MyBatisPlus多表分页查询及遇到的坑（分页插件查询COUNT(1)和LIMIT ?,? 都正确，但返回数据错误）

深藏阁楼爱情的钟 2021-09-01 09:19 1103阅读 0赞

## 1.遇到的坑===》分页插件查询COUNT(1)和LIMIT ?,? 都正确，但返回数据错误 ##

**问题回溯：**

**1.1创建多表数据对应VO**

@Data
    @AllArgsConstructor
    @NoArgsConstructor
    public class ArticleVO { 
    
        private Article article;
        private String tName;
        private User user;
    }

**1.2XML**

<resultMap id="ArticleVOMap" type="com.dxf.userservice.entity.vo.ArticleVO">
                <result column="t_name" property="tName" />
            <association property="article" javaType="com.dxf.userservice.entity.Article">
                <id column="a_id" property="aId" />
                <result column="a_title" property="aTitle" />
                <result column="a_cont" property="aCont" />
                <result column="a_html" property="aHtml" />
                <result column="a_good" property="aGood" />
                <result column="a_look" property="aLook" />
                <result column="t_id" property="tId" />
                <result column="u_id" property="uId" />
                <result column="a_time" property="aTime" />
            </association>
    
            <association property="user" javaType="com.dxf.userservice.entity.User">
                <id column="u_id" property="uId" />
                <result column="username" property="username" />
                <result column="password" property="password" />
                <result column="nick_name" property="nickName" />
                <result column="sex" property="sex" />
                <result column="school" property="school" />
                <result column="img" property="img" />
                <result column="date" property="date" />
                <result column="login" property="login" />
                <result column="openid" property="openid" />
            </association>
        </resultMap>
    
        <sql id="columns">
           a.a_id,a.a_title,a.a_cont,a.a_good,a.a_look,a.a_time,a.t_id,t.t_name,u.u_id,u.nick_name,u.img
        </sql>
    
        <select id="selectArticleVOListPage" resultMap="ArticleVOMap">
            select
            <include refid="columns" />
            from article a,user u,type t
            <where>
                a.u_id=u.u_id and a.t_id=t.t_id
                <if test="uid!='' and uid!=null">
                    and u.u_id = #{ uid}
                </if>
                <if test="tid!='' and tid!=null">
                    and t.t_id = #{ tid}
                </if>
                <if test="title!='' and title!=null">
                   and a.a_title like concat('%', #{ title}, '%')
                </if>
            </where>
            order by a.a_look DESC
        </select>

**1.3mapper**

import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
    
    public interface ArticleMapper extends BaseMapper<Article> { 
    
        Page<ArticleVO> selectArticleVOListPage(Page pagination,
                                                @Param("uid") String uid,
                                                @Param("tid") String tid,
                                                @Param("title") String title);
    }

**1.4使用**

public ResultJson getHomeData() { 
            Page<ArticleVO> page=new Page<>(1,8);
            return ResultJson.ok().data("data",
                    baseMapper.selectArticleVOListPage(page,"","",""));
        }

**Page page=new Page<>(1,8);  
查询的总量和对应的分页数据都是正确地，但是返回的数据却一直不对，没有8条那么多。**  
![在这里插入图片描述][20200812191423472.png_pic_left]  
![在这里插入图片描述][20200812191803534.png_pic_left]  
**为此我找了很多资料，浪费了一个下午的时间,才发现返回的数据有一个特殊地方！他们的tName没有重复的，但是对象类型里却有重复的数据，我猜想MyBatisPlus在存值的时候把string类型tName相同的值覆盖了（或者丢弃），于是我试着把tName直接使用对象存。**

public class ArticleVO { 
    
        private Article article;
        private Type type;
        private User user;
    }

## 2.结果 ##

**如我所猜想的MyBatisPlus在存值的时候把string类型tName相同的值覆盖了（或者丢弃）导致最后的数据有问题，修改过后返回的数据就正确了。**

[20200812191423472.png_pic_left]: /images/20210813/28831b5aab2c4da3bc23d8a80c59aa1c.png
[20200812191803534.png_pic_left]: /images/20210813/5adcc51ad79947818d9ca49778fc3daa.png