System.IndexOutOfRangeException: Index was outside

问题:

This question already has an answer here:

• What is an IndexOutOfRangeException / ArgumentOutOfRangeException and how do I fix it? 4 answers

I am developing an ATM Software as a home work in which i want to know the total amount of transaction which is processed today, for this purpose I am writting the following code

 public decimal getDayTransaction(int accountid, string date, string transactiontype)
        {
            decimal totalamount = 0;
            int i = 0; 
            string connectionString = 
                     "Persist Security Info=False;User ID=sa; Password=123;Initial Catalog=ATMSoftware;Server=Bilal-PC";
            try
            {
                using (SqlConnection connection = 
                                 new SqlConnection(connectionString))
                {


                    SqlCommand command = new SqlCommand(
                         "Select Amount From [Transaction] where AccountID = "
                         + accountid + " AND CurrDate ='" + date
                         + "' AND TransactionType = '" 
                         + transactiontype + "';", connection);

                    connection.Open();
                    SqlDataReader dr = command.ExecuteReader();
                    while (dr.Read())
                    {
                        totalamount += Convert.ToDecimal(dr.GetString(i));

                        i++;

                    }
                    return totalamount;
                }


            }
            catch (Exception e)
            {

                return -1;
            }
        }

But i am getting the exception System.IndexOutOfRangeException: Index was outside the bounds of the array, although in database more than one records are available which are getting by running the same query in query window. But I don't know how to get it through coding.

Please help me.

Regards

回答1:

Thats because you're trying to read too many columns IMO.

           while (dr.Read())
            {
                totalamount += Convert.ToDecimal(dr.GetString(i));

                i++;

            }

Who said there are more columns than rows? It seems like you're trying to sum a single column.

You're wasting time by selecting all rows. if you're looking for the SUM, use SUM(COLUMN1) instead

                SqlCommand command = new SqlCommand("Select SUM(Amount) as sAmount From [Transaction] where AccountID = " + accountid + " AND CurrDate ='" + date+ "' AND TransactionType = '" + transactiontype + "';", connection);

                connection.Open();
                SqlDataReader dr = command.ExecuteReader();
                while (dr.Read())
                {
                    totalamount += Convert.ToDecimal(dr.GetString(0));
                    break; // Only read once, since it returns only 1 line.

                }
                return totalamount;

回答2:

Change the while like this.

while (dr.Read())
{
    totalamount += Convert.ToDecimal(dr.GetString(0));
}

There is no need of an i there

回答3:

I think problem is in this line

 totalamount += Convert.ToDecimal(dr.GetString(i));
  i++;

Why are incrementing i for? you don't need to increment i

i represents the column index here. You are suppose to read from same column so you don't need to increment i.

Also it is a recommended practise to retrieve value using column name instead of index

回答4:

When you should get only one value, use the SqlCommand.ExecuteScalar, which returns a single value.

SqlCommand command = new SqlCommand("Select SUM(Amount) as TotalAmount From [Transaction] where AccountID = " + accountid + " AND CurrDate ='" + date + "' AND TransactionType = '" + transactiontype + "';", connection);   

connection.Open();   
decimal totalAmount = (decimal)command.ExecuteScalar();   

To avoid SQL injection attacks, consider to use parameterized commands. You can find information about Execute.Scalar and Parametrized command example in the MSDN Documentation for SqlCommand.