MyBatis级联操作 MyBatis使用级联操作解决lombok构造方法识别失败问题
viewts 人气:0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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