MyBatis3.0 添加了association和collection标签专门用于对多个相关实体类数据进行级联查询，但仍不支持多个相关实体类数据的级联保存和级联删除操作
一、创建student、teacher和stu_teach_rel三张张表
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
`id` int(11) NOT NULL,
`name` varchar(255) DEFAULT NULL,
`age` int(11) DEFAULT NULL,
`gender` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO `student` VALUES ('', '刘德华', '', '');
INSERT INTO `student` VALUES ('', '张惠妹', '', '');
INSERT INTO `student` VALUES ('', '谢霆锋', '', '');
INSERT INTO `student` VALUES ('', '王菲', '', '');
INSERT INTO `student` VALUES ('', '汪峰', '', '');
INSERT INTO `student` VALUES ('', '章子怡', '', '');
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
`id` int(11) NOT NULL,
`name` varchar(255) DEFAULT NULL,
`gender` varchar(255) DEFAULT NULL,
`subject` varchar(255) DEFAULT NULL,
`degree` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO `teacher` VALUES ('', '王晶', '', 'CHINESE', '大专');
INSERT INTO `teacher` VALUES ('', '冯小刚', '', 'ENGLISH', '本科');
INSERT INTO `teacher` VALUES ('', '吴京', '', 'MATHEMATICS', '大专');
INSERT INTO `teacher` VALUES ('', '王倦', '', 'MATHEMATICS', '研究生');
DROP TABLE IF EXISTS `stu_teach_rel`;
CREATE TABLE `stu_teach_rel` (
`id` int(11) NOT NULL,
`stu_id` int(11) NOT NULL,
`teach_id` int(11) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
INSERT INTO `stu_teach_rel` VALUES ('', '', '');
二、新建和表相关的实体类
package com.yihaomen.mybatis.model;
import com.yihaomen.mybatis.enums.Gender;
import java.util.List; public class Student {
private String id;
private String name;
private int age;
private Gender gender;
private List<Teacher> teachers; setters&getters }
package com.yihaomen.mybatis.model;
import com.yihaomen.mybatis.enums.Gender;
import com.yihaomen.mybatis.enums.Subject;
import java.util.List; public class Teacher {
private int id;
private String name;
private Gender gender;
private Subject subject;
private String degree;
private List<Student> students; setters&getters
}
三、新建映射关系
package com.yihaomen.mybatis.dao;
import com.yihaomen.mybatis.model.Student;
import org.springframework.stereotype.Repository;
import java.util.List; @Repository
public interface StudentMapper {
List<Student> selectStudents();
}
student.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.yihaomen.mybatis.dao.StudentMapper">
<resultMap id="studentMap" type="Student">
<id property="id" column="id" />
<result property="name" column="name" />
<result property="age" column="age" />
<result property="gender" column="gender" typeHandler="org.apache.ibatis.type.EnumOrdinalTypeHandler" />
</resultMap>
<resultMap id="collectionMap" type="Student" extends="studentMap">
<collection property="teachers" ofType="Teacher">
<id property="id" column="teach_id" />
<result property="name" column="tname"/>
<result property="gender" column="tgender" typeHandler="org.apache.ibatis.type.EnumOrdinalTypeHandler"/>
<result property="subject" column="tsubject" typeHandler="org.apache.ibatis.type.EnumTypeHandler"/>
<result property="degree" column="tdegree" javaType="string" jdbcType="VARCHAR"/>
</collection>
</resultMap>
<select id="selectStudents" resultMap="collectionMap">
SELECT
s.id, s.name, s.gender, t.id teach_id, t.name tname, t.gender tgender, t.subject tsubject, t.degree tdegree
FROM
student s
LEFT JOIN
stu_teach_rel str
ON
s.id = str.stu_id
LEFT JOIN
teacher t
ON
t.id = str.teach_id
</select>
</mapper>
四、在configuration.xml中配置相关mapper
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="jdbc.properties"/>
<typeAliases>
<typeAlias alias="Student" type="com.yihaomen.mybatis.model.Student" />
<typeAlias alias="Teacher" type="com.yihaomen.mybatis.model.Teacher" />
</typeAliases> <environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}" />
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments> <mappers>
<mapper resource="com/yihaomen/mybatis/model/Student.xml"/>
</mappers>
</configuration>
五、测试
package com.yihaomen.service.student;
import com.yihaomen.mybatis.dao.StudentMapper;
import com.yihaomen.mybatis.model.Student;
import com.yihaomen.mybatis.model.Teacher;
import com.yihaomen.service.BaseTest;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import java.util.List; public class TestStudent extends BaseTest {
public static void testStuTeachRela() {
SqlSessionFactory sqlSessionFactory = getSession();
SqlSession session = sqlSessionFactory.openSession();
StudentMapper mapper = session.getMapper(StudentMapper.class);
List<Student> list = mapper.selectStudents(); for(Student s : list) {
System.out.println("------------------");
System.out.println(s.getName() + "," + s.getAge() + "," + s.getGender());
for(Teacher t : s.getTeachers()) {
System.out.println(t.getName() + "," + t.getGender() + "," + t.getSubject());
}
}
} public static void main(String[] args) {
testStuTeachRela();
}
}
https://gitee.com/huayicompany/springmvc-mybatis
参考：
[1]《mybati实战教程》