mybatis--多对一关联

Posted 2022-05-10 longlyseul

（1）首先，创建数据库mybatismanytoone并插入数据

create database mybatismanytoone;
use mybatismanytoone;
create table user(
id int(10) unsigned not null auto_increment,
username varchar(64) not null default ‘‘,
mobile int(10) unsigned not null default ‘0‘,
created datetime not null default ‘0000-00-00 00:00:00‘,
primary key(id)
);

INSERT INTO user VALUES (‘1‘, ‘yiibai‘, ‘100‘, ‘2015-09-23 20:11:23‘);

CREATE TABLE post(
  post_id int(10) unsigned NOT NULL AUTO_INCREMENT,
  userid int(10) unsigned NOT NULL,
  title varchar(254) NOT NULL DEFAULT ‘‘,
  content text,
  created datetime NOT NULL DEFAULT ‘0000-00-00 00:00:00‘,
  PRIMARY KEY (post_id)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

INSERT INTO post VALUES (‘1‘, ‘1‘, ‘MyBatis关联数据查询‘, ‘在实际项目中，经常使用关联表的查询，比如：多对一，一对多等。这些查询是如何处理的呢，这一讲就讲这个问题。
我们首先创建一个 post 表，并初始化数据.‘, ‘2015-09-23 21:40:17‘);
INSERT INTO post VALUES (‘2‘, ‘1‘, ‘MyBatis开发环境搭建‘, ‘为了方便学习，这里直接建立java 工程，但一般都是开发 Web 项目。‘, ‘2015-09-23 21:42:14‘);
INSERT INTO post VALUES (‘3‘, ‘2‘, ‘这个是别人发的‘, ‘content,内容...‘, ‘0000-00-00 00:00:00‘);

（2）接着我们创建两个java bean Post.java和User.java

Post.java

package mybatis.bean;

import java.io.Serializable;

public class Post implements Serializable
	private int id;
	private User user;
	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;
	

User.java

package mybatis.bean;

import java.io.Serializable;
import java.util.Date;
import java.util.List;

public class User implements Serializable
	private int id;
	private String username;
	private String mobile;
	private List<Post> posts;

	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 getMobile() 
		return mobile;
	

	public void setMobile(String mobile) 
		this.mobile = mobile;
	

	public List<Post> getPosts() 
		return posts;
	
	public void setPosts(List<Post> posts) 
		this.posts = posts;
	

	@Override
	public String toString() 
		return "User [id=" + id + ", name=" + username + "]";
	

（3）其次，我们创建config/config.xml配置文件

<?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>
<typeAliases>
		<typeAlias alias="User" type="mybatis.bean.User" />
		<typeAlias alias="Post" type="mybatis.bean.Post" />
</typeAliases>
<environments default="development">
	    <environment id="development">
		<transactionManager type="JDBC" />
		<dataSource type="POOLED">
		<property name="driver" value="com.mysql.jdbc.Driver" />
		<property name="url" value="jdbc:mysql://localhost:3306/mybatismanytoone"/>
		<property name="username" value="root"/>
		<property name="password" value="123456"/>
		</dataSource>
		</environment>
</environments>

<mappers>
	    <!-- // power by http://www.yiibai.com -->
	    <mapper resource="mybatis/bean/User.xml" />
</mappers>
</configuration>

（4）再次，我们创建User.xml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="com.mybatis.userMaper">
	<!-- User 级联文章查询 方法配置 (多个文章对一个用户)  -->
	<resultMap type="Post" id="resultPostsMap">
		<result property="id" column="post_id" />
		<result property="title" column="title" />
		<result property="content" column="content" />
		<association property="user" javaType="User">  
	        <id property="id" column="userid"/>   
	        <result property="username" column="username"/>   
	        <result property="mobile" column="mobile"/>   
        </association> 
	</resultMap>

	<select id="getPosts" resultMap="resultPostsMap" parameterType="int">
		SELECT u.*,p.*
		FROM user u, post p
		WHERE u.id=p.userid AND p.post_id=#post_id 
  </select>
</mapper>

（5）最后，我们执行main函数，进行查询

package Main;

import java.io.Reader;

import mybatis.bean.Post;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;


public class Main 
	private static SqlSessionFactory sqlSessionFactory;
	private static Reader reader;

	static 
		try 
			reader = Resources.getResourceAsReader("config/config.xml");
			sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
		 catch (Exception e) 
			e.printStackTrace();
		
	

	public static SqlSessionFactory getSession() 
		return sqlSessionFactory;
	

	/**
	 * @param args
	 */
	public static void main(String[] args) 
		// TODO Auto-generated method stub
		SqlSession session = sqlSessionFactory.openSession();
		try 
			int postId = 1;
			Post post = session.selectOne("com.zk.userMaper", postId); 
			System.out.println("title: "+post.getTitle());
			System.out.println("userName: "+post.getUser().getUsername());
		 finally 
			session.close();
		
	

　查询结果如下图显示：

程序结构如下图所示：