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这篇“Mybatis对sql表的一对多查询问题怎么解决”文章的知识点大部分人都不太理解,所以小编给大家总结了以下内容,内容详细,步骤清晰,具有一定的借鉴价值,希望大家阅读完这篇文章能有所收获,下面我们一起来看看这篇“Mybatis对sql表的一对多查询问题怎么解决”文章吧。
Mybatisd对sql表的一对多查询
select * from projectrecord pr left join projects po on po.pid=pr.pid left join emp e on e.empno = pr.empno where 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 { /** * 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 @NoArgsConstructor public 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 @Data public 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 @NoArgsConstructor public 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.Driver jdbc_url=jdbc:mysql://127.0.0.1:3306/testtable?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai jdbc_username=root jdbc_password=root
log4j.rootLogger=debug,stdout log4j.appender.stdout=org.apache.log4j.ConsoleAppender log4j.appender.stdout.Target=System.err log4j.appender.stdout.layout=org.apache.log4j.SimpleLayout log4j.appender.logfile=org.apache.log4j.FileAppender log4j.appender.logfile.File=d:/msb.log log4j.appender.logfile.layout=org.apache.log4j.PatternLayout log4j.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(); } /*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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