mybatis--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。因此在进行实体类多对多映射表设计时，需要专门建立一个关联对象类对相关实体类的关联关系进行描述。

（1）首先创建数据库manytomany，并在数据库下创建三个表t_classes、t_classteacher、t_teacher

create database manytomany;

use manytomany;

CREATE TABLE `t_classes` (
  `cid` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `cname` varchar(64) NOT NULL DEFAULT '',
  PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
Insert into t_classes(cid,cname) values(1,'大一');
Insert into t_classes(cid,cname) values(2,'大二');
Insert into t_classes(cid,cname) values(3,'大三');

CREATE TABLE `t_teacher` (
  `tid` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `tname` varchar(64) NOT NULL DEFAULT '',
  PRIMARY KEY (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
Insert into t_teacher(tid,tname) values(1,'王老师');
Insert into t_teacher(tid,tname) values(2,'李老师');
Insert into t_teacher(tid,tname) values(3,'张老师');

CREATE TABLE `t_classTeacher` (
 `id` int(10) unsigned Not NULL AUTO_INCREMENT,
  `cid` int(10) unsigned NOT NULL,
  `tid` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
insert into t_classTeacher values(1,1,1);
insert into t_classTeacher values(2,2,1);
insert into t_classTeacher values(3,1,3);
insert into t_classTeacher values(4,2,3);

　

（2）创建mybatis_007项目，项目结构如下：

（3）配置两个实体类Classes.java、Teacher.java

Classes.java

package mybatis.model;

import java.util.List;

public class Classes {
	private Integer cid;
	private String cname;
	private List<Teacher> teachers;
	public Integer getCid() {
		return cid;
	}
	public void setCid(Integer cid) {
		this.cid = cid;
	}
	public String getCname() {
		return cname;
	}
	public void setCname(String cname) {
		this.cname = cname;
	}
	public List<Teacher> getTeachers() {
		return teachers;
	}
	public void setTeachers(List<Teacher> teachers) {
		this.teachers = teachers;
	}
	@Override
	public String toString() {
		return "Classes [cid=" + cid + ", cname=" + cname + ", teachers=" + teachers + "]";
	}
}

　Teacher.java

package mybatis.model;

import java.util.List;

import javax.security.auth.Subject;

public class Teacher {
	private Integer tid;
	private String tname;
	private List<Classes> classes;
	public Integer getTid() {
		return tid;
	}
	public void setTid(Integer tid) {
		this.tid = tid;
	}
	public String getTname() {
		return tname;
	}
	public void setTname(String tname) {
		this.tname = tname;
	}
	public List<Classes> getClasses() {
		return classes;
	}
	public void setClasses(List<Classes> classes) {
		this.classes = classes;
	}
	@Override
	public String toString() {
		return "Teacher [tid=" + tid + ", tname=" + tname + "]";
	}
}

（4）配置数据库连接文件config/config.xml

<?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>
 <typeAliases>
  <typeAlias alias="Classes" type="mybatis.model.Classes" />
  <typeAlias alias="Teacher" type="mybatis.model.Teacher" />
 </typeAliases>

<environments default="development">
	    <environment id="development">
		<transactionManager type="JDBC" />
		<dataSource type="POOLED">
		<property name="driver" value="com.mysql.jdbc.Driver" />
		<property name="url" value="jdbc:mysql://localhost:3306/manytomany"/>
		<property name="username" value="root"/>
		<property name="password" value="123456"/>
		</dataSource>
		</environment>
</environments>

 <mappers>
  <mapper resource="mybatis/model/ClassMapper.xml"/>
 </mappers>
</configuration>

（5）配置ClassMapper.xml文件

<?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.mapper.ClassesMapper">
	<!-- 自定义结果映射 -->
	<resultMap type="mybatis.model.Classes" id="ClassesWithTeacherResult">
		<id property="cid" column="cid"/>
		<result property="cname" column="cname"/>
		<!-- 多表关联映射 -->
		<collection property="teachers" ofType="mybatis.model.Teacher">
			<id property="tid" column="tid"/>
			<result property="tname" column="tname"/>
		</collection>
	</resultMap>
	<select id="findClassesWithTeacher" parameterType="Integer" resultMap="ClassesWithTeacherResult">
		select * from t_classes c,t_teacher t,t_classteacher ct
		where ct.cid=c.cid
		and ct.tid=t.tid
		and c.cid=#{cid}
	</select>
</mapper>

　（6）最后执行Main

package Main;

import java.io.Reader;

import mybatis.model.Classes;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

public class Main {
	private static SqlSessionFactory sqlSessionFactory;
	private static Reader reader;

	static {
		try {
			reader = Resources.getResourceAsReader("config/config.xml");
			sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public static SqlSessionFactory getSession() {
		return sqlSessionFactory;
	}
	@Test
	public void findClassesWithTeacher() {
		SqlSession session = sqlSessionFactory.openSession();
		for(int i=1;i<=2;i++){
		Classes classess=session.selectOne("com.mapper.ClassesMapper.findClassesWithTeacher", i);
		System.out.println(classess);
		}
	}
}

　　程序结果如下：