Move concern to concerns directory

app/models/concerns/payment_method_distributors.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require 'active_support/concern'
+
+# This concern is used to duplicate the associations distributors and distributor_ids
+#   across payment method and gateway
+#   this fixes the inheritance problem https://github.com/openfoodfoundation/openfoodnetwork/issues/2781
+module PaymentMethodDistributors
+  extend ActiveSupport::Concern
+
+  def self.included(base)
+    base.class_eval do
+      has_and_belongs_to_many :distributors, join_table: 'distributors_payment_methods',
+                                             class_name: 'Enterprise',
+                                             foreign_key: 'payment_method_id',
+                                             association_foreign_key: 'distributor_id'
+    end
+  end
+end

app/models/spree/gateway.rb

@@ -1,10 +1,8 @@
 # frozen_string_literal: true
 
-require 'spree/concerns/payment_method_distributors'
-
 module Spree
   class Gateway < PaymentMethod
-    include Spree::PaymentMethodDistributors
+    include PaymentMethodDistributors
 
     delegate_belongs_to :provider, :authorize, :purchase, :capture, :void, :credit
 

app/models/spree/payment_method.rb

@@ -1,11 +1,9 @@
 # frozen_string_literal: true
 
-require 'spree/concerns/payment_method_distributors'
-
 module Spree
   class PaymentMethod < ActiveRecord::Base
     include Spree::Core::CalculatedAdjustments
-    include Spree::PaymentMethodDistributors
+    include PaymentMethodDistributors
 
     acts_as_taggable
     acts_as_paranoid