2021-07-26mybatis 一对多查询_mapper 一对多 2021-优快云博客

本文链接：https://blog.youkuaiyun.com/Jason980915/article/details/119104694

本文介绍使用MyBatis实现数据库一对多查询的方法。通过配置mybatis.xml文件和student.xml映射文件，设置环境参数并定义SQL语句，实现根据班级ID查询学生信息的功能。最后通过Java测试类展示查询结果。

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1.一对多查询

数据库创建

2.mybatis.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>
    <properties resource="jdbc.properties"/>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="classes.xml"/>
        <mapper resource="student.xml"/>
    </mappers>
</configuration>

3.student.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="xxx">
    <select id="selectStu" parameterType="int" resultType="com.pro.domain.Student">
        select * from student where classId=#{classId}
    </select>
</mapper>

4.student.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="xx">
    <resultMap id="classMap" type="com.pro.domain.Classes">
        <id property="classId" column="classId"/>
        <result property="className" column="className"/>
        <collection property="stuList" select="xxx.selectStu"  column="classId"></collection>
    </resultMap>
    <select id="selectClass" parameterType="int" resultMap="classMap">
        select * from classes where classId=#{classId}
    </select>
</mapper>

5.jdbc.properties配置连接数据库

6.创建student classes实体类

7.编写test类

package com.pro.test;

import com.pro.domain.Classes;
import com.pro.domain.Student;
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 org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.InputStream;

public class XxTest {
    SqlSession sqlSession = null;
    SqlSessionFactory sqlSessionFactory = null;

    @Before
    public void setUp() throws Exception {
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession();
    }

    @After
    public void tearDown() throws Exception {
        sqlSession.close();
    }

    @Test
    public void test() {

        Classes classes = sqlSession.selectOne("xx.selectClass", 1);
        for (Student s : classes.getStuList()
        ) {
            System.out.println(s.toString());
        }
    }
}