WCF + EF 4.1 Eager Loading and Serialization Problem

The simple case where my OperationContract implementation is like:

public List<Directory> GetDirectories(bool includeFiles)
{
    if (includeFiles)
    {
        return this.db.Directories.Include(e => e.Files).ToList();
    }
    else
    {
        return this.db.Directories.ToList();
    }
}

where GetDirectories(false); works perfectly ok and GetDirectories(true); throws a CommunicationObjectFaultedException with message:

The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state.

Obviously my File entities have reference to Directory entities, and the Directory entities have a list of files. First I thought this would be the typical c开发者_如何学Cyclic reference trap but I get no signs of it in the exception message. Any ideas on this problem?

---

It will be cyclic reference trap (here is something about this topic) and reason for your CommunicationObjectFaultedException will be something like:

using (var client = new ServiceClient())
{
    data = client.GetDirectories(true);
}

The reason is that unhandled exception has faulted the channel and using is trying to call Close on that faulted channel - it is invalid transition in channel state machine (and one big WCF strangeness) resulting it the exception you mentioned. There are many ways to avoid it but the basis is:

ServiceClient client = null;

try
{
    client = new ServiceClient();
    data = client.GetDirectories(true);
}
finally
{
    if (client != null)
    {
        if (client.State == CommunicationState.Faulted) 
        {
            client.Abort();
        } 
        else 
        {
            client.Close();
        }
    }
}