Mybatis多对一关联

 `CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL,
  `name` VARCHAr(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8
​
INSERT INTO teacher(`id`, `name`) VALUES (1, '秦老师'); 
​
CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAr(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fktid` (`tid`),
  ConSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1', '小明', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('2', '小红', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('3', '小张', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('4', '小李', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('5', '小王', '1');

    org.projectlombok
    lombok
    1.18.20

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybtias03?useSSL=false&useUnicode=true&characterEncoding=utf8
username=root
password=123456

    
​
    
        
    
    
        
            
            
                
                
                
                
            
        
    
    
        
    

package com.lele.util;
​
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 java.io.IOException;
import java.io.InputStream;
​
public class MybatisUtil {
    private static SqlSessionFactory sqlSessionFactory;
​
    static {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //获取SqlSession连接
    public static SqlSession getSession(){
        return sqlSessionFactory.openSession(true);
    }
}

package com.lele.pojo;
​
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
​
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private int id;
    private String name;
    private Teacher teacher;
​
}

package com.lele.pojo;
​
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
​
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Teacher {
    private int id;
    private String name;
}

public interface StudentMapper {
    List selectTeacher();
}

package com.lele.dao;
​
public interface TeacherMapper {
}

    
        
        
        
            
            
        
    
    
        select s.id sid, s.name sname , t.name tname,t.id tid
        from student s,teacher t
        where s.tid = t.id
    

​

package com.lele.test;
import com.lele.dao.StudentMapper;
import com.lele.pojo.Student;
import com.lele.util.MybatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
​
import java.util.List;
​
​
public class Test01 {
     @Test
     public void test2(){
         SqlSession session = MybatisUtil.getSession();
         StudentMapper mapper = session.getMapper(StudentMapper.class);
         List students = mapper.selectTeacher();
         for (Student student : students) {
             System.out.println(student);
         }
     }
}

接口映射文件xml的namespace为"包名+sql映射文件名"

映射文件xml的id名要与接口的方法名一致

resultMap结果映射集

collection用于 一对多关联

assocication用于一对一 多对一关联

使用接口类导入
    
        
     
使用包名导入
    
        
    
使用类路径导入