标签：encoding open varchar Opens dea and stat resource cti
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)); } }
标签：encoding open varchar Opens dea and stat resource cti
原文地址：https://www.cnblogs.com/viewts/p/13213352.html
