标签:name -- 笔记 TeacherMapper sqlSession tid private Mybatis id
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
- TeacherMapper
Teacher getTeacher();
- 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>
- 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();
}
}
- 结果
方式二:按照查询嵌套处理
- TeacherMapper
Teacher getTeacher2();
- 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>
- 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();
}
}
- 结果
注意点:
- 保证SQL的可读性,尽量保证通俗易懂
- 注意一对多和多对一中,属性名和字段的问题!
标签:name,--,笔记,TeacherMapper,sqlSession,tid,private,Mybatis,id 来源: https://blog.csdn.net/qq_37132495/article/details/113774379
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