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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 mapper PUBLIC "-//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 e inner join projectrecord pr on pr.empno=e.empno inner join projects po on po.pid= pr.pid where 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 { 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=rootlog4j.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 configuration PUBLIC "-//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(); } @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(); } }}以上就是关于“Mybatis对sql表的一对多查询问题怎么解决”这篇文章的内容，相信大家都有了一定的了解，希望小编分享的内容对大家有帮助，若想了解更多相关的知识内容，请关注编程网行业资讯频道。
