MyBatis "Set nested Query" and "set nested result" two methods to implement database one-to-many relationship

The two entity classes are as follows: User class and goods commodity class. One user corresponds to multiple items (a pair of multiple)

Package com.leo.entity;
Import java.util.List;
	public class User {private Integer ID;
	Private String username;
	Private Integer age;
	Private String address;

	Private list<goods> goodslist;
	Public list<goods> getgoodslist () {return goodslist;
	} public void Setgoodslist (list<goods> goodslist) {this.goodslist = goodslist;
	} public Integer GetId () {return id;
	} public void SetId (Integer id) {this.id = ID;
	} public String GetUserName () {return username;
	} public void Setusername (String username) {this.username = username;
	} public Integer Getage () {return age;
	public void Setage (Integer age) {this.age = age;
	} public String getaddress () {return address;
	The public void setaddress (String address) {this.address = address;
		Public User () {super (); TODO auto-generated Constructor stub} @Override public String toString () {return ' User [id= ' + ID + ', username= "+ Username +", age= "+ Age +", address="+ Address +", goodslist= "+ goodslist +"] ";

 }
	
	
	
	
	
}

Goods commodity category

Package com.leo.entity;

public class Goods {
	private Integer ID;
	Private String goodsname;
	Private Integer Goodsnumber;
	Private Integer user_id;
	
	
	
	Public Integer getId () {
		return ID;
	}
	public void SetId (Integer id) {
		this.id = ID;
	}
	Public String Getgoodsname () {
		return goodsname;
	}
	public void Setgoodsname (String goodsname) {
		this.goodsname = goodsname;
	}
	Public Integer Getgoodsnumber () {
		return goodsnumber;
	}
	public void Setgoodsnumber (Integer goodsnumber) {
		this.goodsnumber = goodsnumber;
	}
	Public Integer getuser_id () {
		return user_id;
	}
	public void setuser_id (Integer user_id) {
		this.user_id = user_id;
	}
	
	
	
	
}

Mapper mapping file for user entity class: Userdao.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" > <map Per namespace= "Com.leo.mapper.UserDao" > <resultmap type= "User" id= "UserMap" > <id column= "u_id" Propert
			y= "id"/> <result column= "username" property= "username"/> <result column= "age" property= "age"/> <result column= "Address" property= "Address"/> <!--when the relationship between tables is a couple of long, collection--> <!--here column= "u_id" is to pass parameters to the nested query select= "..."-<collection property= "goodslist" oftype= "Goods" column=													
		Com.leo.mapper.GoodsDao.selectGoodsForUser "/> </resultMap> <!--goodslist is a collection of private properties in the user entity class-- <select id= "Getuserinfobyid" parametertype= "int" resultmap= "UserMap" > select U.id as u_id, u.u
		Sername, U.age, u.address from user u where u.id =${value};
	</select></mapper>  

Goods Mapper mapping file for entity classes: Goodsdao.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" >
	<!--that's the nested query map--   
	<mapper namespace= "Com.leo.mapper.GoodsDao" >
		<select id= " Selectgoodsforuser "parametertype=" int "resulttype=" Goods ">
		  select id,goodsname,goodsnumber,user_id from Goods WHERE user_id = #{value}
		</select>
	</mapper>  

Mabatis Environment configuration file Mabatis-config.xml

<?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> <!--I put the contents of the data source in the Db.properties file--<properties resource= "com/leo/resources/  Db.properties "/> <!--start-type aliases: Take an alias for Resulttype in Mapper.xml and look not very redundant--<typeAliases> <typealias alias= "User" type= "Com.leo.entity.User"/> <typealias alias= "Goods" type= "Com.leo.entity.Goods"/> </ typealiases> <!--end-type alias--<!--start-environments configuration-<environments default= "development "> <environment id=" Development "> <transactionmanager type=" JDBC "/> & Lt;datasource type= "Pooled" > <property name= "Driver" value= "${driverclass}"/><!--data Source Configuration--&G 
               T <property name= "url" value= "${url}"/> <property name= "UsernAme "value=" ${username} "/> <property name=" password "value=" ${password} "/> </d   
    
    Atasource> </environment> </environments> <!--end-environments configuration--
        <!--Map file resources connected to the entity class-<mappers> <mapper resource= "Com/leo/entity/userdao.xml"/> <mapper resource= "Com/leo/entity/goodsdao.xml"/> </mappers> </configuration>

Test servlet (can also be tested with the main function)

Package com.leo.servlet;
Import java.io.IOException;
Import Java.io.InputStream;

Import java.util.List;
Import javax.servlet.ServletException;
Import Javax.servlet.annotation.WebServlet;
Import Javax.servlet.http.HttpServlet;
Import Javax.servlet.http.HttpServletRequest;

Import Javax.servlet.http.HttpServletResponse;
Import org.apache.ibatis.io.Resources;
Import Org.apache.ibatis.session.ResultHandler;
Import org.apache.ibatis.session.SqlSession;
Import Org.apache.ibatis.session.SqlSessionFactory;

Import Org.apache.ibatis.session.SqlSessionFactoryBuilder;
Import Com.leo.entity.Goods;
Import Com.leo.entity.User;
Import Com.leo.mapper.GoodsDao;



Import Com.leo.mapper.UserDao; /** * Servlet Implementation class Mybatisservlet */@WebServlet ("/mybatisservlet") public class Mybatisservlet extends

	HttpServlet {private static final long serialversionuid = 1L; protected void doget (HttpServletRequest request, httpservletresponse response) throws Servletexception, IOException {in PUtstream is = Resources.getresourceasstream ("Com/leo/resources/mybatis-config.xml");
		Sqlsessionfactory factory = new Sqlsessionfactorybuilder (). Build (IS);
		
sqlsession session = Factory.opensession ();
		Userdao ud = session.getmapper (Userdao.class);

		Goodsdao gd = Session.getmapper (Goodsdao.class);
		
List<goods> goodslist= Gd.selectgoodsforuser (1);		
User user = Ud.getuserinfobyid (1);
SYSTEM.OUT.PRINTLN (user);
		list<goods> goodslist = User.getgoodslist (); for (Goods goods:goodslist) {System.out.println (Goods.getid () + "" + goods.getgoodsname () + "" +goods.getgoodsnumber
		() + "" + goods.getuser_id ());
		} session.commit ();
		
	Session.close (); } protected void DoPost (HttpServletRequest request, httpservletresponse response) throws Servletexception, IOException
		
	{doget (request, response); }

}

The above is a collection of nested queries, there is also a way to set nested results, this way only requires an entity class file, it is a cascade query, automatic completion of the

Here's how to nest the results in a collection:

Just need to change userdao.xml, and just use this one mapping file can complete

<?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" > <map Per namespace= "Com.leo.mapper.UserDao" > <resultmap type= "Goods" id= "Goodsmap" > <id column= "g_id" PR operty= "id"/> <result column= "goodsname" property= "Goodsname"/> <result column= "GoodsNumber" property= "G Oodsnumber "/> <result column=" user_id "property=" user_id "/> </resultMap> <resultmap type=" user
			"Id=" UserMap "> <id column=" u_id "property=" id "/> <result column=" username "property=" username "/> <result column= "Age" property= "age"/> <result column= "Address" property= "Address"/> <collection Property= "Goodslist" oftype= "Goods" resultmap= "Goodsmap"/><!--the difference between the two ways here, your own analysis can know--</resultmap 
			> <select id= "Getuserinfobyid" parametertype= "int" resultmap= "UserMap" > select	U.id as u_id, U.username, U.age, u.address, g.id as g_id, <!--nested results This method uses a connection query, and the nested query uses two times-- 
				G.goodsname, G.goodsnumber, g.user_id from the user U inner join goods g on u.id = g.user_id where
		U.id =${value};   </select> </mapper>

Hope can help everyone, what wording is not correct, hope to be corrected, hope progress