Refactor prices

#475

db/migrate/20170423225333_add_zone_to_prices.rb

@@ -0,0 +1,23 @@
+class AddZoneToPrices < ActiveRecord::Migration
+  def up
+    add_reference :prices, :zone, index: true
+    add_foreign_key :prices, :zones
+    assign_zone_to_current_prices
+    change_column :prices, :zone_id, :integer, null: false
+    remove_column :prices, :category, :string
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+
+  private
+
+  def assign_zone_to_current_prices
+    Billing::Price.all.each do |price|
+      zone = DNS::Zone.find_by!(origin: price.category)
+      price.zone = zone
+      price.save!
+    end
+  end
+end