ActiveRecord 组和计数得到错误结果

Question

# == Schema Information
#
# Table name: posts
#
#  title      :string
#  published  :boolean
#

执行 Post.group(:title).count(:title)

irb(main):001:0> Post.group(:title).count(:title)
   (1.0ms)  SELECT COUNT("posts"."title") AS count_title, "posts"."title" AS posts_title FROM "posts" GROUP BY "posts"."title"
=> {"2"=>2, "4"=>1, "11"=>3, "3"=>1, "5324"=>1}

cmets 表中的相同函数

# == Schema Information
#
# Table name: comments
#
#  commentable_id   :integer
#  commentable_type :string
#  title            :string
#  body             :text
#  subject          :string
#  user_id          :integer          not null
#  parent_id        :integer
#  lft              :integer
#  rgt              :integer
#  is_name_hide     :boolean          default(FALSE)
#



   irb(main):001:0> Comment.group("commentable_id").count("commentable_id")
       (1.2ms)  SELECT COUNT("comments"."commentable_id") AS count_commentable_id, "comments"."commentable_id" AS comments_commentable_id FROM "comments" GROUP BY "comments"."commentable_id"  ORDER BY "comments"."created_at" DESC
    ActiveRecord::StatementInvalid: PG::GroupingError: ERROR:  column "comments.created_at" must appear in the GROUP BY clause or be used in an aggregate function
    LINE 1: ...s" GROUP BY "comments"."commentable_id"  ORDER BY "comments"...

exec Comment.group("commentable_id").count("commentable_id")

得到错误信息，但是 ORDER BY "cmets"."created_at" DESC 是在哪里生成的？如果我们将此列添加到组中，将得到无异常的结果！ 感谢您的帮助。

Answer 1

我错了

在

class Comment < ActiveRecord::Base
 default_scope { order :created_at => 'DESC' }
...
end

注释掉default_scope { order :created_at => 'DESC' } 将按预期工作