A misbehaving WCF service asynch call - wcf

Question

Okay, I have a WCF service which is going to be acting as a way to access my SQL database. That part has become largely irrelevant to this question, since for some reason my WCF service crashes. Or, at least, it causes my client Silverlight application to crash. This is why I come here to ask you guys about it.
So here's the code. Bear in mind that it is called asynchronously from my Silverlight client. When it is done, the string that is returned from this method is put on the screen for the client.
public string AddClients(IEnumerable<Client> newClients)
{
int nAdded = 0;
int nelse = 0;
string str = "";
List<Client> newClientsList = newClients.ToList();
List<Client> existingClients = dc.Clients.ToList();
List<Client> clientsToAdd = new List<Client>();
return newClientsList.Count.ToString();
foreach (Client client in newClientsList)
{
var clt = existingClients.FirstOrDefault(c => c.ClientName == client.ClientName);
if (clt == null)
{
return clt.ClientName;
//str = str + " found: " + clt.ClientName + "\n";
//dc.Clients.(clt);
//existingClients.Add(clt);
// clientsToAdd.Add(clt);
nAdded++;
}
else
{
nelse++;
}
}
if (nAdded > 0)
{
//str = str + " more than one nAdded";
// dc.Clients.InsertAllOnSubmit(clientsToAdd);
// dc.SubmitChanges();
}
return nelse.ToString();
}
You may be able to figure out what's supposed to be happening, but most of it's not happening now due to the fact that it's not working out for me very well.
At the moment, as you can see, there is a return quite early on (before the foreach). With things as they are, that works okay. You press a button in the client, it makes the call, and then returns. So as it is, you get '3' returned as a string (this is the size of newClients, the parameter). That is okay, and at least proves that the service can be connected to, that it returns messages okay, and what not.
If I remove that top most return, this is where it gets interesting (well, problematic). It should either return clt.ClientName, in the if (clt==null) condition, or it should return nelse.ToString() which is right at the end.
What do I actually get? Nothing. The method for the completion never seems to get called (the message box it shows never appears).
I've commented most of the stuff out. Surely it has to get to one of these conditions! Have I missed something really obvious here? I really have been attempting to debug this for ages, but nothing! Can someone see something obvious that I can't see?
For the record, 'dc' is the data context, and dc.Clients is a list of Client entities.

Answer 1

I could be missing something, but won't this throw a NullReferenceException? That has to be at least part of your problem.
if (clt == null)
{
return clt.ClientName;
...

Answer 2

I dont understand why you are trying to return the name of the first newly found client from the list you received. Why not just return an integer with total count of newly found clients that you are inserting in the database.
Try:
public string AddClients(IEnumerable<Client> newClients)
{
string str = "";
List<Client> newClientsList = newClients.ToList();
//to save processor and network
List<string> existingClients = dc.Clients.Select(x => x.ClientName).ToList();
List<Client> clientsToAdd = (from nc in newClientsList
join ec in existingClients on nc.ClientName equals ec into nec
from ec in nec.DefaultIfEmpty()
where ec == null
select nc).ToList();
if (clientsToAdd.Count > 0)
{
dc.Clients.InsertAllOnSubmit(clientsToAdd);
foreach (Client c in clientsToAdd)
str += "found: " + c.ClientName + "\n";
return str;
}
return "0 new clients found";
}
easier, simpler, cleaner.