c# - 在 C# 中存储来自 SQL 的结果

Question

我正在尝试运行 SQL 查询来收集数据并写入数组。我希望能够使用此数组稍后运行一些 if 语句以查看检索到的数据是否满足所需的某些要求。我是 C# 的新手，如果有更好的方法，请指出正确的方向。这是我目前所拥有的:

public static class DBconnect
    { 

        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }

        public static void sqlConnect()

        {
            var qSql = "Select con.FIRSTNAME, Con.LASTNAME, Con.EMAIL, Act.USERFIELD1 'SerialNumber', ACT.ACCOUNT, TTC.SOFTWAREMAINTENANCE, TTC.HARDWAREMAINTENANCE " +
                    "from CONTACT CON Inner join ACCOUNT ACT on ACT.ACCOUNTID = CON.ACCOUNTID " +
                    "Inner join TTCONTRACTS TTC on TTC.ACCOUNTID = ACT.ACCOUNTID " +
                    "Where Con.EMAIL is not null and Act.USERFIELD1 is not null and " +
                    "ISNUMERIC(Act.USERFIELD1) = 1 and con.EMAIL like '%@%'";

            //Creates connection to sql database
            string connectionString = null;
            SqlConnection cnn;
            connectionString = @"Data Source=DESKTOP-MO813OQ\SalesLogic; Initial Catalog=SalesLogix_Pull; Integrated Security = True";
            cnn = new SqlConnection(connectionString);
            //Sql command to run the query's
            SqlCommand query = new SqlCommand(qSql, cnn);

            QueryResults[] allRecords = null;

            using (query)
            {
                cnn.Open();
                using (var reader = query.ExecuteReader())
                {
                    var list = new List<QueryResults>();
                    while (reader.Read())
                        list.Add(new QueryResults
                        {
                            FIRSTNAME = reader.GetString(0),
                            LASTNAME = reader.GetString(1),
                            EMAIL = reader.GetString(2),
                            SERIALNUMBER = reader.GetInt32(3),
                            ACCOUNT = reader.GetString(4),
                            USERFIELD1 = reader.GetInt32(5),
                            SOFTWAREMAINTENANCE = reader.GetBoolean(6),
                            HARDWAREMAINTENANCE = reader.GetBoolean(7)
                        });
                    allRecords = list.ToArray();
                }

                try
                {
                    cnn.Close();
                    MessageBox.Show("Connection Closed");
                }
                catch (Exception)
                {
                    MessageBox.Show("Error has occured.");
                }
            }


        }


    }

和

class QueryResults
    {
        public string  FIRSTNAME { get; set; }

        public string LASTNAME { get; set; }

        public string EMAIL { get; set; }

        public int USERFIELD1 {get; set;}

        public int SERIALNUMBER { get; set; }

        public string ACCOUNT { get; set; }

        public bool SOFTWAREMAINTENANCE { get; set; }

        public bool HARDWAREMAINTENANCE { get; set; }
    }

当我运行它时，我通常会遇到这些错误:

在这部分代码的 System.Data.dll 中发生类型为“System.InvalidCastException”的未处理异常:

list.Add(new QueryResults
                        {
                            FIRSTNAME = reader.GetString(0),
                            LASTNAME = reader.GetString(1),
                            EMAIL = reader.GetString(2),
                            SERIALNUMBER = reader.GetInt32(3),
                            ACCOUNT = reader.GetString(4),
                            USERFIELD1 = reader.GetInt32(5),
                            SOFTWAREMAINTENANCE = reader.GetBoolean(6),
                            HARDWAREMAINTENANCE = reader.GetBoolean(7)
                        });

如有任何帮助或指点，我们将不胜感激!

Answer 1

您的某些数据列可能没有返回您预期的输出，例如空值。

试试这个

if(!reader.IsDBNull(colIndex))
   return reader.GetString(colIndex); 
else 
   return string.Empty;

如果这不起作用，您可以尝试调试哪个列有问题并提供更多信息。

希望这对您有所帮助。