mybatis 关联数据的查询多对一一对多_mybatis查询用户年龄最大的那一个用户数据-优快云博客

本文介绍了一个简单的Java程序设计案例，通过两个类User和Article实现用户与文章的一对多关联关系。同时展示了数据库表的创建及初始化数据，并提供了MyBatis中一对多和多对一的数据映射配置。

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创建两个类 User 和 article

package entity;

public class User {

   private int id;
   public User(){

   }
   public User(int id, String userName, String userAge, String userAddress) {
       super();
       this.id = id;
       this.userName = userName;
       this.userAge = userAge;
       this.userAddress = userAddress;
   }
   public int getId() {
       return id;
   }
   public void setId(int id) {
       this.id = id;
   }
   private String userName;
   private String userAge;
   private String userAddress;

   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;
   }

}

package entity;

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;
}
public Article(){

}

public Article(int id, User user, String title, String content) {
   super();
   this.id = id;
   this.user = user;
   this.title = title;
   this.content = content;
}

}

数据库创建代码

Drop TABLE IF EXISTS `article`;
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;

-- ----------------------------
-- 添加几条测试数据
-- ----------------------------
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');

CREATE TABLE `user` (
`id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键',
`userName` varchar(50) DEFAULT NULL COMMENT '名称',
`userAge` int(11) DEFAULT NULL COMMENT '年龄',
`userAddress` varchar(200) DEFAULT NULL COMMENT '地址',
PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8;

INSERT INTO `user` VALUES (1, '查看', 23, '精彩内容');
INSERT INTO `user` VALUES (2, '查看', 23, '精彩内容');
INSERT INTO `user` VALUES (3, '查看', 23, '精彩内容');
INSERT INTO `user` VALUES (4, '查看', 23, '精彩内容');
INSERT INTO `user` VALUES (5, '查看', 23, '精彩内容');

多对一的配置文件编写方式：引入了association元素

<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>

一对多的文件配置方式：

</resultMap>

<!-- User联合文件进行查询方法之二的配置（多对一的方式）--》

</resultMap>

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>