Refactored ordering part two. Integrated stock order.

app/models/order_article.rb

@@ -99,6 +99,13 @@ class OrderArticle < ActiveRecord::Base
     end
   end
 
+  # Units missing for the next full unit_quantity of the article
+  def missing_units
+    units = article.unit_quantity - ((quantity  % article.unit_quantity) + tolerance)
+    units = 0 if units < 0
+    units
+  end
+
   private
   
   def article_and_price_exist