在MyBatis中实现一对多查询和多对一查询代码方式解析

本篇文章小编给大家分享一下在MyBatis中实现一对多查询和多对一查询代码方式解析，文章代码介绍的很详细，小编觉得挺不错的，现在分享给大家供大家参考，有需要的小伙伴们可以来看看。

1、多对一

1、1环境搭建

数据库

CREATE TABLE teacher (
id INT(10) NOT NULL,
NAME VARCHAR(64) DEFAULT NULL,

PRIMARY KEY (id),
)ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO teacher (id ,NAME) VALUES (1,'罗老师');

CREATE TABLE student (
id INT(10) NOT NULL,
NAME VARCHAR(64) DEFAULT NULL,
tid INT(10) DEFAULT NULL,
PRIMARY KEY (id),
KEY fktid (tid),
CONSTRAINT fktid FOREIGN KEY (tid) REFERENCES teacher (id)
)
ALTER TABLE student ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT 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 (5,'小罗',1);

MyBatis.xml配置

1、2编写实体类、

学生·

@Data
public class Student {
    private int id;
    private String name;
    private Teacher teacher;
}

老师·

@Data
public class Teacher {
    private int id;
    private String name;
}

1、3编写接口方法

public interface  StudentMapper {
    List getStudentList();
    List getStudentList1();
}

1、4编写Mapper

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

1、5实现

package com.Google.Dao;

import com.Google.pojo.Student;
import com.Google.units.sqlSessionFactory;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class StudentMapperText {
    @Test
    public void getStudent(){
        SqlSession sqlSession = sqlSessionFactory.getsqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List studentList = mapper.getStudentList();
        for (Student student : studentList) {
            System.out.println(student);
        }
        sqlSession.close();
    }
    @Test
    public void getStudent1(){
        SqlSession sqlSession = sqlSessionFactory.getsqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List studentList = mapper.getStudentList1();
        for (Student student : studentList) {
            System.out.println(student);
        }
        sqlSession.close();
    }
}

1、6运行结果

Student(id=1, name=小明, teacher=Teacher(id=0, name=罗老师))

Student(id=2, name=小红, teacher=Teacher(id=0, name=罗老师))

Student(id=3, name=小张, teacher=Teacher(id=0, name=罗老师))

Student(id=4, name=小王, teacher=Teacher(id=0, name=罗老师))

Student(id=5, name=小罗, teacher=Teacher(id=0, name=罗老师))

2、一对多

2、1环境搭建和一对多一样

2、2编写实体类

@Data
public class Student {
    private int id;
    private String name;
    private int tid;
}

@Data
public class Teacher {
    private int id;
    private String name;
    //一个老师拥有多个学生,给老师创建一个学生集合
    private List student;
}

2、3编写接口的方法

public interface TeacherMapper {
    Teacher getTeacher(@Param("tid") int id);

    Teacher getTeacher1(@Param("tid") int id);
}

2、4编写Mapper配置

    
    
        select s.id sid, s.name sname, t.id tid, t.name tname
        from student s,
             teacher t
        where s.tid = t.id
          and t.id = #{tid}
    
    
        
        
        
        
            
            
            
        
    
    
    
        select * from teacher where id=#{tid}
    
    
        
        
    
    
        select * from student where tid=#{tid}
    

2、5实现

public class TeacherMapperText {
    @Test
    public void getTeacher(){
        SqlSession sqlSession = sqlSessionFactory.getsqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);
        sqlSession.close();
    }
    @Test
    public void getTeacher1(){
        SqlSession sqlSession = sqlSessionFactory.getsqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher1 = mapper.getTeacher1(1);
        System.out.println(teacher1);
        sqlSession.close();
    }
}

2、6运行结果

Teacher(id=1, name=罗老师, student=[Student(id=1, name=小明, tid=1), Student(id=2, name=小红, tid=1), Student(id=3, name=小张, tid=1), Student(id=4, name=小王, tid=1), Student(id=5, name=小罗, tid=1)])