Init Subscription model

app/models/concerns/subscribable.rb

@@ -0,0 +1,7 @@
+module Subscribable
+  extend ActiveSupport::Concern
+
+  included do
+    has_many :subscriptions, as: 'subscribable', dependent: :delete_all
+  end
+end

app/models/subscription.rb

@@ -0,0 +1,8 @@
+class Subscription < ActiveRecord::Base
+  enum status: [ :subscribed, :ignored ]
+
+  belongs_to :user
+  belongs_to :subscribable, polymorphic: true, counter_cache: true
+
+  validates :user, :subscribable, presence: true
+end

app/models/topic.rb

@@ -1,6 +1,7 @@
 class Topic < ActiveRecord::Base
   include Likeable
   include Trashable
+  include Subscribable
 
   belongs_to :user
   has_many :comments, as: 'commentable'

db/migrate/20140104125105_create_topics.rb

@@ -7,6 +7,7 @@ class CreateTopics < ActiveRecord::Migration
       t.float :hot, index: true, default: 0.0
       t.integer :comments_count, default: 0
       t.integer :likes_count, default: 0
+      t.integer :subscriptions_count, default: 0
       t.boolean :trashed, default: false
 
       t.timestamps

db/migrate/20140204164212_create_subscriptions.rb

@@ -0,0 +1,11 @@
+class CreateSubscriptions < ActiveRecord::Migration
+  def change
+    create_table :subscriptions do |t|
+      t.belongs_to :user, index: true
+      t.belongs_to :subscribable, polymorphic: true, index: true
+      t.integer :status, default: 0
+
+      t.timestamps
+    end
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20140204053314) do
+ActiveRecord::Schema.define(version: 20140204164212) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -61,14 +61,27 @@ ActiveRecord::Schema.define(version: 20140204053314) do
 
   add_index "post_likes", ["user_id", "post_id"], name: "index_post_likes_on_user_id_and_post_id", unique: true, using: :btree
 
+  create_table "subscriptions", force: true do |t|
+    t.integer  "user_id"
+    t.integer  "subscribable_id"
+    t.string   "subscribable_type"
+    t.integer  "status",            default: 0
+    t.datetime "created_at"
+    t.datetime "updated_at"
+  end
+
+  add_index "subscriptions", ["subscribable_id", "subscribable_type"], name: "index_subscriptions_on_subscribable_id_and_subscribable_type", using: :btree
+  add_index "subscriptions", ["user_id"], name: "index_subscriptions_on_user_id", using: :btree
+
   create_table "topics", force: true do |t|
     t.integer  "user_id"
     t.string   "title"
     t.text     "content"
-    t.float    "hot",            default: 0.0
-    t.integer  "comments_count", default: 0
-    t.integer  "likes_count",    default: 0
-    t.boolean  "trashed",        default: false
+    t.float    "hot",                 default: 0.0
+    t.integer  "comments_count",      default: 0
+    t.integer  "likes_count",         default: 0
+    t.integer  "subscriptions_count", default: 0
+    t.boolean  "trashed",             default: false
     t.datetime "created_at"
     t.datetime "updated_at"
   end

test/factories/subscriptions.rb

@@ -0,0 +1,6 @@
+FactoryGirl.define do
+  factory :subscription do
+    user
+    association :subscribable, factory: 'topic'
+  end
+end

test/models/subscription_test.rb

@@ -0,0 +1,7 @@
+require 'test_helper'
+
+class SubscriptionTest < ActiveSupport::TestCase
+  # test "the truth" do
+  #   assert true
+  # end
+end