MyBatis-06-多對一

看完以下內容接着看：https://blog.csdn.net/lgz0921/article/details/104557260

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-06</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;

    //學生需要關聯一個老師
    private Teacher teacher;
}

Teacher:

package com.kuang.pojo;

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

@Data
@Alias("tea")
public class Teacher {
    private int id;
    private String name;
}

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);
    }
}

StudentMapper:

package com.kuang.dao;

import com.kuang.pojo.Student;

import java.util.List;

public interface StudentMapper {
    //查詢所有的學生的信息，以及對應的老師的信息
    public List<Student> getStudent();
    public List<Student> getStudent2();
}

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">

    <!--
        方法二：
        按照結果嵌套處理
    -->
    <select id="getStudent2" resultMap="stutea2">
        select s.id sid,s.name sname,t.name tname from student s, teacher t
        where s.tid=t.id;
    </select>
    <resultMap id="stutea2" type="stu">
        <result property="id" column="sid"/>
        <result property="name" column="sname" />
        <association property="teacher" javaType="tea">
            <result property="name" column="tname"/>
        </association>
    </resultMap>





    <!--
        方法一：
        思路：
        1.查詢所有的學生信息
        2.根據查詢出來的學生id，尋找對應的老師！ 子查詢

    -->
    <select id="getStudent" resultMap="stutea">
        select * from student;
    </select>

    <resultMap id="stutea" type="stu">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
        <!--
            複雜的屬性單獨處理
            對象：association
            集合：collection
        -->
        <association property="teacher" column="tid" javaType="tea" select="getTeacher"/>
    </resultMap>

    <select id="getTeacher" resultType="tea">
        select * from teacher where id=#{tid};
    </select>

</mapper>

TeacherMapper

package com.kuang.dao;

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

public interface TeacherMapper {

    @Select("select * from teacher where id = #{tid}")
    Teacher getTeacher(@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">


</mapper>

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

import java.util.List;

public class MyTest {
    public static void main(String[] args) {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        Teacher teacher = mapper.getTeacher(1);
        System.out.println(teacher);
        sqlSession.close();
    }
    @Test
    public void TestGetStudent() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> studentList =mapper.getStudent();
        for (Student student : studentList) {
            System.out.println(student);
        }
        sqlSession.close();
    }
    @Test
    public void TestGetStudent2() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List<Student> studentList =mapper.getStudent2();
        for (Student student : studentList) {
            System.out.println(student);
        }
        sqlSession.close();
    }
}