remove rails-observers

Rails yanked out observers many many years ago, instead the functionality
was yanked out to a gem that is very lightly maintained.

For example: if we want to upgrade to rails 5 there is no published gem

Internally the usage of observers had quite a few problem.

The series of refactors renamed a bunch of classes to give us more clarity
and removed some magic.

Gemfile

@@ -9,7 +9,6 @@ end
 if rails_master?
   gem 'arel', git: 'https://github.com/rails/arel.git'
   gem 'rails', git: 'https://github.com/rails/rails.git'
-  gem 'rails-observers', git: 'https://github.com/rails/rails-observers.git'
   gem 'seed-fu', git: 'https://github.com/SamSaffron/seed-fu.git', branch: 'discourse'
 else
   # Rails 5 is going to ship with Action Cable, we have no use for it as
@@ -29,8 +28,6 @@ else
   # gem 'railties'
   # gem 'sprockets-rails'
   gem 'rails', '~> 4.2'
-
-  gem 'rails-observers'
   gem 'seed-fu', '~> 2.3.5'
 end
 

Gemfile.lock

@@ -260,8 +260,6 @@ GEM
       rails-deprecated_sanitizer (>= 1.0.1)
     rails-html-sanitizer (1.0.3)
       loofah (~> 2.0)
-    rails-observers (0.1.2)
-      activemodel (~> 4.0)
     rails_multisite (1.0.6)
       rails (> 4.2, < 5)
     railties (4.2.7.1)
@@ -453,7 +451,6 @@ DEPENDENCIES
   rack-mini-profiler
   rack-protection
   rails (~> 4.2)
-  rails-observers
   rails_multisite
   rake
   rb-fsevent

app/models/anon_site_json_cache_observer.rb

@@ -1,12 +0,0 @@
-class AnonSiteJsonCacheObserver < ActiveRecord::Observer
-  observe :category, :post_action_type, :user_field, :group
-
-  def after_destroy(object)
-    Site.clear_anon_cache!
-  end
-
-  def after_save(object)
-    Site.clear_anon_cache!
-  end
-
-end

app/models/category.rb

@@ -6,6 +6,7 @@ class Category < ActiveRecord::Base
   include Positionable
   include HasCustomFields
   include CategoryHashtag
+  include AnonCacheInvalidator
 
   belongs_to :topic, dependent: :destroy
   belongs_to :topic_only_relative_url,

app/models/concerns/anon_cache_invalidator.rb

@@ -0,0 +1,13 @@
+module AnonCacheInvalidator
+  extend ActiveSupport::Concern
+
+  included do
+    after_destroy do
+      Site.clear_anon_cache!
+    end
+
+    after_save do
+      Site.clear_anon_cache!
+    end
+  end
+end

app/models/group.rb

@@ -1,5 +1,6 @@
 class Group < ActiveRecord::Base
   include HasCustomFields
+  include AnonCacheInvalidator
 
   has_many :category_groups, dependent: :destroy
   has_many :group_users, dependent: :destroy

app/models/post_action.rb

@@ -23,6 +23,8 @@ class PostAction < ActiveRecord::Base
   after_save :update_counters
   after_save :enforce_rules
   after_save :create_user_action
+  after_save :update_notifications
+  after_create :create_notifications
   after_commit :notify_subscribers
 
   def disposed_by_id
@@ -281,7 +283,7 @@ SQL
       post_action.recover!
       action_attrs.each { |attr, val| post_action.send("#{attr}=", val) }
       post_action.save
-      PostAlertObserver.after_create_post_action(post_action)
+      PostActionNotifier.post_action_created(post_action)
     else
       post_action = create(where_attrs.merge(action_attrs))
       if post_action && post_action.errors.count == 0
@@ -460,6 +462,16 @@ SQL
     end
   end
 
+  def update_notifications
+    if self.deleted_at.present?
+      PostActionNotifier.post_action_deleted(self)
+    end
+  end
+
+  def create_notifications
+    PostActionNotifier.post_action_created(self)
+  end
+
   def notify_subscribers
     if (is_like? || is_flag?) && post
       post.publish_change_to_clients! :acted

app/models/post_action_type.rb

@@ -5,6 +5,8 @@ class PostActionType < ActiveRecord::Base
   after_save :expire_cache
   after_destroy :expire_cache
 
+  include AnonCacheInvalidator
+
   def expire_cache
     ApplicationSerializer.expire_cache_fragment!("post_action_types")
     ApplicationSerializer.expire_cache_fragment!("post_action_flag_types")

app/models/post_revision.rb

@@ -6,6 +6,8 @@ class PostRevision < ActiveRecord::Base
 
   serialize :modifications, Hash
 
+  after_create :create_notification
+
   def self.ensure_consistency!
     # 1 - fix the numbers
     PostRevision.exec_sql <<-SQL
@@ -34,6 +36,10 @@ class PostRevision < ActiveRecord::Base
     update_column(:hidden, false)
   end
 
+  def create_notification
+    PostActionNotifier.after_create_post_revision(self)
+  end
+
 end
 
 # == Schema Information

app/models/user_field.rb

@@ -1,4 +1,7 @@
 class UserField < ActiveRecord::Base
+
+  include AnonCacheInvalidator
+
   validates_presence_of :name, :description, :field_type
   has_many :user_field_options, dependent: :destroy
   accepts_nested_attributes_for :user_field_options

app/services/post_action_notifier.rb

@@ -1,27 +1,18 @@
-class PostAlertObserver < ActiveRecord::Observer
+class PostActionNotifier
-  observe :post_action, :post_revision
+
+  def self.disable
+    @disabled = true
+  end
+
+  def self.enable
+    @disabled = false
+  end
 
   def self.alerter
     @alerter ||= PostAlerter.new
   end
 
-  def alerter
+  def self.refresh_like_notification(post, read)
-    self.class.alerter
-  end
-
-  # Dispatch to an after_save_#{class_name} method
-  def after_save(model)
-    method_name = callback_for('after_save', model)
-    send(method_name, model) if respond_to?(method_name)
-  end
-
-  # Dispatch to an after_create_#{class_name} method
-  def after_create(model)
-    method_name = callback_for('after_create', model)
-    send(method_name, model) if respond_to?(method_name)
-  end
-
-  def refresh_like_notification(post, read)
     return unless post && post.user_id
 
     usernames = post.post_actions.where(post_action_type_id: PostActionType.types[:like])
@@ -49,7 +40,10 @@ class PostAlertObserver < ActiveRecord::Observer
     end
   end
 
-  def after_save_post_action(post_action)
+  def self.post_action_deleted(post_action)
+
+    return if @disabled
+
     # We only care about deleting post actions for now
     return if post_action.deleted_at.blank?
 
@@ -74,7 +68,10 @@ class PostAlertObserver < ActiveRecord::Observer
     end
   end
 
-  def self.after_create_post_action(post_action)
+  def self.post_action_created(post_action)
+
+    return if @disabled
+
     # We only notify on likes for now
     return unless post_action.is_like?
 
@@ -91,11 +88,10 @@ class PostAlertObserver < ActiveRecord::Observer
     )
   end
 
-  def after_create_post_action(post_action)
+  def self.after_create_post_revision(post_revision)
-    self.class.after_create_post_action(post_action)
+
-  end
+    return if @disabled
 
-  def after_create_post_revision(post_revision)
     post = post_revision.post
 
     return unless post
@@ -113,10 +109,4 @@ class PostAlertObserver < ActiveRecord::Observer
     )
   end
 
-  protected
-
-    def callback_for(action, model)
-      "#{action}_#{model.class.name.underscore.gsub(/.+\//, '')}"
-    end
-
 end

config/application.rb

@@ -80,11 +80,6 @@ module Discourse
       config.assets.precompile << "locales/#{file.match(/([a-z_A-Z]+\.js)\.erb$/)[1]}"
     end
 
-    # Activate observers that should always be running.
-    config.active_record.observers = [
-        :post_alert_observer,
-    ]
-
     # Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
     # Run "rake -D time" for a list of tasks for finding time zone names. Default is UTC.
     config.time_zone = 'UTC'

spec/components/post_creator_spec.rb

@@ -5,7 +5,6 @@ require 'topic_subtype'
 describe PostCreator do
 
   before do
-    ActiveRecord::Base.observers.enable :all
   end
 
   let(:user) { Fabricate(:user) }

spec/components/post_destroyer_spec.rb

@@ -4,7 +4,6 @@ require 'post_destroyer'
 describe PostDestroyer do
 
   before do
-    ActiveRecord::Base.observers.enable :all
     UserActionCreator.enable
   end
 

spec/controllers/user_actions_controller_spec.rb

@@ -9,7 +9,6 @@ describe UserActionsController do
     end
 
     it 'renders list correctly' do
-      ActiveRecord::Base.observers.enable :all
       UserActionCreator.enable
       post = Fabricate(:post)
 

spec/models/category_user_spec.rb

@@ -68,7 +68,6 @@ describe CategoryUser do
 
   context 'integration' do
     before do
-      ActiveRecord::Base.observers.enable :all
       NotificationEmailer.enable
     end
 

spec/models/directory_item_spec.rb

@@ -20,7 +20,6 @@ describe DirectoryItem do
 
   context 'refresh' do
     before do
-      ActiveRecord::Base.observers.enable :all
       UserActionCreator.enable
     end
 

spec/models/notification_spec.rb

@@ -2,7 +2,6 @@ require 'rails_helper'
 
 describe Notification do
   before do
-    ActiveRecord::Base.observers.enable :all
     NotificationEmailer.enable
   end
 
@@ -235,7 +234,6 @@ describe Notification do
   describe 'ensure consistency' do
     it 'deletes notifications if post is missing or deleted' do
 
-      ActiveRecord::Base.observers.disable :all
       NotificationEmailer.disable
 
       p = Fabricate(:post)

spec/models/post_action_spec.rb

@@ -220,7 +220,9 @@ describe PostAction do
   describe 'when a user likes something' do
 
     it 'should generate notifications correctly' do
-      ActiveRecord::Base.observers.enable :all
+
+      PostActionNotifier.enable
+
       PostAction.act(codinghorror, post, PostActionType.types[:like])
       expect(Notification.count).to eq(1)
 

spec/models/post_mover_spec.rb

@@ -31,8 +31,6 @@ describe PostMover do
     before do
       p1.replies << p3
       p2.replies << p4
-      # add a like to a post, enable observers so we get user actions
-      ActiveRecord::Base.observers.enable :all
       UserActionCreator.enable
       @like = PostAction.act(another_user, p4, PostActionType.types[:like])
     end

spec/models/post_timing_spec.rb

@@ -81,8 +81,7 @@ describe PostTiming do
     # integration test
 
     it 'processes timings correctly' do
-
+      PostActionNotifier.enable
-      ActiveRecord::Base.observers.enable :all
 
       post = Fabricate(:post)
       user2 = Fabricate(:coding_horror, created_at: 1.day.ago)

spec/models/site_spec.rb

@@ -3,9 +3,6 @@ require_dependency 'site'
 
 describe Site do
   it "omits categories users can not write to from the category list" do
-
-    ActiveRecord::Base.observers.enable :anon_site_json_cache_observer
-
     category = Fabricate(:category)
     user = Fabricate(:user)
 

spec/models/tag_user_spec.rb

@@ -68,12 +68,7 @@ describe TagUser do
   end
 
   context "integration" do
-    before do
-      ActiveRecord::Base.observers.enable :all
-    end
-
     let(:user) { Fabricate(:user) }
-
     let(:watched_tag) { Fabricate(:tag) }
     let(:muted_tag)   { Fabricate(:tag) }
     let(:tracked_tag) { Fabricate(:tag) }

spec/models/topic_spec.rb

@@ -429,7 +429,6 @@ describe Topic do
       let(:actions) { topic.user.user_actions }
 
       it "should set up actions correctly" do
-        ActiveRecord::Base.observers.enable :all
         UserActionCreator.enable
 
         expect(actions.map{|a| a.action_type}).not_to include(UserAction::NEW_TOPIC)

spec/models/topic_user_spec.rb

@@ -208,7 +208,6 @@ describe TopicUser do
 
     context 'private messages' do
       it 'should ensure recepients and senders are watching' do
-        ActiveRecord::Base.observers.enable :all
 
         target_user = Fabricate(:user)
         post = create_post(archetype: Archetype.private_message, target_usernames: target_user.username);

spec/models/user_action_spec.rb

@@ -3,7 +3,6 @@ require 'rails_helper'
 describe UserAction do
 
   before do
-    ActiveRecord::Base.observers.enable :all
     UserActionCreator.enable
   end
 
@@ -51,6 +50,8 @@ describe UserAction do
     end
 
     it 'includes the events correctly' do
+      PostActionNotifier.enable
+
       mystats = stats_for_user(user)
       expecting = [UserAction::NEW_TOPIC, UserAction::NEW_PRIVATE_MESSAGE, UserAction::GOT_PRIVATE_MESSAGE, UserAction::BOOKMARK].sort
       expect(mystats).to eq(expecting)

spec/rails_helper.rb

@@ -104,9 +104,7 @@ Spork.prefork do
       #
       # $redis = DiscourseMockRedis.new
       #
-      # disable all observers, enable as needed during specs
+      PostActionNotifier.disable
-      #
-      ActiveRecord::Base.observers.disable :all
       SearchIndexer.disable
       UserActionCreator.disable
       NotificationEmailer.disable

spec/services/post_action_notifier_spec.rb

@@ -1,10 +1,10 @@
 require 'rails_helper'
 require_dependency 'post_destroyer'
 
-describe PostAlertObserver do
+describe PostActionNotifier do
 
   before do
-    ActiveRecord::Base.observers.enable :post_alert_observer
+    PostActionNotifier.enable
   end
 
   let!(:evil_trout) { Fabricate(:evil_trout) }

spec/services/post_alerter_spec.rb

@@ -63,8 +63,7 @@ describe PostAlerter do
 
   context 'edits' do
     it 'notifies correctly on edits' do
-
+      PostActionNotifier.enable
-      ActiveRecord::Base.observers.enable :all
 
       post = Fabricate(:post, raw: 'I love waffles')
 
@@ -89,7 +88,7 @@ describe PostAlerter do
   context 'likes' do
 
     it 'notifies on likes after an undo' do
-      ActiveRecord::Base.observers.enable :all
+      PostActionNotifier.enable
 
       post = Fabricate(:post, raw: 'I love waffles')
 
@@ -101,7 +100,7 @@ describe PostAlerter do
     end
 
     it 'notifies on does not notify when never is selected' do
-      ActiveRecord::Base.observers.enable :all
+      PostActionNotifier.enable
 
       post = Fabricate(:post, raw: 'I love waffles')
 
@@ -110,12 +109,11 @@ describe PostAlerter do
 
       PostAction.act(evil_trout, post, PostActionType.types[:like])
 
-
       expect(Notification.where(post_number: 1, topic_id: post.topic_id).count).to eq(0)
     end
 
     it 'notifies on likes correctly' do
-      ActiveRecord::Base.observers.enable :all
+      PostActionNotifier.enable
 
       post = Fabricate(:post, raw: 'I love waffles')