Change relationship of invoices #390

This change will allow us to have invoices for more than one order/delivery
in the future. There are no UI changes for now.

app/models/delivery.rb

@@ -1,7 +1,7 @@
 class Delivery < ActiveRecord::Base
 
   belongs_to :supplier
-  has_one :invoice
+  belongs_to :invoice
   has_many :stock_changes, -> { includes(:stock_article).order('articles.name ASC') }, :dependent => :destroy
 
   scope :recent, -> { order('created_at DESC').limit(10) }

app/models/invoice.rb

@@ -1,9 +1,9 @@
 class Invoice < ActiveRecord::Base
 
   belongs_to :supplier
-  belongs_to :delivery
-  belongs_to :order
   belongs_to :created_by, :class_name => 'User', :foreign_key => 'created_by_user_id'
+  has_many :deliveries
+  has_many :orders
 
   validates_presence_of :supplier_id
   validates_numericality_of :amount, :deposit, :deposit_credit

app/models/order.rb

@@ -9,9 +9,9 @@ class Order < ActiveRecord::Base
   has_many :group_orders, :dependent => :destroy
   has_many :ordergroups, :through => :group_orders
   has_many :users_ordered, :through => :ordergroups, :source => :users
-  has_one :invoice
   has_many :comments, -> { order('created_at') }, :class_name => "OrderComment"
   has_many :stock_changes
+  belongs_to :invoice
   belongs_to :supplier
   belongs_to :updated_by, :class_name => 'User', :foreign_key => 'updated_by_user_id'
   belongs_to :created_by, :class_name => 'User', :foreign_key => 'created_by_user_id'