查询，无法选择列数 [英] query , can not select column count

问题描述

Tag.joins(:quote_tags).group('quote_tags.tag_id').order('count desc').select('count(tags.id) AS count, tags.id, tags.name')

Build query:
SELECT count(tags.id) AS count, tags.id, tags.name FROM `tags` INNER JOIN `quote_tags` ON `quote_tags`.`tag_id` = `tags`.`id` GROUP BY quote_tags.tag_id ORDER BY count desc

结果：

[#<Tag id: 401, name: "different">, ... , #<Tag id: 4, name: "family">]

不返回计数列为了我。我怎么得到它？

It not return count column for me. How can I get it?

推荐答案

您是否尝试过调用 count 返回的 Tag 对象之一上的方法？仅仅因为检查没有提到 count 并不意味着它不存在。 检查输出：

Have you tried calling the count method on one of the returned Tag objects? Just because inspect doesn't mention the count doesn't mean that it isn't there. The inspect output:

[#<Tag id: 401, name: "different">, ... , #<Tag id: 4, name: "family">]

仅包含 Tag 类知道的内容，而 Tag 仅包含有关内容的信息。 标签表中的列：您只有 id 和 name

will only include things that the Tag class knows about and Tag will only know about the columns in the tags table: you only have id and name in the table so that's all you see.

如果您这样做：

tags = Tag.joins(:quote_tags).group('quote_tags.tag_id').order('count desc').select('count(tags.id) AS count, tags.id, tags.name')

，然后查看计数 s：

tags.map(&:count)

您将看到期望的计数数组。

You'll see the array of counts that you're expecting.

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