public jmp_network FindBytime(string start, string end) { var where = new List <string>(); if (!string.IsNullOrEmpty(start)) { where.Add("convert(varchar(10),n_time,120)>='" + start + "' "); } if (!string.IsNullOrEmpty(end)) { where.Add("convert(varchar(10),n_time,120)<='" + end + "' "); } return(_repository.FindBytime(string.Join(" AND ", where))); }