首页 > 代码库 > MyBatis系列：（8）多对多映射
MyBatis系列：（8）多对多映射
0、准备SQL（mysql）
CREATE TABLE Teachers( tid INT(5) PRIMARY KEY, tname VARCHAR(10) ); CREATE TABLE Courses( cid INT(5) PRIMARY KEY, cname VARCHAR(10) ); CREATE TABLE R_Teacher_Course( tid INT(5), cid INT(5), PRIMARY KEY(tid,cid), CONSTRAINT r_teacher_fk FOREIGN KEY(tid) REFERENCES Teachers(tid), CONSTRAINT r_course_fk FOREIGN KEY(cid) REFERENCES Courses(cid) ); INSERT INTO Teachers(tid,tname) VALUES(1,‘张老师‘); INSERT INTO Teachers(tid,tname) VALUES(2,‘李老师‘); INSERT INTO Teachers(tid,tname) VALUES(3,‘方老师‘); INSERT INTO Courses(cid,cname) VALUES(1,‘语文‘); INSERT INTO Courses(cid,cname) VALUES(2,‘数学‘); INSERT INTO Courses(cid,cname) VALUES(3,‘英语‘); INSERT INTO R_Teacher_Course(tid,cid) VALUES(1,1); INSERT INTO R_Teacher_Course(tid,cid) VALUES(1,2); INSERT INTO R_Teacher_Course(tid,cid) VALUES(2,2); INSERT INTO R_Teacher_Course(tid,cid) VALUES(2,3); INSERT INTO R_Teacher_Course(tid,cid) VALUES(3,3); INSERT INTO R_Teacher_Course(tid,cid) VALUES(3,1); SELECT * FROM Teachers; SELECT * FROM Courses; SELECT * FROM R_Teacher_Course; SELECT t.tid,t.tname,c.cid,c.cname FROM teachers t INNER JOIN r_teacher_course r ON t.tid=r.tid INNER JOIN courses c ON r.cid=c.cid
1、entity类
Teacher.java
package com.rk.entity;
import java.util.ArrayList;
import java.util.List;
public class Teacher {
private Integer id;
private String name;
private List<Course> courses = new ArrayList<Course>();
public Teacher(){}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Course> getCourses() {
return courses;
}
public void setCourses(List<Course> courses) {
this.courses = courses;
}
}Course.java
package com.rk.entity;
import java.util.ArrayList;
import java.util.List;
public class Course {
private Integer id;
private String name;
private List<Teacher> teachers = new ArrayList<Teacher>();
public Course(){}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Teacher> getTeachers() {
return teachers;
}
public void setTeachers(List<Teacher> teachers) {
this.teachers = teachers;
}
}2、mybatis的映射文件
TeacherMapper.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">
<mapper namespace="teacherNamespace">
<resultMap type="com.rk.entity.Teacher" id="teacherMap">
<id property="id" column="tid"/>
<result property="name" column="tname"/>
</resultMap>
<select id="findTeacherByCourseName" parameterType="string" resultMap="teacherMap">
select t.tid,t.tname,c.cid,c.cname
from teachers t
inner join r_teacher_course r on t.tid=r.tid
inner join courses c on r.cid=c.cid
where c.cname=#{courseName}
</select>
</mapper>CourseMapper.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">
<mapper namespace="courseNamespace">
<resultMap type="com.rk.entity.Course" id="courseMap">
<id property="id" column="cid"/>
<result property="name" column="cname"/>
</resultMap>
<select id="findCourseByTeacherName" parameterType="string" resultMap="courseMap">
select c.cid,c.cname
from teachers t
inner join r_teacher_course r on t.tid=r.tid
inner join courses c on r.cid=c.cid
where t.tname=#{teacherName}
</select>
</mapper>3、mybatis的主配置文件
mybatis.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>
<properties resource="db.properties"></properties>
<typeAliases>
<typeAlias type="com.rk.entity.Emp" alias="emp"/>
</typeAliases>
<environments default="mysql_developement">
<environment id="mysql_developement">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="http://www.mamicode.com/${mysql.driver}"/>
<property name="url" value="http://www.mamicode.com/${mysql.url}"/>
<property name="username" value="http://www.mamicode.com/${mysql.username}"/>
<property name="password" value="http://www.mamicode.com/${mysql.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/rk/entity/TeacherMapper.xml"/>
<mapper resource="com/rk/entity/CourseMapper.xml"/>
</mappers>
</configuration>db.properties
mysql.driver=com.mysql.jdbc.Driver mysql.url=jdbc:mysql://127.0.0.1:3306/testdb mysql.username=root mysql.password=root
4、MyBatisUtils.java
package com.rk.utils;
import java.io.IOException;
import java.io.Reader;
import java.sql.Connection;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MyBatisUtils {
private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
private static SqlSessionFactory sqlSessionFactory;
static{
try {
Reader reader = Resources.getResourceAsReader("mybatis.xml");
sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
} catch (IOException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
private MyBatisUtils(){}
public static SqlSession getSqlSession(){
SqlSession sqlSession = threadLocal.get();
if(sqlSession == null){
sqlSession = sqlSessionFactory.openSession();
threadLocal.set(sqlSession);
}
return sqlSession;
}
public static void closeSqlSession(){
SqlSession sqlSession = threadLocal.get();
if(sqlSession != null){
sqlSession.close();
threadLocal.remove();
}
}
public static void main(String[] args) {
SqlSession sqlSession = MyBatisUtils.getSqlSession();
Connection conn = sqlSession.getConnection();
System.out.println(conn);
}
}5、TeacherCourseDao.java
package com.rk.dao;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import com.rk.entity.Course;
import com.rk.entity.Teacher;
import com.rk.utils.MyBatisUtils;
public class TeacherCourseDao {
public List<Teacher> findTeacherByCourseName(String courseName){
SqlSession sqlSession = null;
try{
sqlSession = MyBatisUtils.getSqlSession();
List<Teacher> list = sqlSession.selectList("teacherNamespace.findTeacherByCourseName", courseName);
sqlSession.commit();
return list;
}
catch(Exception e){
e.printStackTrace();
sqlSession.rollback();
throw new RuntimeException(e);
}
finally{
MyBatisUtils.closeSqlSession();
}
}
public List<Course> findCourseByTeacherName(String teacherName){
SqlSession sqlSession = null;
try{
sqlSession = MyBatisUtils.getSqlSession();
List<Course> list = sqlSession.selectList("courseNamespace.findCourseByTeacherName", teacherName);
sqlSession.commit();
return list;
}
catch(Exception e){
e.printStackTrace();
sqlSession.rollback();
throw new RuntimeException(e);
}
finally{
MyBatisUtils.closeSqlSession();
}
}
public static void main(String[] args) {
TeacherCourseDao dao = new TeacherCourseDao();
List<Teacher> teacherList = dao.findTeacherByCourseName("数学");
for(Teacher teacher : teacherList){
System.out.println(teacher.getName());
}
List<Course> courseList = dao.findCourseByTeacherName("李老师");
for(Course course : courseList){
System.out.println(course.getName());
}
}
}MyBatis系列：（8）多对多映射
声明：以上内容来自用户投稿及互联网公开渠道收集整理发布，本网站不拥有所有权，未作人工编辑处理，也不承担相关法律责任，若内容有误或涉及侵权可进行投诉： 投诉/举报 工作人员会在5个工作日内联系你，一经查实，本站将立刻删除涉嫌侵权内容。