Retrieve data source by using the DataReader

A DbDataReader is a forward-only, read-only, server-side cursor, which provides a high-performance method of retrieving data from the data store.

The DbDataReader object contains a Read method that retrieves data into its buffer. Only one row of data is ever available at a time, which means that all the data from the database does not need to be completely read into the application before it is processed.

You can use Read method to get selection results and continuously loop through the results until the end of data has been reached (when the Read method returns false).

Example with while loop

var nw = ConfigurationManager.ConnectionStrings["nw"];
var connection = new SqlConnection();
connection.ConnectionString = nw.ConnectionString;
var cmd = connection.CreateCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = "SELECT ProductID, UnitPrice FROM Products";
connection.Open();
DbDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
    MessageBox.Show(rdr["ProductID"] + ": " + rdr["UnitPrice"]);
}
connection.Close();

Example with DataTable

var nw = ConfigurationManager.ConnectionStrings["nw"];
var connection = new SqlConnection();
connection.ConnectionString = nw.ConnectionString;
var cmd = connection.CreateCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = "SELECT ProductID, ProductName FROM Products";
connection.Open();
var rdr = cmd.ExecuteReader();
var products = new DataTable();
products.Load(rdr, LoadOption.Upsert);
connection.Close();
cmbProducts.DataSource = products;
cmbProducts.DisplayMember = "ProductName";
cmbProducts.ValueMember = "ProductID";