Is closing/disposing an SqlDataReader needed if you are already closing the SqlConnection?

Question

I noticed This question, but my question is a bit more specific.

Is there any advantage to using

using (SqlConnection conn = new SqlConnection(conStr))
{
     using (SqlCommand command = new SqlCommand())
     {
        // dostuff
     } 
}

instead of

using (SqlConnection conn = new SqlConnection(conStr))
{
     SqlCommand command = new SqlCommand();
     // dostuff
}

Obviously it does matter if you plan to run more than one command with the same connection, since closing an SqlDataReader is more efficient than closing and reopening a connection (calling conn.Close();conn.Open(); will also free up the connection).

I see many people insist that failure to close the SqlDataReader means leaving open connection resources around, but doesn't that only apply if you don't close the connection?

Answer 1

In my opinion, there are two rules to follow here:

1. Classes that implement IDisposable should be wrapped in a using block.
2. You should not rely on a class's implementation of IDisposable to ignore rule 1.

That is, even if you know that disposing the connection object took care of disposing its associated command object, you should not rely on this behavior.

By the way, it's possible to nest using blocks in a cleaner fashion:

using (SqlConnection conn = new SqlConnection(conStr))
using (SqlCommand command = new SqlCommand())
{
    // dostuff
}

and I would use

SqlCommand command = conn.CreateCommand();

instead of creating a new SqlCommand and then associating it with the connection.