Mybatis 多对多关系

用的是IDea

建个mavan的项目记得勾选webapp的
首先导入三个依赖

<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>3.4.5</version>
</dependency>


<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.43</version>
</dependency>
 
  <dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.12</version>
  <scope>test</scope>
</dependency>

一个是mybatis的依赖一个连接数据库的依赖和一个测试junit的依赖其他版本的junit 有bug 所以更改一下版本号就行了

等编译ok之后在src main包下面建二个东西一个是java 一个是resources
java 专门手写代码
resources写配置文件

在这里插入图片描述

首先在resources 写配置文件

命名为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>
    <typeAliases>
        <!-- 配置包 -->
        <package name="com.ch.entity"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/sys?characterEncoding=utf-8"/>
                <property name="username" value="root"/>
                <property name="password" value="tiger"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 配置映射信息 -->


</configuration>

这说白了就是连接mysql的属性
注意与连接mysql数据的密码账号以及数据库是否存在

配置包的属性是说明在该包下面所有的都可以使用

我们在java包里面建个实体类的包
然后建二个实体类
这是我的可以参考一下

一个学生的实体类

package com.ch.entity;
import java.util.List;
public class Student {
    private int sid;
    private String sname;
   //课程
    private List<Course>  courses;
    public Student(int sid, String sname, List<Course> courses) {
        this.sid = sid;
        this.sname = sname;
        this.courses = courses;
    }
    public Student(int sid, String sname) {
        this.sid = sid;
        this.sname = sname;
    }
    public Student() {
    }
    public int getSid() {
        return sid;
    }
    public void setSid(int sid) {
        this.sid = sid;
    }
    public String getSname() {
        return sname;
    }
    public void setSname(String sname) {
        this.sname = sname;
    }
    public List<Course> getCourses() {
        return courses;
    }
    public void setCourses(List<Course> courses) {
        this.courses = courses;
    }
}

一个课程的实体类

package com.ch.entity;
public class Course {
    private int cid;
    private  String cname;
    public Course(int cid, String cname) {
        this.cid = cid;
        this.cname = cname;
    }
    public int getCid() {
        return cid;
    }
    public void setCid(int cid) {
        this.cid = cid;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
}

然后配置student.xml 就在该实体包里面

<?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="student">
    <resultMap id="stuInfo" type="Student">
    <id property="sid" column="sid"></id>
    <result property="sname" column="sname"></result>
</resultMap>
    <resultMap id="studentCourseInfo" type="Student" extends="stuInfo">
        <collection property="courses" ofType="Course" column="sid" select="courseInfo">
            <id property="cid" column="cid"></id>
            <result property="cname" column="cname"></result>
        </collection>
    </resultMap>
    <!--课程 课程表关联第三方表-->
    <select id="courseInfo" resultType="Course" parameterType="int">
        select *  from course c inner join stu_cou sc on c.cid=sc.cid where sc.sid=#{sid}
    </select>
    <!--查询的学生信息-->
    <select id="selectStudentById" parameterType="int" resultMap="studentCourseInfo">
        select * from student where sid=#{sid}
    </select>
</mapper>

这里因为内容过多不一一多说注意列段名必须与数据库相同关系搞清楚就没什么问题了
最后就可以测试了

在test下面建个测试的类去测试

package com.ch.test;
import com.ch.entity.Course;
import com.ch.entity.Student;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import java.util.List;
public class TestStudent {
    private SqlSession sqlSession;

    @Before
    public void before(){
        SqlSessionFactory sessionFactory=new SqlSessionFactoryBuilder().build(getClass().getClassLoader().getResourceAsStream("mybatis-config.xml"));
        sqlSession = sessionFactory.openSession();

    }
    @Test
    public void testStudent(){
        Student student=sqlSession.selectOne("student.selectStudentById",1);
        System.out.println(student.getSname());
        for (Course course : student.getCourses()) {
            System.out.println(course.getCname());
        }
    }
}

根据学生查询到该学生的课程如果查询到了
表示多对多关系已经成功了

Mybatis 多对多关系

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