Java SSM框架之MyBatis3（四）MyBatis之一对一、一对多、多对多

项目搭建Springboot 1.5

 pom.xml

<?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>cn.cnki</groupId>
    <artifactId>ref</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>war</packaging>

    <name>ref</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.14.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.3.2</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- mysql连接 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <!-- mybatis -->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>1.1.1</version>
        </dependency>
        <!-- 阿里系的Druid依赖包 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.5</version>
        </dependency>
        <!--pageHelper分页插件 -->
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.1.1</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-spring</artifactId>
            <version>1.3.2</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>4.3.18.RELEASE</version>
        </dependency>
        <!--To display the auto-configuration report re-run your application with 'debug' enabled. -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.0.7.Final</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

application.properties

server.port = 8080
########################################################
###mybatis-mysql-druid
########################################################
#sql配置文件的路径
mybatis.mapper-locations="classpath:mapper/*.xml"
#这个是mybatis全局配置文件路径
mybatis.config-location="classpath:mapper/config/mybatis-config.xml"
#实体类路径
mybatis.type-aliases-package="cn.cnki.ref.pojo"
# 驱动配置信息
spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.url = jdbc:mysql://127.0.0.1:3306/springbootmybatis?useUnicode=true&characterEncoding=utf-8
spring.datasource.username = root
spring.datasource.password = root
spring.datasource.driverClassName = com.mysql.jdbc.Driver
########################################################

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>
    <properties>
        <property name="dialect" value="mysql" />
    </properties>
    <settings>
        <!-- 这个配置使全局的映射器启用或禁用缓存。系统默认值是true，设置只是为了展示出来 -->
        <setting name="cacheEnabled" value="true" />
        <!-- 全局启用或禁用延迟加载。当禁用时，所有关联对象都会即时加载。 系统默认值是true，设置只是为了展示出来 -->
        <setting name="lazyLoadingEnabled" value="true" />
        <!-- 允许或不允许多种结果集从一个单独的语句中返回（需要适合的驱动）。 系统默认值是true，设置只是为了展示出来 -->
        <setting name="multipleResultSetsEnabled" value="true" />
        <!--使用列标签代替列名。不同的驱动在这方便表现不同。参考驱动文档或充分测试两种方法来决定所使用的驱动。 系统默认值是true，设置只是为了展示出来 -->
        <setting name="useColumnLabel" value="true" />
        <!--允许 JDBC 支持生成的键。需要适合的驱动。如果设置为 true 则这个设置强制生成的键被使用，尽管一些驱动拒绝兼容但仍然有效（比如
            Derby）。 系统默认值是false，设置只是为了展示出来 -->
        <setting name="useGeneratedKeys" value="false" />
        <!--配置默认的执行器。SIMPLE 执行器没有什么特别之处。REUSE 执行器重用预处理语句。BATCH 执行器重用语句和批量更新 系统默认值是SIMPLE，设置只是为了展示出来 -->
        <setting name="defaultExecutorType" value="SIMPLE" />
        <!--设置超时时间，它决定驱动等待一个数据库响应的时间。 系统默认值是null，设置只是为了展示出来 -->
        <setting name="defaultStatementTimeout" value="25000" />
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <plugins>
        <plugin interceptor="com.github.pagehelper.PageHelper">
            <property name="dialect" value="mysql" />
            <property name="offsetAsPageNum" value="true" />
            <property name="rowBoundsWithCount" value="true" />
            <property name="pageSizeZero" value="true" />
            <property name="reasonable" value="true" />
        </plugin>
    </plugins>
</configuration>

RefApplication

package cn.cnki.ref;

import com.alibaba.druid.pool.DruidDataSource;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
import org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.transaction.PlatformTransactionManager;

@SpringBootApplication(exclude={DataSourceAutoConfiguration.class,HibernateJpaAutoConfiguration.class})
@MapperScan("cn.cnki.ref.mapper")
public class RefApplication {

    public static void main(String[] args) {
        SpringApplication.run(RefApplication.class, args);
    }

    //datasource注入
    @Bean(initMethod = "init", destroyMethod = "close")
    @ConfigurationProperties(prefix = "spring.datasource")
    public DruidDataSource dataSource() {
        return new DruidDataSource();
    }

    //mybatis SQLSession注入
    @Bean
    public SqlSessionFactory sqlSessionFactoryBean() throws Exception {
        PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        sqlSessionFactoryBean.setDataSource(dataSource());
        sqlSessionFactoryBean.setMapperLocations(resolver.getResources("classpath*:/mapper/*Mapper.xml"));
        return sqlSessionFactoryBean.getObject();
    }

    //事务支持
    @Bean
    public PlatformTransactionManager transactionManager() {
        return new DataSourceTransactionManager(dataSource());
    }

}

一对一association

　　每个学生对应一张身份证，每张身份证上有身份证号cardId、开始日期、结束日期。并且建立与student表的外键关系。

cardid表、student表

/*Table structure for table `cardid` */

DROP TABLE IF EXISTS `cardid`;

CREATE TABLE `cardid` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `cardId` varchar(18) NOT NULL,
  `sid` int(10) NOT NULL,
  `beginTime` datetime NOT NULL,
  `endTime` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

/*Data for the table `cardid` */

insert  into `cardid`(`id`,`cardId`,`sid`,`beginTime`,`endTime`) values (1,'',1,'2008-07-19 11:19:27','2018-07-19 11:19:30'),(2,'',2,'2008-04-01 11:20:13','2018-04-01 11:20:13'),(3,'',3,'2008-07-19 11:21:06','2018-07-19 11:21:16');

/*Table structure for table `student` */

DROP TABLE IF EXISTS `student`;

CREATE TABLE `student` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(50) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

/*Data for the table `student` */

insert  into `student`(`id`,`name`) values (1,'张三'),(2,'李四'),(3,'王五');

Cardid实体

package cn.cnki.ref.pojo;

import java.util.Date;

public class Cardid {
    private Integer id;

    private String cardid;

    private Integer sid;

    private Date begintime;

    private Date endtime;

    private Student student;

    public Student getStudent() {
        return student;
    }
    public void setStudent(Student student) {
        this.student = student;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getCardid() {
        return cardid;
    }

    public void setCardid(String cardid) {
        this.cardid = cardid == null ? null : cardid.trim();
    }

    public Integer getSid() {
        return sid;
    }

    public void setSid(Integer sid) {
        this.sid = sid;
    }

    public Date getBegintime() {
        return begintime;
    }

    public void setBegintime(Date begintime) {
        this.begintime = begintime;
    }

    public Date getEndtime() {
        return endtime;
    }

    public void setEndtime(Date endtime) {
        this.endtime = endtime;
    }
}

Student实体

package cn.cnki.ref.pojo;

public class Student {
    private Integer id;

    private String name;

    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 == null ? null : name.trim();
    }
}

CardidMapper

package cn.cnki.ref.mapper;

import cn.cnki.ref.pojo.Cardid;
import java.util.List;

public interface CardidMapper {
    /**
     * 获取包括学生信息的身份证列表
     * @return
     */
    public List<Cardid>  getListIdOfStudent();
}

CardidMapper.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="cn.cnki.ref.mapper.CardidMapper" >

  <!--  学生表与身份证表的一对一映射-->
  <resultMap type="cn.cnki.ref.pojo.Cardid" id="IDCardOfStudentMap">
    <id property="id" column="id"  jdbcType="INTEGER"/>
    <result property="cardid" column="cardid"  jdbcType="VARCHAR" />
    <result property="begintime" column="beginTime" jdbcType="TIMESTAMP"/>
    <result property="endtime" column="endTime" jdbcType="TIMESTAMP"/>
    <association property="student" javaType="cn.cnki.ref.pojo.Student">
      <id property="id" column="id" jdbcType="INTEGER"/>
      <result property="name" column="name" jdbcType="VARCHAR"/>
    </association>
  </resultMap>

  <!-- 查出带有学生信息的身份证列表 -->
  <select id="getListIdOfStudent" resultMap="IDCardOfStudentMap">
    SELECT * FROM cardid a,student b WHERE a.sid=b.id;
  </select>

</mapper>

CardidController

package cn.cnki.ref.controller;

import cn.cnki.ref.mapper.CardidMapper;
import cn.cnki.ref.pojo.Cardid;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@RequestMapping("/Cardid")
public class CardidController {

    @Autowired
    private CardidMapper CardidMapper;
    @RequestMapping(value = "/GetListIdOfStudent", method = RequestMethod.GET)
    public List<Cardid> index() {
        return CardidMapper.getListIdOfStudent();
    }

}

测试

http://localhost:8080/Cardid/GetListIdOfStudent

一对多Collection

　　一个人有好多本书，每本书的主人只有一个人。当我们查询某个人拥有的所有书籍时，就涉及到了一对多的映射关系。

 book表

/*Table structure for table `book` */

DROP TABLE IF EXISTS `book`;

CREATE TABLE `book` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(50) NOT NULL,
  `sid` int(10) NOT NULL,
  `price` decimal(10,0) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

/*Data for the table `book` */

insert  into `book`(`id`,`name`,`sid`,`price`) values (1,'《黑客与画家》',1,''),(2,'《北方的空地》',1,'');

Book实体

package cn.cnki.ref.pojo;

public class Book {
    private Integer id;

    private String name;

    private Integer sid;

    private Long price;

    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 == null ? null : name.trim();
    }

    public Integer getSid() {
        return sid;
    }

    public void setSid(Integer sid) {
        this.sid = sid;
    }

    public Long getPrice() {
        return price;
    }

    public void setPrice(Long price) {
        this.price = price;
    }
}

Student实体

package cn.cnki.ref.pojo;

import java.util.List;

public class Student {
    private Integer id;

    private String name;

    private List<Book> books;

    public Student() {

    }

    public List<Book> getBooks() {
        return books;
    }

    public void setBooks(List<Book> books) {
        this.books = books;
    }

    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 == null ? null : name.trim();
    }
}

StudentMapper

package cn.cnki.ref.mapper;

import cn.cnki.ref.pojo.Student;

import java.util.List;

public interface StudentMapper {

    /**
     * 根据id查询
     * @param id
     * @return
     */
    public Student getById(Integer id);

    /**
     * 查询全部
     * @return
     */
    public List<Student> list();

    /**
     * 插入
     * @param student
     */
    public int insert(Student student);
    /**
     * 主键回填的插入
     * @param student
     * @return
     */
    public int insertToId(Student student);

    /**
     * 根据student的id修改
     * @param student
     */
    public void update(Student student);

    /**
     * 根据id删除
     * @param id
     */
    public void delete(Integer id);

    /**
     * 根据id查询所有的书
     * @param id
     */
    public Student selectBookById(Integer id);

}

StudentMapper.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="cn.cnki.ref.mapper.StudentMapper">

    <!-- 根据id查询 -->
    <select id="getById" parameterType="int" resultType="cn.cnki.ref.pojo.Student">
    select * from student where id=#{id}
    </select>
    <!-- 查询所有 -->
    <select id="list" parameterType="int" resultType="cn.cnki.ref.pojo.Student">
    select * from student
    </select>

    <!-- 插入一个学生 -->
    <insert id="insert" parameterType="cn.cnki.ref.pojo.Student">
    insert into student(name) values(#{name})
    </insert>
    <!-- 主键回填的插入 -->
    <insert id="insertToId" parameterType="cn.cnki.ref.pojo.Student" useGeneratedKeys="true" keyProperty="id">
    insert into student(name) values(#{name})
    </insert>

    <!-- 根据id修改学生信息 -->
    <update id="update" parameterType="cn.cnki.ref.pojo.Student">
    update student set name=#{name} where id=#{id}
    </update>

    <!-- 根据id删除学生 -->
    <delete id="delete" parameterType="int">
    delete  from student where id=#{id}
    </delete>

    <resultMap type="cn.cnki.ref.pojo.Student" id="bookMap">
        <id property="id" column="id" jdbcType="INTEGER"/>
        <result property="name" column="name" jdbcType="VARCHAR"/>
        <collection property="books" ofType="cn.cnki.ref.pojo.Book" javaType="ArrayList" >
            <id property="id" column="bid" jdbcType="INTEGER"/>
            <result property="name" column="bname" jdbcType="VARCHAR" />
            <result property="price" column="price" jdbcType="DECIMAL"/>
        </collection>
    </resultMap>
    <!--根据id查询所有的书  -->
    <select id="selectBookById" parameterType="int" resultMap="bookMap">
      select a.*,b.id bid,b.name bname,b.price from student a,book b where a.id=b.sid and a.id=#{id};
    </select>
</mapper>

StudentController

package cn.cnki.ref.controller;

import cn.cnki.ref.mapper.StudentMapper;
import cn.cnki.ref.pojo.Student;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
public class StudentController {
    @Autowired
    private StudentMapper studentMapper;

    /**
     * 根据id查询学生
     * @param id
     * @return
     */
    @GetMapping("/student/{id}")
    public Student getById(@PathVariable("id") Integer id) {

        Student student = studentMapper.getById(id);
        return student;

    }

    /**
     * 查询全部
     * @return
     */
    @GetMapping("/students")
    public List<Student> list(){
        List<Student> students = studentMapper.list();
        return students;
    }

    /**
     * 插入
     * @param student
     */
    @PostMapping("/student")
    public void insert( Student student) {
        studentMapper.insert(student);
    }

    /**
     * 修改
     * @param student
     */
    @PutMapping("/student/{id}")
    public void update(Student student,@PathVariable("id")Integer id) {
        studentMapper.update(student);
    }

    /**
     * 根据id删除
     * @param id
     */
    @DeleteMapping("/student/{id}")
    public void delete(@PathVariable("id") Integer id) {
        studentMapper.delete(id);
    }

    /**
     * 根据id查询所有的书
     */
    @GetMapping("/student/book/{id}")
    public Student getBooks(@PathVariable("id") Integer id) {
        Student student = studentMapper.selectBookById(id);
        return student;
    }

}

测试

http://localhost:8080//student/book/1

多对多——查询某个学生所选的全部课程代码实现

　　之前我们探讨了一对一、一对多的映射关系，今天我们来讨论多对多的映射关系。

　　多对多，其实可以拆成多个一对多来理解。

　　比如：

　　学生-------课程----------学生选课的关系：

　　（1）查询某个学生所选的全部课程；

　　（2）查询选修某个课程的全部学生；

 course表、student_course表

/*Table structure for table `course` */

DROP TABLE IF EXISTS `course`;

CREATE TABLE `course` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(50) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

/*Data for the table `course` */

insert  into `course`(`id`,`name`) values (1,'语文'),(2,'数学'),(3,'英语');

/*Table structure for table `student_course` */

DROP TABLE IF EXISTS `student_course`;

CREATE TABLE `student_course` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `sid` int(10) NOT NULL,
  `cid` int(10) NOT NULL,
  `score` int(3) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

/*Data for the table `student_course` */

insert  into `student_course`(`id`,`sid`,`cid`,`score`) values (1,1,1,91),(2,1,2,92),(3,1,3,93),(4,2,1,81),(5,2,2,82),(6,2,3,83),(7,3,1,71),(8,3,2,72),(9,3,3,73);

Course实体

package cn.cnki.ref.pojo;

public class Course {
    private Integer id;

    private String name;

    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 == null ? null : name.trim();
    }
}

 StudentCourse实体

package cn.cnki.ref.pojo;

import java.util.List;

public class StudentCourse {
    private Integer id;

    private Integer sid;

    private Integer cid;

    private Integer score;

    private List<Student> students;//一门课有多名学生

    private List<Course> courses;//一名学生有多门课

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getSid() {
        return sid;
    }

    public void setSid(Integer sid) {
        this.sid = sid;
    }

    public Integer getCid() {
        return cid;
    }

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

    public Integer getScore() {
        return score;
    }

    public void setScore(Integer score) {
        this.score = score;
    }

    public List<Student> getStudents() {
        return students;
    }
    public void setStudents(List<Student> students) {
        this.students = students;
    }
    public List<Course> getCourses() {
        return courses;
    }
    public void setCourses(List<Course> courses) {
        this.courses = courses;
    }
}

在Studnent实体中添加StudentCourse列表

package cn.cnki.ref.pojo;

import java.util.List;

public class Student {
    private Integer id;

    private String name;

    private List<Book> books;//一名学生有多本书

    private List<StudentCourse> studentCourses;

    public Student() {

    }

    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 == null ? null : name.trim();
    }

    public List<Book> getBooks() {
        return books;
    }

    public List<StudentCourse> getStudentCourses() {
        return studentCourses;
    }

    public void setStudentCourses(List<StudentCourse> studentCourses) {
        this.studentCourses = studentCourses;
    }

    public void setBooks(List<Book> books) {
        this.books = books;
    }
}

StudentCourseMapper

package cn.cnki.ref.mapper;

import cn.cnki.ref.pojo.Student;

public interface  StudentCourseMapper {
    /**
     * 根据学生id查询该学生选修的所有课程
     * @param id
     * @return
     */
    public Student selectCourseById(Integer id);
}

StudentCourseMapper.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="cn.cnki.ref.mapper.StudentCourseMapper">

    <resultMap type="cn.cnki.ref.pojo.Student" id="studentMap">
        <id property="id" column="id" jdbcType="INTEGER"/>
        <result property="name" column="name" jdbcType="VARCHAR"/>
    </resultMap>

    <resultMap type="cn.cnki.ref.pojo.Student" id="courseMap" extends="studentMap">
        <collection property="studentCourses" ofType="cn.cnki.ref.pojo.StudentCourse" javaType="ArrayList">
            <result property="score" column="score" jdbcType="INTEGER"/>
            <collection property="courses" ofType="cn.cnki.ref.pojo.Course" javaType="ArrayList">
                <id property="id" column="cid" jdbcType="INTEGER"/>
                <result property="name" column="cname" jdbcType="VARCHAR"/>
            </collection>
        </collection>
    </resultMap>

    <!-- 根据学生id查询该学生选修的所有课程 -->
    <select id="selectCourseById" parameterType="int" resultMap="courseMap" >
        select a.*,b.score,c.id cid,c.name cname from student a,student_course b,course c where a.id=b.sid and b.cid=c.id and a.id=#{id}
    </select>
</mapper>

StudentCourseController

package cn.cnki.ref.controller;

import cn.cnki.ref.mapper.StudentCourseMapper;
import cn.cnki.ref.pojo.Student;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class StudentCourseController {
    @Autowired
    private StudentCourseMapper studentCourseMapper;

    /************/

    /**
     * 根据学生id查询该学生选修的所有课程
     * @param id
     * @return
     */
    @GetMapping("/student/course/{id}")
    public Student selectCourseById(@PathVariable("id") Integer id) {
        Student student = studentCourseMapper.selectCourseById(id);
        return student;
    }
}

测试

http://localhost:8080/student/course/1

多对多——查询选修某个课程的全部学生代码实现

Course实体中添加StudentCourse列表

package cn.cnki.ref.pojo;

import java.util.List;

public class Course {
    private Integer id;

    private String name;

    private List<StudentCourse> studentCourses;//

    public List<StudentCourse> getStudentCourses() {
        return studentCourses;
    }
    public void setStudentCourses(List<StudentCourse> studentCourses) {
        this.studentCourses = studentCourses;
    }

    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 == null ? null : name.trim();
    }
}

CourseMapper

package cn.cnki.ref.mapper;

import cn.cnki.ref.pojo.Course;

public interface CourseMapper {
    /**
     * 根据课程id查询选修此课程的全部学生
     * @param id
     * @return
     */
    public Course selectStudentById(Integer id);

}

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="cn.cnki.ref.mapper.CourseMapper">
    <resultMap type="cn.cnki.ref.pojo.Course" id="courseMap">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
    </resultMap>
    <resultMap type="cn.cnki.ref.pojo.Course" id="studentMap" extends="courseMap">
        <collection property="studentCourses" ofType="cn.cnki.ref.pojo.StudentCourse">
            <result property="score" column="score"/>
            <collection property="students" ofType="cn.cnki.ref.pojo.Student">
                <id property="id" column="sid" jdbcType="INTEGER"/>
                <result property="name" column="sname" jdbcType="VARCHAR"/>
            </collection>
        </collection>
    </resultMap>
    <!-- 根据课程id查询选修此课程的全部学生 -->
    <select id="selectStudentById" parameterType="int" resultMap="studentMap">
     select a.*,b.score,c.id sid,c.name sname from student c,student_course b,course a where a.id=b.cid and b.sid=c.id and a.id=#{id}
    </select>
</mapper>

CourseController

package cn.cnki.ref.controller;

import cn.cnki.ref.mapper.CourseMapper;
import cn.cnki.ref.pojo.Course;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class CourseController {
    @Autowired
    private CourseMapper courseMapper;

    /**
     * 根据课程id查询选修此课程的全部学生
     * @param id
     * @return
     */
    @GetMapping("/course/student/{id}")
    public Course selectStudentById(@PathVariable("id")Integer id) {

        Course course = courseMapper.selectStudentById(id);
        return course;

    }

}

测试

http://localhost:8080//course/student/1

资料

源码下载

http://www.cnblogs.com/TimerHotel/tag/mybatis/

https://www.cnblogs.com/ashleyboy/p/9271597.html