测试环境搭建

1.导入lombok
2.新建实体类Teacher,Student

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

@Data
public class Student {
    private int id;
    private String name;
   // private int tid;
    //学生需要关联一个老师！
    private Teacher teacher;
}

3.建立Mapper接口

public interface TeacherMapper {
    @Select("select * from teacher where id=#{tid}")
    Teacher getTeacher(@Param("tid") int id);
}

4.建立Mapper.xml文件
5.在核心配置文件中绑定注册Mapper接口或者文件！
6.测试查询是否能够成功

按照查询嵌套处理

<!--
    思路：
    1.查询所有的学生信息
    2.根据查询出来的学生表的tid，寻找对应的老师！
    -->
    <select id="getStudent" resultMap="StudentTeacher">
   select * from student
    </select>
    <resultMap id="StudentTeacher" type="Student">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
       <!--复杂的属性需要单独处理
       对象：association
       集合：collection
       -->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    </resultMap>

    <select id="getTeacher" resultType="Teacher">
        select * from teacher where id = #{id}
    </select>

按照结果嵌套处理

<!--按照结果嵌套处理-->
    <select id="getStudent2" resultMap="StudentTeacher2">
    select s.id sid,s.name sname,t.name tname
    from student s,teacher t
    where s.tid = t.id
    </select>

    <resultMap id="StudentTeacher2" type="Student">
        <result property="id"    column="sid"/>
        <result property="name"  column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"/>
        </association>
    </resultMap>