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() );
// }
}
输出结果:
可以看出实现了延迟加载。