cache artist domains, show artist domains in wiki excerpt on post listing

app/models/artist.rb

@@ -108,13 +108,15 @@ class Artist < ActiveRecord::Base
     end
 
     def domains
-      Post.raw_tag_match(name).pluck(:source).map do |x| 
-        begin
-          map_domain(Addressable::URI.parse(x).domain)
-        rescue Addressable::URI::InvalidURIError
-          nil
-        end
-      end.compact.inject(Hash.new(0)) {|h, x| h[x] += 1; h}
+      Cache.get("artist-domains-#{id}", 1.day) do
+        Post.raw_tag_match(name).pluck(:source).map do |x| 
+          begin
+            map_domain(Addressable::URI.parse(x).domain)
+          rescue Addressable::URI::InvalidURIError
+            nil
+          end
+        end.compact.inject(Hash.new(0)) {|h, x| h[x] += 1; h}.sort {|a, b| b[1] <=> a[1]}
+      end
     end
   end