小编给大家分享一下lombok构造方法识别失败怎么办,希望大家阅读完这篇文章后大所收获,下面让我们一起去探讨吧!
先解决一下idea无法识别lombok构造方法的问题,解决方案是在idea的插件中下载并安装lombok插件。
MyBatis级联操作,列举最简单的student-classes(学生与班级)的关系表:
create table if not exists student (
id int primary key auto_increment,
name varchar(20) not null comment '学生姓名',
cid int not null comment '班级id'
);
create table if not exists classes (
id int primary key auto_increment,
name varchar(20) not null comment '班级名'
);
接下来,创建关系表对应的实体类:
@Data
public class Student {
private long id;
private String name;
private Classes classes;
}
@Data
public class Classes {
private long id;
private String name;
private List<Student> students;
}
在repository包下新建StudentRepository接口:
public interface StudentRepository {
public Student findById(long id);
}
然后创建对应的mapper文件StudentRepository.xml:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.wts.repository.StudentRepository">
<resultMap id="studentMap" type="com.wts.entity.Student">
<id column="id" property="id"></id>
<result column="name" property="name"></result>
<association property="classes" javaType="com.wts.entity.Classes">
<id column="cid" property="id"></id>
<result column="cname" property="name"></result>
</association>
</resultMap>
<select id="findById" parameterType="long" resultMap="studentMap">
select s.id,s.name,c.id as cid,c.name as cname from student s,classes c where s.id = #{id} and s.cid = c.id
</select>
</mapper>
注意这里有几个限制:
1.命名空间,xml文件的namespace必须是对应接口的全类名
2.Statement标签的id必须与接口方法相同,其中parameterType为参数,resultType为返回类型,复杂类型用resultMap
3.复杂类型resultMap中多对一用association,一堆多用集合collection
MyBatis执行sql返回的结果集会和关系对象映射起来,注意列与字段的对应关系。
然后将mapper引入:
<mappers>
<mapper resource="com/wts/repository/StudentRepository.xml"></mapper>
</mappers>
编写测试方法:
@Test
public void test03() {
InputStream inputStream = AppTest.class.getClassLoader().getResourceAsStream("config.xml");
SqlSessionFactory sqlSessionFactory = (new SqlSessionFactoryBuilder()).build(inputStream);
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
// 级联查询
StudentRepository studentRepository = sqlSession.getMapper(StudentRepository.class);
System.out.println(studentRepository.findById(1L));
}
}
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