PostgreSQL - group by子句或用于聚合函数中（错误）

Question

我正在关注此导演视频： http://railscasts.com/episodes/382-tagging。 在Postgres上使用我的Rails 3.2应用程序进行标记。

除标签云功能外，一切都很完美。出于某种原因，云功能在使用Heroku的Production中不起作用。

我得到这个错误

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

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

我知道错误来自于Heroku的使用的是Postgres，但我不知道如何解决它。我已经在下面发布了我的代码。

新来的Rails ....请帮助:)

VIEWS

##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> 

模型

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 

SCHEMA

ActiveRecord::Schema.define(:version => 20130728204128) do 

    create_table "dailyposts", :force => true do |t| 
    t.string "title" 
    t.text  "content" 
    t.text  "content_html" 
    t.integer "user_id" 
    t.integer "to_id" 
    t.datetime "created_at",   :null => false 
    t.datetime "updated_at",   :null => false 
    t.string "photo_file_name" 
    t.string "photo_content_type" 
    t.integer "photo_file_size" 
    end 

    add_index "dailyposts", ["user_id", "created_at"], :name => "index_dailyposts_on_user_id_and_created_at" 

    create_table "taggings", :force => true do |t| 
    t.integer "tag_id" 
    t.integer "dailypost_id" 
    t.datetime "created_at", :null => false 
    t.datetime "updated_at", :null => false 
    end 

    add_index "taggings", ["dailypost_id"], :name => "index_taggings_on_dailypost_id" 
    add_index "taggings", ["tag_id"], :name => "index_taggings_on_tag_id" 

    create_table "tags", :force => true do |t| 
    t.string "name" 
    t.datetime "created_at", :null => false 
    t.datetime "updated_at", :null => false 
    end 

    create_table "users", :force => true do |t| 
    t.string "name" 
    t.string "email" 
    t.datetime "created_at",        :null => false 
    t.datetime "updated_at",        :null => false 
    t.string "password_digest" 
    t.string "remember_token" 
    t.string "password_reset_token" 
    t.datetime "password_reset_sent_at" 
    end 

    add_index "users", ["email"], :name => "index_users_on_email", :unique => true 
    add_index "users", ["remember_token"], :name => "index_users_on_remember_token" 
    add_index "users", ["username"], :name => "index_users_on_username", :unique => true 

end 

Answer 1

这解决了我的问题:)

Dailypost型号

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  

AplicationHelper

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