GAE NamedModel - własny klucz w modelu

gistfile1.py

class NamedModel(db.Model):
    """A Model subclass for entities which automatically generate their own key
    names on creation. See documentation for _generate_key function for
    requirements."""

    def __init__(self, *args, **kwargs):
        kwargs['key_name'] = _generate_key(self, kwargs)
        super(NamedModel, self).__init__(*args, **kwargs)
def _generate_key(entity, kwargs):
	"""Generates a key name for the given entity, which was constructed with
	the given keyword args.  The entity must have a KEY_NAME property, which
	can either be a string or a callable.

	If KEY_NAME is a string, the keyword args are interpolated into it.  If
	it's a callable, it is called, with the keyword args passed to it as a
	single dict."""

	# Make sure the class has its KEY_NAME property set
	if not hasattr(entity, 'KEY_NAME'):
		raise RuntimeError, '%s entity missing KEY_NAME property' % (
			entity.entity_type())

	# Make a copy of the kwargs dict, so any modifications down the line don't
	# hurt anything
	kwargs = dict(kwargs)

	# The KEY_NAME must either be a callable or a string.  If it's a callable,
	# we call it with the given keyword args.
	if callable(entity.KEY_NAME):
		return entity.KEY_NAME(kwargs)

	# If it's a string, we just interpolate the keyword args into the string,
	# ensuring that this results in a different string.
	elif isinstance(entity.KEY_NAME, basestring):
		# Try to create the key name, catching any key errors arising from the
		# string interpolation
		try:
			key_name = entity.KEY_NAME % kwargs
		except KeyError:
			raise RuntimeError, 'Missing keys required by %s entity\'s KEY_NAME '\
				'property (got %r)' % (entity.entity_type(), kwargs)

		# Make sure the generated key name is actually different from the
		# template
		if key_name == entity.KEY_NAME:
			raise RuntimeError, 'Key name generated for %s entity is same as '\
				'KEY_NAME template' % entity.entity_type()

		return key_name

	# Otherwise, the KEY_NAME is invalid
	else:
		raise TypeError, 'KEY_NAME of %s must be a string or callable' % (
			entity.entity_type())