Mybatis中一对多查询实现延迟加载

基于Mybatis中一对一查询实现延迟加载的基础上进行修改：

AccountDao接口：

package com.qublog.dao;

import com.qublog.domain.Account;

import java.util.List;

public interface AccountDao {
    //查询所有账户，同时还要获取到当前账户的所属用户信息
    List<Account> findAll();

    //根据用户id查询账户信息
    List<Account> findAccountByUid(Integer uid);
}

UserDao接口：
package com.qublog.dao;


import com.qublog.domain.User;

import java.util.List;

//用户的持久层接口
public interface UserDao {

    //查询所有用户，同时获取到用户下所有账户的信息
    List<User> findAll();

    User findById();
}

AccountDao.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qublog.dao.AccountDao">
    <!-- 定义封装account和user的resultMap -->
    <resultMap id="accountUserMap" type="account">
        <id property="id" column="id"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
        <!-- 一对一的关系映射，配置封装user的内容
             select属性指定的内容：查询用户的唯一标识
             column属性指定的内容：用户根据id查询时，所需要的参数的值
        -->
        <association property="user" column="uid" javaType="user" select="com.qublog.dao.UserDao.findById"></association>
    </resultMap>

    <!-- 配置查询所有 -->
    <select id="findAll" resultMap="accountUserMap">
        select * from account;
    </select>

    <select id="findAccountByUid" parameterType="Integer" resultType="account">
        select * from account where uid=#{uid}
    </select>
</mapper>

UserDao.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.qublog.dao.UserDao">
    <!-- 定义user的resultMap -->
    <resultMap id="userAccountMap" type="user">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="address" column="address"></result>
        <result property="sex" column="sex"></result>
        <result property="birthday" column="birthday"></result>
        <!-- 配置user对象中accounts集合的映射 -->
        <collection property="accounts" ofType="account" select="com.qublog.dao.AccountDao.findAccountByUid" column="id"></collection>
    </resultMap>

    <!-- 配置查询所有 -->
    <select id="findAll" resultMap="userAccountMap">
        select * from user;
    </select>

    <!-- 根据id查询用户 -->
    <select id="findById" parameterType="Integer" resultType="user">
        select * from user where id=#{id};
    </select>
</mapper>

UserTest类：
package com.qublog.test;

import com.qublog.dao.UserDao;
import com.qublog.domain.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.InputStream;
import java.util.List;

public class UserTest {
    private InputStream in = null;
    private SqlSession sqlSession = null;
    UserDao userDao = null;

    @Before //用于在测试方法执行之前执行
    public void init() throws Exception {
        //读取配置文件，生成字节输入流
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //获取SqlSessionFactory对象
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        //获取SqlSession对象
        sqlSession = factory.openSession();
        //获取dao代理对象
        userDao = sqlSession.getMapper(UserDao.class);
    }

    @After //用于在测试方法执行之后执行
    public void destroy() throws Exception {
        //提交事务
        sqlSession.commit();
        //释放资源
        sqlSession.close();
        in.close();
    }

    @Test
    public void testFindAll() throws Exception {
        //执行查询所有方法
        List<User> users = userDao.findAll();
        for (User user:users) {
            System.out.println(user);
            System.out.println(user.getAccounts() );
        }
    }

}

输出结果：


修改后：
    @Test
    public void testFindAll() throws Exception {
        //执行查询所有方法
        List<User> users = userDao.findAll();
//        for (User user:users) {
//            System.out.println(user);
//            System.out.println(user.getAccounts() );
//        }
   


可以看出实现了延迟加载。