MyBatis懒加载

环境准备

工程

工程结构

配置文件

环境配置

SqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <properties resource="db.properties">
    </properties>

    <settings>
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"></setting>
    </settings>

    <environments default="development">
        <environment id="development">
            <!-- 配置JDBC事务控制，由mybatis进行管理 -->
            <transactionManager type="JDBC"></transactionManager>
            <!-- 配置数据源，采用mybatis连接池 -->
            <dataSource type="POOLED">
                <property name="driver" value="${db.driver}"/>
                <property name="url" value="${db.url}"/>
                <property name="username" value="${db.username}"/>
                <property name="password" value="${db.password}"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 加载映射文件 -->
    <mappers>
        <package name="dao.mapper"></package>
    </mappers>
</configuration>

log4j.properties

# Global logging configuration
log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

db.properties

db.driver = com.mysql.jdbc.Driver
db.url = jdbc:mysql://localhost:3306/ee19_batis_day03?useUnicode=true&characterEncoding=utf-8
db.username = root
db.password = 123

Mapper配置

主要讲一对一结构另一种写法
另一种写法参照MyBatis框架学习Ⅷ

UserMapper.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="dao.mapper.UserMapper">

    <select id="findUserById" parameterType="int" resultType="entity.User">
      SELECT * FROM USER WHERE id = #{id}
    </select>

</mapper>

CacheMapper.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="dao.mapper.CacheMapper">

    <resultMap id="OrderAndLazyLoading" type="entity.OrdersExt">
        <id column="id" property="id"></id>
        <result column="user_id" property="userId"></result>
        <result column="number" property="number"></result>
        <association property="user" select="dao.mapper.UserMapper.findUserById" column="user_id"></association>
    </resultMap>

    <select id="findOrderAndLazyLoading" resultMap="OrderAndLazyLoading">
        select * from orders
    </select>

</mapper>

CacheMapper

package dao.mapper;

import entity.OrdersExt;

import java.util.List;

public interface CacheMapper {
    List<OrdersExt> findOrderAndLazyLoading() throws Exception;
}

测试代码

package execute;

import dao.mapper.CacheMapper;
import dao.mapper.OrdersMapper;
import entity.OrderMapExt;
import entity.OrdersExt;
import entity.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.Test;
import sun.misc.Cache;

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

public class MyBatis2 {
    @Test
    public void testFindOrderAndUser() throws Exception {
        //读取配置文件
        //全局配置文件的路径
        String resource = "SqlMapConfig.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);

        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();

        CacheMapper mapper = sqlSession.getMapper(CacheMapper.class);
        List<OrdersExt> orderAndLazyLoading = mapper.findOrderAndLazyLoading();

        sqlSession.close();
    }
}

没使用懒加载测试结果

使用懒加载测试结果