MyBatis-07-一對多

看完以下內容接着看：https://blog.csdn.net/lgz0921/article/details/104557630

目錄結構：

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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>mybatis-study</artifactId>
        <groupId>org.kuang</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>mybatis-07</artifactId>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.10</version>
        </dependency>

    </dependencies>

</project>

Student

package com.kuang.pojo;

import lombok.Data;
import org.apache.ibatis.type.Alias;

@Data
@Alias("stu")
public class Student {
    private int id;
    private String name;
    private int tid;
}

StudentMapper

package com.kuang.dao;

import com.kuang.pojo.Student;

import java.util.List;

public interface StudentMapper {

}

StudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.kuang.dao.StudentMapper">

</mapper>

Teacher

package com.kuang.pojo;

import lombok.Data;
import org.apache.ibatis.type.Alias;

import java.util.List;

@Data
@Alias("tea")
public class Teacher {
    private int id;
    private String name;
    //一個老師擁有多個學生
    private List<Student> students;
}

TeacherMapper

package com.kuang.dao;

import com.kuang.pojo.Teacher;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface TeacherMapper {
    //獲取老師
   // List<Teacher> getTeacher();
    //獲取指定老師下的所有學生及老師的信息

    Teacher getTeacher(@Param("tid") int id);
    Teacher getTeacher2(@Param("tid") int id);
}

TeacherMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.kuang.dao.TeacherMapper">

    <!--按結果嵌套查詢-->
    <select id="getTeacher" resultMap="teastu1">
        select s.id sid,s.name sname ,
        t.name tname,t.id tid
         from student s , teacher t where s.tid=t.id and t.id=#{tid};
    </select>
    <resultMap id="teastu1" type="tea">
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>
        <collection property="students" ofType="stu">
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>
    <!--====================================================================-->
    <select id="getTeacher2" resultMap="teastu2">
        select * from teacher where id=#{tid};
    </select>
    <resultMap id="teastu2" type="tea">
        <collection property="students" javaType="ArrayList" ofType="stu" select="selstu" column="id"/>
    </resultMap>
    <select id="selstu" resultType="stu">
        select * from student where tid=#{tid};
    </select>
</mapper>

MybatisUtils

package com.kuang.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.IOException;
import java.io.InputStream;

//SqlSessionFactory -> SqlSession
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        try {
            //獲取使用Mybatis第一步SqlSessionFactory對象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession(true);
    }
}

db.properties

driver = com.mysql.cj.jdbc.Driver
url = jdbc:mysql://localhost:3306/mybatis?useSSL=true&usUnicode=true&characterEncoding=UTF-8&autoReconnect=true&failOverReadOnly=false&serverTimezone=UTC
username = root
password = lgz0921

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">
<!--configuration 核心配置文件 -->
<configuration>

    <!--引入外部配置文件-->
    <properties resource="db.properties" />

    <settings>
        <!--標準的日誌工廠實現-->
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>
    <typeAliases>
        <package name="com.kuang.pojo"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="com.kuang.dao.StudentMapper" />
        <mapper class="com.kuang.dao.TeacherMapper" />
    </mappers>
</configuration>

MyTest

import com.kuang.dao.TeacherMapper;
import com.kuang.pojo.Teacher;
import com.kuang.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

public class MyTest {
    @Test
    public void test(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        System.out.println(sqlSession.getMapper(TeacherMapper.class).getTeacher2(1));
        sqlSession.close();
    }
}