MyBatis多对多映射初识教程

-- 多对多映射
-- 删除数据库
drop database if exists mybatis;
-- 创建数据库
create database if not exists mybatis default character set utf8;
-- 选择数据库
use mybatis;
-- 删除数据表
drop table if exists student;
drop table if exists course;
drop table if exists student_course;
-- 创建数据表
create table student(
sid int(255),
sname varchar(32),
constraint pk_sid primary key (sid)
);
create table course(
cid int(255),
cname varchar(32),
constraint pk_cid primary key (cid)
);
create table student_course(
sid int(255),
cid int(255),
constraint pk_sid_cid primary key(sid,cid),
constraint fk_sid foreign key (sid) references student(sid),
constraint fk_cid foreign key (cid) references course(cid) 
);
-- 测试数据
insert into student (sid,sname) values (1,'哈哈');
insert into student (sid,sname) values (2,'呵呵');
insert into course (cid,cname) values (1,'java');
insert into course (cid,cname) values (2,'.NET');
insert into student_course (sid,cid) values (1,1);
insert into student_course (sid,cid) values (1,2);
insert into student_course (sid,cid) values (2,1);
insert into student_course (sid,cid) values (2,2);

package many2many;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
/**
* 课程
* @author Administrator
*
*/
@SuppressWarnings("serial")
public class Course implements Serializable{
private Integer cid;
private String cname;
private List<Student> students = new ArrayList<Student>();
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<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
}

package many2many;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
/**
* 学生类
* @author Administrator
*
*/
@SuppressWarnings("serial")
public class Student implements Serializable {
private Integer sid;
private String sname;
private List<Course> courses = new ArrayList<Course>();
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;
}
}

<?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="studentMapper">
<resultMap type="many2many.Student" id="studentMap">
<id property="sid" column="sid"/>
<result property="sname" column="sname"/>
</resultMap>
</mapper>
<?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="many2many.Course" id="courseMap">
<id property="cid" column="cid"/>
<result property="cname" column="cname"/>
</resultMap>
<!-- 查询“哈哈”选修了那几门课程 -->
<select id="findAllByName" parameterType="string" resultMap="courseMap">
select c.cname,c.cid
from student s,course c,student_course sc
where s.sid = sc.sid and c.cid = sc.cid and s.sname = #{sname};
</select>
</mapper>

package many2many;
import java.util.Iterator;
import java.util.List;
import one2many.Student;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import util.MyBatisUtil;
public class StudentCourseDAO {
/**
* 查询“哈哈”选修了那几门课程
* @param name 学生的姓名
* @return
* @throws Exception
*/
public List<Course> findAllByName(String name) throws Exception{
SqlSession sqlSession = null;
try {
sqlSession = MyBatisUtil.getSqlSession();
return sqlSession.selectList("courseNamespace.findAllByName", name);
} catch (Exception e) {
e.printStackTrace();
throw e;
}finally{
MyBatisUtil.closeSqlSession();
}
}
@Test
public void testFindAllByName() throws Exception{
StudentCourseDAO dao = new StudentCourseDAO();
List<Course> courses = dao.findAllByName("哈哈");
for (Course course : courses) {
System.out.println(course.getCid()+":"+course.getCname());
}
}
}

<!-- 加载映射文件 -->
<mappers>
<mapper resource="one2one/CardMapper.xml"/>
<mapper resource="one2one/StudentMapper.xml"/>
<mapper resource="one2many/GradeMapper.xml"/>
<mapper resource="one2many/StudentMapper.xml"/>
<mapper resource="many2many/StudentMapper.xml"/>
<mapper resource="many2many/CourseMapper.xml"/>
</mappers>