Merge pull request activeadmin#30 from profmaad/master

Make activeadmin-mongoid play nice with ActiveRecord Resources

Author: elia

lib/active_admin/mongoid/helpers/collection.rb

@@ -1,8 +1,15 @@
 module ActiveAdmin
   module Helpers
     module Collection
+
+      alias original_collection_size collection_size
+      original_collection_size = instance_method(:collection_size)
       def collection_size(collection=collection)
-        collection.count(true)
+        if(not collection.empty? and collection.first.class.included_modules.include?(Mongoid::Document))
+          collection.count(true)
+        else
+          original_collection_size(collection)
+        end
       end
     end
   end