Retrieve information from database in a MessageBox | IndexOutOfBoundsException

Question

I have a GetProduct method that is supposed to return the product code, description, and price in a MessageBox. Currently, I am only able to display the word "Price" with a title on the box "IndexOutOfBoundsException" when it actually finds a product matching the code. If not, it displays that it is not found.

Here is the code:

        public static Product GetProduct(string code)
    {
        SqlConnection connection = Connection.GetConnection();

        string select = @"SELECT ProductCode, Description, UnitPrice FROM Products WHERE ProductCode = @ProductCode";

        SqlCommand selectCommand = new SqlCommand(select, connection);


        SqlParameter pCode = new SqlParameter();
        pCode.ParameterName = "@ProductCode";
        pCode.Value = product.Code;
        SqlParameter pDesc = new SqlParameter();
        pDesc.ParameterName = "@Description";
        pDesc.Value = product.Description;
        SqlParameter pPrice = new SqlParameter();
        pPrice.ParameterName = "@UnitPrice";
        pPrice.Value = product.Price;

        selectCommand.Parameters.AddWithValue("@ProductCode", code);

        try
        {
            connection.Open();

            SqlDataReader prodReader = selectCommand.ExecuteReader(CommandBehavior.SingleRow);

            if (prodReader.Read())
            {
                product.Code = prodReader["ProductCode"].ToString(); ;
                product.Description = prodReader["Description"].ToString();
                product.Price = ((decimal)prodReader["Price"]);

                return product;
            }
            else
            {
                return null;
            }
        }
        catch (SqlException ex)
        {
            throw ex;
        }
        finally
        {
            connection.Close();
        }

    }

The field is named UnitPrice, you try to read from an indexer called Price, Is it a typo or is it your real problem? — Steve, May 01 '18 at 18:50
Thanks @Steve, silly error on my part. Now to try and figure out the next step. — GSto, May 01 '18 at 18:54

score 0 · Accepted Answer · answered May 01 '18 at 18:55

You have a field named UnitPrice while the reader's string indexer used is named Price. This produces the IndexOutOfRangeException.
While this is a common typo it is interesting to know why this happens.

Internally the string indexer for the data reader contains this code

override public object this[string name] {
    get {
        return GetValue(GetOrdinal(name));
    }
}

As you can see it uses the GetOrdinal public method to retrieve the index of the field from its name. However, if the name passed is not found the call to GetOrdinal returns -1 and of course this is not a valid index on the underlying fields array going from 0 to FieldCount - 1

Retrieve information from database in a MessageBox | IndexOutOfBoundsException

1 Answers1