How could I check if import this text file into DB or not ?

Question

Hello everyone .

 

I have wrote a code which is reading Text Files and save them in a list after that import this list into DB so far it's fine the problem is i have until now 400 text fiels each text fiel has around 300000 until 500000 line and each time want to import a new text flel it will reinsert or reimport the text files which are already imported . that's meaing my data will be always duplicated.

so how could i check with C# code if this text files is already imported or exist in DB  ?!

 

here is some code to be more clear : 

private static List<WebShopDataAccess> GetWebShopDataAccesses(string path)
        {
            List<WebShopDataAccess> elements = new List<WebShopDataAccess();

            List<string> lines = File.ReadAllLines(path).ToList();
return elements;

// here i am gettng the list back then import this list into DB during an extensions method with sqlbulk
}

 private static void ImportToDB()
        {
            string CS =""
            using (SqlConnection connection = new SqlConnection(CS))
            {
                SqlBulkCopy bulkCopy = new SqlBulkCopy(connection, SqlBulkCopyOptions.TableLock | SqlBulkCopyOptions.FireTriggers | SqlBulkCopyOptions.UseInternalTransaction, null);

                bulkCopy.DestinationTableName = "TestWebShop";

                connection.Open();

                bulkCopy.WriteToServer(GetListOfWebShop.AsDataTable());
            }
        }