mybatis实战教程三：多对多关联

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》

巴特西

mybatis实战教程三：多对多关联

一、创建student、teacher和stu_teach_rel三张张表

二、新建和表相关的实体类

三、新建映射关系

student.xml

四、在configuration.xml中配置相关mapper

五、测试

参考：

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