Add project_id to subscriptions

app/models/subscription.rb

 class Subscription < ActiveRecord::Base
   belongs_to :user
+  belongs_to :project
   belongs_to :subscribable, polymorphic: true
 
+  validates :user, :project, :subscribable, presence: true
+
   validates :user_id,
             uniqueness: { scope: [:subscribable_id, :subscribable_type] },
             presence: true

db/migrate/20161031171301_add_project_id_to_subscriptions.rb

+class AddProjectIdToSubscriptions < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    add_column :subscriptions, :project_id, :integer
+    add_foreign_key :subscriptions, :projects, column: :project_id, on_delete: :cascade
+  end
+
+  def down
+    remove_column :subscriptions, :project_id
+  end
+end

db/schema.rb

@@ -1052,6 +1052,7 @@ ActiveRecord::Schema.define(version: 20161109150329) do
     t.boolean "subscribed"
     t.datetime "created_at"
     t.datetime "updated_at"
+    t.integer "project_id"
   end
 
   add_index "subscriptions", ["subscribable_id", "subscribable_type", "user_id"], name: "subscriptions_user_id_and_ref_fields", unique: true, using: :btree
@@ -1250,6 +1251,7 @@ ActiveRecord::Schema.define(version: 20161109150329) do
   add_foreign_key "personal_access_tokens", "users"
   add_foreign_key "protected_branch_merge_access_levels", "protected_branches"
   add_foreign_key "protected_branch_push_access_levels", "protected_branches"
+  add_foreign_key "subscriptions", "projects", on_delete: :cascade
   add_foreign_key "trending_projects", "projects", on_delete: :cascade
   add_foreign_key "u2f_registrations", "users"
 end

spec/models/subscription_spec.rb

+require 'spec_helper'
+
+describe Subscription, models: true do
+  describe 'relationships' do
+    it { is_expected.to belong_to(:project) }
+    it { is_expected.to belong_to(:subscribable) }
+    it { is_expected.to belong_to(:user) }
+  end
+
+  describe 'validations' do
+    it { is_expected.to validate_presence_of(:project) }
+    it { is_expected.to validate_presence_of(:subscribable) }
+    it { is_expected.to validate_presence_of(:user) }
+  end
+end