Hibernate 菜鸟教程 4 单向多对一

项目图片

这里写图片描述

配置文件hibernate.cfg.xml

<mapping resource="com/jege/hibernate/one/way/manytoone/User.hbm.xml" />
        <mapping resource="com/jege/hibernate/one/way/manytoone/Dept.hbm.xml" />

映射文件

User.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.jege.hibernate.one.way.manytoone">
    <class name="User" table="t_user">
        <id name="id">
            <generator class="native" />
        </id>
        <property name="username" column="name" />
        <!-- class属性:配置一方的全限定类名或者类名，也可以不用配置,Hibernate可以通过反射获取 -->
        <!-- column属性：配置外键，对应于一方Dept的主键id，也可以不配置默认用属性名称name=dept作为多方的外键列名 -->
        <many-to-one name="dept" class="Dept" column="dept_id" />
    </class>
</hibernate-mapping>

Dept.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.jege.hibernate.one.way.manytoone">
    <class name="Dept" table="t_dept">
        <id name="id">
            <generator class="native" />
        </id>
        <property name="name" />
    </class>
</hibernate-mapping>

测试类CrudTest.java

package com.jege.hibernate.one.way.manytoone;

import org.hibernate.Session;
import org.junit.Before;
import org.junit.Test;

import com.jege.hibernate.util.HibernateUtils;

/**
 * @author JE哥
 * @email 1272434821@qq.com
 * @description:单向多对一的处理
 */
public class CrudTest {
  // 单个保存:一次性保存1个部门，保存3个员工
  // 在单向多对一保存的时候需要先保存一方，不是会出现多余的update语句，影响性能
  @Before
  public void before() throws Exception {
    Dept dept = new Dept();
    dept.setName("部门1");

    // 传入dept的本质是处理数据库user表的dept_id外键
    User user1 = new User("员工1", dept);
    User user2 = new User("员工2", dept);

    Session session = HibernateUtils.INSTANCE.getSession();
    session.beginTransaction();

    System.out.println("保存之前：" + dept);
    session.save(dept);// Hibernate会自动把保存后的主键放到当前对象的id里面
    System.out.println("保存之后：" + dept);
    session.save(user1);
    session.save(user2);

    session.getTransaction().commit();
    session.close();
  }

  @Test
  public void save() throws Exception {

  }
  
  @Test
  public void update() throws Exception {
    Session session = HibernateUtils.INSTANCE.getSession();
    User user = (User) session.get(User.class, 1L);
    user.setUsername("jege");
    
    session.beginTransaction();
    session.update(user);
    session.getTransaction().commit();
    session.close();
  }
  
  @Test
  public void delete() throws Exception {
    Session session = HibernateUtils.INSTANCE.getSession();
    User user = (User) session.get(User.class, 1L);
    
    session.beginTransaction();
    session.delete(user);
    session.getTransaction().commit();
    session.close();
  }

  @Test
  public void get() throws Exception {
    Session session = HibernateUtils.INSTANCE.getSession();
    User user = (User) session.get(User.class, 1L);
    System.out.println(user);
    System.out.println(user.getDept());
  }

}

源码地址

https://github.com/je-ge/hibernate

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