Mybatis--其他查询操作和数据库连接池（下下）

news2024/11/15 21:21:32

序

准备工作：

mysql数据库和表的信息更新：

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';

-- 插入测试数据
INSERT INTO articleinfo ( title, content, uid ) VALUES ( '十日游戏', 'snh48群像', 1 );

对应实体类model：

package com.example.zxslzw_mybaties.model;

import lombok.Data;

import java.util.Date;

@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;
    //用户相关的信息
    private String username;
    private Integer gender;
}

1. 多表查询

多表查询和单表查询差不多，只是SQL代码不同，下面是xml的配置文件：

<?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.example.zxslzw_mybaties.mapper.ArticleInfoMapper">
    <select id="selectArticleAndUserById" resultType="com.example.zxslzw_mybaties.model.ArticleInfo">
        select ta.*, tb.username, tb.gender from articleinfo ta
        left join userinfo tb
        on ta.uid = tb.id
        where ta.id = #{id}
    </select>
</mapper>

ArticleInfoMapper接口代码如下：

package com.example.zxslzw_mybaties.mapper;

import com.example.zxslzw_mybaties.model.ArticleInfo;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

@Mapper
public interface ArticleInfoMapper {
    List<ArticleInfo> selectArticleAndUserById(Integer id);
}

测试类代码如下：

package com.example.zxslzw_mybaties.mapper;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import static org.junit.jupiter.api.Assertions.*;
@SpringBootTest
class ArticleInfoMapperTest {
    @Autowired
    private ArticleInfoMapper articleInfoMapper;

    @Test
    void selectArticleAndUserById() {
        System.out.println(articleInfoMapper.selectArticleAndUserById(1));
    }
}

articleInfo和userinfo表如下：