=============
后端_最热标签
=============

每个标签对应一到多篇文章，所对应文章的数量即为该标签的热度。

1 标签数据访问

1.1 标签数据访问接口

/ysdblog-api/src/main/java/com/weihome/ysdblog/dao/mapper/TagMapper.java：

public interface TagMapper extends BaseMapper<Tag> {
    ...
    /**
     * 查询最热标签ID列表
     */
    public List<Long> findHottestTagIds(int limit);
    /**
     * 根据标签ID列表查询标签列表
     */
    public List<Tag> findTagsByTagIds(List<Long> tagIds);
    ...
}

1.2 标签数据访问实现

SQL> select tag_id from t_article_tag group by tag_id order by count(*) desc limit 5

SQL> select id, tag_name from t_tag where id in (2, 1)

/src/main/resources/com/weihome/ysdblog/dao/mapper/TagMapper.xml：

...
<mapper namespace="com.weihome.ysdblog.dao.mapper.TagMapper">
    ...
    <!-- List<Long> findHottestTagIds(int limit) -->
    <select id="findHottestTagIds" parameterType="int"
            resultType="java.lang.Long">
        select tag_id from t_article_tag group by tag_id
        order by count(*) desc limit #{limit}
    </select>
    <!-- List<Tag> findTagsByTagIds(List<Long> tagIds) -->
    <select id="findTagsByTagIds" parameterType="list"
            resultType="com.weihome.ysdblog.dao.pojo.Tag">
        select id, tag_name as tagName from t_tag
        where id in
        <foreach collection="tagIds" item="tagId" separator=","
                 open="(" close=")">
            #{tagId}
        </foreach>
    </select>
    ...
</mapper>

2 标签服务

2.1 标签服务接口

/ysdblog-api/src/main/java/com/weihome/ysdblog/service/TagService.java：

public interface TagService {
    ...
    /**
     * 查询最热标签
     */
    public Result hottest(int limit);
    ...
}

2.2 标签服务实现

/ysdblog-api/src/main/java/com/weihome/ysdblog/service/impl/TagServiceImpl.java：

...
public class TagServiceImpl implements TagService {
    ...
    @Override
    public Result hottest(int limit) {
        List<Long> tagIds = tagMapper.findHottestTagIds(limit);
        if (CollectionUtils.isEmpty(tagIds))
            return Result.success(Collections.emptyList());

        List<Tag> tags = tagMapper.findTagsByTagIds(tagIds);
        return Result.success(copyList(tags));
    }
    ...
}

3 标签控制器

/ysdblog-api/src/main/java/com/weihome/ysdblog/controller/TagController.java：

@RestController
@RequestMapping("tag")
public class TagController {
    @Autowired
    private TagService tagService;
    /**
     * 查询最热标签
     */
    @GetMapping("hottest")
    public Result hottest() {
        return tagService.hottest(5);
    }
}

4 运行测试

Postman
    GET
        localhost:8888/tag/hottest
----------------------------------
{
    "success": true,
    "code": 200,
    "msg": "success",
    "data": [
        {
            "id": 1,
            "tagName": "tag_a"
        },
        {
            "id": 2,
            "tagName": "tag_b"
        }
    ]
}