Dealing with nulls and exceptions in query syntax

If I want to dump the running processes where the company name is Microsoft I have to write a somewhat grody query:

var msProcesses =
    from p in processes
    where p.Id > 4 &&
          p.MainModule.FileName.IndexOf(' ') == -1 &&
          p.MainModule.FileVersionInfo.CompanyName != null &&
          p.MainModule.FileVersionInfo.CompanyName.StartsWith("Microsoft")
    select new { p.MainModule.ModuleName,
                 p.MainModule.FileVersionInfo.CompanyName };

If you ask for certain properties on the System or Idle processes you get exceptions and certain processes don't have a company name specified. It might be nice to have a way to coalesce nulls (kind of like Lisp or ObjC does). Is there a way to catch exceptions within the query syntax so that I can ignore certain exceptions and continue processing the query or am I stuck writing a lot of defense code in my query

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Dealing with nulls and exceptions in query syntax

wiz

Funny you should ask...

I started working today on a way to encapsulate retry/ignore/abort/throw logic in IEnumerable<T>.

example:

foreach (byte b in GetBytesWithTimeout(port, maxBytes, RecoveryStrategies.RetryNTimesThenAbort(maxRetries)))
{
Console.Write("{0:x2} ", b);
}

where

public static RecoveryStrategy<SerialPortReaderState, FullRecoveryOption> RetryNTimesThenAbort(int n)
{
   return
      delegate(Exception ex, SerialPortReaderState state)
      {
         if (state.RetriesAttempted < n)
         {
            state.RetriesAttempted++;

            return FullRecoveryOption.Retry;
         }
         else
         {
            return FullRecoveryOption.Abort;
         }
      };
}

and

static IEnumerable<byte> GetBytesWithTimeout(SerialPort port, int maxBytes, RecoveryStrategy<SerialPortReaderState, FullRecoveryOption> recoveryStrategy)
{
   SerialPortReaderState state = new SerialPortReaderState();

   int byteCount = 0;

   while (byteCount < maxBytes)
   {
      byte b = 0;

      try
      {
         int read = port.BaseStream.ReadByte();

         b = (byte)read;
      }
      catch (Exception ex)
      {
         Console.WriteLine("Exception Encountered: {0}", ex.Message);

         FullRecoveryOption recoveryOption = recoveryStrategy(ex, state);

         if (recoveryOption == FullRecoveryOption.Retry)
         {
            Console.WriteLine("Retrying: # attempts = {0}", state.RetriesAttempted);

            continue;
         }
         else if (recoveryOption == FullRecoveryOption.RaiseException)
         {
            throw ex;
         }
         else if (recoveryOption == FullRecoveryOption.Abort)
         {
            Console.WriteLine("in Abort");

            yield break;
         }
         else if (recoveryOption == FullRecoveryOption.Ignore)
         {
            continue;
         }
      }

      byteCount++;

      yield return (byte)b;
   }
}

Oddly, I seem to have encounted a strange bug in the debugger or compiler, where if I issue the continue in that if/else/if block in GetBytesWithTimeout, it'll actually jump to the yield break for FullRecoveryOption.Abort (skipping the Console.WriteLine on the previous line) before looping back. It behaves the same if it's a switch block.

I'm being coerced into turning this into an article somewhere, but it needs more time to simmer.

Larry Guger
I wonder if the coolest feature to come out of LINQ is the fact that it is extensible. Nice extension!
tomahawk009
I haven't started dealing with LINQ on this, but it should be usable from there as a wrapper to some other data source.

Actually, I've been dealing mostly with querying cell phones for their debug logs (my company writes cell phone software -- anybody here using a Samsung A840 ).
Dealing with nulls and exceptions in query syntax

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Dealing with nulls and exceptions in query syntax

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Dealing with nulls and exceptions in query syntax

Dealing with nulls and exceptions in query syntax

wiz

Larry Guger

tomahawk009