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Mybatis学习笔记--一对多关系的处理

作者:互联网

文章目录

本文章涉及环境版本:

  • mysql 5.7
  • Mybatis 3.5.x
  • Maven 3.6.x
  • JDK 1.8

项目代码仓库:
https://github.com/Gang-bb/Study-Record/tree/main/bzhan-mybatis-study
需要clone整个bzhan-mybatis-study项目
(整体是一个maven多module工程)
该文章对应:《bzhan-mybatis-study06 》module项目

1. 测试环境搭建

主要关键类代码修改:

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

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Teacher {
    private Integer id;
    private String name;
    
    private List<Student> students;
}

2. 实例测试

查询教师及其所有学生

方式一:按照结果嵌套处理

  1. TeacherMapper
Teacher getTeacher();
  1. TeacherMapper.xml
<!--按结果嵌套查询-->
<select id="getTeacher" resultMap="TeacherStudent">
    select s.id sid, s.name sname, t.name tname,t.id tid
    from student s,teacher t
    where s.tid = t.id and t.id = #{tid}
</select>

<resultMap id="TeacherStudent" type="Teacher">
    <result property="id" column="tid"/>
    <result property="name" column="tname"/>
    <!--复杂的属性,我们需要单独处理 对象: association 集合: collection
    javaType="" 指定属性的类型!
    集合中的泛型信息,我们使用ofType获取
    -->
    <collection property="students" ofType="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <result property="tid" column="tid"/>
    </collection>
</resultMap>
  1. 测试类
@Test
public void getTeacher(){
    SqlSession sqlSession = null;
    try {
        sqlSession = MybatisUtil.openSession();
        TeacherMapper teacherMapper = sqlSession.getMapper(TeacherMapper.class);

        System.out.println(teacherMapper.getTeacher(1));
    } finally {
        sqlSession.close();
    }
}
  1. 结果
image-20210209105313073

方式二:按照查询嵌套处理

  1. TeacherMapper
Teacher getTeacher2();
  1. TeacherMapper.xml
<!-- 一对多模型 按照查询嵌套处理-->
<select id="getTeacher2" resultMap="TeacherStudent2">
    select id, name from teacher where id = #{id}
</select>

<resultMap id="TeacherStudent2" type="Teacher">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
    <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>
</resultMap>

<select id="getStudentByTeacherId" resultType="Student">
    select * from student where tid = #{tid}
</select>
  1. 测试类
@Test
public void getTeacher(){
    SqlSession sqlSession = null;
    try {
        sqlSession = MybatisUtil.openSession();
        TeacherMapper teacherMapper = sqlSession.getMapper(TeacherMapper.class);

        System.out.println(teacherMapper.getTeacher2(1));
    } finally {
        sqlSession.close();
    }
}
  1. 结果
image-20210209113935466

注意点:

标签:name,--,笔记,TeacherMapper,sqlSession,tid,private,Mybatis,id
来源: https://blog.csdn.net/qq_37132495/article/details/113774379