hibernate树状映射

例如公司的组织机构：一个公司可以有多个子公司，一个子公司子有多个部门。

其实就是一张表，

例子程序:

Organization类：

package com.oracle.hibernate;

import java.util.HashSet;

import java.util.Set;

import javax.persistence.CascadeType;

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;

@Entity

public class Organization {

    private int id;

    private String name;

    //父机构

    private Organization  parent;

    //一个父机构可有多个子机构

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

    @Id

    @GeneratedValue

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    /**

     * 对于父机构：多对一

     * pid是本机构的外键，指向父机构的标识，其实就是指向父机构的id

     */

    @ManyToOne

    @JoinColumn(name="pid")

    public Organization getParent() {

        return parent;

    }

    public void setParent(Organization parent) {

        this.parent = parent;

    }

    /**

     * 对于子机构：一对多

     *设mappedBy，

     *fetch=EAGER可以加载父机构时全部加载子机构。机构树小 时可以用，树大时可用ajax异步

     *

     */

    @OneToMany(mappedBy="parent",cascade=CascadeType.ALL,fetch=FetchType.EAGER)

    public Set<Organization> getChildren() {

        return children;

    }

    public void setChildren(Set<Organization> children) {

        this.children = children;

    }

}

测试类：

package com.oracle.hibernate;

import org.hibernate.HibernateException;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.AnnotationConfiguration;

import org.hibernate.tool.hbm2ddl.SchemaExport;

import org.junit.AfterClass;

import org.junit.BeforeClass;

public class Test {

    private static SessionFactory sf = null;

    @BeforeClass

    public static void beforeClass() {

        try {

            // 生成表

            new SchemaExport(new AnnotationConfiguration().configure()).create(

                    false, true);

            sf = new AnnotationConfiguration().configure()

                    .buildSessionFactory();

        } catch (HibernateException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

    @org.junit.Test

    public void testSchemaExport() {

        new SchemaExport(new AnnotationConfiguration().configure()).create(

                false, true);

    }

    @AfterClass

    public static void afterClass() {

        sf.close();

    }

    @org.junit.Test

    public void testSave() {

        Session s = sf.getCurrentSession();

        s.beginTransaction();

        Organization org = new Organization();

        org.setName("总公司");

        Organization org2 = new Organization();

        Organization org3 = new Organization();

        Organization org4 = new Organization();

        Organization org5 = new Organization();

        org2.setName("分公司1");

        org3.setName("分公司2");

        org4.setName("分公司1_部门1");

        org5.setName("分公司1_部门2");

        org2.setParent(org);

        org3.setParent(org);

        org4.setParent(org2);

        org5.setParent(org2);

        org.getChildren().add(org2);

        org.getChildren().add(org3);

        org.getChildren().add(org4);

        org.getChildren().add(org5);

        s.save(org);

        s.getTransaction().commit();

    }

    @org.junit.Test

    public void testLoad() {

        testSave();// 生成数据

        Session s = sf.getCurrentSession();

        s.beginTransaction();

        Organization org = (Organization) s.load(Organization.class, 1);

        print(org, 0);

        s.getTransaction().commit();

    }

    // 递归显示目录结构

    private void print(Organization org, int level) {// level标识级别

        String preStr = "";

        for (int i = 0; i < level; i++) {

            preStr += "---"; // 级别往下一级，缩进

        }

        System.out.println(preStr + org.getName());

        for (Organization o : org.getChildren()) {

            print(o, level + 1);

        }

    }

}

生成的表：

打印树状结构：

总公司
---分公司1
------分公司1_部门2
------分公司1_部门1
---分公司2