Mybatis实例

数据库中:USERT t , WEBINFOR t(表中有一列关联usert某列)

建模型,分析好哪个表是一对一(webinfo ),哪个表是一对多(usert)(一条数据对另一个表中多条数据).

对象级联

建包

建xml和interface接口类

 

xml

<?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">

第一种方式:结果是从一对一这个表(WebinfoMapper)查看

对象级联 方法查询 

WebinfoMapper.xml

 

<mapper namespace="com.hanqi.mapper.WebInfoMapper">//复制的对应的接口里面的限定名

<resultMap type="webInfo" id="webinfoResult2">
		<id property="ids" column="IDS"/> 
		<association property="usert" column="USERID" select="com.hanqi.mapper.UsertMapper.selectUsertById" />	
</resultMap>
  	<select id="selectWebInfo" resultMap="webinfoResult2">
            select * from webinfor 	//注意表名别写错了	
	</select>    
</mapper>

　

WebInfoMapper.java

package com.hanqi.mapper;

import java.util.List;
import com.hanqi.model.webInfo;

public interface WebInfoMapper {
	List<webInfo> selectWebInfo();
}

　

UsertMapper.xml

<?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.hanqi.mapper.UsertMapper">
  	
  	<select id="selectUsertById" resultType="Usert" >
  		select * from usert u where u.ids=#{userid}
  	</select>
</mapper>

　

UsertMapper.java 

package com.hanqi.mapper;

import java.util.List;
import com.hanqi.model.Usert;

public interface UsertMapper {
	List<Usert> selectUsertById();  //返回值只在想打印时有用,否则可以写int型

}

　

test表

package com.hanqi.test;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import com.hanqi.mapper.WebInfoMapper;
import com.hanqi.model.webInfo;
import com.hanqi.util.MyBatisDButil;

class JTest {
	private SqlSession sqlSession;
	private WebInfoMapper webinfoMapper;

	@Test
	void test() {
		
		 List<webInfo> list = webinfoMapper.selectWebInfo();
		  for (webInfo webInfo : list) {
				System.out.println(webInfo);
			}
		}
	
	@BeforeEach
	void setUp() throws Exception {
		sqlSession = MyBatisDButil.getSqlSession();
		webinfoMapper = sqlSession.getMapper(WebInfoMapper.class);
		
	}
	@AfterEach
	void tearDown() throws Exception {
		sqlSession.commit();
		sqlSession.close();
	}

	

}

 

　第二种方式:结果是从一对多这个表(Usert)查看

　　

UsertMapper.java

package com.hanqi.mapper;

import java.util.List;
import com.hanqi.model.Usert;


public interface UsertMapper {
	//Usert selectUsertById(Integer ids);  查某一个人的详细数据时
	List<Usert> selectUsertById();  /*查所有人的详细数据时,
这两种方式的差别主要是打印的时候,想看几个人的数据还是所有人的数据*/

}

　

UsertMapper.xml

<?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.hanqi.mapper.UsertMapper">
  	
  	<resultMap type="Usert" id="usertResult">
  		<id property="ids" column="IDS"/> 
  		<collection property="webinfoList" column="IDS" 
  		select="com.hanqi.mapper.WebInfoMapper.selectWebInfoByUsert" />
  	</resultMap>	
  	<select id="selectUsertById" resultMap="usertResult">
  		select * from usert u where u.ids=#{userid}
  	</select>
</mapper>

　

WebInfoMapper .java　

package com.hanqi.mapper;

import java.util.List;
import com.hanqi.model.webInfo;
public interface WebInfoMapper {

	List<webInfo> selectWebInfoByUsert(Integer ids);

}

　　

WebInfoMapper .xml　

<?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.hanqi.mapper.WebInfoMapper">

	<select id="selectWebInfoByUsert" resultType="webInfo">
		select * from webinfor w where w.userid=#{ids}
	</select>
	
</mapper>

　　

package com.hanqi.test;

import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import com.hanqi.mapper.UsertMapper;
import com.hanqi.mapper.WebInfoMapper;
import com.hanqi.model.webInfo;
import com.hanqi.util.MyBatisDButil;

class JTest {
	private SqlSession sqlSession;
	private WebInfoMapper webinfoMapper;
	private UsertMapper usertmapper;
	//private GirlMapper gm;
	@Test
	void test() {
		
		/*1对多第三种方法
		 * List<Usert> list = usertmapper.selectUsertById();
		for (Usert usert : list) {
			System.out.println(usert);
		}*/
	}
	@BeforeEach
	void setUp() throws Exception {
		sqlSession = MyBatisDButil.getSqlSession();
		webinfoMapper = sqlSession.getMapper(WebInfoMapper.class);
		usertmapper = sqlSession.getMapper(UsertMapper.class);
		//gm = sqlSession.getMapper(GirlMapper.class);
	}
	@AfterEach
	void tearDown() throws Exception {
		sqlSession.commit();
		sqlSession.close();
	}
}

　　

 

 

 

 

 

 

 

 

 

 

　

　

 

来源：https://www.cnblogs.com/ziyanxiaozhu/p/8358754.html