MyBatis学习（五）resultMap测试

resultMap是MyBatis最强大的元素，它的作用是告诉MyBatis将从结果集中取出的数据转换成开发者所需要得对象。

接下来我们对resultMap进行一个简单测试。（当所需要返回的对象是一个对象关联到另一个对象的结果时）

1.创建一个项目，导入所需的jar包，在src目录下加入两个属性文件db.properyies和log4j.properties。

2.创建两个表，编写两个实体类分别映射这两张表。

-- Table structure for `t_student` -- ---------------------------- DROP TABLE IF EXISTS `t_student`; CREATE TABLE `t_student` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(18) NOT NULL, `sex` varchar(3) NOT NULL, `age` int(11) NOT NULL, `cid` int(11) NOT NULL, PRIMARY KEY (`id`), KEY `cid` (`cid`), CONSTRAINT `cid` FOREIGN KEY (`cid`) REFERENCES `t_clazz` (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of t_student -- ---------------------------- INSERT INTO `t_student` VALUES ('1', '张三', '男', '11', '1'); INSERT INTO `t_student` VALUES ('2', '李四', '男', '12', '2'); INSERT INTO `t_student` VALUES ('3', '小红', '女', '13', '1'); -- ---------------------------- -- Table structure for `t_clazz` -- ---------------------------- DROP TABLE IF EXISTS `t_clazz`; CREATE TABLE `t_clazz` ( `id` int(11) NOT NULL, `code` varchar(18) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of t_clazz -- ---------------------------- INSERT INTO `t_clazz` VALUES ('1', '一班'); INSERT INTO `t_clazz` VALUES ('2', '二班'); public class Student { private Integer id; private String name; private String sex; private Integer age; //关联的clazz对象 private Clazz clazz; //省略get、set、toString方法 public class Clazz { private Integer id; private String code; //省略get、set、toString方法

3.编写mybatis-config.xml和SQL映射文件

mybatis-config.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> <!-- 引入 外部db.properties文件--> <properties resource="db.properties"/> <!-- 指定 MyBatis 所用日志的具体实现--> <settings> <setting name="logImpl" value="log4j"/> </settings> <!-- 环境配置 --> <environments default="mysql"> <environment id="mysql"> <!-- 指定事务类型 --> <transactionManager type="JDBC"/> <!-- dataSource指数据源配置，POOLED是JDBC连接对象的数据源连接池的实现。 --> <dataSource type="POOLED"> <property name="driver" value="${driver}"/> <property name="url" value="${url}"/> <property name="username" value="${username}"/> <property name="password" value="${password}"/> </dataSource> </environment> </environments> <!-- SQL映射文件位置 --> <mappers> <mapper resource="com/dj/mapper/StudentMapper.xml"/> </mappers> </configuration>

StudetMapper.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"> <!-- namespace指用户自定义的命名空间 --> <mapper namespace="com.dj.mapper.StudentMapper"> <!-- 映射学生对象的resultMap --> <resultMap type="com.dj.domain.Student" id="studentResultMap"> <id property="id" column="id"/> <id property="name" column="name"/> <id property="sex" column="sex"/> <id property="age" column="age"/> <!-- 关联映射 property：表示返回类型student的属性名 clazz column：表示数据库的列名 javaType：表示property属性对应的类型名称 select：表示执行一条查询语句，将查询到的结果封装到property所代表的类型对象中。 --> <association property="clazz" column="cid" javaType="com.dj.domain.Clazz" select="selectClazzById"/> </resultMap> <select id="selectClazzById" resultType="com.dj.domain.Clazz"> select * from t_clazz where id=#{id} </select> <select id="selectStudent" resultMap="studentResultMap"> select * from t_student </select> </mapper>

4.进行测试，在控制台输出从数据库查询到的学生信息

StudentTest.java

package com.dj.test; import java.io.IOException; import java.io.InputStream; import java.util.Iterator; import java.util.List; 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 com.dj.domain.Student; public class StudentTest { public static void main(String[] args) throws IOException { InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); List<Student> list = sqlSession.selectList("com.dj.mapper.StudentMapper.selectStudent"); for (Student student : list) { System.out.println(student); } sqlSession.commit(); sqlSession.close(); } }

运行后可以在控制台看到如下结果：

源码下载路径：https://files.cnblogs.com/files/dj-blog/resultMapest.zip

 

转载于:https://www.cnblogs.com/dj-blog/p/7563037.html