Handling IDisposables within another IDisposable "using" statement

Question

I'm still relatively new to C# and have only within the past several days been exposed to "IDisposables". I can grasp the concept of the using block to take care of objects which must be disposed of without needing to manually remember to call the .Dispose() method - convenient!

Let's say though that I start with a new SqlConnection which I handle within a using statement. Within that block of code I create some additional IDisposables, for example a SqlDataAdapter. Does that adapter need it's own using statement?

For example, if I have code...

using (SqlConnection myConnection = new SqlConnection()) { SqlCommand myCommand = new SqlCommand(); SqlDataAdapter myAdapter = new SqlDataAdapter(); // Do things }

... will myCommand and myAdapter be disposed of when myConnection is disposed (since they are within the scope of that code block)? Or do I need multiple using statements, maybe something like:

using (SqlConnection myConnection = new SqlConnection()) { using (SqlCommand myCommand = new SqlCommand()) { using (SqlDataAdapter myAdapter = new SqlDataAdapter()) { // Do things } } }

Yes you need multiple using block so that each object dispose function is invoked when the scope of using block ends. — Deepak Bhatia
– Deepak Bhatia, Commented Sep 28, 2013 at 14:43
Note that the need to remember to Dispose() just shifts to the need to remember using() {}. The main plusses of this are readability and exception-safety. — Henk Holterman
– Henk Holterman, Commented Sep 28, 2013 at 15:15

Marc Gravell · Accepted Answer · 2013-09-28 14:43:37Z

Strictly speaking, it would indeed be best to dispose all of them. However, you can avoid the indenting by nesting them directly:

using (var myConnection = new SqlConnection()) using (var myCommand = new SqlCommand()) using (var myAdapter = new SqlDataAdapter()) { // Do things }

Alternatively, specifically in the case of ADO.NET (which does, let's be fair, have a lot of disposable types), you might find it easier to use one of the libraries that hides away a lot of the plumbing - for example, with "dapper":

using(var conn = new SqlConnection(...)) { return conn.Query<Customer>( "select * from Customers where Region=@region", new { region }).ToList(); }

Henk Holterman · Accepted Answer · 2013-09-28 15:13:56Z

Does that adapter need it's own using statement?

In this case, no. But that depends on detailed knowledge of the Connection and Adapter objects so as a best practice: use one using() per IDisposable. Even for MemoryStream where Dispose() does nothing. They are inexpensive.

Your code is correct but we usually economize on the {} :

using (SqlConnection myConnection = new SqlConnection()) using (SqlCommand myCommand = new SqlCommand()) using (SqlDataAdapter myAdapter = new SqlDataAdapter()) { // Do things }

We use the rule here that when a using() controls 1 statement (the next using()), you don't need braces. And then we fudge on the indentation a little.

Sebastian Ðymel · Accepted Answer · 2013-09-28 14:43:08Z

Using is just syntatic sugar for

 var connection = new Connection(); try { connection.DoSomething(); } finally { // Check for a null resource. if (connection != null) { ((IDisposable)connection).Dispose(); } }

So yes, you need nested using statements to be sure to dispose all of these

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