@classmethod
def _cls_genitem(cls, key):
    """ Generates an item for the given relation key.
        
        :param key: Relation key for which to create related item instance.
        :returns: Generated item.
        """
    relation = cls.relations[key]
    if relation['relation_type'].is_x_to_many():
        item = relation['item_cls'].Bulk()
    else:
        item = relation['item_cls']()
    return item
