场景：使用三张数据表：student学生表、teacher教师表、position职位表
一个学生可以有多为老师、一位老师可以有多个学生、但是一个老师只能有一个职位：教授、副教授、讲师；但是一个职位可以有多个老师：例如教授可以多人
这里则产生了：
一对一关系，从老师角度：老师对职位一对一
一对多关系，从职位角度：职位对老师一对多
多对多关系：查找被教授教导的所有学生（首先职位对老师一对多，老师再对学生再对多、这里便有了一对多对多）
数据表：
老师表
CREATE TABLE `tb_teacher` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`t_no` varchar(20) DEFAULT NULL,
`t_name` varchar(20) DEFAULT NULL,
`position_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
/*Data for the table `tb_teacher` */
insert into `tb_teacher`(`id`,`t_no`,`t_name`,`position_id`) values
(1,'163314001','张文远',1),
(2,'163314002','赵传智',1),
(3,'163314003','风清扬',2),
(4,'163314004','王汇智',2),
(5,'163314005','汪思远',3);学生表
CREATE TABLE `tb_student` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`t_stu_name` varchar(20) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;
/*Data for the table `tb_student` */
insert into `tb_student`(`id`,`t_stu_name`) values
(1,'赵依'),
(2,'钱迩'),
(3,'张山'),
(4,'李石'),
(5,'王武'),
(6,'马柳');职位表
CREATE TABLE `tb_position` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`t_pos_name` varchar(20) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
/*Data for the table `tb_position` */
insert into `tb_position`(`id`,`t_pos_name`) values
(1,'教授'),
(2,'副教授'),
(3,'讲师');最后是教师学生关系表
CREATE TABLE `tb_stu_teach` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`t_stu_id` int(11) DEFAULT NULL,
`t_teach_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=14 DEFAULT CHARSET=utf8;
/*Data for the table `tb_stu_teach` */
insert into `tb_stu_teach`(`id`,`t_stu_id`,`t_teach_id`) values
(1,1,1),
(2,1,2),
(3,1,3),
(4,2,2),
(5,2,3),
(6,2,4),
(7,3,3),
(8,3,4),
(9,3,5),
(10,4,4),
(11,4,5),
(12,4,1);
最后在eclipse中的目录结构如下：
希望您明白sqlMapConfig该如何配置，以及jdbc.properties和log4j的作用。
贴出POJO中的三个实体(注意：以下的POJO都用了lombok来快速生成setter和getter等，lomok具体使用，请见此文)：
Position.java
package com.pojo;
import java.io.Serializable;
import lombok.Data;
@Data
public class Position implements Serializable {
private int id;
private String name;
private Teacher teacher;
}
Student.java
package com.pojo;
import java.io.Serializable;
import java.util.List;
import lombok.Data;
@Data
public class Student implements Serializable {
private String id;
private String name;
private List list;
} Teacher.java
package com.pojo;
import java.io.Serializable;
import java.util.List;
import lombok.Data;
@Data
public class Teacher implements Serializable {
private int id;
private String no;
private String name;
private List studentList;
private Position pos;
}
注意：关系表不用以实体表示出来，表示外键关系的ID也不用写在实体中(一般我们也不使用外键)
再贴另一个MybatisUtil.java工具类
package com.util;
import java.io.IOException;
import java.io.InputStream;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MyBatisUtil {
private static SqlSessionFactory sqlSessionFactory = null;
static {
String resource = "sqlMapConfig.xml";
// 首先要加载核心配置文件：从classpath下开始找。
InputStream in;
try {
in = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
} catch (IOException e) {
throw new RuntimeException(e.getMessage());
}
}
public static SqlSession getSqlSession() {
return sqlSessionFactory.openSession();
}
public static SqlSessionFactory getSqlSessionFactory() {
return sqlSessionFactory;
}
}
一对一：老师对职位
TeacherMapper.xml
TeacherMapper.java接口
package com.mapper;
import java.util.List;
import com.pojo.Teacher;
public interface TeacherMapper {
public List queryTeacherPositionResultMap();
public Teacher queryTeacherPositionResultMapById(Integer id);
}
测试一对一：
package com.test;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import com.mapper.TeacherMapper;
import com.pojo.Teacher;
import com.util.MyBatisUtil;
public class TestOneToOne {
@Test
public void testOneToOne() {
SqlSession sqlSession = MyBatisUtil.getSqlSession();
System.err.println(sqlSession);
TeacherMapper teacherMapper = sqlSession.getMapper(TeacherMapper.class);
List list = teacherMapper.queryTeacherPositionResultMap();
System.out.println(list);
Teacher teacher = teacherMapper.queryTeacherPositionResultMapById(1);
System.out.println(teacher);
}
}
一对多：职位对老师
PositionMapper.xml
TeacherMapper.java接口
package com.mapper;
import java.util.List;
import com.pojo.Position;
public interface PositionMapper {
public Position queryPositionTeacherResultMapById(Integer id);
public List queryPositionTeacherResultMap();
}
测试一对多：
package com.test;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import com.mapper.PositionMapper;
import com.pojo.Position;
import com.util.MyBatisUtil;
public class TestOneToMany {
@Test
public void testOneToMany() {
SqlSession sqlSession = MyBatisUtil.getSqlSession();
PositionMapper positionMapper = sqlSession.getMapper(PositionMapper.class);
List list = positionMapper.queryPositionTeacherResultMap();
System.out.println(list);
Position pos = positionMapper.queryPositionTeacherResultMapById(1);
System.out.println(pos);
}
}
多对多：职位是教授的老师教授的所有学生(一对多对多：只要你愿意可以一直对多下去...)
PositionMapper.xml
PositionMapper.java接口
package com.mapper;
import com.pojo.Position;
public interface PositionMapper {
public Position selectPositionStudentByPosId(Integer id);
}
测试：
package com.test;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import com.mapper.PositionMapper;
import com.pojo.Position;
import com.util.MyBatisUtil;
public class TestManyToMany {
@Test
public void testManyToMany() {
SqlSession sqlSession = MyBatisUtil.getSqlSession();
PositionMapper positionMapper = sqlSession.getMapper(PositionMapper.class);
Position pos = positionMapper.selectPositionStudentByPosId(1);
System.out.println(pos);
}
}