransaction().begin();        //儲存廣州        em.persist(gzOrg);        em.getTransaction().commit();        em.close();    }        /**     * 根據子組織查詢父組織     */    @Test    public void testQueryParentByChild() {        EntityManager em = emf.createEntityManager();        //找出廣州        Organization gzOrg = em.find(Organization.class, 4L);        //找出父組織        Organization parent = gzOrg.getParent();        System.out.println("父組織名稱："+parent.getName());        em.close();    }        /**     * 根據父組織查詢子組織     */    @Test    public void testQueryChildrenByParent() {        EntityManager em = emf.createEntityManager();        //找出廣東        Organization gdOrg = em.find(Organization.class, 3L);        //找出子組織        Set<Organization> children = gdOrg.getChildren();        Iterator<Organization> it = children.iterator();        while(it.hasNext()) {            Organization  child = it.next();            System.out.println("子組織名稱："+child.getName());        }        em.close();    }                /**     * 關閉EntityManagerFactory     */    @After    public void after() {        if(null != emf) {            emf.close();        }    }}

　　1）執行完testAddParentOrg()方法，表中的資料為：

                                                                   

　　2）執行完testAddChildOrg()方法，表中的資料為：