myBatis学习笔记（5）——一对多关联表查询

柔情只为你懂 2022-08-08 07:01 159阅读 0赞

# 需求 #

上一篇笔记是一对一，一个学生对应一个老师，本次我们修改一下需求，一个老师有多个学生  
参考：[myBatis学习笔记（4）——一对一关联表查询][myBatis_4]  
老师类：

package com.bank.entities;
    
    import java.util.List;
    
    public class Teacher { 
        private int teacherId;
        private String teacherName;
        private List<Student> stuList;
    
        public List<Student> getStuList() {
            return stuList;
        }
        public void setStuList(List<Student> stuList) {
            this.stuList = stuList;
        }
        public int getTeacherId() {
            return teacherId;
        }
        public void setTeacherId(int teacherId) {
            this.teacherId = teacherId;
        }
        public String getTeacherName() {
            return teacherName;
        }
        public void setTeacherName(String teacherName) {
            this.teacherName = teacherName;
        }
        @Override
        public String toString() {
            return "Teacher [teacherId=" + teacherId + ", teacherName="
                    + teacherName + ", stuList=" + stuList + "]";
        }
    
    
    }

# 方法一 #

与上一个笔记，有两种方法，套路都是一样的，直接看代码，不多解释

<resultMap type="Teacher" id="teacherResultMap1">
            <id property="teacherId" column="teacher_id" />
            <result property="teacherName" column="teacher_name" />
            
            <collection property="stuList" ofType="Student">
                <id property="stuId" column="stu_id" />
                <result property="stuName" column="stu_name" />
            </collection>
        </resultMap>
    
        <select id="getTeacher" parameterType="int" resultMap="teacherResultMap1">
            select * from student s,teacher t 
            where 
                s.teacher_id = t.teacher_id 
            and t.teacher_id = #{id}
        </select>

> 跟一对一不同的主要是用了`collection` 标签，`ofType` 属性表示该集合内元素的类型

# 方法二 #

<select id="getTeacher2" parameterType="int" resultMap="teacherResultMap2">
            select teacher_id teacherId,teacher_name teacherName from teacher where teacher_id=#{id}
        </select>
    
        <select id="getStudents" parameterType="int" resultType="Student">
            select stu_id stuId,stu_name stuName,teacher_id teacherId from student where teacher_id=#{id}
        </select>
    
        <resultMap type="Teacher" id="teacherResultMap2">
            <id property="teacherId" column="teacher_id" />
            <result property="teacherName" column="teacher_name" />
            
            <collection property="stuList" column="teacherId" select="getStudents">
            </collection>
        </resultMap>

[myBatis_4]: http://blog.csdn.net/u010837612/article/details/45671769