Ruby on rails PostgreSQL-GROUPBY子句或在聚合函数中使用（错误）

我正在关注rails的这段视频： . 在Postgres上使用my Rails 3.2应用程序进行标记。

除了标签云功能外，一切都很完美。由于某些原因，云功能在使用Heroku的生产环境中不起作用

我收到这个错误

ActionView::Template::Error (PGError: ERROR:  column "tags.id" must appear 

in the GROUP BY clause or be used in an aggregate function

def tag_cloud(tags, classes)
  max = tags.sort_by(&:count).last
  tags.each do |tag|
    index = tag.count.to_f / Integer(max.count) * (classes.size - 1)
    yield(tag, classes[index.round])
  end
end

我知道错误来自于在Heroku中使用Postgres，但我不知道如何修复它。我已经在下面发布了我的代码

Rails新手…请帮助：）

视图

##The error occurs here..

  <div id="tag_cloud">
    <% tag_cloud Dailypost.tag_counts, %w[s m l] do |tag, css_class| %>
      <%= link_to tag.name, tag_path(tag.name), class: css_class %>
    <% end %>
  </div>

class Tag < ActiveRecord::Base
  attr_accessible :name
  has_many :taggings
  has_many :dailyposts, through: :taggings
end

class Tagging < ActiveRecord::Base
  attr_accessible :dailypost_id, :tag_id

  belongs_to :tag
  belongs_to :dailypost
end

class Dailypost < ActiveRecord::Base  
  attr_accessible :title, :content, :content_html, :tag_list
  belongs_to :user

  has_many :taggings
  has_many :tags, through: :taggings

  def self.tagged_with(name)
    Tag.find_by_name!(name).dailyposts
  end

  ##I know i have to change the method below, but I do not understand how...Please Help

  def self.tag_counts
    Tag.select("tags.*, count(taggings.tag_id) as count").
      joins(:taggings).group("taggings.tag_id")
  end

  def tag_list
    tags.map(&:name).join(", ")
  end

  def tag_list=(names)
    self.tags = names.split(",").map do |n|
      Tag.where(name: n.strip).first_or_create!
    end
  end

end


class User < ActiveRecord::Base
  attr_accessible :name, :email, :password, :password_confirmation

  has_many :dailyposts, dependent: :destroy

end

这解决了我的问题：）

每日邮报模式

def self.tag_counts
  Tag.select("tags.id, tags.name,count(taggings.tag_id) as count").
    joins(:taggings).group("taggings.tag_id, tags.id, tags.name")
end    

应用程序助手

ActionView::Template::Error (PGError: ERROR:  column "tags.id" must appear 

in the GROUP BY clause or be used in an aggregate function

def tag_cloud(tags, classes)
  max = tags.sort_by(&:count).last
  tags.each do |tag|
    index = tag.count.to_f / Integer(max.count) * (classes.size - 1)
    yield(tag, classes[index.round])
  end
end