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
<?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
