Mybatis实现一对一、一对多关联查询的方法(示例详解)

Mybatis实现一对一、一对多关联查询，关联查询：多个表联合查询，只查询一次，通过resultMap里面的、标签配置一对一、一对多。

涉及的sql文件、idea工程文件：Mybatis实现一对一、一对多关联查询资源

本篇文章涉及的一对一、一对多关系

• 班级classes、班主任teacher是一对一的关系
• 班级classes、学生student是一对多的关系

使用IDEA快速构建一个MyBatis工程

pom.xml

    4.0.0

    com
    sun
    1.0-SNAPSHOT
    mybatisTest

    
        UTF-8
        1.8
        1.8
        5.8.2
    

    
        
            org.mybatis
            mybatis
            3.2.2
        
        
            mysql
            mysql-connector-java
            8.0.30
        
        
            org.projectlombok
            lombok
            1.18.24
        
        
            log4j
            log4j
            1.2.17
        
        
            org.apache.logging.log4j
            log4j-core
            2.13.3
        
        
            org.junit.jupiter
            junit-jupiter-api
            ${junit.version}
            test
        
        
            org.junit.jupiter
            junit-jupiter-engine
            ${junit.version}
            test
        
        
            junit
            junit
            4.13.2
            test
        
    
    
        
            
                
                src/main/java
                
                    
                    
                    **/*.properties
                    **/*.xml
                
                
                false
            
            
                src/main/resources
            
        
    

mybatis-config.xml

database.properties

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/mybatis?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
user=root
password=root

MybatisUtil.java

package com.sun.utils;

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.InputStream;

/**
 * @author JumperSun
 * @date 2023-03-26-14:46
 */
public class MyBatisUtil {
    private static SqlSessionFactory factory;

    static {
        try {
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            factory = new SqlSessionFactoryBuilder().build(is);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static SqlSession createSqlSession(){
        return factory.openSession(false); // true为自动提交事务
    }

    public static void closeSqlSession(SqlSession sqlSession){
        if(null != sqlSession)
            sqlSession.close();
    }
}

Teacher.java

package com.sun.pojo;

import lombok.Data;

/**
 * @author JumperSun
 * @date 2023-03-26-14:51
 */
@Data
public class Teacher {
    private int id;
    private String name;
}

Student.java

package com.sun.pojo;

import lombok.Data;

/**
 * @author JumperSun
 * @date 2023-03-26-14:53
 */
@Data
public class Student {
    private int id;
    private String name;
}

Classes.java

package com.sun.pojo;

import lombok.Data;

import java.util.List;

/**
 * @author JumperSun
 * @date 2023-03-26-14:52
 */
@Data
public class Classes {
    private int id;
    private String name;
    private Teacher teacher;
    private List studentList;
}

classMapper.java

package com.sun.mapper;

import com.sun.pojo.Classes;
import org.apache.ibatis.annotations.Param;

import java.util.List;

/**
 * @author JumperSun
 * @date 2023-03-26-14:54
 */
public interface ClassesMapper {
    List getClassesTeacher(@Param("id") int id);

    List getClassesTeacherStudentList(@Param("id") int id);
}

classMapper.xml

    
    
        select * from classes c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
    

    
        
        
        
        
            
            
        
    

    
    
        select * from classes c,teacher t,student s where c.teacher_id=t.t_id and c.c_id=s.class_id and c.c_id=#{id}
    

    
        
        
        
            
            
        
        
            
            
        
    

MapperTest.java

import com.sun.mapper.ClassesMapper;
import com.sun.pojo.Classes;
import com.sun.utils.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

/**
 * @author JumperSun
 * @date 2023-03-26-15:10
 */
public class MapperTest {
    /**
     * 测试班级与班主任老师一对一的关联关系
     */
    @Test
    public void test1() {
        SqlSession sqlSession = MyBatisUtil.createSqlSession();
        ClassesMapper classesMapper = sqlSession.getMapper(ClassesMapper.class);
        List classes = classesMapper.getClassesTeacher(1);
        for (Classes Classes : classes) {
            System.out.println(classes);
        }

    }

    /**
     * 测试班级与学生一对多关联关系
     */
    @Test
    public void test2() {
        SqlSession sqlSession = MyBatisUtil.createSqlSession();
        ClassesMapper classesMapper = sqlSession.getMapper(ClassesMapper.class);
        List classes = classesMapper.getClassesTeacherStudentList(1);
        for (Classes Classes : classes) {
            System.out.println(classes);
        }

    }
}

test1:

test2:

总结：一对一关联查询需要在resultMap里面配置association，一对多关联查询需要在resultMap里面配置collection；

List classes = classesMapper.getClassesTeacherStudentList(1);
for (Classes Classes : classes) {
System.out.println(classes);
}}

}
test1:
[外链图片转存中...(img-qon5qYiR-1680248446105)]
test2:
[外链图片转存中...(img-DZayGx8q-1680248446107)]
总结：一对一关联查询需要在resultMap里面配置association，一对多关联查询需要在resultMap里面配置collection；

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