Order-refactoring part II.

app/models/order_article.rb

@@ -34,8 +34,8 @@ class OrderArticle < ActiveRecord::Base
 #
 #  before_validation_on_create :create_new_article
 
-  # This method returns either the Article or the ArticlePrice
-  # The latter will be set, when the the order is finished
+  # This method returns either the ArticlePrice or the Article
+  # The first will be set, when the the order is finished
   def price
     article_price || article
   end
@@ -47,6 +47,39 @@ class OrderArticle < ActiveRecord::Base
     {:quantity => quantity, :price => quantity * price.fc_price}
   end
 
+  # Update quantity/tolerance/units_to_order from group_order_articles
+  def update_results!
+    quantity = group_order_articles.collect(&:quantity).sum
+    tolerance = group_order_articles.collect(&:tolerance).sum
+    update_attributes(:quantity => quantity, :tolerance => tolerance,
+                      :units_to_order => calculate_units_to_order(quantity, tolerance))
+  end
+
+  # Returns how many units of the belonging article need to be ordered given the specified order quantity and tolerance.
+  # This is determined by calculating how many units can be ordered from the given order quantity, using
+  # the tolerance to order an additional unit if the order quantity is not quiet sufficient.
+  # There must always be at least one item in a unit that is an ordered quantity (no units are ever entirely
+  # filled by tolerance items only).
+  #
+  # Example:
+  #
+  # unit_quantity | quantity | tolerance | calculate_units_to_order
+  # --------------+----------+-----------+-----------------------
+  #      4        |    0     |     2     |           0
+  #      4        |    0     |     5     |           0
+  #      4        |    2     |     2     |           1
+  #      4        |    4     |     2     |           1
+  #      4        |    4     |     4     |           1
+  #      4        |    5     |     3     |           2
+  #      4        |    5     |     4     |           2
+  #
+  def calculate_units_to_order(quantity, tolerance = 0)
+    unit_size = price.unit_quantity
+    units = quantity / unit_size
+    remainder = quantity % unit_size
+    units += ((remainder > 0) && (remainder + tolerance >= unit_size) ? 1 : 0)
+  end
+
   private
   
   def article_and_price_exist