discourse/app/models/category_featured_topic.rb

class CategoryFeaturedTopic < ActiveRecord::Base
  belongs_to :category
  belongs_to :topic

  # Populates the category featured topics
  def self.feature_topics
    transaction do
      Category.all.each do |c|
        feature_topics_for(c)
        CategoryFeaturedUser.feature_users_in(c)
      end
    end
  end

  def self.feature_topics_for(c)
    return if c.blank?

    CategoryFeaturedTopic.transaction do
      CategoryFeaturedTopic.delete_all(category_id: c.id)

      # fake an admin
      admin = User.new
      admin.admin = true
      admin.id = -1

      query = TopicQuery.new(admin, per_page: SiteSetting.category_featured_topics, except_topic_id: c.topic_id, visible: true)
      results = query.list_category(c)
      if results.present?
        results.topic_ids.each_with_index do |topic_id, idx|
          c.category_featured_topics.create(topic_id: topic_id, rank: idx)
        end
      end
    end
  end

end

# == Schema Information
#
# Table name: category_featured_topics
#
#  category_id :integer          not null
#  topic_id    :integer          not null
#  created_at  :datetime         not null
#  updated_at  :datetime         not null
#  rank        :integer          default(0), not null
#  id          :integer          not null, primary key
#
# Indexes
#
#  cat_featured_threads                                    (category_id,topic_id) UNIQUE
#  index_category_featured_topics_on_category_id_and_rank  (category_id,rank)
#