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;@Repositorypublic 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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