Include ItemAdjustments handling in Adjustment class

Currently only applies to shipments, but will later include line items, etc

app/models/spree/adjustment.rb

@@ -47,6 +47,8 @@ module Spree
     validates :label, presence: true
     validates :amount, numericality: true
 
+    after_create :update_adjustable_adjustment_total
+
     state_machine :state, initial: :open do
       event :close do
         transition from: :open, to: :closed
@@ -149,5 +151,11 @@ module Spree
 
       originator_type.constantize.unscoped { super }
     end
+
+    private
+
+    def update_adjustable_adjustment_total
+      Spree::ItemAdjustments.new(adjustable).update if adjustable
+    end
   end
 end

app/models/spree/item_adjustments.rb

@@ -12,7 +12,7 @@ module Spree
     end
 
     def update
-      update_adjustments if item.persisted?
+      update_adjustments if updatable_totals?
       item
     end
 
@@ -31,6 +31,10 @@ module Spree
 
     private
 
+    def updatable_totals?
+      item.persisted? && item.is_a?(Spree::Shipment)
+    end
+
     def tax_adjustments
       (item.respond_to?(:all_adjustments) ? item.all_adjustments : item.adjustments).tax
     end