本文将阐述mybatis中的延迟加载。
1、环境约束
- win10 64位操作系统
- idea2018.1.5
- jdk-8u162-windows-x64
- mybatis3.2.8
- mysql 6.5
2、前提约束
- 完成mybatis一对一查询 https://www.jianshu.com/p/71ccf2f13f45
3、操作步骤
- 在pom.xml中加入依赖
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>2.2.2</version>
</dependency>
- 在resources下新建log4j.properties
### set log levels ###
log4j.rootLogger = debug,stdout,file
# MyBatis logging configuration...
log4j.logger.org.mybatis.example=DEBUG
log4j.appender.stdout = org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target = System.out
log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern =[%-d{yyyy-MM-dd HH:mm:ss}]-[%t-%5p]-[%C-%M(%L)]: %m%n
#所有文件输出
log4j.appender.file = org.apache.log4j.FileAppender
log4j.appender.file.File = D:/class134.log
log4j.appender.file.Encoding=UTF-8
log4j.appender.file.name = fileLogDemo
log4j.appender.file.Threshold=DEBUG
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=[%-d{yyyy-MM-dd HH:mm:ss}]-[%t-%5p]-[%C-%M(%L)]: %m%n
log4j.appender.file.append = true
- 在mybatis-config.xml中加入以下内容以便打开懒加载开关
<settings>
<setting name="lazyLoadingEnabled" value="true"/>
</settings>
- 在UserMapper.java中新增一个方法声明
List<Login> selectLogin1();
- 在UserMapper.xml中加入标签
<select id="selectLogin1" resultMap="loginMap1">
select * from t_login
</select>
<resultMap id="loginMap1" type="net.wanho.entity.Login">
<result column="id" property="id" javaType="int"></result>
<result column="username" property="username" javaType="String"></result>
<result column="password" property="password" javaType="String"></result>
<association property="user" select="selectUser1" column="userid">
</association>
</resultMap>
<select id="selectUser1" resultType="net.wanho.entity.User">
select * from t_user where id=#{userid}
</select>
- 测试
//关键代码
String resource ="mybatis-config.xml";
Reader reader = Resources.getResourceAsReader(resource);
SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(reader);
SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
//这句代码执行完毕,便能看到后台日志只打印了一张表t_login的查询记录
List<Login> loginList = userMapper.selectLogin1();
if(!loginList.isEmpty())
{
//这句代码执行完毕,才会看到后台日志有打印的另一张表t_user的查询记录
System.out.println(loginList.get(0).getUser());
}
以上就是mybatis完成延迟加载的过程。