mybatis 一对多查询

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Course {
    private Integer id;
    private String courseCode; // 课程编号
    private String courseName;// 课程名称
    private List<Student> students;// 选课学生

    public Course(Integer id, String courseCode, String courseName) {
        super();
        this.id = id;
        this.courseCode = courseCode;
        this.courseName = courseName;
    }

@Data
@AllArgsConstructor
@NoArgsConstructor
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) {
        super();
        this.id = id;
        this.name = name;
        this.gender = gender;
        this.major = major;
        this.grade = grade;
    }
}

xml写法

	<!--  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="com.chyangwu.demo.entity.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="com.chyangwu.demo.entity.Course" extends="CourseResult">
		<collection property="students" resultMap="StudentResult"></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="com.chyangwu.demo.entity.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"  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
		left join student_course sc on s.id=sc.student_id
		right join course c on sc.course_id=c.id
  	</select>

一种课程对应多个学生

{
    "data":[
        {
            "courseCode":"001",
            "courseName":"心理学",
            "id":1,
            "students":[
                {
                    "gender":"男",
                    "grade":"大一",
                    "id":1,
                    "major":"专业1",
                    "name":"苗文平"
                },
                {
                    "gender":"男",
                    "grade":"大二",
                    "id":3,
                    "major":"大师专业",
                    "name":"景永春"
                },
                {
                    "gender":"男",
                    "grade":"大四",
                    "id":4,
                    "major":"专业3",
                    "name":"老赵"
                }
            ]
        },
        {
            "courseCode":"002",
            "courseName":"犯罪心理学",
            "id":2,
            "students":[
                {
                    "gender":"男",
                    "grade":"大一",
                    "id":1,
                    "major":"专业1",
                    "name":"苗文平"
                },
                {
                    "gender":"男",
                    "grade":"大一",
                    "id":2,
                    "major":"专业1",
                    "name":"谢升伟"
                },
                {
                    "gender":"男",
                    "grade":"大二",
                    "id":3,
                    "major":"大师专业",
                    "name":"景永春"
                }
            ]
        },
        {
            "courseCode":"003",
            "courseName":"统筹学",
            "id":3,
            "students":[
                {
                    "gender":"男",
                    "grade":"大一",
                    "id":2,
                    "major":"专业1",
                    "name":"谢升伟"
                },
                {
                    "gender":"男",
                    "grade":"大二",
                    "id":3,
                    "major":"大师专业",
                    "name":"景永春"
                }
            ]
        },
        {
            "courseCode":"004",
            "courseName":"土木工程",
            "id":4,
            "students":[
                {
                    "gender":"女",
                    "grade":"大三",
                    "id":5,
                    "major":"专业2",
                    "name":"老五"
                }
            ]
        },
        {
            "courseCode":"005",
            "courseName":"催眠学",
            "id":5,
            "students":[

            ]
        }
    ],
    "message":"请求成功",
    "state":1
}