Move promotion-related associations to legacy_promotions

core/app/models/spree/order.rb

@@ -108,8 +108,6 @@ def states
              foreign_key: :order_id,
              dependent: :destroy,
              inverse_of: :order
-    has_many :order_promotions, class_name: 'Spree::OrderPromotion', dependent: :destroy
-    has_many :promotions, through: :order_promotions
 
     # Payments
     has_many :payments, dependent: :destroy, inverse_of: :order

core/spec/models/spree/order_spec.rb

@@ -1806,20 +1806,6 @@ def validate(line_item)
     end
   end
 
-  describe "order deletion" do
-    let(:order) { create(:order) }
-    let(:promotion) { create(:promotion) }
-
-    subject { order.destroy }
-    before do
-      order.promotions << promotion
-    end
-
-    it "deletes join table entries when deleting an order" do
-      expect { subject }.to change { Spree::OrderPromotion.count }.from(1).to(0)
-    end
-  end
-
   describe ".find_by_param" do
     let(:order) { create(:order) }
     let(:param) { order.number }

legacy_promotions/app/decorators/solidus_legacy_promotions/models/spree_order_decorator.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module SolidusLegacyPromotions
+  module SpreeOrderDecorator
+    def self.prepended(base)
+      base.has_many :order_promotions, class_name: 'Spree::OrderPromotion', dependent: :destroy
+      base.has_many :promotions, through: :order_promotions
+    end
+
+    def apply_shipping_promotions(_event = nil)
+      Spree::Config.promotions.shipping_promotion_handler_class.new(self).activate
+      recalculate
+    end
+
+    Spree::Order.prepend(self)
+  end
+end