mybatis学习（二）

爱被打了一巴掌 2022-05-09 11:03 217阅读 0赞

## 映射关系：一对一，一对多 ##

## 一对一:举例一个人与身份证 ##

一：建表  
数据库信息如下：

CREATE TABLE person(
     id INT PRIMARY KEY AUTO_INCREMENT,
     NAME VARCHAR(20)
    )
    
    CREATE TABLE idCard(
     id INT PRIMARY KEY AUTO_INCREMENT,
     number INT ,
     p_id INT
    )

二：建bean  
idCard对象

public class idCard {
    	private int id;
    	private int number;
    	private person person;
    		get,set.......
    	}

person对象

public class person {
    	private int id;
    	private String name;
    	private idCard idCard;
    		........
    	}

三：建方法接口及映射文件  
接口方法如下：

public interface person_idCardDao {
    	//查idCard
    	public idCard findIdCardById(Serializable id);
    	//查person
    	public person findPersonById(Serializable id);
    	//查person和idCard
    	public person findPerson_IdCard(Serializable id);
    }

映射文件：

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="dao.person_idCardDao">
    	
    	<resultMap type="bean.person" id="person_idMap">
    		<id property="id" column="id"/>
    		<result property="name" column="name"/>
    		
    		<association property="idCard" column="id" select="findIdCardById"></association>
    	</resultMap>
    	
    	<select id="findPersonById" resultType="bean.person">
    	select * from person where id=#{id}
    	</select>
    	
    	<select id="findIdCardById" resultType="bean.idCard">
    	select * from idcard where id=#{id}
    	</select>
    	
    	<select id="findPerson_IdCard" resultMap="person_idMap">
    	select * from person where id=#{id}
    	</select>
    	
    </mapper>

配好这些之后，之后需要在mybatis.cfg.xml中注册该xml

四：测试  
自定一个DBtool

public class DBtool {
    	private static SqlSessionFactory ssf;
    	static{
    		Reader reader;
    		try {
    			reader = Resources.getResourceAsReader("resource/mybatis.cfg.xml");
    			ssf = new SqlSessionFactoryBuilder().build(reader);
    		} catch (IOException e) {
    			e.printStackTrace();
    		}
    	}
    	public static SqlSession getSession(){
    		return ssf.openSession();
    	}
    }

测试：

public class test {
    	@Test
    	public void test(){
    		SqlSession session = DBtool.getSession();
    		person_idCardDao mapper = session.getMapper(person_idCardDao.class);
    		System.out.println(mapper.findPersonById(1));
    		System.out.println(mapper.findIdCardById(1));
    		System.out.println(mapper.findPerson_IdCard(1));
    	}
    }

五：结果  
![在这里插入图片描述][70]ok

## 下面进行一对多：老师与学生 ##

一：建表  
先后建立老师与学生两张表

CREATE TABLE teacher(
     id INT PRIMARY KEY AUTO_INCREMENT,
     NAME VARCHAR(20)
    )
    CREATE  TABLE student(
     id INT PRIMARY KEY AUTO_INCREMENT,
     NAME VARCHAR(20),
     teach_id INT
    )

二：建对象  
student

public class student {
    	private int id;
    	private String name;
    	private teacher teacher;
    	}

teacher:

public class teacher {
    	private int id;
    	private String name;
    	private List<student> student;
    	}

三：建接口及映射文件  
接口与方法：

public interface teach_stuDao {
    	//查询所有学生
    	public List<student> findAllStu();
    	//根据老师id查询所有学生
    	public List<student> findStuByTeachId(Serializable id);
    	//根据id查询老师
    	public teacher findTeachById(Serializable id);
    	//根据老师id查询该老师及学生
    	public List<teacher> findTeach_stu(Serializable id);
    	
    }

映射文件：

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="dao.teach_stuDao">
    	<resultMap type="bean.teacher" id="teach_stuMap">
    		<id property="id" column="id"/>
    		<result property="name" column="name"/>
    		<collection property="student" column="id" select="findStuByTeachId"></collection>
    	</resultMap>
    	
    	<resultMap type="bean.student" id="stuMap">
    		<id property="id" column="id"/>
    		<result property="name" column="name"/>
    	</resultMap>
    	
    	<select id="findAllStu" resultMap="stuMap">
    	select * from student
    	</select>
    	
    	<select id="findStuByTeachId" resultMap="stuMap">
    	select * from student where teach_id=#{id}
    	</select>
    	
    	<select id="findTeachById" resultType="bean.teacher">
    	select * from teacher where id=#{id}
    	</select>
    	
    	<select id="findTeach_stu" resultMap="teach_stuMap">
    	select * from teacher where id=#{id}
    	</select>
    	
    </mapper>

四：测试

public class test {
    	@Test
    	public void test(){
    		SqlSession session = DBtool.getSession();
    		teach_stuDao mapper = session.getMapper(teach_stuDao.class);
    		System.out.println(mapper.findStuByTeachId(1));
    		System.out.println(mapper.findTeachById(1));
    		System.out.println(mapper.findTeach_stu(1));
    		System.out.println(mapper.findAllStu());
    		}

五：结果  
![70 1][]  
ok!!

[70]: /images/20220509/2ae611dc5bb14f7fa9da144e316ecd7a.png
[70 1]: /images/20220509/7073893b421e4ec4b272f2f8f8115ed4.png