Introduced StockChange. Implemented first part of stockit-logic with updating article's quantity.

db/migrate/20090115232435_create_stock_changes.rb

@@ -0,0 +1,17 @@
+class CreateStockChanges < ActiveRecord::Migration
+  def self.up
+    create_table :stock_changes do |t|
+      t.references :delivery
+      t.references :order
+      t.references :article
+      t.decimal :quantity, :precision => 6, :scale => 2, :default => 0.0
+      t.datetime :created_at
+    end
+
+    add_column :articles, :quantity, :decimal, :precision => 6, :scale => 2, :default => 0.0
+  end
+
+  def self.down
+    drop_table :stock_changes
+  end
+end