mybatis多对多映射【学生与课程】

1）如图

2）创建students.sql和courses.sql和middles.sql

drop table middles;
drop table students;
drop table courses;
create table students(
    sid int(5) primary key,
    sname varchar(10)
);
create table courses(
    cid int(5) primary key,
    cname varchar(10)
);
create table middles(
    sid int(5),
    cid int(5),
    primary key(sid,cid)
);
insert into students(sid,sname) values(1,'哈哈');
insert into students(sid,sname) values(2,'呵呵');
insert into courses(cid,cname) values(1,'java');
insert into courses(cid,cname) values(2,'net');
insert into middles(sid,cid) values(1,1);
insert into middles(sid,cid) values(1,2);
insert into middles(sid,cid) values(2,1);
insert into middles(sid,cid) values(2,2);
select * from students;
select * from courses;
select * from middles;

3）创建Student.java和Course.java

/**
 * 学生(多方)*/
public class Student {
    private Integer id;
    private String name;
    private List<Course> courseList = new ArrayList<Course>();
    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;
    }
    public List<Course> getCourseList() {
        return courseList;
    }
    public void setCourseList(List<Course> courseList) {
        this.courseList = courseList;
    }
}
/**
 * 课程(多方)
*/
public class Course {
    private Integer id;
    private String name;
    private List<Student> studentList = new ArrayList<Student>();
    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<Student> getStudentList() {
        return studentList;
    }
    public void setStudentList(List<Student> studentList) {
        this.studentList = studentList;
    }
}

4）创建StudentMapper.xml和CourseMapper.xml

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="studentNamespace">
    <resultMap type="loaderman.many2many.Student" id="studentMap">
        <id property="id" column="sid" />
        <result property="name" column="sname"/>
    </resultMap>
    <select id="findStudentByName" parameterType="string" resultMap="studentMap">
        select s.sid,s.sname
        from students s,middles m,courses c
        where s.sid = m.sid
        and m.cid = c.cid
        and c.cname = #{name}
    </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="loaderman.many2many.Course" id="courseMap">
        <id property="id" column="cid" />
        <result property="name" column="cname"/>
    </resultMap>
    <select id="findCourseByName" parameterType="string" resultMap="courseMap">
        select c.cid,c.cname
        from students s,middles m,courses c
        where s.sid = m.sid
        and m.cid = c.cid
        and s.sname = #{name}
    </select>
</mapper>

5）创建students.dao

public class StudentDao {
    /**
     * 查询哈哈选学的【课程】
     */
    public List<Course> findCourseByName(String name) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();
            return sqlSession.selectList("courseNamespace.findCourseByName",name);
        }catch(Exception e){
            e.printStackTrace();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }
    /**
     * 查询java课程有哪些【学生】
     */
    public List<Student> findStudentByName(String name) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();
            return sqlSession.selectList("studentNamespace.findStudentByName",name);
        }catch(Exception e){
            e.printStackTrace();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }
    public static void main(String[] args) throws Exception{
        StudentCourseDao dao = new StudentCourseDao();
        //List<Course> courseList = dao.findCourseByName("哈哈");
        //for(Course c : courseList){
        //    System.out.println(c.getId()+":"+c.getName());
        //}
        List<Student> studentList = dao.findStudentByName("java");
        for(Student s : studentList){
            System.out.println(s.getId()+":"+s.getName());
        }
    }
}