Second part of stock-integration.

Introduced StockArticle and a special page for ordering from stock. StockChanges will be created and the StockArticle.quantity
updated in 'order.close!'.

app/models/stock_article.rb

@@ -0,0 +1,49 @@
+# == Schema Information
+# Schema version: 20090120184410
+#
+# Table name: articles
+#
+#  id                  :integer         not null, primary key
+#  name                :string(255)     default(""), not null
+#  supplier_id         :integer         default(0), not null
+#  article_category_id :integer         default(0), not null
+#  unit                :string(255)     default(""), not null
+#  note                :string(255)
+#  availability        :boolean         default(TRUE), not null
+#  manufacturer        :string(255)
+#  origin              :string(255)
+#  shared_updated_on   :datetime
+#  price               :decimal(, )
+#  tax                 :float
+#  deposit             :decimal(, )     default(0.0)
+#  unit_quantity       :integer         default(1), not null
+#  order_number        :string(255)
+#  created_at          :datetime
+#  updated_at          :datetime
+#  quantity            :decimal(, )     default(0.0)
+#  deleted_at          :datetime
+#  type                :string(255)
+#
+
+class StockArticle < Article
+  has_many :stock_changes
+
+  named_scope :available, :conditions => "quantity > 0"
+
+  # Update the quantity of items in stock
+  def update_quantity!
+    update_attribute :quantity, stock_changes.collect(&:quantity).sum
+  end
+
+  # Check for unclosed orders and substract its ordered quantity
+  def quantity_available(exclude_order = nil)
+    available = quantity
+    for order in Order.stockit.all(:conditions => "state = 'open' OR state = 'finished'")
+      unless order == exclude_order
+        order_article = order.order_articles.first(:conditions => {:article_id => id})
+        available -= order_article.units_to_order if order_article
+      end
+    end
+    available
+  end
+end