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, 7 insertions, 0 deletions

diff --git a/spec/models/snippet_spec.rb b/spec/models/snippet_spec.rb
index e6bc5296398..f62f6bacbaa 100644
--- a/spec/models/snippet_spec.rb
+++ b/spec/models/snippet_spec.rb
@@ -46,6 +46,13 @@ describe Snippet, models: true do
     end
   end
 
+  describe "#content_html_invalidated?" do
+    let(:snippet) { create(:snippet, content: "md", content_html: "html", file_name: "foo.md") }
+    it "invalidates the HTML cache of content when the filename changes" do
+      expect { snippet.file_name = "foo.rb" }.to change { snippet.content_html_invalidated? }.from(false).to(true)
+    end
+  end
+
   describe '.search' do
     let(:snippet) { create(:snippet) }