enable actions for multi (group) orders and ordergroup invoices

app/models/multi_group_order.rb

@@ -1,21 +1,21 @@
 class MultiGroupOrder < ApplicationRecord
   belongs_to :multi_order
-  has_many :group_orders, dependent: :nullify
-
-  after_destroy :delete_ordergroup_invoices
-
-  def ordergroup_invoice
-    #TODO: delete if deleted
-    group_orders.joins(:ordergroup_invoice).first&.ordergroup_invoice
-  end
+  has_many :group_orders
+  has_one :ordergroup_invoice, dependent: :destroy
 
   def ordergroup
-    ordergroup_invoice&.ordergroup
+    group_orders.first&.ordergroup
   end
 
-  private
+  def price
+    group_orders.map(&:price).sum
+  end
 
-  def delete_ordergroup_invoices
-    ordergroup_invoice&.destroy
+  def group_order_invoice
+    ordergroup_invoice
+  end
+
+  def order
+    multi_order
   end
 end