Question

I have an app that’s a simple clone of reddit. Using Devise you can sign up and submit links and vote on them. I started out trying vote_fu_rails_3 but was having a db issue and some other troubles so I went with my own voting solution which just records the link_id, user_id and has timestamps.

I’m trying to implement a way for the votes on your links to count towards a total ‘karma’ score, ala reddit. Your karma would be your positive votes less your negative votes in total. I’m thinking I need to write a method in the User model (perhaps link model?)

Right now there is no field in the users table for ‘karma’ or ‘link_score’ or anything like that. Maybe adding a simple integer column to the Link table and adding or subtracting to it when it’s voted on would allow me to do this?

Right now to display the number of votes i’m using link.votes.count which may not be correct (maybe it shows total votes and not total as Up – Down).

Github Link

Answer 1

I’m going to use the features of has_many :votes, :through => :links and the sum method.

For additional information check:

• Ruby on Rails Guide on Associations
• Ruby on Rails Guide on Calculations

so here’s the solution:

User Table

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string :name
      t.timestamps
    end
  end

  def self.down
    drop_table :users
  end
end

Links Table

class CreateLinks < ActiveRecord::Migration
  def self.up
    create_table :links do |t|
      t.integer :user_id
      t.string  :url
      t.timestamps
    end
  end

  def self.down
    drop_table :links
  end
end

Vote Table

class CreateVotes < ActiveRecord::Migration
  def self.up
    create_table :votes do |t|
      t.integer :user_id
      t.integer :link_id
      t.integer :score
      t.timestamps
    end
  end

  def self.down
    drop_table :votes
  end
end

User Model

class User < ActiveRecord::Base
  has_many :links
  has_many :votes, :through => :links

  def karma
    self.votes.sum(:score)
  end

  def positive_votes
    self.votes.sum(:score, :conditions => 'score > 0')
  end

  def negative_votes
    self.votes.sum(:score, :conditions => 'score < 0')
  end

end

Link Model

class Link < ActiveRecord::Base
  belongs_to :user
  has_many  :votes
end

Vote Model

class Vote < ActiveRecord::Base
  belongs_to :user
  belongs_to :link
end

The trick is that you set the score to a positive or negative value let’s say “+1” for a positive vote and “-1” for a negative vote. NOTE: Every vote is a record. The sum will be the total score.

How to use:

User.first.karma # gives you total karma
User.first.positive_votes # gives you total positive votes
User.first.negative_votes # gives you total negative votes

There are other features you can use like a vote of a “trusted” user could score +5 or -5 etc. etc.

Enjoy!