解析Mybatis对sql表的一对多查询问题

Mybatisd对sql表的一对多查询

select * fromprojectrecord prleft join projects poon po.pid=pr.pidleft join emp eon e.empno = pr.empnowhere pr.pid=1

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.msb.mapper.EmpMapper">    <!--resultMap是一个映射表，对应的字段会对应数据表的字段    -->    <resultMap id="projectMap" type="projects"><id column="pid" property="pid"></id><result column="pname" property="pname"></result><result column="money" property="money"></result><collection property="projectrecordList" ofType="projectrecord">    <id property="pid" column="pid"></id>    <id property="empno" column="empno"></id>    <association property="emp" javaType="emp"><id property="empno" column="empno"></id><result property="ename" column="ename"></result><result property="job" column="job"></result><result property="sal" column="sal"></result><result property="hiredate" column="hiredate"></result><result property="mgr" column="mgr"></result><result property="comm" column="comm"></result><result property="deptno" column="deptno"></result>    </association></collection>    </resultMap>    <!--Projects findPiddle(int pid);-->    <select id="findPiddle" resultMap="projectMap">select *from    emp einner join    projectrecord pr    on pr.empno=e.empnoinner join    projects po    on po.pid= pr.pidwhere pr.pid=#{pid}    </select></mapper>

//mapper表package com.msb.mapper;import com.msb.pojo.Dept;import com.msb.pojo.Emp;import com.msb.pojo.Projects;import java.util.List;public interface EmpMapper {    /**     * 实现根据项目编号查看所有参与项目的人员信息     * @param pid 传入项目号     * @return 返回一个project的对象     */    Projects findPiddle(int pid);}

package com.msb.pojo;//一对一关系引入import lombok.AllArgsConstructor;import lombok.Data;import lombok.NoArgsConstructor;import java.io.Serializable;@Data@AllArgsConstructor@NoArgsConstructorpublic class Projectrecord implements Serializable {    private int empno;    private int pid;    //pr和e是一对一的关系    private Emp emp;}

package com.msb.pojo;//一对多关系实体类设计import lombok.AllArgsConstructor;import lombok.Data;import lombok.NoArgsConstructor;import java.io.Serializable;import java.util.List;@NoArgsConstructor@AllArgsConstructor@Datapublic class Projects implements Serializable {    private int pid;    private String pname;    private int money;    //po和pr是一对多的关系    List<Projectrecord> projectrecordList;}

package com.msb.pojo;import lombok.AllArgsConstructor;import lombok.Data;import lombok.NoArgsConstructor;import java.sql.Date;@Data@AllArgsConstructor@NoArgsConstructorpublic class Emp {    private Integer empno;    private String ename;    private String job;    private Integer mgr;    private Date hiredate;    private  Integer sal;    private Integer comm;    private  Integer deptno;    private Dept dept;}

jdbc_driver=com.mysql.cj.jdbc.Driverjdbc_url=jdbc:mysql://127.0.0.1:3306/testtable?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghaijdbc_username=rootjdbc_password=root

log4j.rootLogger=debug,stdoutlog4j.appender.stdout=org.apache.log4j.ConsoleAppenderlog4j.appender.stdout.Target=System.errlog4j.appender.stdout.layout=org.apache.log4j.SimpleLayoutlog4j.appender.logfile=org.apache.log4j.FileAppenderlog4j.appender.logfile.File=d:/msb.loglog4j.appender.logfile.layout=org.apache.log4j.PatternLayoutlog4j.appender.logfile.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %l %F %p %m%n

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration>    <!--引入外部配置文件-->    <properties resource="jdbc.properties"></properties>    <!--这里是起的别名，前面是名，后面是路径-->    <!--<typeAliases><typeAlias alias="dept" type="com.msb.pojo.Dept"/>    </typeAliases>-->    <!--包别名，用到时候调用名字小写即可,就会扫描msb下的所以实体类，用的时候实体类名小写-->    <typeAliases><package name="com.msb"/>    </typeAliases>    <environments default="development"><environment id="development">    <!--   简单使用了 JDBC 的提交和回滚设置  -->    <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>    <!--加载mapper映射文件-->    <mappers><package name="com.msb.mapper"/>    </mappers></configuration>

import com.msb.mapper.EmpMapper;import com.msb.pojo.Dept;import com.msb.pojo.Emp;import com.msb.pojo.Projectrecord;import com.msb.pojo.Projects;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.IOException;import java.io.InputStream;import java.util.List;public class Test1 {    SqlSession sqlSession = null;    EmpMapper mapper =null;   @Before   public void test1(){       //首先做一个对象SqlSessionFactoryBuilder建立一个绘话       SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder();       //有一个文本输入的io流进行读取操作       InputStream stream = null;       try {   //这里的路径直接会定位到配置文件classes下面；所以这个文件在次目录下--编译和   //-图纸；对数据库文件进行读取，获取一个io流，由于配置文件在classes下面，直接写文件名即可   stream = Resources.getResourceAsStream("sqlMapConfig.xml");       } catch (IOException e) {   e.printStackTrace();       }       //build需要指向一个文件进行读取出来--工厂       SqlSessionFactory factory = ssfb.build(stream);//需要用sqlSession去调用增删改查--工人去获取数据，打开这个绘话       sqlSession = factory.openSession();   }        /*多对多的查询*/    @Test    public void test7(){mapper = sqlSession.getMapper(EmpMapper.class);Projects piddle = mapper.findPiddle(1);System.out.println("Pid");System.out.println(piddle.getPid());System.out.println("Pname");System.out.println(piddle.getPname());System.out.println("Money");System.out.println(piddle.getMoney());System.out.println("ProjectrecordList");List<Projectrecord> projectrecordList = piddle.getProjectrecordList();projectrecordList.forEach(System.out::println);    }        @After    public void test3(){       if (sqlSession!=null){   sqlSession.close();       }    }}

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