java

关注公众号 jb51net

关闭
首页 > 软件编程 > java > MyBatis多表查询

MyBatis多表查询的操作方法注解和XML实现SQL语句

作者：Code哈哈笑

这篇文章主要介绍了MyBatis多表查询的操作方法注解和XML实现SQL语句,本文通过实例代码给大家介绍的非常详细,感兴趣的朋友一起看看吧

1.准备工作

1.1创建数据库

（1）创建数据库：

CREATE DATABASE mybatis_test DEFAULT CHARACTER SET utf8mb4;

（2）使用数据库

-- 使⽤数据数据
USE mybatis_test;

1.2 创建用户表和实体类

创建用户表

-- 创建表[⽤⼾表]
CREATE TABLE `user_info` (
 `id` INT ( 11 ) NOT NULL AUTO_INCREMENT,
 `username` VARCHAR ( 127 ) NOT NULL,
 `password` VARCHAR ( 127 ) NOT NULL,
 `age` TINYINT ( 4 ) NOT NULL,
 `gender` TINYINT ( 4 ) DEFAULT '0' COMMENT '1-男 2-⼥ 0-默认',
 `phone` VARCHAR ( 15 ) DEFAULT NULL,
 `delete_flag` TINYINT ( 4 ) DEFAULT 0 COMMENT '0-正常, 1-删除',
 `create_time` DATETIME DEFAULT now(),
 `update_time` DATETIME DEFAULT now() ON UPDATE now(),
 PRIMARY KEY ( `id` ) 
) ENGINE = INNODB DEFAULT CHARSET = utf8mb4;

添加用户信息

-- 添加⽤⼾信息
INSERT INTO user_info( username, `password`, age, gender, phone )
VALUES ( 'admin', 'admin', 18, 1, '18612340001' );
INSERT INTO user_info( username, `password`, age, gender, phone )
VALUES ( 'zhangsan', 'zhangsan', 18, 1, '18612340002' );
INSERT INTO user_info( username, `password`, age, gender, phone )
VALUES ( 'lisi', 'lisi', 18, 1, '18612340003' );
INSERT INTO user_info( username, `password`, age, gender, phone )
VALUES ( 'wangwu', 'wangwu', 18, 1, '18612340004' );

实体类的属性名与表中的字段名⼀⼀对应

@Data
public class UserInfo {
    private Integer id;
    private String username;
    private String password;
    private Integer age;
    private Integer gender;
    private String phone;
    private Integer deleteFlag;
    private Date createTime;
    private Date updateTime;
}

1.3 创建文章表和实体类

上⾯建了⼀张⽤⼾表, 我们再来建⼀张⽂章表, 进⾏多表关联查询.
⽂章表的uid, 对应⽤⼾表的id.

创建文章表：

-- 创建⽂章表
DROP TABLE IF EXISTS articleinfo;
CREATE TABLE articleinfo (
id INT PRIMARY KEY auto_increment, title VARCHAR ( 100 ) NOT NULL,
content TEXT NOT NULL, uid INT NOT NULL,
delete_flag TINYINT ( 4 ) DEFAULT 0 COMMENT '0-正常, 1-删除',
create_time DATETIME DEFAULT now(), update_time DATETIME DEFAULT now()
) DEFAULT charset 'utf8mb4';

插入数据

-- 插⼊测试数据
INSERT INTO articleinfo ( title, content, uid ) VALUES ( 'Java', 'Java正文', 1
);
INSERT INTO articleinfo ( title, content, uid ) VALUES ( 'MySQL', 'MySQL正文', 1
);
INSERT INTO articleinfo ( title, content, uid ) VALUES ( 'C', 'C正文', 2
);

实体类的属性名与表中的字段名⼀⼀对应

@Data
public class ArticleInfo { 
	private Integer id; 
	private String title; 
	private String content; 
	private Integer uid; 
	private Integer deleteFlag; 
	private Date createTime; 
	private Date updateTime;
}

1.4 配置文件

在Application.yml文件中配置：

# 数据库连接配置
spring:
  datasource:
    # MySQL在远程服务器上
    url: jdbc:mysql://x.x.x.x:3306/mybatis_test?characterEncoding=utf8&useSSL=false
    username: root  #MySQL账号
    password: root  #MySQL密码
    driver-class-name: com.mysql.cj.jdbc.Driver
mybatis:
  configuration: # 配置打印 MyBatis⽇志
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
    map-underscore-to-camel-case: true #配置驼峰⾃动转换
  # 配置 mybatis xml 的⽂件路径，在 resources/mapper 创建所有表的 xml ⽂件
  mapper-locations: classpath:mapper/**Mapper.xml

2.多表查询

2.1 需求: 根据uid查询书的作者等相关信息

2.1.1 注解实现

SQL命令：

SELECT
	a.id,
	a.title,
	a.content,
	a.uid,
	b.username,
	b.age,
	b.gender
FROM
	articleinfo a
	LEFT JOIN user_info b ON a.uid = b.id
WHERE
	a.id =1;

根据查询的结果在ArticleInfo 类补充相关的属性：

@Data
public class ArticleInfo {
	private Integer id;
	private String title;
	private String content;
	private Integer uid;
	private Integer deleteFlag;
	private Date createTime;
	private Date updateTime;
	// 补充⽤⼾相关信息
	private String username;
	private Integer age;
	private Integer gender;
 }

ArticleInfoMapper接口：

@Mapper
public interface ArticleInfoMapper {
    @Select("select a.id,a.title,a.content,a.uid, b.username, b.age, b.gender " + // 注意最后的空格
            "from articleinfo a left join user_info b on a.uid=b.id " +
            "where a.id = #{id}")
    ArticleInfo queryArticleAndUser(Integer id);
}

测试代码：

@Slf4j
@SpringBootTest
class ArticleInfoMapperTest {
    @Autowired
    private ArticleInfoMapper articleInfoMapper;
    @Test
    void queryArticleAndUser() {
        articleInfoMapper.queryArticleAndUser(1);
    }
}

运行结果：

如果名称不⼀致的, 采⽤Results, 或者别名的⽅式解决, 和单表查询⼀样 Mybatis 不分单表还是多表, 主要就是三部分: SQL, 映射关系和实体类

2.1.2 XML实现

SQL命令：

SELECT
	a.id,
	a.title,
	a.content,
	a.uid,
	b.username,
	b.age,
	b.gender
FROM
	articleinfo a
	LEFT JOIN user_info b ON a.uid = b.id
WHERE
	a.id =1;

根据查询的结果在ArticleInfo 类补充相关的属性：

@Data
public class ArticleInfo {
	private Integer id;
	private String title;
	private String content;
	private Integer uid;
	private Integer deleteFlag;
	private Date createTime;
	private Date updateTime;
	// 补充⽤⼾相关信息
	private String username;
	private Integer age;
	private Integer gender;
 }

ArticleInfoMapper接口：

@Mapper
public interface ArticleInfoXMLMapper {
    ArticleInfo queryArticleAndUser(Integer id);
}

ArticleInfoXMLMapper.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="org.example.mybatis.mapper.ArticleInfoXMLMapper">
    <select id ="queryArticleAndUser" resultType="org.example.mybatis.model.ArticleInfo">
        select a.id,a.title,a.content,a.uid, b.username, b.age, b.gender
            from articleinfo a left join user_info b on a.uid=b.id
            where a.id = #{id}
    </select>
</mapper>

测试代码：

@Slf4j
@SpringBootTest
class ArticleInfoXMLMapperTest {
    @Autowired
    private ArticleInfoXMLMapper articleInfoXMLMapper;
    @Test
    void queryArticleAndUser() {
        articleInfoXMLMapper.queryArticleAndUser(1);
    }
}

运行结果：

如果名称不⼀致的, 采⽤ResultMap, 或者别名的⽅式解决, 和单表查询⼀样 Mybatis 不分单表还是多表, 主要就是三部分: SQL, 映射关系和实体类

2.2 需求: 根据user_in的id查询作者创作的书相关信息

2.1.1 注解实现

SQL命令：

SELECT
	b.username,
	b.age,
	b.gender,
	a.id,
	a.title,
	a.content,
	a.uid
FROM
	articleinfo a
	RIGTH JOIN user_info  b ON b.uid = a.id
WHERE
	b.id =1;

根据查询的结果在ArticleInfo 类补充相关的属性：

@Data
public class ArticleInfo {
	private Integer id;
	private String title;
	private String content;
	private Integer uid;
	private Integer deleteFlag;
	private Date createTime;
	private Date updateTime;
	// 补充⽤⼾相关信息
	private String username;
	private Integer age;
	private Integer gender;
 }

ArticleInfoMapper接口：

@Mapper
public interface ArticleInfoMapper {
    @Select("select b.username, b.age,b.gender,a.id,a.title,a.content,a.uid " + // 注意最后的空格
            "from articleinfo a right join user_info b on a.uid=b.id " +
            "where b.id = #{id}")
    List<ArticleInfo> queryArticleAndUser(Integer id);
}

测试代码：

@Slf4j
@SpringBootTest
class ArticleInfoMapperTest {
    @Autowired
    private ArticleInfoMapper articleInfoMapper;
    @Test
    void queryArticleAndUser() {
        articleInfoMapper.queryArticleAndUser(1);
    }
}

运行结果：

如果名称不⼀致的, 采⽤Results, 或者别名的⽅式解决, 和单表查询⼀样 Mybatis 不分单表还是多表, 主要就是三部分: SQL, 映射关系和实体类

2.1.2 XML实现

SQL命令：

SELECT
	b.username,
	b.age,
	b.gender,
	a.id,
	a.title,
	a.content,
	a.uid
FROM
	articleinfo a
	RIGHT JOIN user_info b ON a.uid = b.id
WHERE
	a.id =1;

根据查询的结果在ArticleInfo 类补充相关的属性：

@Data
public class ArticleInfo {
	private Integer id;
	private String title;
	private String content;
	private Integer uid;
	private Integer deleteFlag;
	private Date createTime;
	private Date updateTime;
	// 补充⽤⼾相关信息
	private String username;
	private Integer age;
	private Integer gender;
 }

ArticleInfoMapper接口：

@Mapper
public interface ArticleInfoXMLMapper {
    List<ArticleInfo> queryArticleAndUser(Integer id);
}

ArticleInfoXMLMapper.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="org.example.mybatis.mapper.ArticleInfoXMLMapper">
    <select id ="queryArticleAndUser" resultType="org.example.mybatis.model.ArticleInfo">
        select b.username, b.age, b.gender,a.id,a.title,a.content,a.uid
            from articleinfo a right join user_info b on a.uid=b.id
            where b.id = #{id}
    </select>
</mapper>

测试代码：

@Slf4j
@SpringBootTest
class ArticleInfoXMLMapperTest {
    @Autowired
    private ArticleInfoXMLMapper articleInfoXMLMapper;
    @Test
    void queryArticleAndUser() {
        articleInfoXMLMapper.queryArticleAndUser(1);
    }
}

运行结果：

如果名称不⼀致的, 采⽤ResultMap, 或者别名的⽅式解决, 和单表查询⼀样 Mybatis 不分单表还是多表, 主要就是三部分: SQL, 映射关系和实体类

到此这篇关于MyBatis多表查询的操作方法注解和XML实现SQL语句的文章就介绍到这了,更多相关MyBatis多表查询内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！

您可能感兴趣的文章:
阅读全文