Add markdown cache columns to the database, but don't use them yet

This commit adds a number of _html columns and, with the exception of Note,
starts updating them whenever the content of their partner fields changes.

Note has a collision with the note_html attr_accessor; that will be fixed later

A background worker for clearing these cache columns is also introduced - use
`rake cache:clear` to set it off. You can clear the database or Redis caches
separately by running `rake cache:clear:db` or `rake cache:clear:redis`,
respectively.

1 files changed, 10 insertions, 0 deletions

diff --git a/app/models/snippet.rb b/app/models/snippet.rb
index 8a1730f3f36..2373b445009 100644
--- a/app/models/snippet.rb
+++ b/app/models/snippet.rb
@@ -1,11 +1,21 @@
 class Snippet < ActiveRecord::Base
   include Gitlab::VisibilityLevel
   include Linguist::BlobHelper
+  include CacheMarkdownField
   include Participable
   include Referable
   include Sortable
   include Awardable
 
+  cache_markdown_field :title, pipeline: :single_line
+  cache_markdown_field :content
+
+  # If file_name changes, it invalidates content
+  alias_method :default_content_html_invalidator, :content_html_invalidated?
+  def content_html_invalidated?
+    default_content_html_invalidator || file_name_changed?
+  end
+
   default_value_for :visibility_level, Snippet::PRIVATE
 
   belongs_to :author, class_name: 'User'