mybatis多对多关联实战教程(推荐)

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 ('1', '刘德华', '55', '0');
insert into `student` values ('2', '张惠妹', '49', '1');
insert into `student` values ('3', '谢霆锋', '35', '0');
insert into `student` values ('4', '王菲', '47', '1');
insert into `student` values ('5', '汪峰', '48', '0');
insert into `student` values ('6', '章子怡', '36', '1');

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 ('1', '王晶', '0', 'chinese', '大专');
insert into `teacher` values ('2', '冯小刚', '0', 'english', '本科');
insert into `teacher` values ('3', '吴京', '0', 'mathematics', '大专');
insert into `teacher` values ('4', '王倦', '1', '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 ('1', '1', '1');
insert into `stu_teach_rel` values ('2', '2', '1');
insert into `stu_teach_rel` values ('3', '1', '2');
insert into `stu_teach_rel` values ('4', '2', '2');
insert into `stu_teach_rel` values ('5', '2', '3');
insert into `stu_teach_rel` values ('6', '3', '1');
insert into `stu_teach_rel` values ('7', '3', '2');
insert into `stu_teach_rel` values ('8', '1', '3');
insert into `stu_teach_rel` values ('9', '4', '1');
insert into `stu_teach_rel` values ('10', '4', '2');
insert into `stu_teach_rel` values ('11', '5', '3');
insert into `stu_teach_rel` values ('12', '5', '4');
insert into `stu_teach_rel` values ('13', '6', '1');
insert into `stu_teach_rel` values ('14', '6', '3');

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();
 }
}

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