Mybatis官方文檔說明處

Mybatis 一對多 結果集映射 簡單入門 易懂

• • 一、搭建數據庫環境
  • 二、idea 搭建maven 項目 （mybatis-demo）
  • • 2.1、項目結構
    • 2.2、導入依賴
    • 2.3、mysql 配置文件
    • 2.4、創建pojo 類
    • 2.5、寫一個mybatis 的工具類
    • 2.7、 寫一個TeacherMapper
    • 2.8、mybatis-config.xml 文件
  • 測試：
  • 自言自語

一、搭建數據庫環境

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, '楊大哥', 1); INSERT INTO `student_2` VALUES (5, '楊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, '小王老師'); INSERT INTO `teacher` VALUES (2, '小李老師'); INSERT INTO `teacher` VALUES (3, '小黑老師');

二、idea 搭建maven 項目 （mybatis-demo）

2.1、項目結構

2.2、導入依賴

<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>

2.3、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

2.4、創建pojo 類

學生

/*** @Author: crush* @Date: 2021-06-17 18:23* version 1.0*/ public class Student {/*** 學生id*/private Integer id;/*** xueshneg xingming*/private String name;/*** 老師id*/private Integer tid; }

老師

/*** @Author: crush* @Date: 2021-06-17 18:23* version 1.0*/ public class Teacher {/*** 老師id*/private Integer id;/*** 老師的姓名*/private String name;/*** 每個老師是不是有很多學生*/private List<Student> students; }

2.5、寫一個mybatis 的工具類

/*** @author crush*/ 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);} }

2.7、 寫一個TeacherMapper

import com.crush.pojo.Teacher; import org.apache.ibatis.annotations.Param;import java.util.List;public interface TeacherMapper {// 獲取老師List<Teacher> getTeacher();//獲取指定老師下的所有學生及老師的信息Teacher getTeacher2(@Param("tid") Integer id);//獲取指定老師下的所有學生及老師的信息Teacher getTeacher3(@Param("tid") Integer id);}

寫一個TeacherMapper.xml文件

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapperPUBLIC "-//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"/><!--復雜的屬性，我們需要單獨處理 對象 association 集合collectionjavaType ="" 是指屬性的類型集合中的泛型的信息 我們使用ofType 獲取--><collection property="students" ofType="Student"><result property="id" column="sid"/><result property="name" column="sname"/><result property="tid" column="tid"/></collection></resultMap><!--========================= 結果集映射=============================--><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>

2.8、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><!--屬性--><properties resource="dbconfig.properties"/><!--設置--><settings><!-- STDOUT_LOGGING 打印到控制臺 --><setting name="logImpl" value="STDOUT_LOGGING"/><!-- 開啟駝峰 --><setting name="mapUnderscoreToCamelCase" value="true"/></settings><!--別名--><typeAliases><!--這是 自己 取別名--><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>

測試：

/*** @Author: crush* @Date: 2021-06-17 18:22* version 1.0*/ public class MyTest {@Testpublic void getTeacher(){SqlSession session = MybatisUtil.getSession();TeacherMapper mapper = session.getMapper(TeacherMapper.class);List<Teacher> teacher = mapper.getTeacher();System.out.println(teacher);session.close();}@Testpublic void getTeacher2(){SqlSession session = MybatisUtil.getSession();TeacherMapper mapper = session.getMapper(TeacherMapper.class);Teacher teacher2 = mapper.getTeacher2(1);System.out.println(teacher2);session.close();}@Testpublic void getTeacher3(){SqlSession session = MybatisUtil.getSession();TeacherMapper mapper = session.getMapper(TeacherMapper.class);Teacher teacher2 = mapper.getTeacher3(1);System.out.println(teacher2);session.close();} }

自言自語

難啊，加油吧

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