mybatis--一对多关联

今天来介绍mybatis的一对多关联

（1）首先创建数据库mybatisonetomany，并创建数据库表post和user，并向其中插入一定的数据：

create database mybatisonetomany;

use mybatisonetomany;
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)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

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');

插入数据后，表数据如下所示：

（2）其次，在mybatis.bean目录下创建两个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）第三步配置config.xml文件，放在config文件夹下：

<?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/mybatisonetomany"/>
		<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）配置User.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.zk.userMaper">
	<!-- User 级联文章查询 方法配置 (一个用户对多个文章)  -->

	<resultMap type="User" id="resultUserMap">
		<result property="id" column="user_id" />
		<result property="username" column="username" />
		<result property="mobile" column="mobile" />
		<collection property="posts" ofType="mybatis.bean.Post" column="userid">
			<id property="id" column="post_id" javaType="int" jdbcType="INTEGER"/>
            <result property="title" column="title" javaType="string" jdbcType="VARCHAR"/>
            <result property="content" column="content" javaType="string" jdbcType="VARCHAR"/>
		</collection>
	</resultMap>

	<select id="getUser" resultMap="resultUserMap" parameterType="int">
		SELECT u.*,p.*
		FROM user u, post p
		WHERE u.id=p.userid AND id=#{user_id}
  </select>

</mapper>

（5）最后构建Main.java

package MainApp;

import java.io.Reader;
import java.text.MessageFormat;
import java.util.List;

import mybatis.bean.Post;
import mybatis.bean.User;

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 userid = 1;
			User user = session.selectOne("com.zk.userMaper.getUser", 1);
		     System.out.println("username: "+user.getUsername()+",");
                     List<Post> posts = user.getPosts();
                     for(Post p : posts) {
                         System.out.println("Title:" + p.getTitle());
                         System.out.println("Content:" + p.getContent());
                      }
		 } finally {
			session.close();
		 }
	}
}

　运行结果如下：

程序结构如下：