Mybatis 一对多 简单入门 易懂
搭建数据库环境
student 表
DROP TABLE IF EXISTS `student_2`;
CREATE TABLE `student_2` (
`id` int(10) NOT NULL,
`name` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
`tid` int(10) NULL DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE,
INDEX `fktid`(`tid`) USING BTREE,
CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
INSERT INTO `student_2` VALUES (1, '小明', 1);
INSERT INTO `student_2` VALUES (2, '邱ss', 2);
INSERT INTO `student_2` VALUES (3, '邱大哥', 3);
INSERT INTO `student_2` VALUES (4, '杨大哥', 1);
INSERT INTO `student_2` VALUES (5, '杨ss', 2);teacher
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
`id` int(10) NOT NULL AUTO_INCREMENT,
`name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = latin1 COLLATE = latin1_swedish_ci ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of teacher
-- ----------------------------
INSERT INTO `teacher` VALUES (1, '小王老师');
INSERT INTO `teacher` VALUES (2, '小李老师');
INSERT INTO `teacher` VALUES (3, '小黑老师');idea 搭建maven 项目 （mybatis-demo）
项目结构
导入依赖
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.48</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.20</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.6</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>
</dependencies>mysql 配置文件
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ssm-study?useSSL=false
jdbc.username=root
jdbc.password=123456创建pojo 类
学生
public class Student {
private Integer id;
private String name;
private Integer tid;
}老师
public class Teacher {
private Integer id;
private String name;
private List<Student> students;
}写一个mybatis 的工具类
public class MybatisUtil {
private static SqlSessionFactory sqlSessionFactory;
static {
try {
String resource="mybatis-config.xml";
InputStream inputStream= Resources.getResourceAsStream(resource);
sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
public static SqlSession getSession(){
return sqlSessionFactory.openSession(true);
}
}写一个TeacherMapper
import com.crush.pojo.Teacher;
import org.apache.ibatis.annotations.Param;
import java.util.List;
public interface TeacherMapper {
// 获取老师
List<Teacher> getTeacher();
//获取指定老师下的所有学生及老师的信息
Teacher getTeacher2(@Param("tid") Integer id);
//获取指定老师下的所有学生及老师的信息
Teacher getTeacher3(@Param("tid") Integer id);
}写一个TeacherMapper.xml文件
<?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.crush.dao.TeacherMapper">
<select id="getTeacher" resultType="Teacher">
select * from teacher
</select>
<select id="getTeacher2" resultMap="TeacherStudent">
select s.id sid,s.name sname,t.name tname,
t.id tid from student_2 s,teacher t where s.tid=t.id and t.id=#{tid}
</select>
<resultMap id="TeacherStudent" type="Teacher">
<result property="id" column="tid"/>
<result property="name" column="tname"/>
<!--
复杂的属性，我们需要单独处理 对象 association 集合collection
javaType ="" 是指属性的类型
集合中的泛型的信息 我们使用ofType 获取
-->
<collection property="students" ofType="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<result property="tid" column="tid"/>
</collection>
</resultMap>
<!--========================= 结果集映射=============================-->
<select id="getTeacher3" resultMap="TeacherStudent3">
select * from teacher where id=#{tid}
</select>
<resultMap id="TeacherStudent3" type="Teacher">
<collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id" />
</resultMap>
<select id="getStudentByTeacherId" resultType="Student">
select * from student_2 where tid=#{tid}
</select>
</mapper>mybatis-config.xml 文件
<?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>
<!--属性-->
<properties resource="dbconfig.properties"/>
<!--设置-->
<settings>
<!-- STDOUT_LOGGING 打印到控制台 -->
<setting name="logImpl" value="STDOUT_LOGGING"/>
<!-- 开启驼峰 -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!--别名-->
<typeAliases>
<!--这是 自己 取别名-->
<typeAlias alias="Student" type="com.crush.pojo.Student"/>
<typeAlias alias="Teacher" type="com.crush.pojo.Teacher"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mapper/StudentMapper.xml"/>
<mapper resource="mapper/TeacherMapper.xml"/>
</mappers>
</configuration>测试：
public class MyTest {
@Test
public void getTeacher(){
SqlSession session = MybatisUtil.getSession();
TeacherMapper mapper = session.getMapper(TeacherMapper.class);
List<Teacher> teacher = mapper.getTeacher();
System.out.println(teacher);
session.close();
}
@Test
public void getTeacher2(){
SqlSession session = MybatisUtil.getSession();
TeacherMapper mapper = session.getMapper(TeacherMapper.class);
Teacher teacher2 = mapper.getTeacher2(1);
System.out.println(teacher2);
session.close();
}
@Test
public void getTeacher3(){
SqlSession session = MybatisUtil.getSession();
TeacherMapper mapper = session.getMapper(TeacherMapper.class);
Teacher teacher2 = mapper.getTeacher3(1);
System.out.println(teacher2);
session.close();
}
}以上就是Mybatis结果集映射一对多 的详细内容，更多关于Mybatis结果集映射的资料请关注编程网其它相关文章！
