Mybatis 一对多 的数据处理（学习笔记15）

先搭建环境，配置文件都是一样的，实体类不一样了 

package com.li.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.List;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Teacher {
    private int id;
    private String name;

    //一个老师对应多个学生老师实体类下需要有一个学生类型的集合
    private List<Student> students;

}

package com.li.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Student {
    private int id;
    private String name;
    private int tid ;
}

<!--按照结果嵌套处理-->

   <select id="getTeacher1" resultMap="TeacherStudent">
        SELECT s.id sid,s.name sname,t.name tname,t.id tid
        FROM teacher t,student s
        WHERE t.id = s.tid and tid = #{tid}
    </select>

<!--id对应上面的resultMap值 type对应需要映射的实体类-->
    <resultMap id="TeacherStudent" type="Teacher">
<!--property对应实体类属性，column对应数据库表的列名-->
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>

<!--复杂属性单独处理对象用 association  集合用collection -->

<!--property需要处理的集合名称 ofType集合内的泛型-->
        <collection property="students" ofType="Student">
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>

    </resultMap>

二、按照sql语句嵌套处理

    <select id="getTeacher1" resultMap="TeacherStudent">
        select * from mybatis1.teacher where tid = #{id}
    </select>

    <resultMap id="TeacherStudent" type="Teacher">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
<!--property实体类中的特俗属性 javaType对应集合类型 ofType对应泛型的类型 select需要关联的sql语句名称 column需要传递过去关联的参数-->
        <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherid" column="id"/>
    </resultMap>
    <select id="getStudentByTeacherid" resultType="Student">
        select * from mybatis1.student where tid = #{tid}
    </select>

没怎么学明白按照语句嵌套处理，后面来补