Application settings development

This document provides a development guide for contributors to add application settings to GitLab.

Application settings are stored in the application_settings table. Each setting has its own column and there should only be one row.

Add a new application setting

First of all, you have to decide if it is necessary to add an application setting. Consider our configuration principles when adding a new setting.

To add a new setting, you have to:

• Add a new column to the application_settings table.
• Add the new setting to the list of visible attributes.
• Add the new setting to it to ApplicationSettingImplementation#defaults, if the setting has a default value.
• Add a test for the default value, if the setting has a default value.
• Add a validation for the new field to the ApplicationSetting model.
• Add a model test for the validation and default value
• Find the right view file or create a new one and add a form field to the new setting.
• Update the API documentation. Application settings will automatically be available on the REST API.

Database migration example

class AddNewSetting < Gitlab::Database::Migration[2.1]
  disable_ddl_transaction!

  def up
    with_lock_retries do
      add_column :application_settings, :new_setting, :text, if_not_exists: true
    end

    add_text_limit :application_settings, :new_setting, 255
  end

  def down
    with_lock_retries do
      remove_column :application_settings, :new_setting, if_exists: true
    end
  end
end

Model validation example

validates :new_setting,
          length: { maximum: 255, message: N_('is too long (maximum is %{count} characters)') },
          allow_blank: true