nested attributes in controllers concern

app/controllers/clients_controller.rb

 class ClientsController < ApplicationController
+  include NestedAttributes
+
   before_action :set_client, only: [:show, :edit, :update, :destroy]
 
   def index
@@ -59,19 +61,11 @@ class ClientsController < ApplicationController
   end
 
   def client_params
-    params.require(:client).permit(
-      :id, :first_name, :last_name, :date_of_birth, :nationality, :permit, :gender,
-      :street, :zip, :city, :phone, :email, :goals, :education, :hobbies,
+    params.require(:client).permit(:id, :first_name, :last_name, :date_of_birth, :nationality,
+      :permit, :gender, :street, :zip, :city, :phone, :email, :goals, :education, :hobbies,
       :interests, :state, :comments, :competent_authority, :involved_authority, :user_id,
-      language_skills_attributes: [
-        :id, :language, :level, :_destroy
-      ],
-      relatives_attributes: [
-        :id, :first_name, :last_name, :date_of_birth, :relation, :_destroy
-      ],
-      schedules_attributes: [
-        :id, :day, :time, :available
-      ]
-    )
+      language_skills_attributes: language_skills_attributes,
+      relatives_attributes: relatives_attributes,
+      schedules_attributes: schedules_attributes)
   end
 end

app/controllers/concerns/nested_attributes.rb

+module NestedAttributes
+  extend ActiveSupport::Concern
+
+  included do
+    def language_skills_attributes
+      [:id, :language, :level, :_destroy]
+    end
+
+    def relatives_attributes
+      [:id, :first_name, :last_name, :date_of_birth, :relation, :_destroy]
+    end
+
+    def schedules_attributes
+      [:id, :day, :time, :available]
+    end
+  end
+end

app/controllers/volunteers_controller.rb

 class VolunteersController < ApplicationController
+  include NestedAttributes
   before_action :set_volunteer, only: [:show, :edit, :update, :destroy]
 
   def index
@@ -48,14 +49,8 @@ class VolunteersController < ApplicationController
       :education, :motivation, :experience, :expectations, :strengths, :skills, :interests, :state,
       :duration, :man, :woman, :family, :kid, :sport, :creative, :music, :culture, :training,
       :german_course, :adults, :teenagers, :children, :region,
-      language_skills_attributes: [
-        :id, :language, :level, :_destroy
-      ],
-      relatives_attributes: [
-        :id, :first_name, :last_name, :date_of_birth, :relation, :_destroy
-      ],
-      schedules_attributes: [
-        :id, :day, :time, :available
-      ])
+      language_skills_attributes: language_skills_attributes,
+      relatives_attributes: relatives_attributes,
+      schedules_attributes: schedules_attributes)
   end
 end