Mybatis ---- data cascade query (Multiple-to-one)

Project directory structure:

There are two tables: an article table article and a user table user.

Create table article (id int (11) not null auto_increment, userid int (11) not null, title varchar (100) not null, content text not null, primary key (id )) ENGINE = InnoDB default charset = utf8; insert into article (id, userid, title, content) values (1, 1, 'test _ title', 'text _ content '); insert into article (id, userid, title, content) values (2, 1, 'test _ title_2 ', 'text _ content_2'); insert into article (id, userid, title, content) values (, 'test _ title_3 ', 'text _ content_3'); insert into article (id, userid, title, content) values, 'test _ title_4 ', 'text _ content_4'); create table user (id int (11) not null auto_increment, userName varchar (50) default null, userAge int (11) default null, userAddress varchar (200) default null, primary key (id) ENGINE = InnoDB default charset = utf8; insert into user (id, userName, userAge, userAddress) values (1, 'summer ', '123', 'shanghai ');

Now, you need to query the articles owned by the user based on the user ID.You need to write the following SQL statement:

select a.id, a.userName ,a.userAddress ,b.id aid, b.title,b.content                                          from user a,article b                                          where a.id=b.userid and a.id=#{id}

Now I will paste the relevant JAVA code and ing files, all of which are in the annotations.

User. java

package com.mybatis.model;public class User { private int id; private String userName; private String userAge; private String userAddress; public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getUserAge() {return userAge;}public void setUserAge(String userAge) {this.userAge = userAge;}public String getUserAddress() {return userAddress;} public void setUserAddress(String userAddress) {this.userAddress = userAddress;  } }

Article. java

Package com. mybatis. model; public class Article {private int id; private User user; // The document defines a User object, instead of the int type private String title; private String content; public int getId () {return id;} public void setId (int id) {this. id = id;} public User getUser () {return user;} public void setUser (User user) {this. user = user;} public String getTitle () {return title;} public void setTitle (String title) {this. title = title;} public String getContent () {return content;} public void setContent (String content) {this. content = content ;}}

Interface Class

IUserDao. java

package com.mybatis.dao;import java.util.List;import com.mybatis.model.Article;public interface IUserDao { public List getUserArticles(int id);}

Configution. xml

User. xml

     
        
         
               
                
                
                             
                
                      
                      
                      
                      
                 
  Select. id,. userName,. userAddress, B. id aid, B. title, B. content from user a, article B where. id = B. userid and. id = # {id}
 

Compile a test class.

Package com. mybatis. test; import java. io. IOException; import java. util. list; 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 com. mybatis. dao. IUserDao; import com. mybatis. model. article; public class Test {/***** obtain MyBatis SqlSessionFactory * SqlSessionFactory to create SqlSession. Once created successfully, you can use the SqlSession instance to execute the ing statement *, commit, rollback, close and other methods * @ return */private static SqlSessionFactory getSessionFactory () {SqlSessionFactory sessionFactory = null; String resource = "configuration. xml "; try {sessionFactory = new SqlSessionFactoryBuilder (). build (Resources. getResourceAsReader (resource);} catch (IOException e) {e. printStackTrace ();} return sessionFactory;}/*** main method * @ param args */public static void main (String [] args) {SqlSession session = getSessionFactory (). openSession (); try {IUserDao userDao = session. getMapper (IUserDao. class); // input the user's id = 1 List listArticle = userDao. getUserArticles (1); for (Article article: listArticle) {System. out. println (article. getTitle () + ":" + article. getContent () + ": Author:" + article. getUser (). getUserName () + ": Address:" + article. getUser (). getUserAddress () ;}} catch (Exception e) {e. printStackTrace ();} finally {session. close ();}}}

The result is as follows:

Test_title: text_content: Author: summer: Address: Shanghai test_title_2: text_content_2: Author: summer: Address: Shanghai test_title_3: text_content_3: Author: summer: Address: Shanghai Region: text_content_4: author: summer: Address: Shanghai