def [](namespace = :default, index)
      obj = get_setting(namespace, index)
      return obj.read_attribute(setting_value_field) if obj
      SettingsDB::Defaults[namespace, index]
    end
def [](namespace = :default, index)
      obj = get_setting(namespace, index)
      return obj.read_attribute(setting_value_field) if obj
      SettingsDB::Defaults[namespace, index]
    end
:call-seq:
   Model[:key] -> value
   Model[:namespace, :key] -> value

 Returns the value for the given key.
 If a namespace is given then the key lookup is restricted
 to that namespace. Unqualified keys are looked up in the
 +:default+ namespace.