Require EnterpriseFee.belongs_to by default

app/models/enterprise_fee.rb

@@ -3,10 +3,12 @@
 class EnterpriseFee < ApplicationRecord
   include CalculatedAdjustments
 
+  self.belongs_to_required_by_default = true
+
   acts_as_paranoid
 
   belongs_to :enterprise
-  belongs_to :tax_category, class_name: 'Spree::TaxCategory'
+  belongs_to :tax_category, optional: true, class_name: 'Spree::TaxCategory'
 
   has_many :coordinator_fees, dependent: :destroy
   has_many :order_cycles, through: :coordinator_fees

db/migrate/20230616055032_require_enterprise_on_enterprise_fee.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class RequireEnterpriseOnEnterpriseFee < ActiveRecord::Migration[7.0]
+  def change
+    change_column_null :enterprise_fees, :enterprise_id, false
+  end
+end

db/schema.rb

@@ -121,7 +121,7 @@ ActiveRecord::Schema[7.0].define(version: 2023_08_09_201542) do
   end
 
   create_table "enterprise_fees", id: :serial, force: :cascade do |t|
-    t.integer "enterprise_id"
+    t.integer "enterprise_id", null: false
     t.string "fee_type", limit: 255
     t.string "name", limit: 255
     t.datetime "created_at", precision: nil, null: false

spec/models/enterprise_fee_spec.rb

@@ -4,7 +4,7 @@ require 'spec_helper'
 
 describe EnterpriseFee do
   describe "associations" do
-    it { is_expected.to belong_to(:enterprise) }
+    it { is_expected.to belong_to(:enterprise).required }
   end
 
   describe "validations" do