Use default_value_for to set default NotificationSetting#level

app/controllers/projects_controller.rb

@@ -106,7 +106,6 @@ class ProjectsController < Projects::ApplicationController
 
           if @membership
             @notification_setting = current_user.notification_settings.find_or_initialize_by(source: @project)
-            @notification_setting.set_defaults unless @notification_setting.persisted?
           end
         end
 

app/models/notification_setting.rb

 class NotificationSetting < ActiveRecord::Base
+  # Notification level
+  # Note: When adding an option, it MUST go on the end of the array.
+  enum level: [:disabled, :participating, :watch, :global, :mention]
+
+  default_value_for :level, NotificationSetting.levels[:global]
+
   belongs_to :user
   belongs_to :source, polymorphic: true
 
@@ -8,9 +14,6 @@ class NotificationSetting < ActiveRecord::Base
   validates :user_id, uniqueness: { scope: [:source_type, :source_id],
                                     message: "already exists in source",
                                     allow_nil: true }
-  # Notification level
-  # Note: When adding an option, it MUST go on the end of the array.
-  enum level: [:disabled, :participating, :watch, :global, :mention]
 
   scope :for_groups, -> { where(source_type: 'Namespace') }
   scope :for_projects, -> { where(source_type: 'Project') }
@@ -19,14 +22,9 @@ class NotificationSetting < ActiveRecord::Base
     setting = find_or_initialize_by(source: source)
 
     unless setting.persisted?
-      setting.set_defaults
       setting.save
     end
 
     setting
   end
-
-  def set_defaults
-    self.level = :global
-  end
 end