sqlserver ADO.net 查询数据库加锁，事务提交

//逻辑：查询表最大单号，然后锁表（TABLOKX） ,然后执行事务
using (SqlConnection conn = EFContext.Database.Connection as SqlConnection)
{
                    System.Data.SqlClient.SqlCommand cm = new System.Data.SqlClient.SqlCommand();
                    cm.Connection = conn;
                    conn.Open();
                    System.Data.SqlClient.SqlTransaction trans = conn.BeginTransaction();
                    try
                    {
                        cm.Transaction = trans;
                            //获取写进ERP的单据号
                            cm.CommandText = "select max(MasterId) from TBusTran WITH (TABLOCKX)";
                            SqlDataReader dr = cm.ExecuteReader();
 
                                while (dr.Read())
                                {
                                    int n = 0;
                                    while (n < dr.FieldCount) //.FieldCount获取当前行的列数
                                    {
                                        newMasterId = GetSerialNumber_Tran(dr[n].ToString(), "P");
                                        n++;
                                    }

                                }
                                dr.Close();
                 string sql8 = string.Format("insert into TBusQualityProblem_FlowView([FlowNo],[OperatName],[OperatDate],[OperatType],[Status])values('{0}','{1}','{2}','{3}','{4}')",
                    MasterId, Opr_LoginId, DatetimeNow, OperatType, Status);
                        cm.CommandText = sql8;
                        cm.ExecuteNonQuery();
                        trans.Commit();
                    }    
                    catch (Exception)
                    {
                        trans.Rollback();
                        result.Success = false;
                        result.Message = "操作异常!";

                        throw;
                    }
                    finally
                    {
                        conn.Close();
                        trans.Dispose();
                        conn.Dispose();
                    }
                }