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今天小編給大家分享一下Mybatis怎么實現一對一、一對多關聯查詢的相關知識點，內容詳細，邏輯清晰，相信大部分人都還太了解這方面的知識，所以分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后有所收獲，下面我們一起來了解一下吧。
Mybatis實現一對一、一對多關聯查詢，關聯查詢：多個表聯合查詢，只查詢一次，通過resultMap里面的<association>、<collection>標簽配置一對一、一對多。
涉及的sql文件、idea工程文件：Mybatis實現一對一、一對多關聯查詢資源
班級classes、班主任teacher是一對一的關系
班級classes、學生student是一對多的關系
使用IDEA快速構建一個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：指定資源文件的位置 --> <directory>src/main/java</directory> <includes> <!-- “**” 表示任意級目錄 “*”表示任意任意文件 --> <!-- mvn resources:resources ：對資源做出處理，先于compile階段 --> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <!-- filtering：開啟過濾，用指定的參數替換directory下的文件中的參數(eg. ${name}) --> <filtering>false</filtering> </resource> <resource> <directory>src/main/resources</directory> </resource> </resources> </build> </project>
mybatis-config.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<!-- 通過這個配置文件完成mybatis與數據庫的連接 -->
<configuration>
<!-- 引入 database.properties 文件-->
<properties resource="database.properties"/>
<!-- 配置mybatis的log實現為LOG4J -->
<settings>
<setting name="logImpl" value="LOG4J" />
</settings>
<environments default="development">
<environment id="development">
<!--配置事務管理，采用JDBC的事務管理 -->
<transactionManager type="JDBC"></transactionManager>
<!-- POOLED:mybatis自帶的數據源，JNDI:基于tomcat的數據源 -->
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${user}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!-- 將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為自動提交事務
}
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">
<!-- 一對一關聯查詢 -->
<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">
<!-- 實體類的字段名和數據表的字段名映射 -->
<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>
<!-- 一對多關聯查詢 -->
<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 {
/**
* 測試班級與班主任老師一對一的關聯關系
*/
@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);
}
}
/**
* 測試班級與學生一對多關聯關系
*/
@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:
總結：一對一關聯查詢需要在resultMap里面配置association，一對多關聯查詢需要在resultMap里面配置collection；
List classes = classesMapper.getClassesTeacherStudentList(1);
for (Classes Classes : classes) {
System.out.println(classes);
}}
}
test1:
[外鏈圖片轉存中...(img-qon5qYiR-1680248446105)]
test2:
[外鏈圖片轉存中...(img-DZayGx8q-1680248446107)]
總結：一對一關聯查詢需要在resultMap里面配置association，一對多關聯查詢需要在resultMap里面配置collection；以上就是“Mybatis怎么實現一對一、一對多關聯查詢”這篇文章的所有內容，感謝各位的閱讀！相信大家閱讀完這篇文章都有很大的收獲，小編每天都會為大家更新不同的知識，如果還想學習更多的知識，請關注億速云行業資訊頻道。
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