1 多对一处理
多个学生关联一个老师
1.1 环境配置
pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<parent>
<artifactId>myBatis</artifactId>
<groupId>org.example</groupId>
<version>1.0-SNAPSHOT</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>myBatis_01</artifactId>
<properties>
<maven.compiler.source>8</maven.compiler.source>
<maven.compiler.target>8</maven.compiler.target>
</properties>
<!--可能出现问题说明：Maven静态资源过滤问题-->
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
<include>**/*.properties</include>
</includes>
</resource>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.xml</include>
<include>**/*.properties</include>
</includes>
</resource>
</resources>
</build>
<dependencies>
<!-- https://mvnrepository.com/artifact/log4j/log4j -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.16.10</version>
</dependency>
</dependencies>
</project>
核心配置文件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>
<!-- 引入外部配置文件-->
<properties resource="db.properties"/>
<settings>
<!-- 标椎日志输出-->
<setting name="logImpl" value="LOG4J"/>
</settings>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<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>
<!-- 绑定接口-->
<mappers>
<mapper class="com.xxxx.dao.TeacherMapper"/>
<mapper class="com.xxxx.dao.StudentMapper"/>
</mappers>
</configuration>
数据库
/*
Navicat Premium Data Transfer
Source Server : localhost
Source Server Type : MySQL
Source Server Version : 50527
Source Host : localhost:3306
Source Schema : mybatis
Target Server Type : MySQL
Target Server Version : 50527
File Encoding : 65001
Date: 20/01/2021 12:12:55
*/
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
`id` int(11) NOT NULL,
`name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
`tid` int(11) DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE,
INDEX `tid`(`tid`) USING BTREE,
CONSTRAINT `tid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;
SET FOREIGN_KEY_CHECKS = 1;
/*
Navicat Premium Data Transfer
Source Server : localhost
Source Server Type : MySQL
Source Server Version : 50527
Source Host : localhost:3306
Source Schema : mybatis
Target Server Type : MySQL
Target Server Version : 50527
File Encoding : 65001
Date: 20/01/2021 12:25:12
*/
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for teacher
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
`id` int(11) NOT NULL,
`name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Compact;
-- ----------------------------
-- Records of teacher
-- ----------------------------
INSERT INTO `teacher` VALUES (1, 'teacher_zs');
SET FOREIGN_KEY_CHECKS = 1;
实体类的构建
@Data
public class Student {
private int id;
private String name;
//多个学生可以是同一个老师，即多对一
private Teacher teacher;
}
@Data
public class Teacher {
private int id;
private String name;
}
接口的构建
public interface TeacherMapper {
@Select("select * from teacher where id = #{id}")
Teacher getTeacherById(@Param("id") int id);
}
测试类的编写
public class DaoTest {
//注意导包：org.apache.log4j.Logger
static Logger logger = Logger.getLogger(DaoTest.class);
@Test
public void test(){
try(SqlSession sqlSession = MyBatisUtils.getSqlSesion();){
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = mapper.getTeacherById(1);
System.out.println(teacher);
}
}
}
测试成功！！！
1.2 按查询嵌套处理
StudentMapper.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 绑定一个对应的Dao/Mapper接口-->
<!-- SELECT s.id , s.name , t.name FROM student s , teacher t WHERE s.tid = t.id;-->
<!--查询所有学生的信息
根据查询的学生信息tid 寻找对应的老师-->
<mapper namespace="com.zs.mapper.StudentMapper">
<select id="getStudents" resultMap="StudentTeacher">
select * from student
</select>
<resultMap id="StudentTeacher" type="com.xxxx.pojo.Student">
<!-- 复杂的属性我们需要单独处理
对象：assocication
集合：collection
-->
<association property="teacher" column="tid" javaType="com.zs.pojo.Teacher" select="getTeacherById"/>
</resultMap>
<select id="getTeacherById" resultType="com.zs.pojo.Teacher">
select * from teacher where id = #{
id}
</select>
</mapper>
测试类
@Test
public void getStudent() {
try(SqlSession sqlSession = MyBatisUtils.getSqlSesion();){
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
List<Student> studentList = mapper.getStudents();
System.out.println(studentList);
}
}
1.3 按结果嵌套处理
<?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 绑定一个对应的Dao/Mapper接口-->
<!-- SELECT s.id , s.name , t.name FROM student s , teacher t WHERE s.tid = t.id;-->
<!--查询所有学生的信息
根据查询的学生信息tid 寻找对应的老师-->
<mapper namespace="com.xxxx.dao.StudentMapper">
<select id="getStudents" resultMap="StudentTeacher">
SELECT s.id sid , s.name sname , t.name tname
FROM student s , teacher t
WHERE s.tid = t.id
</select>
<resultMap id="StudentTeacher" type="com.xxxx.pojo.Student">
<result property="name" column="sname"/>
<result property="id" column="sid"/>
<association property="teacher" column="tid" javaType="com.xxxx.pojo.Teacher">
<result property="name" column="tname"/>
</association>
</resultMap>
</mapper>
2 一对多处理
2.1 按结果嵌套处理
实体类的编写
@Data
public class Student {
private int id;
private String name;
private int tid;
}
@Data
public class Teacher {
private int id;
private String name;
//一个老师多个学生
private List<Student> students;
}
TeacherMapper接口编写方法
public interface TeacherMapper {
Teacher getTeacher(@Param("id") int id);
}
编写接口对应的Mapper配置文件
<?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.xxxx.dao.TeacherMapper">
<select id="getTeacher" resultMap="TeacherStudent">
SELECT s.id sid, s.name sname , t.name tname, t.id tid
FROM student s,teacher t
WHERE s.tid = t.id and t.id=#{
id}
</select>
<resultMap id="TeacherStudent" type="com.xxxx.pojo.Teacher">
<result property="name" column="tname"/>
<collection property="students" ofType="com.xxxx.pojo.Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
</collection>
</resultMap>
</mapper>
测试类
public class DaoTest {
//注意导包：org.apache.log4j.Logger
static Logger logger = Logger.getLogger(DaoTest.class);
@Test
public void test(){
try(SqlSession sqlSession = MyBatisUtils.getSqlSesion();){
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = mapper.getTeacher(1);
System.out.println(teacher);
}
}
}
