今天小编给大家分享一下Mybatis怎么实现一对一、一对多关联查询的相关知识点，内容详细，逻辑清晰，相信大部分人都还太了解这方面的知识，所以分享这篇文章给大家参考一下，希望大家阅读完这篇文章后有所收获，下面我们一起来了解一下吧。
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
-
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
<?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. ${name}) -->
<filtering>false</filtering>
</resource>
<resource>
<directory>src/main/resources</directory>
</resource>
</resources>
</build>
</project>
mybatis-config.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!-- 通过这个配置文件完成mybatis与数据库的连接 -->
<configuration>
<!-- 引入 database.properties 文件-->
<properties resource="database.properties"/>
<!-- 配置mybatis的log实现为LOG4J -->
<settings>
<setting name="logImpl" value="LOG4J" />
</settings>
<environments default="development">
<environment id="development">
<!--配置事务管理，采用JDBC的事务管理 -->
<transactionManager type="JDBC"></transactionManager>
<!-- POOLED:mybatis自带的数据源，JNDI:基于tomcat的数据源 -->
<dataSource type="POOLED">
<property name="driver" value="${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>
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<Student> 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<Classes> getClassesTeacher(@Param("id") int id);
List<Classes> getClassesTeacherStudentList(@Param("id") int id);
}
classMapper.xml
<?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>
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> 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);
}
}
}
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；