Change migration to respect multiple rows in application settings table

Add cr remarks

db/post_migrate/20200325162730_schedule_backfill_push_rules_id_in_projects.rb

@@ -18,7 +18,10 @@ class ScheduleBackfillPushRulesIdInProjects < ActiveRecord::Migration[6.0]
     # Update one record that is connected to the instance
     value_to_be_updated_to = ScheduleBackfillPushRulesIdInProjects::PushRules.find_by(is_sample: true)&.id
 
-    execute "UPDATE application_settings SET push_rule_id = #{value_to_be_updated_to}" if value_to_be_updated_to
+    if value_to_be_updated_to
+      execute "UPDATE application_settings SET push_rule_id = #{value_to_be_updated_to}
+        WHERE id IN (SELECT MAX(id) FROM application_settings);"
+    end
 
     ApplicationSetting.expire
 

spec/migrations/schedule_backfill_push_rules_id_in_projects_spec.rb

@@ -20,6 +20,20 @@ describe ScheduleBackfillPushRulesIdInProjects do
     expect(setting.push_rule_id).to eq(sample_rule.id)
   end
 
+  it 'adds global rule association to last application settings when there is more than one record without failing' do
+    application_settings = table(:application_settings)
+    setting_old = application_settings.create!
+    setting = application_settings.create!
+    sample_rule = push_rules.create!(is_sample: true)
+
+    Sidekiq::Testing.fake! do
+      disable_migrations_output { migrate! }
+    end
+
+    expect(setting_old.reload.push_rule_id).to be_nil
+    expect(setting.reload.push_rule_id).to eq(sample_rule.id)
+  end
+
   it 'schedules worker to migrate project push rules' do
     rule_1 = push_rules.create!
     rule_2 = push_rules.create!