如何在Ruby on Rails中获得未投票数

Question

I am using Thumbs_up gem for creating vote function. I have 3 tables - Post, User and Vote where Post is acts_as_voteable and User is acts_as_voter .

Model Post.rb

class Post < ActiveRecord::Base
  attr_accessible :title, :content, :user_type
  acts_as_voteable
  validates_presence_of :title,:content
  default_scope order: 'posts.created_at DESC'
end

Model Vote.rb

class Vote < ActiveRecord::Base
    scope :for_voter, lambda { |*args| where(["voter_id = ? AND voter_type = ?", args.first.id, args.first.class.base_class.name]) }
    scope :for_voteable, lambda { |*args| where(["voteable_id = ? AND voteable_type = ?", args.first.id, args.first.class.base_class.name]) }
    scope :recent, lambda { |*args| where(["created_at > ?", (args.first || 2.weeks.ago)]) }
    scope :descending, order("created_at DESC")
    belongs_to :voteable, :polymorphic => true
    belongs_to :voter, :polymorphic => true
    attr_accessible :vote, :voter, :voteable

end

Model User.rb

class User < ActiveRecord::Base
   attr_accessible :name, :email, :password, :password_confirmation
   has_secure_password
   acts_as_voter
   has_many :posts, dependent: :destroy
end

Now I want to count posts number which are NOT VOTED . I am trying to do like this..

<%= Post.joins(:votes).where("dont_know_how_to_write_condition").count %>

Any help?? Thanks in advance

Answer 1

I am not sure if this will work in sqlite, it should on postgresql though.

  def self.not_voted
    joins("left outer join votes on votes.voteable_id = posts.id").
    where("votes.id is null")
  end

Then:

Post.not_voted.count

Answer 2

There are ways to do that condition in SQL with NOT EXISTS but they are very heavy queries. If this si going to be an action facing the public or performed multiple times, it might be too heavy to do it like that. I would recommend you to denormalize the tables and include a count of votes on the post. Just use an observer on vote creation and deletion to update the vote count for the post. The query then would be like

Post.where('votecount = 0')

This query is much lighter and scalable than the previous one