create the User.admins and User.moderators scopes

app/models/admin_dashboard_data.rb

@@ -12,8 +12,8 @@ def as_json
     @json ||= {
       reports: REPORTS.map { |type| Report.find(type) },
       problems: [rails_env_check, host_names_check, gc_checks, sidekiq_check || clockwork_check, ram_check].compact,
-      admins: User.where(admin: true).count,
-      moderators: User.where(moderator: true).count
+      admins: User.admins.count,
+      moderators: User.moderators.count
     }.merge(
       SiteSetting.version_checks? ? {version_check: DiscourseUpdates.check_version} : {}
     )
@@ -43,4 +43,4 @@ def clockwork_check
   def ram_check
     I18n.t('dashboard.memory_warning') if MemInfo.new.mem_total and MemInfo.new.mem_total < 1_000_000
   end
-end
+end

app/models/post_action.rb

@@ -25,7 +25,7 @@ def self.update_flagged_posts_count
                                            'topics.deleted_at' => nil).count('DISTINCT posts.id')
 
     $redis.set('posts_flagged_count', posts_flagged_count)
-    admins = User.where(admin: true).select(:id).map {|u| u.id}
+    admins = User.admins.select(:id).map {|u| u.id}
     MessageBus.publish('/flagged_counts', { total: posts_flagged_count }, { user_ids: admins })
   end
 

app/models/user.rb

@@ -47,6 +47,9 @@ class User < ActiveRecord::Base
   # This is just used to pass some information into the serializer
   attr_accessor :notification_channel_position
 
+  scope :admins, ->{ where(admin: true) }
+  scope :moderators, ->{ where(moderator: true) }
+
   module NewTopicDuration
     ALWAYS = -1
     LAST_VISIT = -2

lib/admin_constraint.rb

@@ -4,7 +4,7 @@ class AdminConstraint
 
   def matches?(request)
     return false unless request.session[:current_user_id].present?
-    User.where(id: request.session[:current_user_id].to_i).where(admin: true).exists?
+    User.admins.where(id: request.session[:current_user_id].to_i).exists?
   end
 
-end
+end

lib/system_message.rb

@@ -41,7 +41,7 @@ def create(type, params = {})
   # Either returns the system_username user or the first admin.
   def self.system_user
     user = User.where(username_lower: SiteSetting.system_username).first if SiteSetting.system_username.present?
-    user = User.where(admin: true).order(:id).first if user.blank?
+    user = User.admins.order(:id).first if user.blank?
     user
   end