ProductOptionType: Add foreign key constraints

This is a join table, both values must be present and pointing to an
entry in the correct table.

Author: mamhoff

core/app/models/spree/product_option_type.rb

@@ -2,8 +2,8 @@
 
 module Spree
   class ProductOptionType < Spree::Base
-    belongs_to :product, class_name: 'Spree::Product', inverse_of: :product_option_types, touch: true, optional: true
-    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :product_option_types, optional: true
+    belongs_to :product, class_name: 'Spree::Product', inverse_of: :product_option_types, touch: true
+    belongs_to :option_type, class_name: 'Spree::OptionType', inverse_of: :product_option_types
     acts_as_list scope: :product
   end
 end

core/db/migrate/20250604072948_add_fk_to_product_option_types.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class AddFkToProductOptionTypes < ActiveRecord::Migration[7.0]
+  def change
+    add_foreign_key :spree_product_option_types, :spree_products, column: :product_id
+    add_foreign_key :spree_product_option_types, :spree_option_types, column: :option_type_id
+  end
+end