Add column to store group ID in application_settings

Migrations to add a column, foreign key constraint and index into
application_settings table.

app/models/application_setting.rb

@@ -11,6 +11,7 @@ class ApplicationSetting < ApplicationRecord
   add_authentication_token_field :static_objects_external_storage_auth_token
 
   belongs_to :instance_administration_project, class_name: "Project"
+  belongs_to :instance_administrators_group, class_name: "Group"
 
   # Include here so it can override methods from
   # `add_authentication_token_field`

changelogs/unreleased/add-group-id-column.yml

+---
+title: Save Instance Administrators group ID in DB
+merge_request: 22600
+author:
+type: changed

db/migrate/20200103190741_add_column_for_instance_administrators_group.rb

+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddColumnForInstanceAdministratorsGroup < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    add_column :application_settings, :instance_administrators_group_id, :integer
+  end
+end

db/migrate/20200103192859_add_fk_for_instance_administrators_group.rb

+# frozen_string_literal: true
+
+class AddFkForInstanceAdministratorsGroup < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_foreign_key(
+      :application_settings,
+      :namespaces,
+      column: :instance_administrators_group_id,
+      on_delete: :nullify
+    )
+  end
+
+  def down
+    remove_foreign_key :application_settings, column: :instance_administrators_group_id
+  end
+end

db/migrate/20200103192914_add_index_for_instance_administrators_group.rb

+# frozen_string_literal: true
+
+class AddIndexForInstanceAdministratorsGroup < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :application_settings, :instance_administrators_group_id
+  end
+
+  def down
+    remove_concurrent_index :application_settings, :instance_administrators_group_id
+  end
+end

db/schema.rb

@@ -365,9 +365,11 @@ ActiveRecord::Schema.define(version: 2020_01_08_233040) do
     t.text "encrypted_slack_app_verification_token"
     t.string "encrypted_slack_app_verification_token_iv", limit: 255
     t.boolean "updating_name_disabled_for_users", default: false, null: false
+    t.integer "instance_administrators_group_id"
     t.index ["custom_project_templates_group_id"], name: "index_application_settings_on_custom_project_templates_group_id"
     t.index ["file_template_project_id"], name: "index_application_settings_on_file_template_project_id"
     t.index ["instance_administration_project_id"], name: "index_applicationsettings_on_instance_administration_project_id"
+    t.index ["instance_administrators_group_id"], name: "index_application_settings_on_instance_administrators_group_id"
     t.index ["usage_stats_set_by_user_id"], name: "index_application_settings_on_usage_stats_set_by_user_id"
   end
 
@@ -4414,6 +4416,7 @@ ActiveRecord::Schema.define(version: 2020_01_08_233040) do
   add_foreign_key "analytics_repository_file_edits", "projects", on_delete: :cascade
   add_foreign_key "analytics_repository_files", "projects", on_delete: :cascade
   add_foreign_key "application_settings", "namespaces", column: "custom_project_templates_group_id", on_delete: :nullify
+  add_foreign_key "application_settings", "namespaces", column: "instance_administrators_group_id", name: "fk_e8a145f3a7", on_delete: :nullify
   add_foreign_key "application_settings", "projects", column: "file_template_project_id", name: "fk_ec757bd087", on_delete: :nullify
   add_foreign_key "application_settings", "projects", column: "instance_administration_project_id", on_delete: :nullify
   add_foreign_key "application_settings", "users", column: "usage_stats_set_by_user_id", name: "fk_964370041d", on_delete: :nullify