1.在数据库中创建班级表和老师表
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CREATE TABLE teacher( t_id INT PRIMARY KEY AUTO_INCREMENT, t_name VARCHAR(20) ); CREATE TABLE class( c_id INT PRIMARY KEY AUTO_INCREMENT, c_name VARCHAR(20), teacher_id INT ); ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id); INSERT INTO teacher(t_name) VALUES(‘LS1‘); INSERT INTO teacher(t_name) VALUES(‘LS2‘); INSERT INTO class(c_name, teacher_id) VALUES(‘bj_a‘, 1); INSERT INTO class(c_name, teacher_id) VALUES(‘bj_b‘, 2); |
2.创建相应的实体类Classes和Teacher
3.配置映射文件ClassesMapper.xml
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<?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.zhiyou100.kfs.dao.ClassesMapper"> <!-- 通过cid查询班级信息和对应的老师信息 -->
<resultMap type="com.zhiyou100.kfs.bean.Classes" id="BaseMap"> <!-- id标签数据库表主键对应实体类属性 result标签数据库表除了主键对应的实体类属性 column属性是对应数据库表的栏，property属性是对应实体类的属性 --> <id column="c_id" property="cid"/> <result column="c_name" property="cname"/> <result column="teacher_id" property="teacherid"/> <!-- association标签是一对一关联返回的配置标签 property属性是实体类中的对象名，javaType是对象的全类名 --> <association property="teacher" javaType="com.zhiyou100.kfs.bean.Teacher"> <id column="t_id" property="tid"/> <result column="t_name" property="tname"/> </association> </resultMap> <!-- 1.直接用联表sql语句查询，返回结果集再配置一下 --> <select id="select1" resultMap="BaseMap"> select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{cid} </select> </mapper> |
4.创建dao接口ClassesMapper.java
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public interface ClassesMapper{ /** * 一对一关联 * @param cid * @return */ public Classes select1(int cid); } |
5.创建单元测试
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@Test void testSelect1() throws IOException { //1.获取配置文件config.xml加入到io流中 InputStream inputStream = Resources.getResourceAsStream("config.xml"); //2.通过SqlSessionFatoryBuilder的builder创建sqlsessionfatory SqlSessionFactory sqlSessionFatory = new SqlSessionFactoryBuilder().build(inputStream); //3.通过sqlSessionFactory的openSession方法创建SqlSession SqlSession sqlSession=sqlSessionFatory.openSession(); //4.通过sqlSession的getMapper传入dao全类名的方法创建UserMapper对象 ClassesMapper um=sqlSession.getMapper(com.zhiyou100.kfs.dao.ClassesMapper.class); //5.调用UserMapper的selectById来使用通过id查询一个用户 Classes classes=um.select1(1); System.out.println(classes); //最后一个页是很重要的一个：关闭资源 sqlSession.close(); } |
1.在数据库里创建学生表
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CREATE TABLE student( s_id INT PRIMARY KEY AUTO_INCREMENT, s_name VARCHAR(20), class_id INT ); INSERT INTO student(s_name, class_id) VALUES(‘xs_A‘, 1); INSERT INTO student(s_name, class_id) VALUES(‘xs_B‘, 1); INSERT INTO student(s_name, class_id) VALUES(‘xs_C‘, 1); INSERT INTO student(s_name, class_id) VALUES(‘xs_D‘, 2); INSERT INTO student(s_name, class_id) VALUES(‘xs_E‘, 2); INSERT INTO student(s_name, class_id) VALUES(‘xs_F‘, 2); |
2.创建对应Student实体类
3.配置映射文件ClassesMapper.xml
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<?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.zhiyou100.kfs.dao.ClassesMapper"> <!-- 通过cid查询班级信息和对应的学生信息 -->
<resultMap type="com.zhiyou100.kfs.bean.Classes" id="BaseMap"> <!-- id标签数据库表主键对应实体类属性 result标签数据库表除了主键对应的实体类属性 column属性是对应数据库表的栏，property属性是对应实体类的属性 --> <id column="c_id" property="cid"/> <result column="c_name" property="cname"/> <result column="teacher_id" property="teacherid"/> <!-- collection标签是一对多关联的配置 property是实体类对应的集合名，ofType是集合类的全类名 --> <collection property="list" ofType="com.zhiyou100.kfs.bean.Student"> <id column="s_id" property="sid"/> <result column="s_name" property="sname"/> <result column="class_id" property="classid"/> </collection> </resultMap> <!-- 1.直接用联表sql语句查询，返回结果集再配置一下 --> <select id="select2" resultMap="BaseMap"> select * from class c,student s where c.c_id=s.class_id and c.c_id=#{cid} </select> </mapper> |
4.创建dao接口ClassesMapper.java
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public interface ClassesMapper{ /** * 一对多关联 * @param cid * @return */ public Classes select2(int cid); } |
5.创建单元测试来测试
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@Test void testSelect2() throws IOException { //1.获取配置文件config.xml加入到io流中 InputStream inputStream = Resources.getResourceAsStream("config.xml"); //2.通过SqlSessionFatoryBuilder的builder创建sqlsessionfatory SqlSessionFactory sqlSessionFatory = new SqlSessionFactoryBuilder().build(inputStream); //3.通过sqlSessionFactory的openSession方法创建SqlSession SqlSession sqlSession=sqlSessionFatory.openSession(); //4.通过sqlSession的getMapper传入dao全类名的方法创建UserMapper对象 ClassesMapper um=sqlSession.getMapper(com.zhiyou100.kfs.dao.ClassesMapper.class); //5.调用UserMapper的selectById来使用通过id查询一个用户 Classes classes=um.select2(1); System.out.println(classes); //最后一个页是很重要的一个：关闭资源 sqlSession.close(); } |
原文：https://www.cnblogs.com/kfsrex/p/11439608.html