Create note subscription table and model

app/models/note.rb

@@ -23,6 +23,8 @@ class Note < ApplicationRecord
 
   has_many :comments, -> { left_joins(:author).where(:visible => true, :users => { :status => [nil, "active", "confirmed"] }).order(:created_at) }, :class_name => "NoteComment", :foreign_key => :note_id
   has_many :all_comments, -> { left_joins(:author).order(:created_at) }, :class_name => "NoteComment", :foreign_key => :note_id, :inverse_of => :note
+  has_many :subscriptions, :class_name => "NoteSubscription"
+  has_many :subscribers, :through => :subscriptions, :source => :user
 
   validates :id, :uniqueness => true, :presence => { :on => :update },
                  :numericality => { :on => :update, :only_integer => true }

app/models/note_subscription.rb

@@ -0,0 +1,20 @@
+# == Schema Information
+#
+# Table name: note_subscriptions
+#
+#  user_id :bigint(8)        not null, primary key
+#  note_id :bigint(8)        not null, primary key
+#
+# Indexes
+#
+#  index_note_subscriptions_on_note_id  (note_id)
+#
+# Foreign Keys
+#
+#  fk_rails_...  (note_id => notes.id)
+#  fk_rails_...  (user_id => users.id)
+#
+class NoteSubscription < ApplicationRecord
+  belongs_to :user
+  belongs_to :note
+end

app/models/user.rb

@@ -66,6 +66,8 @@ class User < ApplicationRecord
   has_and_belongs_to_many :changeset_subscriptions, :class_name => "Changeset", :join_table => "changesets_subscribers", :foreign_key => "subscriber_id"
   has_many :note_comments, :foreign_key => :author_id, :inverse_of => :author
   has_many :notes, :through => :note_comments
+  has_many :note_subscriptions, :class_name => "NoteSubscription"
+  has_many :subscribed_notes, :through => :note_subscriptions, :source => :note
 
   has_many :oauth2_applications, :class_name => Doorkeeper.config.application_model.name, :as => :owner
   has_many :access_grants, :class_name => Doorkeeper.config.access_grant_model.name, :foreign_key => :resource_owner_id