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, 28 insertions, 0 deletions

diff --git a/lib/banzai/renderer.rb b/lib/banzai/renderer.rb
index a4ae27eefd8..6924a293da8 100644
--- a/lib/banzai/renderer.rb
+++ b/lib/banzai/renderer.rb
@@ -31,6 +31,34 @@ module Banzai
       end
     end
 
+    # Convert a Markdown-containing field on an object into an HTML-safe String
+    # of HTML. This method is analogous to calling render(object.field), but it
+    # can cache the rendered HTML in the object, rather than Redis.
+    #
+    # The context to use is learned from the passed-in object by calling
+    # #banzai_render_context(field), and cannot be changed. Use #render, passing
+    # it the field text, if a custom rendering is needed. The generated context
+    # is returned along with the HTML.
+    def render_field(object, field)
+      html_field = object.markdown_cache_field_for(field)
+
+      html = object.__send__(html_field)
+      return html if html.present?
+
+      html = cacheless_render_field(object, field)
+      object.update_column(html_field, html) unless object.new_record? || object.destroyed?
+
+      html
+    end
+
+    # Same as +render_field+, but without consulting or updating the cache field
+    def cacheless_render_field(object, field)
+      text = object.__send__(field)
+      context = object.banzai_render_context(field)
+
+      cacheless_render(text, context)
+    end
+
     # Perform multiple render from an Array of Markdown String into an
     # Array of HTML-safe String of HTML.
     #