Как проверить дубликаты данных для столбца в наборе данных в ASP.NET с помощью C#?

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Я хочу проверить дубликаты данных для столбца в наборе данных в asp.net с помощью c#. Я читаю текстовый файл CSV, преобразую его в набор данных и назначаю объекту. мне нужно проверить наличие дубликатов записей.

Что я уже пробовал:

Код выглядит следующим образом:

foreach (OUT_500_DETAIL objOUT_500_DETAIL in objOUT_500_CONTROL.objOUT_500_DETAIL)
				{


                    #region SponsoringBankSequenceNo
                    if (string.IsNullOrEmpty(objOUT_500_DETAIL.SponsoringBankSequenceNo.ToString().Trim()))
                    {
                        Error += Environment.NewLine + "Row " + Count + " -Sponsoring Bank Trans Ref No Cannot be Empty";
                    }
                    else
                    {
                        if (!Validation.IsNumeric(objOUT_500_DETAIL.SponsoringBankSequenceNo.ToString().Trim()))
                        {
                            Error += Environment.NewLine + "Row " + Count + " -Sponsoring Bank Sequence No Should be Numeric";

                        }
                    }
                    #endregion

                    #region InstructionCode
                    if (string.IsNullOrEmpty(objOUT_500_DETAIL.InstructionCode.ToString().Trim()))
                    {
						Error += Environment.NewLine + "Row " + Count + " -InstructionCode is mandatory";

					}
                    else
                    {
                        if (!Validation.IsAlphabet(objOUT_500_DETAIL.InstructionCode.ToString().Trim()))
                        {
                            Error += Environment.NewLine + "Row " + Count + " -InstructionCode should contain only alphabets";

                        }
                        if (objOUT_500_CONTROL.IsDirect == false)
                        {

                            if (objOUT_500_DETAIL.InstructionCode.ToString().Trim() != "AUTH")
                            {
                                Error += Environment.NewLine + "Row " + Count + " -InstructionCode should be AUTH";

                            }
                        }
                    }
                    #endregion

                    #region OriginatorIdentificationCode
                    if (string.IsNullOrEmpty(objOUT_500_DETAIL.OriginatorIdentificationCode.ToString().Trim()))
					{
						Error += Environment.NewLine + "Row " + Count + " -Originator Identification Code cannot be empty";

					}
                    else
                    {
                        if (objOUT_500_DETAIL.OriginatorIdentificationCode.ToString().Trim().Length > 9)
                        {
                            Error += Environment.NewLine + "Row " + Count + " -Originator Identification Code should not be greater than 9 Characters";

                        }
                        if (!Validation.IsNumeric(objOUT_500_DETAIL.OriginatorIdentificationCode.ToString().Trim()))
                        {
                            Error += Environment.NewLine + "Row " + Count + " -Originator Identification Code should be numeric";

                        }
                    }
                    #endregion


                    #region MandateReference
                    if (objOUT_500_DETAIL.MandateReference.ToString().Trim() == "")
                    {
                        Error += Environment.NewLine + "Row " + Count + " -Mandate Reference cannot be empty";

                    }
                    else
                    {

                        if (objOUT_500_DETAIL.MandateReference.ToString().Trim().Length>23)
                        {
                            Error += Environment.NewLine + "Row " + Count + " -Mandate Reference Length should not be greater than 23 Characters";

                        }
                        if (!Validation.IsNumeric(objOUT_500_DETAIL.MandateReference.ToString().Trim()))
                        {
                            Error += Environment.NewLine + "Row " + Count + " -Mandate Reference should be numeric";

                        }
                    }
                    #endregion

                    #region Currency
                    if (objOUT_500_DETAIL.CurrencyCode.ToString().Trim() != "AED")
					{
						Error += Environment.NewLine + "Row " + Count + " -Currency Code should be AED";

					}
                    #endregion

                    #region ClaimedAmount
                    if (objOUT_500_DETAIL.ClaimedAmount.ToString().Trim() == "")
					{
						Error += Environment.NewLine + "Row " + Count + " -Claimed Amount cannot be empty";

					}
					if (!Validation.IsNumeric(objOUT_500_DETAIL.ClaimedAmount.ToString().Replace(".", "0")))
					{
						Error += Environment.NewLine + "Row " + Count + " -Claimed Amount should be numeric";

					}


                    #endregion

                    #region OriginatorAccountNumber
                    if (objOUT_500_DETAIL.OriginatorAccountNumber.ToString().Trim() == "")
                    {
                        Error += Environment.NewLine + "Row " + Count + " -Originator Account Number cannot be empty";

                    }
                    else
                    {
                        if (!Validation.IsAlphaNumericSp(objOUT_500_DETAIL.OriginatorAccountNumber.ToString().Trim()))
                        {
                            Error += Environment.NewLine + "Row " + Count + " -Originator Account Number should be numeric";

                        }
                    }
                    #endregion

                    #region PayingBank
                    if (objOUT_500_DETAIL.PayingBank.ToString().Trim() == "")
                    {
                        Error += Environment.NewLine + "Row " + Count + " -Paying Bank Value cannot be empty";

                    }
                    else
                    {
                        if (!Validation.IsNumeric(objOUT_500_DETAIL.PayingBank.ToString().Trim()))
                        {
                            Error += Environment.NewLine + "Row " + Count + " -Paying Bank should be numeric";

                        }
                      
                    }
                    #endregion

                    #region Payer
                    if (string.IsNullOrEmpty(objOUT_500_DETAIL.Payer.ToString().Trim()))
                    {
                        Error += Environment.NewLine + "Row " + Count + " -Payer Account No: cannot be empty";

                    }
                    else
                    {
                        if (!Validation.IsAlphaNumericSp(objOUT_500_DETAIL.Payer.ToString().Trim()))
                        {
                            Error += Environment.NewLine + "Row " + Count + " -Payer Account No: should be alphanumeric";

                        }
                        else
                        {

                        }
                    }
                    #endregion

                  

                    Count++;
				}

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