allow non-shared articles to be part of a shared supplier using a blank order number

app/models/article.rb

@@ -61,7 +61,7 @@ class Article < ActiveRecord::Base
   # false will returned and self.shared_updated_on will be updated
   def shared_article_changed?
     # skip early if the timestamp hasn't changed
-    unless self.shared_updated_on == self.shared_article.updated_on
+    unless self.shared_article.nil? or self.shared_updated_on == self.shared_article.updated_on
       
       # try to convert units
       # convert supplier's price and unit_quantity into fc-size
@@ -106,6 +106,7 @@ class Article < ActiveRecord::Base
   
   # to get the correspondent shared article
   def shared_article
+    self.order_number.blank? and return nil
     @shared_article ||= self.supplier.shared_supplier.shared_articles.find_by_number(self.order_number) rescue nil
   end
   

app/models/supplier.rb

@@ -57,7 +57,9 @@ class Supplier < ActiveRecord::Base
           }
           updated_articles << [article, unequal_attributes]
         end
-      else
+      # Articles with no order number can be used to put non-shared articles
+      # in a shared supplier, with sync keeping them.
+      elsif not article.order_number.blank?
         # article isn't in external database anymore
         outlisted_articles << article
       end

spec/models/article_spec.rb

@@ -105,5 +105,10 @@ describe Article do
       expect(article.unit_quantity).to eq 5
       expect(article.price).to be_within(1e-3).of(shared_article.price/5)
     end
+
+    it 'does not synchronise when it has no order number' do
+      article.update_attributes :order_number => nil
+      expect(supplier.sync_all).to eq [[], []]
+    end
   end
 end