Mybatis多对多的关系

版权声明：本文为博主原创文章,版权归原作者小思所有，转载或者引用本文内容请注明来源及原作者 https://blog.csdn.net/zeal9s/article/details/83793725

前言：本项目是使用idea进行开发，数据库使用的是Mysql。



1.搭建maven项目,引入mybatis需要的依赖
默认没有java、resources、test等文件夹，习惯性建立这几个文件夹，建立文件夹的时候注意标记文件夹的用途（不然编译器无法识别，无法编译代码）
pom.xml(注意要将实体包下面的xml文件设置可编译)

<?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">
  <modelVersion>4.0.0</modelVersion>

  <groupId>Mybatis_05</groupId>
  <artifactId>Mybatis_05</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>

  <name>Mybatis_05 Maven Webapp</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
    <!--引入Mybatis依赖 -->
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.4.1</version>
    </dependency>
    <!--引入MySql依赖 -->
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.43</version>
    </dependency>

  </dependencies>

  <build>
    <finalName>Mybatis_05</finalName>
    <resources>
      <resource>
        <directory>src/main/java</directory>
        <includes>
          <include>**/*.xml</include>
        </includes>
      </resource>
    </resources>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.0.0</version>
        </plugin>
        <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.7.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.20.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-war-plugin</artifactId>
          <version>3.2.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

2.项目模块图：

3.在resources目录下新建mybatis的核心配置文件mybatis-config.xml
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>
    <!--给com.zs.entity包取别名-->
    <typeAliases>
        <package name="com.zs.entity"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <!--配置获取数据库连接实例的数据源 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url"
                          value="jdbc:mysql://localhost:3306/zs?characterEncoding=utf-8" />
                <property name="username" value="root" />
                <property name="password" value="1234" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/zs/entity/Students.xml"></mapper>
    </mappers>
</configuration>

4.建立与数据库对应的实体包，包下建立类与对应的xml文件（这里没有使用接口调用方法，是使用xml文件调用方法）
Students.java

package com.zs.entity;

import java.util.List;

/**
 * @author 小思
 * @PackageName:PACKAGE_NAME
 * @ClassName: Students
 * @Description:对应数据库的Students表
 * @date 2018/11/4 22:05
 */
public class Students {
    private Integer sid;//学生的id
    private String sname;//学生的姓名

    private List<Course> courses;

    public Integer getSid() {
        return sid;
    }

    public void setSid(Integer 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;
    }
}

Course.java

package com.zs.entity;

import java.util.List;

/**
 * @author 小思
 * @PackageName:PACKAGE_NAME
 * @ClassName: Course
 * @Description:对应数据库的Course表
 * @date 2018/11/4 22:06
 */
public class Course {
    private Integer cid;//课程的Id
    private String cname;//课程的名称

    private List<Students> students;//单个课程对应的多个学生

    public Integer getCid() {
        return cid;
    }

    public void setCid(Integer cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }

    public List<Students> getStudents() {
        return students;
    }

    public void setStudents(List<Students> students) {
        this.students = students;
    }
}

Students.xml(这里测试多对多的一半，另一半一样的写法，这里的示例是根据学生的Id，查询到相应学生的信息)

<?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="students">
    <!--查询学生的信息（包括课程）-->
    <select id="studentInfo" parameterType="int" resultMap="studentsCourseInfo">
        select * from Students where sid=#{sid}
    </select>
    <!--学生对应的课程集合-->
    <resultMap id="studentsCourseInfo" type="Students">
        <id property="sid" column="sid"></id>
        <result property="sname" column="sname"></result>
        <!--学生对应的课程集合-->
        <collection property="courses" ofType="Course" column="sid" select="courseInfo">
            <id property="cid" column="cid"></id>
            <result property="cname" column="cname"></result>
        </collection>
    </resultMap>
    <!--课程集合-->
    <select id="courseInfo" parameterType="int" resultType="Course">
        select * from course c inner join stu_cou sc on c.cid=sc.cid where sc.sid=#{sid}
    </select>
</mapper>

5.在test文件夹下新建com.zs.test文件夹，并且新建单元测试类TestManyToMany.java
TestManyToMany.java

package com.zs.test;

import com.zs.entity.Course;
import com.zs.entity.Students;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

/**
 * @author 小思
 * @PackageName:com.zs.test
 * @ClassName: TestManyToMany
 * @Description:
 * @date 2018/11/4 22:16
 */
public class TestManyToMany {

    private SqlSessionFactory sessionFactory;
    private SqlSession sqlSession;

    @Before
    public void before(){
        //从配置文件获取SqlSessionFactory实例
        sessionFactory = new SqlSessionFactoryBuilder().build(getClass().getClassLoader().getResourceAsStream("mybatis-config.xml"));
        sqlSession = sessionFactory.openSession();
    }

    @Test
    public void test(){
        Students s=sqlSession.selectOne("students.studentInfo",1);
        //查询学生
        System.out.print(s.getSname()+"______");
        //查询学生对应的课程信息
        for (Course course : s.getCourses()) {
            System.out.print(course.getCname()+"\t");
        }


    }

    @After
    public void after(){
        sqlSession.commit();
        sqlSession.close();
    }
}

6.运行测试类

说在最后的话：编写实属不易，若喜欢或者对你有帮助记得点赞+关注或者收藏哦~