NEventStore PollingClient does nothing

For my next project we’ll use Event Sourcing. Therefore I’m spending some free time in looking at NEventStore, a persistence agnostic Event Store for .NET.

One of the features of NEventStore is a built-in PollingClient allowing you to poll the Event Store for the latest commits. However when I tried to test the PollingClient nothing happened?!

Here is the code I was using:

	class Program
	{
	static void Main(string[] args)
	{
	using (var store = WireupEventStore())
	{
	var client = new NEventStore.Client.PollingClient(store.Advanced);
	string checkpointToken = "6";
	using (IObserveCommits observeCommits = client.ObserveFrom(checkpointToken))
	using (observeCommits.Subscribe(new ReadModelCommitObserver(new DelegateMessageDispatcher(DispatchCommit))))
	{
	observeCommits.Start();
	Console.WriteLine("hit any key");
	Console.ReadKey();
	}
	}
	}
	private static void DispatchCommit(ICommit commit)
	{
	// This is where we'd hook into our messaging infrastructure, such as NServiceBus,
	// MassTransit, WCF, or some other communications infrastructure.
	// This can be a class as well--just implement IDispatchCommits.
	try
	{
	foreach (EventMessage @event in commit.Events)
	Console.WriteLine("Message dispatched");
	}
	catch (Exception)
	{
	Console.WriteLine("Unable to dispatch");
	}
	Console.WriteLine("Checkpoint token= " + commit.CheckpointToken);
	}
	private static IStoreEvents WireupEventStore()
	{
	var store = Wireup.Init()
	.UsingSqlPersistence("NEventStoreSample")
	.WithDialect(new MsSqlDialect())
	.WithStreamIdHasher(s => s)
	.InitializeStorageEngine()
	.TrackPerformanceInstance("NEventStoreSample")
	.UsingJsonSerialization()
	.Compress()
	.Build();
	return store;
	}
	}

view raw Program.cs hosted with ❤ by GitHub

	public class ReadModelCommitObserver : IObserver<ICommit>
	{
	private readonly IDispatchCommits dispatcher;
	public ReadModelCommitObserver( IDispatchCommits dispatcher)
	{
	this.dispatcher = dispatcher;
	}
	public void OnCompleted()
	{
	Console.WriteLine("commit observation completed.");
	}
	public void OnError(Exception error)
	{
	Console.WriteLine("Exception from ReadModelCommitObserver: {0}", error.Message);
	throw error;
	}
	public void OnNext(ICommit commit)
	{
	dispatcher.Dispatch(commit);
	}
	}

view raw ReadModelCommitObserver.cs hosted with ❤ by GitHub

No exception was thrown, however when I browsed through the Output window in Visual Studio I noticed the following message:

A first chance exception of type 'Newtonsoft.Json.JsonSerializationException' occurred in NEventStore.dll

It seems that the PollingClient immediatelly tries to deserialize the committed events, as I didn’t include a reference to the assembly containing the Events, the deserializer (silently) fails.

To fix it, the only thing I had to do was adding a reference to my Events assembly.