public TravelAgent GetById(int id)
 {
     try
     {
         string sql = "SELECT Email, Password FROM TravelAgent WHERE TravelAgentId = @TravelAgentId";
         List<KeyValuePair<string, string>> parameters = new List<KeyValuePair<string, string>>()
         {
             new KeyValuePair<string, string>("@TravelAgentId", id.ToString())
         };
         DataSet results = ExecuteSql(sql, parameters);
         TravelAgent ta = DataSetParser.DataSetToTravelAgent(results, 0);
         return ta;
     }
     catch
     {
         return null;
     }
 }
        public List<TravelAgent> GetAll()
        {
            List<TravelAgent> travelAgentList = new List<TravelAgent>();
            try
            {
                string sql = "SELECT TravelAgentId, Email, Password FROM TravelAgent";
                DataSet results = ExecuteSql(sql, new List<KeyValuePair<string, string>>());

                for (int x = 0; x < results.Tables[0].Rows.Count; x++)
                {
                    TravelAgent ta = DataSetParser.DataSetToTravelAgent(results, x);
                    travelAgentList.Add(ta);
                }
                return travelAgentList;
            }
            catch
            {
                return null;
            }
        }