Close and Dispose - which to call?

Question

Having read the threads Is SqlCommand.Dispose enough? and Closing and Disposing a WCF Service I am wondering for classes such as SqlConnection or one of the several classes

Answer 1

As usual the answer is: it depends. Different classes implement IDisposable in different ways, and it's up to you to do the necessary research.

As far as SqlClient goes, the recommended practice is to do the following:

using (SqlConnection conn = /* Create new instance using your favorite method */)
{
    conn.Open();
    using (SqlCommand command = /* Create new instance using your favorite method */)
    {
        // Do work
    }
    conn.Close(); // Optional
}

You should be calling Dispose (or Close*) on the connection! Do not wait for the garbage collector to clean up your connection, this will tie up connections in the pool until the next GC cycle (at least). If you call Dispose, it is not necessary to call Close, and since the using construct makes it so easy to handle Dispose correctly, there is really no reason to call Close.

Connections are automatically pooled, and calling Dispose/Close on the connection does not physically close the connection (under normal circumstances). Do not attempt to implement your own pooling. SqlClient performs cleanup on the connection when it's retrieved from the pool (like restoring the database context and connection options).

*if you are calling Close, make sure to do it in an exception-safe way (i.e. in a catch or finally block).