1 files changed, 76 insertions, 0 deletions
diff --git a/lib/gitlab/database/migration_helpers/cascading_namespace_settings.rb b/lib/gitlab/database/migration_helpers/cascading_namespace_settings.rb
new file mode 100644
index 00000000000..eecf96acb30
--- /dev/null
+++ b/lib/gitlab/database/migration_helpers/cascading_namespace_settings.rb
@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module MigrationHelpers
+      module CascadingNamespaceSettings
+        include Gitlab::Database::MigrationHelpers
+
+        # Creates the four required columns that constitutes a single cascading
+        # namespace settings attribute. This helper is only appropriate if the
+        # setting is not already present as a non-cascading attribute.
+        #
+        # Creates the `setting_name` column along with the `lock_setting_name`
+        # column in both `namespace_settings` and `application_settings`.
+        #
+        # This helper is not reversible and must be defined in conjunction with
+        # `remove_cascading_namespace_setting` in separate up and down directions.
+        #
+        # setting_name - The name of the cascading attribute - same as defined
+        #                in `NamespaceSetting` with the `cascading_attr` method.
+        # type - The column type for the setting itself (:boolean, :integer, etc.)
+        # options - Standard Rails column options hash. Accepts keys such as
+        #           `null` and `default`.
+        #
+        # `null` and `default` options will only be applied to the `application_settings`
+        # column. In most cases, a non-null default value should be specified.
+        def add_cascading_namespace_setting(setting_name, type, **options)
+          lock_column_name = "lock_#{setting_name}".to_sym
+
+          check_cascading_namespace_setting_consistency(setting_name, lock_column_name)
+
+          namespace_options = options.merge(null: true, default: nil)
+
+          with_lock_retries do
+            add_column(:namespace_settings, setting_name, type, namespace_options)
+            add_column(:namespace_settings, lock_column_name, :boolean, default: false, null: false)
+          end
+
+          add_column(:application_settings, setting_name, type, options)
+          add_column(:application_settings, lock_column_name, :boolean, default: false, null: false)
+        end
+
+        def remove_cascading_namespace_setting(setting_name)
+          lock_column_name = "lock_#{setting_name}".to_sym
+
+          with_lock_retries do
+            remove_column(:namespace_settings, setting_name) if column_exists?(:namespace_settings, setting_name)
+            remove_column(:namespace_settings, lock_column_name) if column_exists?(:namespace_settings, lock_column_name)
+          end
+
+          remove_column(:application_settings, setting_name) if column_exists?(:application_settings, setting_name)
+          remove_column(:application_settings, lock_column_name) if column_exists?(:application_settings, lock_column_name)
+        end
+
+        private
+
+        def check_cascading_namespace_setting_consistency(setting_name, lock_name)
+          existing_columns = []
+
+          %w(namespace_settings application_settings).each do |table|
+            existing_columns << "#{table}.#{setting_name}" if column_exists?(table.to_sym, setting_name)
+            existing_columns << "#{table}.#{lock_name}" if column_exists?(table.to_sym, lock_name)
+          end
+
+          return if existing_columns.empty?
+
+          raise <<~ERROR
+          One or more cascading namespace columns already exist. `add_cascading_namespace_setting` helper
+          can only be used for new settings, when none of the required columns already exist.
+          Existing columns: #{existing_columns.join(', ')}
+          ERROR
+        end
+      end
+    end
+  end
+end