Merge branch 'prevent-creating-multiple-application-settings' into 'master'

Prevent creating multiple ApplicationSetting by forcing it to always have id=1

Closes #34728

See merge request gitlab-org/gitlab-ce!14718

app/models/application_setting.rb

@@ -33,6 +33,8 @@ class ApplicationSetting < ActiveRecord::Base
 
   attr_accessor :domain_whitelist_raw, :domain_blacklist_raw
 
+  default_value_for :id, 1
+
   validates :uuid, presence: true
 
   validates :session_expire_delay,

changelogs/unreleased/prevent-creating-multiple-application-settings.yml

+---
+title: Prevent creating multiple ApplicationSetting instances
+merge_request:
+author:
+type: fixed

spec/models/application_setting_spec.rb

@@ -222,6 +222,16 @@ describe ApplicationSetting do
     end
   end
 
+  context 'restrict creating duplicates' do
+    before do
+      described_class.create_from_defaults
+    end
+
+    it 'raises an record creation violation if already created' do
+      expect { described_class.create_from_defaults }.to raise_error(ActiveRecord::RecordNotUnique)
+    end
+  end
+
   context 'restricted signup domains' do
     it 'sets single domain' do
       setting.domain_whitelist_raw = 'example.com'