docs: def get_value(cls, value):
          '''Takes the class of the item that we want to
          query, along with a potential instance of that class.
          If the value is an instance of int or basestring, then
          we will treat it like an id for that instance.'''
          if isinstance(value, (basestring, int)):
              value = cls.fetch_by(id=value)
          return value if isinstance(value, cls) else None