Require associations on DistributorShippingMethod

app/models/distributor_shipping_method.rb

@@ -2,6 +2,8 @@
 
 class DistributorShippingMethod < ApplicationRecord
   self.table_name = "distributors_shipping_methods"
+  self.belongs_to_required_by_default = true
+
   belongs_to :shipping_method, class_name: "Spree::ShippingMethod", touch: true
   belongs_to :distributor, class_name: "Enterprise", touch: true
 end

app/models/enterprise.rb

@@ -63,7 +63,8 @@ class Enterprise < ApplicationRecord
                      inverse_of: :owned_enterprises
   has_many :distributor_payment_methods,
     inverse_of: :distributor, foreign_key: :distributor_id
-  has_many :distributor_shipping_methods, foreign_key: :distributor_id
+  has_many :distributor_shipping_methods,
+    inverse_of: :distributor, foreign_key: :distributor_id
   has_many :payment_methods, through: :distributor_payment_methods
   has_many :shipping_methods, through: :distributor_shipping_methods
   has_many :customers

db/migrate/20230516054745_require_shipping_method_and_distributor_on_distributor_shipping_methods.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class RequireShippingMethodAndDistributorOnDistributorShippingMethods < ActiveRecord::Migration[7.0]
+  def change
+    change_column_null :distributors_shipping_methods, :shipping_method_id, false
+    change_column_null :distributors_shipping_methods, :distributor_id, false
+  end
+end

db/schema.rb

@@ -125,8 +125,8 @@ ActiveRecord::Schema[7.0].define(version: 2023_05_22_120633) do
   end
 
   create_table "distributors_shipping_methods", id: :serial, force: :cascade do |t|
-    t.integer "distributor_id"
-    t.integer "shipping_method_id"
+    t.integer "distributor_id", null: false
+    t.integer "shipping_method_id", null: false
     t.datetime "created_at", precision: nil, null: false
     t.datetime "updated_at", precision: nil, null: false
     t.index ["distributor_id"], name: "index_distributors_shipping_methods_on_distributor_id"