Starring items with redis

item.rb

class Item < ActiveRecord::Base
  def stars
   User.find star_ids
  end
  
  def stars_count
    $redis.scard redis_key(:stars)
  end

private

  def star_ids
    $redis.smembers redis_key(:stars)
  end

  def redis_key(column)
    "#{self.class.table_name}:#{id}:#{column}"
  end
end

items_controller.rb

class ItemsController < ApplicationController
  before_action :authenticate, :set_item
  
  def show
    @item = Item.find(params[:id])
  end

  def star
    current_user.star! @item
  end

  def unstar
    current_user.unstar! @item
  end

  private

  def authenticate
    redirect_to signin_url unless signed_in?
  end

  def set_item
    @item = Item.find(params[:id])
  end
end

redis.rb

$redis = Redis.new(host: 'localhost', port: 6379)

routes.rb

MyApp::Application.routes.draw do
  resources :items do
    member do
      post 'star'
      delete 'unstar'
    end
  end
end

show.html.erb

<article>
  <% if signed_in? %>
    <% if current_user.star? @item %>
      <%= buttton_to 'Unstar', unstar_item_path(@item), method: :delete %>
    <% else %>
      <%= buttton_to 'Star', star_item_path(@item) %>
    <% end %>
  <% end %>

  <h1><%= @item.name %></h1>
  <%= simple_format @item.description %>
</article>

user.rb

class User < ActiveRecord::Base
  def star!(item)
    $redis.multi do
      $redis.sadd(redis_key(:stars), item.id)
      $redis.sadd(item.redis_key(:stars), id)
    end
  end

  def unstar!(item)
    $redis.multi do
      $redis.srem(redis_key(:stars), item.id)
      $redis.srem(item.redis_key(:stars), id)
    end
  end

  def stars
    Item.find star_ids
  end

  def star?(item)
    $redis.sismember(redis_key(:stars), item.id)
  end

  def stars_count
    $redis.scard redis_key(:stars)
  end
  
private  

  def star_ids
    $redis.smembers redis_key(:stars)
  end

  def redis_key(column)
    "#{self.class.table_name}:#{id}:#{column}"
  end
end