Add scope FederalSubject.order_by_display_name

app/controllers/federal_subjects_controller.rb

@@ -6,7 +6,7 @@ class FederalSubjectsController < ApplicationController
   # GET /federal_subjects
   def index
     authorize :federal_subject
-    @federal_subjects = policy_scope(FederalSubject)
+    @federal_subjects = policy_scope(FederalSubject).order_by_display_name
   end
 
   # GET /federal_subjects/:id

app/models/federal_subject.rb

@@ -1,6 +1,18 @@
 # frozen_string_literal: true
 
 class FederalSubject < ApplicationRecord
+  ##########
+  # Scopes #
+  ##########
+
+  scope :order_by_display_name, lambda { |dir = :asc|
+    if I18n.locale == :ru
+      order(native_name: dir)
+    else
+      order(english_name: dir)
+    end
+  }
+
   ################
   # Associations #
   ################

spec/models/federal_subject_spec.rb

@@ -19,6 +19,82 @@ RSpec.describe FederalSubject do
   it { is_expected.to validate_uniqueness_of :english_name }
   it { is_expected.to validate_uniqueness_of :native_name }
 
+  describe '.order_by_display_name' do
+    let! :federal_subject_1 do
+      create :federal_subject, english_name: '1', native_name: '3'
+    end
+
+    let! :federal_subject_2 do
+      create :federal_subject, english_name: '3', native_name: '5'
+    end
+
+    let! :federal_subject_3 do
+      create :federal_subject, english_name: '4', native_name: '4'
+    end
+
+    let! :federal_subject_4 do
+      create :federal_subject, english_name: '2', native_name: '1'
+    end
+
+    let! :federal_subject_5 do
+      create :federal_subject, english_name: '5', native_name: '2'
+    end
+
+    around do |example|
+      I18n.with_locale locale do
+        example.run
+      end
+    end
+
+    context 'when locale is "en"' do
+      let(:locale) { :en }
+
+      specify do
+        expect(described_class.order_by_display_name).to eq [
+          federal_subject_1,
+          federal_subject_4,
+          federal_subject_2,
+          federal_subject_3,
+          federal_subject_5,
+        ]
+      end
+
+      specify do
+        expect(described_class.order_by_display_name(:desc)).to eq [
+          federal_subject_5,
+          federal_subject_3,
+          federal_subject_2,
+          federal_subject_4,
+          federal_subject_1,
+        ]
+      end
+    end
+
+    context 'when locale is "ru"' do
+      let(:locale) { :ru }
+
+      specify do
+        expect(described_class.order_by_display_name).to eq [
+          federal_subject_4,
+          federal_subject_5,
+          federal_subject_1,
+          federal_subject_3,
+          federal_subject_2,
+        ]
+      end
+
+      specify do
+        expect(described_class.order_by_display_name(:desc)).to eq [
+          federal_subject_2,
+          federal_subject_3,
+          federal_subject_1,
+          federal_subject_5,
+          federal_subject_4,
+        ]
+      end
+    end
+  end
+
   describe '#display_name' do
     subject do
       create :federal_subject, native_name: Faker::Address.unique.state