Question

Which of the following two examples are correct? (Or which one is better and should I use)

In the MSDN I found this:

private static void ReadOrderData(string connectionString)
{
   string queryString = "SELECT OrderID, CustomerID FROM dbo.Orders;"

   using (SqlConnection connection = new SqlConnection(connectionString))
   {
       SqlCommand command = new SqlCommand(queryString, connection);
       connection.Open();

       SqlDataReader reader = command.ExecuteReader();

       // Call Read before accessing data.
       while (reader.Read())
       {
           Console.WriteLine(String.Format("{0}, {1}", reader[0], reader[1]));
       }

       // Call Close when done reading.
       reader.Close();
   }
}

However looking other pages some users suggest to do it this way:

private static void ReadOrderData(string connectionString)
{
   string queryString = "SELECT OrderID, CustomerID FROM dbo.Orders;";

   using (SqlConnection connection = new SqlConnection(connectionString))
   {
       using (SqlCommand command = new SqlCommand(queryString, connection))
       {
          connection.Open();

          using (SqlDataReader reader = command.ExecuteReader())
          {
              // Call Read before accessing data.
              while (reader.Read())
              {
                    Console.WriteLine(String.Format("{0}, {1}", reader[0], reader[1]));
              }
          }
       }
   }
}

So, the question is: should I use the using statement also in the SqlCommand and in the SqlDataReader or they are automatically disposed at the end of the SqlConnection using code block.

Answer 1

The second option means your reader will be closed in the event of an exception after it has been created, so it is preferred.

It is effectively transformed by the compiler to:

SqlDataReader reader = command.ExecuteReader();
try
{
    ....
}
finally
{
  if (reader != null)
      ((IDisposable)reader).Dispose();
}

See MSDN for more info.