Use self.ignored_columns += instead of =

This is to accomodate prepended modules.

app/models/application_setting.rb

@@ -24,7 +24,7 @@ class ApplicationSetting < ApplicationRecord
   serialize :domain_blacklist, Array # rubocop:disable Cop/ActiveRecordSerialize
   serialize :repository_storages # rubocop:disable Cop/ActiveRecordSerialize
 
-  self.ignored_columns = %i[
+  self.ignored_columns += %i[
     clientside_sentry_dsn
     clientside_sentry_enabled
     koding_enabled

app/models/ci/build.rb

@@ -17,7 +17,7 @@ module Ci
 
     BuildArchivedError = Class.new(StandardError)
 
-    self.ignored_columns = %i[
+    self.ignored_columns += %i[
       artifacts_file
       artifacts_file_store
       artifacts_metadata

app/models/deploy_key.rb

@@ -10,7 +10,7 @@ class DeployKey < Key
   scope :are_public,  -> { where(public: true) }
   scope :with_projects, -> { includes(deploy_keys_projects: { project: [:route, :namespace] }) }
 
-  self.ignored_columns = %i[can_push]
+  self.ignored_columns += %i[can_push]
 
   accepts_nested_attributes_for :deploy_keys_projects
 

app/models/note.rb

@@ -33,7 +33,7 @@ class Note < ApplicationRecord
     end
   end
 
-  self.ignored_columns = %i[original_discussion_id]
+  self.ignored_columns += %i[original_discussion_id]
 
   cache_markdown_field :note, pipeline: :note, issuable_state_filter_enabled: true
 

app/models/notification_setting.rb

 # frozen_string_literal: true
 
 class NotificationSetting < ApplicationRecord
-
-  self.ignored_columns = %i[events]
+  self.ignored_columns += %i[events]
 
   enum level: { global: 3, watch: 2, participating: 1, mention: 4, disabled: 0, custom: 5 }
 

app/models/user.rb

@@ -23,7 +23,7 @@ class User < ApplicationRecord
 
   DEFAULT_NOTIFICATION_LEVEL = :participating
 
-  self.ignored_columns = %i[
+  self.ignored_columns += %i[
     authentication_token
     email_provider
     external_email

doc/development/what_requires_downtime.md

@@ -50,7 +50,7 @@ places. This can be done by defining the columns to ignore. For example, to igno
 
 ```ruby
 class User < ApplicationRecord
-  self.ignored_columns = %i[updated_at]
+  self.ignored_columns += %i[updated_at]
 end
 ```