mybatis--多对一关联

（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。<br>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();
        }
    }
}