'Set order of query result.
To use descending order, prepend \'-\' (minus) to the property
name, e.g., \'-date\' rather than \'date\'.
Args:
property: Property to sort on.
Returns:
Self to support method chaining.
Raises:
PropertyError if invalid property is provided.'

def order(self, property):

    if property.startswith('-'):
        property = property[1:]
        order = datastore.Query.DESCENDING
    else:
        order = datastore.Query.ASCENDING
    if (self._model_class is None):
        if ((property != datastore_types.KEY_SPECIAL_PROPERTY) or (order != datastore.Query.ASCENDING)):
            raise BadQueryError(('Only    %s    ascending    orders    are    supported    on    kindless    queries' % datastore_types.KEY_SPECIAL_PROPERTY))
    else:
        if (not issubclass(self._model_class, Expando)):
            if ((property not in self._model_class._all_properties) and (property not in datastore_types._SPECIAL_PROPERTIES)):
                raise PropertyError(("Invalid    property    name    '%s'" % property))
        if (property in self._model_class._unindexed_properties):
            raise PropertyError(("Property    '%s'    is    not    indexed" % property))
    self.__orderings.append((property, order))
    return self
