实战（四）联表查询

1.在数据库新建一个表，并插入数据

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 AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

Insert INTO `article` VALUES ('1', '1', 'test_title', 'test_content');
Insert INTO `article` VALUES ('2', '1', 'test_title_2', 'test_content_2');
Insert INTO `article` VALUES ('3', '1', 'test_title_3', 'test_content_3');
Insert INTO `article` VALUES ('4', '1', 'test_title_4', 'test_content_4');

2.为该表格新建一个类

package com.yihaomen.mybatis.model;

public class Article {
    
    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;
    }

}

3.在Configuration.xml配置改新建的类

<typeAlias alias="Article" type="com.yihaomen.mybatis.model.Article" />

4.在 IUserOperation 接口中，加入 select 对应的id 名称相同的方法：
public List<Article> getUserArticles(int id);

5.<!-- User 联合文章进行查询 方法之一的配置 (多对一的方式)  -->

方法一：    
    <resultMap id="resultUserArticleList" type="Article">
        <id property="id" column="aid" />
        <result property="title" column="title" />
        <result property="content" column="content" />
        
        <association property="user" javaType="User">
            <id property="id" column="id" />
            <result property="userName" column="userName" />
            <result property="userAddress" column="userAddress" />            
        </association>        
    </resultMap>

<select id="getUserArticles" parameterType="int" resultMap="resultUserArticleList">
       select user.id,user.userName,user.userAddress,article.id aid,article.title,article.content from user,article 
              where user.id=article.userid and user.id=#{id}
    </select>

方法二：

<!--之前写好的resultMap User类-->

<resultMap type="User" id="resultListUser">
        <id column="id" property="id" />
        <result column="userName" property="userName" />
        <result column="userAge" property="userAge" />
        <result column="userAddress" property="userAddress" />
    </resultMap>

    <!-- User 联合文章进行查询 方法之二的配置 (多对一的方式) -->    
    <resultMap id="resultUserArticleList-2" type="Article">
        <id property="id" column="aid" />
        <result property="title" column="title" />
        <result property="content" column="content" />        
        <association property="user" javaType="User" resultMap="resultListUser" />             
    </resultMap>
    
    <select id="getUserArticles" parameterType="int" resultMap="resultUserArticleList">
       select user.id,user.userName,user.userAddress,article.id aid,article.title,article.content from user,article 
              where user.id=article.userid and user.id=#{id}
    </select>

6.Test测试类里的调用方法

public void getUserArticles(int userid){
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation=session.getMapper(IUserOperation.class);           
            List<Article> articles = userOperation.getUserArticles(userid);
            for(Article article:articles){
                System.out.println(article.getTitle()+":"+article.getContent()+
                        ":作者是:"+article.getUser().getUserName()+":地址:"+
                         article.getUser().getUserAddress());
            }
        } finally {
            session.close();
        }
    }