多对多映射

<?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">
<!-- com.mybatis.mappers.StudentMapper是我们定义接口的全限定名字 这样就可以使用接口调用映射的SQL语句了 这个名字一定要和接口对应上 -->
<mapper namespace="com.mybatis.mappers.Many2ManyMapper">
	<insert id="insertStudent" parameterType="Student">
	   insert into student values(#{id},#{name},#{gender},#{major},#{grade})
	</insert>
	<insert id="insertCourse" parameterType="Course">
	   insert into course values(#{id},#{courseCode},#{courseName})
	</insert>
	<select id="selectStudentById" parameterType="int" resultType="Student">
		select * from student where id=#{id}
	</select>
	<select id="selectCourseById" parameterType="int" resultType="Course">
		select id,course_code as courseCode,course_name  courseName from course where id=#{id}
	</select>
	<insert id="studentSelectCourse">
        <!-- param1代表方法中第一个参数 以此类推 -->
            insert into
                student_course(id,student_id,course_id)
            values
                (#{param1},#{param2.id},#{param3.id})
	</insert>
      <!-- 如果有特殊符号的话 需要用 <![CDATA[ 特殊符号 ]]>  例如 < & 等等 -->
        <select id="getStudentByIdOnCondition" parameterType="int" resultType="Student">
             <![CDATA[
             select *
             from student
             where id <  #{id}
             ]]>
        </select>
     <!--  这里使用了嵌套结果ResultMap的方式进行级联查询,当然也可以使用嵌套查询select -->
     <!-- 映射一个基本的Student查询结果 -->
        <resultMap id="StudentResult" type="Student">
            <id property="id" column="id"/>
            <result property="name" column="name"/>
            <result property="gender" column="gender"/>
            <result property="major" column="major"/>
            <result property="grade" column="grade"/>
        </resultMap>
        <!-- 继承上面那个基本的映射,再扩展出级联查询 -->
        <resultMap id="StudentResultWithCourses" type="Student" extends="StudentResult">
            <collection property="courses" resultMap="CourseResult"></collection>
        </resultMap>
        <!-- 这里特别要是的是column="cid" 这是和select语句中的 c.id as cid对应的 一定一定一定要对应起来 -->
        <resultMap id="CourseResult" type="Course">
            <id property="id" column="cid"/>
            <result property="courseCode" column="course_code"/>
            <result property="courseName" column="course_name"/>
        </resultMap>
        <!--  
            注意:查询语句的中的c.id as cid这个地方,避免名字相同出现查询结果不正确的情况
            同时在id="CourseResult"的resultMap中也有与这里对应的设置要特别特别注意
        -->
        <select id="getStudentByIdWithCourses" parameterType="int" resultMap="StudentResultWithCourses">
            select s.id,s.name,s.gender,s.major,s.grade,c.id as cid,c.course_code,c.course_name,sc.id,sc.student_id,sc.course_id
            from student s,course c,student_course sc
            where  
            s.id=#{id}
            and
            s.id=sc.student_id  
            and  
            sc.course_id=c.id
        </select>

</mapper>

pojo

public class Student {
            private Integer id;
            private String name; // 姓名
            private String gender; // 性别
            private String major; // 专业
            private String grade; // 年级
            private List<Course> courses;// 所选的课程
		public Student(Integer id, String name, String gender,String major, String grade, List<Course> courses) {
				super();
				this.id = id;
				this.name = name;
				this.gender = gender;
				this.major = major;
				this.grade = grade;
				this.courses = courses;
			}
		public Student(Integer id, String name, String gender, String major,
				String grade) {
			super();
			this.id = id;
			this.name = name;
			this.gender = gender;
			this.major = major;
			this.grade = grade;
		}
		public Student() {
			super();
		}
		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 String getGender() {
			return gender;
		}
		public void setGender(String gender) {
			this.gender = gender;
		}
		public String getMajor() {
			return major;
		}
		public void setMajor(String major) {
			this.major = major;
		}
		public String getGrade() {
			return grade;
		}
		public void setGrade(String grade) {
			this.grade = grade;
		}
		public List<Course> getCourses() {
			return courses;
		}
		public void setCourses(List<Course> courses) {
			this.courses = courses;
		}
		@Override
		public String toString() {
			return "Student [id=" + id + ", name=" + name + ", gender="
					+ gender + ", major=" + major + ", grade=" + grade
					+ ", courses=" + courses + "]";
		}
            

｝