Datareader error while converting string to int

Question

I am getting compile-time error at reader.GetString, any idea why?

Code:

using (var connection = new OleDbConnection())
{
    connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\Sparrow vivek\Documents\Billing.accdb";
    connection.Open();
    var query = "SELECT ItemCode FROM invoice";
    using (var command = new OleDbCommand(query, connection))
    {
        using (var reader = command.ExecuteReader())
        {
            while (reader.Read())
            {
                comboBox1.Items.Add(reader.GetString("ItemCode"));
                comboBox2.Items.Add(reader.GetString("ItemCode"));
            }
        }
    }
}

Answer 1

OleDbDataReader.GetString requires an input of int. It expects the column ordinal, not the column name.

Either use the column ordinal directly, or determine the ordinal ahead of time. You can determine the column ordinal by using OleDbDataReader.GetOrdinal:

comboBox1.Items.Add(reader.GetString(reader.GetOrdinal("ItemCode")));

Since you are doing this in a loop, you could do something like this:

int itemCodeOrdinal = reader.GetOrdinal("ItemCode");
while (reader.Read())
{
    comboBox1.Items.Add(reader.GetString(itemCodeOrdinal));
    comboBox2.Items.Add(reader.GetString(itemCodeOrdinal));
}

Answer 2

OleDbDataReader.GetString method takes int as a parameter, not string.

public override string GetString(
    int i
)

It takes the zero-based column number.

Since you get just one column, change it to;

while (reader.Read())
{
    comboBox1.Items.Add(reader.GetString(0));
    comboBox2.Items.Add(reader.GetString(0));
}