/// <summary>
        ///
        /// </summary>
        /// <returns></returns>
        protected string[] CurrentColumns()
        {
            string p = PropertyPath;

            string[] propertyColumns = PropertyMapping.ToColumns(currentName, p);
            if (propertyColumns == null)
            {
                throw new QueryException("could not resolve property columns: " + p);
            }
            return(propertyColumns);
        }