Cache Appearance instances in Redis

This caches the result of Appearance.first in a similar fashion to how
ApplicationSetting instances are cached. We also add some NOT NULL
constraints to the table and correct the timestamp types.

Fixes gitlab-org/gitlab-ce#36066, fixes gitlab-org/gitlab-ce#31698

3 files changed, 22 insertions, 2 deletions

diff --git a/app/controllers/admin/appearances_controller.rb b/app/controllers/admin/appearances_controller.rb
index 4b0ec54b3f4..92df1c8dff0 100644
--- a/app/controllers/admin/appearances_controller.rb
+++ b/app/controllers/admin/appearances_controller.rb
@@ -45,7 +45,7 @@ class Admin::AppearancesController < Admin::ApplicationController
 
   # Use callbacks to share common setup or constraints between actions.
   def set_appearance
-    @appearance = Appearance.last || Appearance.new
+    @appearance = Appearance.current || Appearance.new
   end
 
   # Only allow a trusted parameter "white list" through.
diff --git a/app/helpers/appearances_helper.rb b/app/helpers/appearances_helper.rb
index 16136d02530..cdf5fa5d4b7 100644
--- a/app/helpers/appearances_helper.rb
+++ b/app/helpers/appearances_helper.rb
@@ -20,7 +20,7 @@ module AppearancesHelper
   end
 
   def brand_item
-    @appearance ||= Appearance.first
+    @appearance ||= Appearance.current
   end
 
   def brand_header_logo
diff --git a/app/models/appearance.rb b/app/models/appearance.rb
index f9c48482be7..ff15689ecac 100644
--- a/app/models/appearance.rb
+++ b/app/models/appearance.rb
@@ -8,7 +8,27 @@ class Appearance < ActiveRecord::Base
   validates :logo,        file_size: { maximum: 1.megabyte }
   validates :header_logo, file_size: { maximum: 1.megabyte }
 
+  validate :single_appearance_row, on: :create
+
   mount_uploader :logo,         AttachmentUploader
   mount_uploader :header_logo,  AttachmentUploader
   has_many :uploads, as: :model, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+
+  CACHE_KEY = 'current_appearance'.freeze
+
+  after_commit :flush_redis_cache
+
+  def self.current
+    Rails.cache.fetch(CACHE_KEY) { first }
+  end
+
+  def flush_redis_cache
+    Rails.cache.delete(CACHE_KEY)
+  end
+
+  def single_appearance_row
+    if self.class.any?
+      errors.add(:single_appearance_row, 'Only 1 appearances row can exist')
+    end
+  end
 end