如何使用NServiceBus部分加载处理程序？

Question

I am running a console application within which there is a multitude of handlers extending <IHandleMessages> . When I run the application, I want to specify command line arguments such that only some of those handlers will be running. I am working in part with existing code, so I am slightly confused, but it seems that the bus is configured as such:

public static BusConfiguration MyMessageConventions(this BusConfiguration config)
{
    config.UseSerialization<JsonSerializer>();
    config.UseTransport<RabbitMQTransport>();
    config.UsePersistence<InMemoryPersistence>();

    var conventionsBuilder = config.Conventions();
    conventionsBuilder.DefiningEventsAs(t => t.Namespace != null && t.Namespace.StartsWith("DE.STEP.Messages") && t.Namespace.EndsWith("Events"));
    return config;
}

That's all there is to it, and as I understand that spares me having to implement an IMessage interface. Now as I see it, NServiceBus will scan for all handlers in my console project, so I am wondering how I can configure it to not do that (while leaving all other behavior in place), and only load up the handlers I specify?

Answer 1

The easiest solution would be to split your messages and handlers to multiple projects. Usually in scenarios like yours, there is some sort of logical separation between these messages/handlers groups that you want to control by your configuration (or command line) parameters.

NServiceBus scans all assemblies it finds in the application folder to find all handlers and other marker interfaces. You can limit the list of assemblies by using (V5):

configuration.AssembliesToScan(myListOfAssemblies);

You can construct the list of assemblies based on your configuration parameters. If you have different deployment where you want to use different set of handlers, you can just deploy those assemblies that you need at that particular installation.

You can use one assembly or set of assemblies for your messages and these are configured using your DefiningEventsAs call, and have separate assemblies for handlers.

The documentation about NServiceBus assembly scanning can be found here .

Answer 2

It sounds like you want to turn off auto subscription:

config.DisableFeature<AutoSubscribe>();

You can then individually subscribe to messages:

Bus.Subscribe<MyMessage>();

You probably want to first unsubscribe to ALL messages at startup (Bus.Unsubscribe), then re-subscribe to the ones you are interested in. Otherwise your subscriptions will still be present from the last time you ran the application.