Mybatis如何将另一个表中的列映射到字符串列表? [英] Mybatis How to map a column from another table to a String list?

问题描述

我有一张桌子t_comment和一张桌子t_comment_photo.

I have a table t_comment, and a table t_comment_photo.

t_comment具有列ID，内容； t_comment_photo具有列ID，comment_id，photo_url. t_comment_pohto包含评论照片的网址，一个评论可以包含0到许多评论照片.

t_comment has column id, content; t_comment_photo has column id, comment_id, photo_url. t_comment_pohto contains the url of comment photos, a comment can have 0 to many comment photos.

这些是他们的java类:

These are their java classes:

public class ToyComment {
    private Integer id;
    private String content;
    private List<String> urls;
    ...
}
public class CommentPhoto {
    private Integer id;
    private String commentId;
    private String comment_url;
    ...
}

这是映射器中的<select>内容:

<select id="getToyCommentList"
    resultType="com.domain.ToyComment">
    c.id, c.content,p.user_photo_url userPhoto
    from t_comment c left join t_comment_photo p
    on c.id = p.comment_id
</select>

当我尝试将从表t_comment_photo查询的userPhoto映射到Java类ToyComment内的列表元素时，出现错误.

When I try to map the userPhoto queried from table t_comment_photo to a element of the list inside the java class ToyComment, I am getting errors.

我要修复的resultMap是:

The resultMap I am trying to fix is:

<resultMap id="ToyCommentResultMap" type="com.domain.ToyComment">
        <result column="id" jdbcType="VARCHAR" property="id" />
        <result column="content" jdbcType="VARCHAR" property="content" />
        <!-- <result property="urls"  jdbcType="VARCHAR" javaType="java.util.ArrayList" column="userPhoto" /> -->
        <collection property="urls" javaType="list" jdbcType="VARCHAR"  column="userPhoto"></collection>
    </resultMap> 

我同时尝试了<property>和<collection>，但是都没有用.

I tried both <property> and <collection>, but neither are working.

使用<collection>时，出现映射语句集合已经包含com.toy.mapper.ToyCommentMapper.getToyCommentListByToyId的值"错误，当我使用<result>时，出现未为属性userPhotos找到类型处理程序". 为javaType使用"java.util.ArrayList"或"list"不会更改输出错误.

When I used <collection>, I got "Mapped Statements collection already contains value for com.toy.mapper.ToyCommentMapper.getToyCommentListByToyId" error, when I used <result>, I got "No typehandler found for property userPhotos". Use "java.util.ArrayList" or "list" for javaType doesn't change the output error.

我尝试搜索"mybatis映射到字符串列表"，但是大多数都与映射到对象列表有关.

I tried to search for "mybatis map to string list", but most are about mapping to a list of objects.

如何正确解决?

推荐答案

结果图应如下所示:

<resultMap id="ToyCommentResultMap" type="com.domain.ToyComment">
  <id column="id" property="id" />
  <result column="content" property="content" />
  <collection property="urls" javaType="list"
    ofType="string">
    <result column="userPhoto" />
  </collection>
</resultMap>

一些注意事项:

• 使用<collection />时指定<id />.它可以提高效率，在某些情况下是必需的.
• 在<select />中，您需要指定resultMap而不是resultType(显然).
• 这是一个棘手的案例，我们添加了

• Specify <id /> when using <collection />. It improves efficiency and is required in some cases.
• In <select />, you need to specify resultMap instead of resultType (obviously).
• This is a tricky case and we have added an FAQ entry just recently.

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