create_table "posts", :force => true do |t|
    t.integer  "user_id"
    t.text     "content"
    t.integer  "upvotes",    :default => 0
    t.integer  "downvotes",  :default => 0
    t.datetime "created_at",                :null => false
    t.datetime "updated_at",                :null => false
  end

create_table "votes", :force => true do |t|
    t.integer  "user_id"
    t.integer  "post_id"
    t.integer  "vote",       :default => 0
    t.datetime "created_at",                :null => false
    t.datetime "updated_at",                :null => false
  end

post_reputation = post.upvotes - post.downvotes

def calculate_post_reputation(post_id)
  some_post = Post.find(post_id)
  vote_count = 0
  some_post.votes.each do |vote|
    if vote.vote.to_i == 2
      vote_count += 1
    elsif vote.vote.to_i == 1
      vote_count -= 1
    end
   end
  vote_count
end

Models:

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

class Post < ActiveRecord::Base
  has_many :votes
  has_many :users, :though => :votes

class Vote < ActiveRecord::Base
  belongs_to :user
  belongs_to :post
  attr_accessor :direction
  UP='Up'
  DOWN='Down'
  DIRECTIONS=[UP,DOWN]
  validates_inclusion_of :direction, in: [DIRECTIONS]
  scope :up_votes where(:direction => UP)
  scope :down_votes where(:direction => DOWN)