为什么SQLite告诉我"没有当前行"？

Question

发送的查询是好的; 运行它:

SELECT line_id, description, department, upc_pack_size, pack_size, unit_cost, unit_list FROM Inventory WHERE siteNum = "03" AND upc_code = "76145513"

...在LINQPad中返回包含以下值的记录:

line_id = 0
description = [empty string]
department = 2.99
upc_pack_size = 333
pack_size = 333
unit_cost = 50.01
unit_list = 50.99

但代码:

public List<String> GetDynamicINVValsForUPCCode(String qry, String siteNum, String upcCode)
{
    ExceptionLoggingService.Instance.WriteLog(String.Format("Reached TestHHSDBUtils.GetDynamicINVValsForUPCCode(); siteNum is {0}; upcCode is {1}; qry is {2}", siteNum, upcCode, qry));
    List<String> dsdValsForUPCCode = new List<string>(); 
    try
    {
        using (SQLiteConnection conn = new SQLiteConnection(HHSUtils.GetDBConnection()))
        {
            conn.Open();
            using (SQLiteCommand cmd = new SQLiteCommand(qry, conn))
            {
                cmd.Parameters.Add(new SQLiteParameter("upcCode", upcCode));
                cmd.Parameters.Add(new SQLiteParameter("SiteNum", siteNum));
                using (SQLiteDataReader rdr = cmd.ExecuteReader())
                {
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Line_id"]));       // Line_id, int32
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Description"]));   // Description
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Department"]));    // Department
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Upc_pack_size"])); // Upc_pack_size (int32)
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Pack_size"]));     // Pack_size (int32)
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Unit_qty"]));      // Unit_qty (single)
                }
            }
            return dsdValsForUPCCode;
        }
    }
    catch (Exception ex)
    {
        String msgInnerExAndStackTrace = String.Format("{0}; Inner Ex: {1}; Stack Trace: {2}", ex.Message, ex.InnerException, ex.StackTrace);
        ExceptionLoggingService.Instance.WriteLog(String.Format("From TestHHSDBUtils.GetDynamicINVValsForUPCCode: {0}", msgInnerExAndStackTrace));
        return null;
    }
}

...失败,错误记录为:

Message: From TestHHSDBUtils.GetDynamicINVValsForUPCCode: No current row; Inner Ex: ; Stack Trace:    at System.Data.SQLite.SQLiteDataReader.CheckValidRow()
   at System.Data.SQLite.SQLiteDataReader.GetValue(Int32 i)
   at System.Data.SQLite.SQLiteDataReader.get_Item(String name)
   at HHS.TestHHSDBUtils.GetDynamicINVValsForUPCCode(String qry, String siteNum, String upcCode)

当有一个时,为什么会说"没有当前行"？

Answer 1

虽然我没有明确地熟悉SqlLiteReader,但其余的读者要求你阅读第一行.我正在使用一个if声明,但你期望你会使用一个数字的行while.DataReader.Read()返回一个布尔值,指示是否已读取记录. https://msdn.microsoft.com/en-us/library/haa3afyz%28v=vs.110%29.aspx

using (SQLiteDataReader rdr = cmd.ExecuteReader())
{
  if (rdr.Read()){
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Line_id"]));       // Line_id, int32
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Description"]));   // Description
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Department"]));    // Department
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Upc_pack_size"])); // Upc_pack_size (int32)
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Pack_size"]));     // Pack_size (int32)
                    dsdValsForUPCCode.Add(Convert.ToString(rdr["Unit_qty"]));      // Unit_qty (single)
                    }
         }