从表中检索数据以确认记录是否存在时，如何解决“指定的转换无效”错误？

Question

I'm using my program to add accounts to a database. I'm generating a random account number, checking if that account number exists in the database, and using it to create a new account if it doesn't. However, I am getting the error "Specified Cast Is Not Valid" on the line Int32? RecordExist = (Int32?)check_Records.ExecuteScalar(); Int32? RecordExist = (Int32?)check_Records.ExecuteScalar(); .

I have tried .Convert.ToInt32 , just int , double and I have tried inspecting it as an object before the cast but I can't figure out what the problem is.

 string AccountNumber;
         bool accountExists = true;

        while (accountExists)
        {
            //GENERATE A RANDOM ACCOUNT NUMBER
            Random rnd = new Random();
            int acc1 = rnd.Next(0000, 9999);
            int acc2 = rnd.Next(0000, 9999);

            AccountNumber = "2000-" + acc1 + "-" + acc2 + ";";

            using (MySqlConnection conn = new MySqlConnection(Properties.Settings.Default.ConnectionString))
            {
                conn.Open();

                //CHECK WHETHER ACCOUNT NUMBER EXISTS. 
                string Query = @"SELECT COUNT(*) FROM accounts WHERE Account_Number = '" + AccountNumber + "'";

                using (MySqlCommand check_Records = new MySqlCommand(Query, conn))
                {
                       Int32? RecordExist = (Int32?)check_Records.ExecuteScalar();

                        if (RecordExist.HasValue && RecordExist.Value > 0)
                        {
                            //ACCOUNT EXISTS, GENERATE ANOTHER ACCOUNT NUMBER 
                            accountExists = true;
                            break;
                        }
                        else
                        {
                            //ACCOUNT DOES NOT EXIST, USE ACCOUNT NUMBER
                            accountExists = false;
                            lblNewAccountNumber.Text = AccountNumber;
                        }
                    }

                    conn.Close();

Thanks for your help in advance, and I apologise if I've made any mistakes!

EDIT: The type I was casting to was incorrect, and using the immediate window I was able to see that it needed to be Int64 . It now works! Thanks!

Answer 1

You should try to hold the ExecuteScalar value to an object type variable, then find out in debugging what is its type, and then apply the cast. As is mentioned by @Alex K in the comments section. Hope it works.