mybatis06-1对多查询

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最新推荐文章于 2025-06-06 08:00:00 发布

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分类专栏： mybatis 文章标签： mybatis 1对多查询

本文链接：https://blog.youkuaiyun.com/qq_32726809/article/details/89314680

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本文介绍了一个使用MyBatis进行级联查询的例子，展示了如何从数据库中获取班级和学生信息，并通过Java对象进行数据整理。通过定义实体类、映射文件和测试代码，实现了1对多的数据查询。

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数据库

/*
Navicat MySQL Data Transfer

Source Server         : localhost
Source Server Version : 50717
Source Host           : localhost:3306
Source Database       : lsq

Target Server Type    : MYSQL
Target Server Version : 50717
File Encoding         : 65001

Date: 2019-04-15 16:25:57
*/

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for tclass
-- ----------------------------
DROP TABLE IF EXISTS `tclass`;
CREATE TABLE `tclass` (
  `cla_classname` varchar(255) DEFAULT NULL,
  `cla_classnum` varchar(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

/*
Navicat MySQL Data Transfer

Source Server         : localhost
Source Server Version : 50717
Source Host           : localhost:3306
Source Database       : lsq

Target Server Type    : MYSQL
Target Server Version : 50717
File Encoding         : 65001

Date: 2019-04-15 16:25:43
*/

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `stu_name` varchar(255) DEFAULT NULL,
  `stu_no` varchar(10) DEFAULT NULL,
  `stu_classnum` varchar(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

bean

package bean;

public class Student {
	
	private String name;
	private String no;
	private String classnum;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getNo() {
		return no;
	}
	public void setNo(String no) {
		this.no = no;
	}
	public String getClassnum() {
		return classnum;
	}
	public void setClassnum(String classnum) {
		this.classnum = classnum;
	}
	@Override
	public String toString() {
		return "学生 [name=" + name + ", no=" + no + ", classnum=" + classnum + "]";
	}
	public Student() {
		super();
	}
	public Student(String name, String no, String classnum) {
		super();
		this.name = name;
		this.no = no;
		this.classnum = classnum;
	}
	
	

}

package bean;

import java.util.List;

public class TClass {
	private String classname;
	private String classnum;
	private List<Student> students;
	
	public String getClassname() {
		return classname;
	}
	public void setClassname(String classname) {
		this.classname = classname;
	}
	public String getClassnum() {
		return classnum;
	}
	public void setClassnum(String classnum) {
		this.classnum = classnum;
	}
	public List<Student> getStudents() {
		return students;
	}
	public void setStudents(List<Student> students) {
		this.students = students;
	}
	@Override
	public String toString() {
		return "TClass [classname=" + classname + ", classnum=" + classnum + ", students=" + students + ", toString()="
				+ super.toString() + "]";
	}
	public TClass() {
		super();
	}
	public TClass(String classname, String classnum, List<Student> students) {
		super();
		this.classname = classname;
		this.classnum = classnum;
		this.students = students;
	}
	

}

映射文件

<?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="test">
	<select id="getClass" resultMap="classResult">
		select * from tclass , student where student.stu_classnum =
		tclass.cla_classnum and tclass.cla_classnum= #{num}
	</select>
	<resultMap id="classResult" type="bean.TClass">
		<result property="classname" column="cla_classname" />
		<result property="classnum" column="cla_classnum" />
		<collection property="students" ofType="bean.Student">
			<result property="name" column="stu_name" />
			<result property="no" column="stu_no" />
			<result property="classnum" column="stu_classnum" />
		</collection>
	</resultMap>
</mapper>

其实就是用级联查询查出内容，然后对内容进行整理，1对多中，collection表示那个“多”。

调用


package bean;

import static org.junit.Assert.*;

import java.io.IOException;
import java.io.Reader;

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.Test;

public class TClassTest {

	static String resource = "config.xml";
	@Test
	public void test() {
		Reader reader = null;
		try {
			reader = Resources.getResourceAsReader(resource);
		} catch (IOException e) {

			e.printStackTrace();
		}
		SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
		SqlSession session = sessionFactory.openSession();
	    TClass user = session.selectOne("test.getClass",303);
	    System.out.println(user);
	    session.close();
	}

}