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 <association> 、 <collection> 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
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<? xml version = "1.0" encoding = "UTF-8" ?>
< project xmlns = "http://maven.apache.org/POM/4.0.0"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" >
< modelVersion >4.0.0</ modelVersion >
< groupId >com</ groupId >
< artifactId >sun</ artifactId >
< version >1.0-SNAPSHOT</ version >
< name >mybatisTest</ name >
< properties >
< project.build.sourceEncoding >UTF-8</ project.build.sourceEncoding >
< maven.compiler.target >1.8</ maven.compiler.target >
< maven.compiler.source >1.8</ maven.compiler.source >
< junit.version >5.8.2</ junit.version >
</ properties >
< dependencies >
< dependency >
< groupId >org.mybatis</ groupId >
< artifactId >mybatis</ artifactId >
< version >3.2.2</ version >
</ dependency >
< dependency >
< groupId >mysql</ groupId >
< artifactId >mysql-connector-java</ artifactId >
< version >8.0.30</ version >
</ dependency >
< dependency >
< groupId >org.projectlombok</ groupId >
< artifactId >lombok</ artifactId >
< version >1.18.24</ version >
</ dependency >
< dependency >
< groupId >log4j</ groupId >
< artifactId >log4j</ artifactId >
< version >1.2.17</ version >
</ dependency >
< dependency >
< groupId >org.apache.logging.log4j</ groupId >
< artifactId >log4j-core</ artifactId >
< version >2.13.3</ version >
</ dependency >
< dependency >
< groupId >org.junit.jupiter</ groupId >
< artifactId >junit-jupiter-api</ artifactId >
< version >${junit.version}</ version >
< scope >test</ scope >
</ dependency >
< dependency >
< groupId >org.junit.jupiter</ groupId >
< artifactId >junit-jupiter-engine</ artifactId >
< version >${junit.version}</ version >
< scope >test</ scope >
</ dependency >
< dependency >
< groupId >junit</ groupId >
< artifactId >junit</ artifactId >
< version >4.13.2</ version >
< scope >test</ scope >
</ dependency >
</ dependencies >
< build >
< resources >
< resource >
<!-- directory：指定资源文件的位置 -->
< directory >src/main/java</ directory >
< includes >
<!-- [**] 表示任意级目录 [*]表示任意任意文件 -->
<!-- mvn resources:resources ：对资源做出处理，先于compile阶段 -->
< include >**/*.properties</ include >
< include >**/*.xml</ include >
</ includes >
<!-- filtering：开启过滤，用指定的参数替换directory下的文件中的参数(eg. ${name}) -->
< filtering >false</ filtering >
</ resource >
< resource >
< directory >src/main/resources</ directory >
</ resource >
</ resources >
</ build >
</ project >
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mybatis-config.xml
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<? xml version = "1.0" encoding = "UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!-- 通过这个配置文件完成mybatis与数据库的连接 -->
< configuration >
<!-- 引入 database.properties 文件-->
< properties resource = "database.properties" />
<!-- 配置mybatis的log实现为LOG4J -->
< settings >
< setting name = "logImpl" value = "LOG4J" />
</ settings >
< environments default = "development" >
< environment id = "development" >
<!--配置事务管理，采用JDBC的事务管理 -->
< transactionManager type = "JDBC" ></ transactionManager >
<!-- POOLED:mybatis自带的数据源，JNDI:基于tomcat的数据源 -->
< dataSource type = "POOLED" >
< property name = "driver" value = "${driver}" />
< property name = "url" value = "${url}" />
< property name = "username" value = "${user}" />
< property name = "password" value = "${password}" />
</ dataSource >
</ environment >
</ environments >
<!-- 将mapper文件加入到配置文件中 -->
< mappers >
< mapper resource = "com/sun/mapper/ClassesMapper.xml" />
</ mappers >
</ configuration >
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database.properties
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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
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MybatisUtil.java
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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();
}
}
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Teacher.java
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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;
}
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Student.java
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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;
}
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Classes.java
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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<Student> studentList;
}
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classMapper.java
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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<Classes> getClassesTeacher( @Param ( "id" ) int id);
List<Classes> getClassesTeacherStudentList( @Param ( "id" ) int id);
}
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classMapper.xml
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<? xml version = "1.0" encoding = "UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
< mapper namespace = "com.sun.mapper.ClassesMapper" >
<!-- 一对一关联查询 -->
< select id = "getClassesTeacher" parameterType = "int" resultMap = "ClassesResultMap" >
select * from classes c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
</ select >
< resultMap type = "com.sun.pojo.Classes" id = "ClassesResultMap" >
<!-- 实体类的字段名和数据表的字段名映射 -->
< id property = "id" column = "c_id" />
< result property = "name" column = "c_name" />
< association property = "teacher" javaType = "com.sun.pojo.Teacher" >
< id property = "id" column = "t_id" />
< result property = "name" column = "t_name" />
</ association >
</ resultMap >
<!-- 一对多关联查询 -->
< select id = "getClassesTeacherStudentList" parameterType = "int" resultMap = "ClassesResultMap2" >
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}
</ select >
< resultMap type = "com.sun.pojo.Classes" id = "ClassesResultMap2" >
< id property = "id" column = "c_id" />
< result property = "name" column = "c_name" />
< association property = "teacher" javaType = "com.sun.pojo.Teacher" >
< id property = "id" column = "t_id" />
< result property = "name" column = "t_name" />
</ association >
< collection property = "studentList" ofType = "com.sun.pojo.Student" >
< id property = "id" column = "s_id" />
< result property = "name" column = "s_name" />
</ collection >
</ resultMap >
</ mapper >
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MapperTest.java
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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> 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> classes = classesMapper.getClassesTeacherStudentList( 1 );
for (Classes Classes : classes) {
System.out.println(classes);
}
}
}
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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；
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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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原文链接：https://blog.csdn.net/qq_51808107/article/details/129881802
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