LINQ query and IDisposable

Question

I'm currently writing a piece of code that does some searches which returns IDisposable objects (DirectoryEntry to be specific from an ADAM instance) and I end up with code similar to

using(var entry = (from result in results
                   let  entry = result.GetDirectoryEntry()
                   where entry != null
                   select entry).Last())
{
  //blah blah
}

but who is then responsible for Disposing the objects not returned by the above query? or more to the point is the above code actually missing a call to Dispose() for all other entries than the last?

Answer 1

if it is Linq to Objects then you are responsible. Yes, objects will not be disposed. You should take the results of query before Last and Dispose them manually.

Answer 2

The dispose is based on the data context. The query itself is pure .Net and will not require a disposer, unless you create objects that require disposing. In which case you would need to individually call the disposer on all objects that you call.

I don't think that using linq in this situation is going to be suitable as you are going to leak resources. AFAIK they are working on a linq to active directory provider, but until then you will probably be better off trying to write your query directly to AD.

Or you can write a loop to deal with the resources:

DirectoryEntry entry = null;
foreach(var result in results)
{
   //Need to add logic to deal with errors.
   var temp = result.GetDirectoryEntry();
   if (temp != null)
   {
       if (entry != null)
       {
            entry.Dispose();
            entry = temp;
       }
       else  
       {
           entry = temp;
       }
   }
}   
using (entry)
{
    //code here
}

BTW you should see this entry under MSDN GetDirectoryEntry: Calling GetDirectoryEntry on each SearchResult returned through DirectorySearcher can be slow.