在MyBatis中实现一对多查询和多对一查询的方式详解(各两种方式)

在MyBatis中实现一对多查询和多对一查询的方式详解(各两种方式)

目录1、多对一1、1环境搭建1、2编写实体类、1、3编写接口方法1、4编写Mapper1、5实现1、6运行结果2、一对多2、1环境搭建和一对多一样2、3编写接口的方法2、4编写Mapper配置2、5实现2、6运行结果

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

PUBLIC "-//mybatis.org//DTD Config 3.0//EN"

"http://mybatis.org/dtd/mybatis-3-config.dtd">

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

PUBLIC "-//mybatis.org//DTD Config 3.0//EN"

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

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

PUBLIC "-//mybatis.org//DTD Config 3.0//EN"

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

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)])

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