ruby

#models/item.rb
class Item < ActiveRecord::Base
  attr_accessible :item_votes_count, :name, :price, :taobaoke_url, :original_url, :topic_id, :image, :image_cache, :remote_image_url
  belongs_to :topic, counter_cache: true
  belongs_to :user
  has_many :item_votes, dependent: :destroy

  validates :name, :taobaoke_url, :topic_id, :original_url, presence: true
  validates :price, presence: true, numericality: true

  mount_uploader :image, ItemImageUploader
  store_in_background :image

  scope :order_by_votes, order('item_votes_count desc')
  scope :order_by_create_time, order('created_at desc')

  def vote(by)
    return false unless by
    return false if voted_by?(by)
    item_votes.create!(vote: 1, user_id: by.id)
  end

  def voted_by?(user)
    return false unless user
    !item_votes.by_user(user).size.zero?
  end

  def votes(options = {})
    reload = options[:reload]
    reload ? item_votes.count : item_votes.size
  end

end

#uploaders/item_image_uploader.rb
class ItemImageUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick
  include CarrierWave::Backgrounder::Delay

  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end
  # Create different versions of your uploaded files:
  version :s250x300 do
    process resize_to_fill: [250, 300]
  end

  version :s100 do
    process resize_to_fill: [100, 100]
  end
end


#models/topic.rb
class Topic < ActiveRecord::Base
  attr_accessible :desc, :items_count, :name, :button_name, :user_id, :image, :image_cache
  has_many :items, dependent: :destroy
  belongs_to :user, counter_cache: true

  validates :name, :button_name, :user_id, presence: true

  mount_uploader :image, TopicImageUploader
  store_in_background :image

end


#controllers/topics_controller.rb
class TopicsController < ApplicationController
  load_and_authorize_resource
  before_filter :require_login, except: [:index, :show]

  def index
    count = params[:count] ? params[:count].to_i : 12
    page = params[:page] ? params[:page].to_i : 1
    @topics = Topic.page(page).per(count)

    respond_to do |format|
        format.html # index.html.erb
      format.json { render json: @topics }
    end
  end


#views/topics/index.html.erb
<header class="header">
<a href="/"><span class="logo"></span></a>
<%= link_to('New Topic', new_topic_path) if can? :create, Topic %>
</header>

<section class="wrapper">
  <ul class="topic-list">
    <% @topics.each do |topic| %>
      <li>
        <a href="<%= topic_path(topic) %>">
          <h3 class="topic-list-title"><%= topic.name %></h3>
          <div class="topic-list-imgs">
            <% items = topic.items.order_by_votes.first(9) %>
            <% if !items.empty? %>
            <ul>
              <% items.each do |item| %>
                <li>
                  <img src="<%= item.image_url(:s100) %>" alt="<%= topic.name %>">
                </li>
              <% end %>
            </ul>
            <% else %>
              <img src="<%= topic.image_url(:s300) %>" alt="<%= topic.name %>">
            <% end %>
          </div>
        </a>
      </li>
    <% end -%>
  </ul>
  <%= paginate @topics %>
</section>